WILBERT

Description: Comparison of digital beamforming algorithms for 3-D terahertz imaging with sparse multistatic line arrays Bessem Baccouche, Patrick Agostini, Falco Schneider, Wolfgang Sauer-Greff, Ralph Urbansky, and Fabian Friederich Adv. Radio Sci., 15, 283-292, https://doi.org/10.5194/ars-15-283-2017, 2017 In this contribution we compare the back-projection algorithm with our recently developed modified range migration algorithm for 3D terahertz imaging using sparse multistatic line arrays. Numerical and experimental investigations show that imaging results from the proposed range migration algorithm approximates very nicely these of the back-projection algorithm, yet with a significant computational saving. These results are appealing for time critical 3D terahertz imaging.

Description: Design of a carrier-depletion Mach-Zehnder modulator in 250 nm silicon-on-insulator technology María Félix Rosa, Lotte Rathgeber, Raik Elster, Niklas Hoppe, Thomas Föhn, Martin Schmidt, Wolfgang Vogel, and Manfred Berroth Adv. Radio Sci., 15, 269-281, https://doi.org/10.5194/ars-15-269-2017, 2017 We present the design of an optical modulator for amplitude modulation in a special silicon-on-insulator technology with 250 nm silicon layer thickness. The design of the modulator is optimized by simulating different parameters like dimension of the structure and doping of the silicon to improve the performance of the device. In addition, a prototype is fabricated and successfully measured to demonstrate the functionality of the technology.

Description: Design of a dual linear polarization antenna using split ring resonators at X-band Sadiq Ahmed and Madhukar Chandra Adv. Radio Sci., 15, 259-267, https://doi.org/10.5194/ars-15-259-2017, 2017 In this paper, a novel approach (using metamaterials) is used to enhance the XPD for a dual linear polarization patch antenna at the frequency of 10 GHz. This improvement is obtained by placing two S-RRs close to the microstrip patch antenna, placing a SRR between two microstrip feed lines, and etching two pairs of CSRRs in the ground plane. An improvement in the XPD by 8.8 dB as compared to the conventional dual linear polarization antenna is noticed.

Description: Results of an intercomparison for electric field strength measurements within the German calibration service Reiner Pape, Uwe Karsten, Frank-Michael Lindner, Frank Rittmann, Joachim von Freeden, Thomas Kleine-Ostmann, and Thorsten Schrader Adv. Radio Sci., 15, 243-248, https://doi.org/10.5194/ars-15-243-2017, 2017 We discuss the results of an intercomparison for electric field strength measurements within the DKD. The comparison has been carried out on the field strength value required to reach a display reading of 20 V m −1 of the field probes. While the results agree well for the small field probe and when the larger commercial 3-axis field probe is oriented in the direction of the magnetic field, larger deviations occur, when the larger 3-axis field probe is oriented into the direction propagation.

Description: Experimentelles FMCW-Radar zur hochfrequenten Charakterisierung von Windenergieanlagen Karsten Schubert, Jens Werner, and Fabian Schwartau Adv. Radio Sci., 15, 1-9, https://doi.org/10.5194/ars-15-1-2017, 2017 A cost-effective and universal FMCW radar is developed for the RF characterisation of wind turbine plants. This radar is modular and can be easily adapted for different measurement tasks. A long-term goal is to investigate high-frequency characteristics of wind turbines at different locations by their Doppler spectrum. The results obtained will be used to derive a statistical model.

Description: Modelling Glaciers in the HARMONIE-AROME NWP model Ruth Mottram, Kristian Pagh Nielsen, Emily Gleeson, and Xiaohua Yang Adv. Sci. Res., 14, 323-334, https://doi.org/10.5194/asr-14-323-2017, 2017 The HARMONIE weather forecasting model is used successfully in Greenland, but there are some problems over the ice sheet due to the lack of realistic glacier surface characteristics. By introducing a correction to the model, preventing glacier surface temperatures over 0 °C, we improve both 2 m air temperature and the surface winds (both strength and direction) forecast by the model. We also identify other corrections needed before HARMONIE can be used for climate and ice sheet modelling.

Description: Evaluating co-creation of knowledge: from quality criteria and indicators to methods Susanne Schuck-Zöller, Jörg Cortekar, and Daniela Jacob Adv. Sci. Res., 14, 305-312, https://doi.org/10.5194/asr-14-305-2017, 2017 Climate services and other fields, that are used to integrate the users in research activities (co-creation), are pledging for existing evaluation methods to be widened up. The authors harmonize the different elements of evaluation in an evaluation cascade , scaling down from very general evaluation dimensions to tangible assessment methods and suggest how to proceed in developing evaluation criteria and indicators. Two examples demonstrate how co-creation of knowledge could be assessed.

Description: Deriving evaluation indicators for knowledge transfer and dialogue processes in the context of climate research Renate Treffeisen, Klaus Grosfeld, and Franziska Kuhlmann Adv. Sci. Res., 14, 313-322, https://doi.org/10.5194/asr-14-313-2017, 2017 Knowledge transfer and dialogue processes (KT) in the field of climate science have captured intensive attention. This paper aims to serve as an input to stimulate further reflection on the field of evaluation of KT in the context of climate sciences. We carry out an analysis of three example activities and derive a set of indicators for measuring the output/outcome by balancing the wide diversity and range of activity contents as well as the different tools to realize them.

Description: Stakeholder-based evaluation categories for regional climate services – a case study at the German Baltic Sea coast Insa Meinke Adv. Sci. Res., 14, 279-291, https://doi.org/10.5194/asr-14-279-2017, 2017 In this study, categories, dimensions and criteria for evaluating regional climate services are derived by a participatory approach with potential service users at the German Baltic Sea coast. The results show that stakeholders do mainly address other components than those found in the literature. This might indicate that an evaluation, following solely literature-based (non-participative) components, is not sufficient to localize deficiencies or efficiencies within a regional climate service.

Description: Comparison between 3D-Var and 4D-Var data assimilation methods for the simulation of a heavy rainfall case in central Italy Vincenzo Mazzarella, Ida Maiello, Vincenzo Capozzi, Giorgio Budillon, and Rossella Ferretti Adv. Sci. Res., 14, 271-278, https://doi.org/10.5194/asr-14-271-2017, 2017 This work aims to provide a comparison between three dimensional and four dimensional variational data assimilation methods (3D-Var and 4D-Var) for a heavy rainfall case in central Italy. Nine simulations are compared in terms of rainfall forecast and precipitation measured by the gauges through three statistical indicators. The assimilation of conventional observations with 4D-Var method improves the quantitative precipitation forecast (QPF) compared to 3D-Var.

Description: Risk management perspective for climate service development – Results from a study on Finnish organizations Atte Harjanne, Riina Haavisto, Heikki Tuomenvirta, and Hilppa Gregow Adv. Sci. Res., 14, 293-304, https://doi.org/10.5194/asr-14-293-2017, 2017 Weather, climate and climate change can cause significant risks to businesses and public administration. By asking Finnish organizations about their weather and climate risk perceptions and management, this study aims to improve ways climate services can support in adapting to current and future climate. The results indicate that climate risk management is often de-centralized and relies on expert networks but that practices differ between actors.

Description: Intrinsic parameters of periodic waves observed in the OI6300 airglow layer over the Brazilian equatorial region Igo Paulino, Joyrles F. Moraes, Gleuson L. Maranhão, Cristiano M. Wrasse, Ricardo Arlen Buriti, Amauri F. Medeiros, Ana Roberta Paulino, Hisao Takahashi, Jonathan J. Makela, John W. Meriwether, and José André V. Campos Ann. Geophys., 36, 265-273, https://doi.org/10.5194/angeo-36-265-2018, 2018 This article presents characteristics of periodic waves observed in the thermosphere from airglow images collected in the Northeast of Brazil. Using simultaneous measurements of the background wind in the airglow emission altitudes, it was possible to estimate the intrinsic parameters and the role of the wind in the propagation of the waves into the thermosphere. An anisotropy in the propagation direction of the waves was observed and it could be explained by the wind filtering process.

Description: Unknown high-frequency (7–12 kHz) quasi-periodic VLF emissions observed on the ground at L ~ 5.5 Jyrki Manninen, Natalia Kleimenova, Tauno Turunen, and Liudmila Gromova Ann. Geophys. Discuss., https//doi.org/10.5194/angeo-2018-18,2018 Manuscript under review for ANGEO (discussion: open, 0 comments) We reveal previously unknown quasi-periodic (QP) VLF emissions at the unusual high-frequency band of ~ 7–11 kHz by applying the digital filtering of strong sferics to the ground-based VLF data recorded at Kannuslehto station (KAN). In one event, the spectral-temporal forms of the emissions looked like a series of giant bullets with the very abrupt cessation. In the second event, the modulation period was about 3 min under the absence of the simultaneous geomagnetic pulsations.

Description: Mesospheric front observations by the OH airglow imager carried out at Ferraz Station on King George Island, Antarctic Peninsula, in 2011 Gabriel Augusto Giongo, José Valentin Bageston, Paulo Prado Batista, Cristiano Max Wrasse, Gabriela Dornelles Bittencourt, Igo Paulino, Neusa Maria Paes Leme, David C. Fritts, Diego Janches, Wayne Hocking, and Nelson Jorge Schuch Ann. Geophys., 36, 253-264, https://doi.org/10.5194/angeo-36-253-2018, 2018 This work presents four events of mesosphere fronts observed on King George Island, Antarctic Peninsula, in the year 2011. The atmospheric background environment was analyzed to investigate the propagation conditions for all cases. To investigate the sources for such cases, satellite images were used. In two cases, we found that strong tropospheric instabilities were potential sources, and in the other two cases, it was not possible to associate them with tropospheric sources.

Description: A statistical study of spatial distribution and source region size of chorus waves using Van Allen Probes data Shangchun Teng, Xin Tao, Wen Li, Yi Qi, Xinliang Gao, Lei Dai, Quanming Lu, and Shui Wang Ann. Geophys. Discuss., https//doi.org/10.5194/angeo-2018-16,2018 Manuscript under review for ANGEO (discussion: open, 0 comments) Spatial distribution and source region size of chorus waves are important parameters in understanding their generation.In this work, we analyze over 3 years of continuous wave burst mode data from Van Allen Probes and build a data set of rising and falling tone chorus. For the L shell range covered by Van Allen Probes data (3.5 ≤  L  ≤ 7), statistical results demonstrate that the sector where rising tones are most likely to be observed is the dayside during geomagnetically quiet and moderate times and the dawnside during active times. Moreover, rising tone chorus waves have a higher occurrence rate near the equatorial plane, while the falling tone chorus waves have a higher possibility to be observed at lower L -shell and higher magnetic latitude. By analyzing the direction of Poynting wave vector, we statistically investigate the chorus source region size along a field line, and compare the results with previous theoretical estimates. Our analysis confirms previous conclusions that both rising tone and falling tone chorus waves are generated near the equatorial plane, and shows that previous theoretical estimates roughly agree with the observation within a factor of two. Our results provide important insights into further understanding of chorus generation.

Description: Case study of ozone anomalies over northern Russia in the 2015/2016 winter: Measurements and numerical modeling Yury M. Timofeyev, Sergei P. Smyshlyaev, Yana A. Virolainen, Alexander S. Garkusha, Alexander V. Polyakov, Maxim A. Motsakov, and Ole Kirner Ann. Geophys. Discuss., https//doi.org/10.5194/angeo-2018-15,2018 Manuscript under review for ANGEO (discussion: open, 0 comments) Atmospheric ozone plays a vital role, absorbing the ultraviolet Sun radiation and heating the air, thus forming the stratosphere itself. If not absorbed, UV radiation would reach Earth surface in amounts that are harmful to a variety of life-forms. Climate change may lead to increasing ozone depletion especially in Arctic. Observation and prediction of the ozone variability is both crucial for the investigation of its nature and for the prediction of potential increase of surface UV-radiation.

Description: Evidence of L -mode electromagnetic wave pumping of ionospheric plasma near geomagnetic zenith Thomas B. Leyser, H. Gordon James, Björn Gustavsson, and Michael T. Rietveld Ann. Geophys., 36, 243-251, https://doi.org/10.5194/angeo-36-243-2018, 2018 Transmission of powerful radio waves into the overhead ionosphere is used to study plasma turbulence processes. It is well known that the ionospheric response to radio waves is the strongest in the direction of the geomagnetic field. We have found evidence that the transmitted radio wave can propagate in a mode that enables the wave to propagate much higher in altitude and deeper into the ionosphere than what is usually expected, which may account for the strong plasma response observed.

Description: Ultrafast Kelvin waves in the MLT airglow and wind, and their interaction with the atmospheric tides Fabio Egito, Ricardo Arlen Buriti, Amauri Fragoso Medeiros, and Hisao Takahashi Ann. Geophys., 36, 231-241, https://doi.org/10.5194/angeo-36-231-2018, 2018 Airglow and wind measurements from the Brazilian equatorial region were used to investigate the presence and the effects of the 3–4-day ultrafast Kelvin waves in the MLT. The airglow integrated intensities of the OI557.7 nm, O 2 b(0-1) and OH(6-2) emissions, as well as the OH rotational temperature, were measured by a multichannel photometer, and the zonal and meridional wind components between 80 and 100 km were obtained from a meteor radar. Both instruments are installed in the Brazilian equatorial region at São João do Cariri (7.4° S, 36.5° W). Data from 2005 were used in this study. The 3–4-day oscillations appear intermittently throughout the year in the airglow. They were identified in January, March, July, August and October–November observations. The amplitudes induced by the waves in the airglow range from 26 to 40 % in the OI557.7 nm, 17 to 43 % in the O 2 b(0-1) and 15 to 20 % in the OH(6-2) emissions. In the OH rotational temperature, the amplitudes were from 4 to 6 K. Common 3–4-day oscillations between airglow and neutral wind compatible with ultrafast Kelvin waves were observed in March, August and October–November. In these cases, the amplitudes in the zonal wind were found to be between 22 and 28 m s −1 and the vertical wavelength ranges from 44 to 62 km. Evidence of the nonlinear interaction between the ultrafast Kelvin wave and diurnal tide was observed.

Description: Seasonal variability of atmospheric tides in the mesosphere and lower thermosphere: meteor radar data and simulations Dimitry Pokhotelov, Erich Becker, Gunter Stober, and Jorge L. Chau Ann. Geophys. Discuss., https//doi.org/10.5194/angeo-2018-17,2018 Manuscript under review for ANGEO (discussion: open, 0 comments) Atmospheric tides are produced by solar heating of the lower atmosphere. The tides propagate to upper atmosphere and ionosphere playing an important role in the vertical coupling. Ground radar measurements of the seasonal variability of tides are compared with global numerical simulations. The agreement with radar data and limitations of the numerical model are discussed. The work represents a first step in modelling the impact of tidal dynamics on the upper atmosphere and ionosphere.

Description: Relative humidity vertical profiling using lidar-based synergistic methods in the framework of the Hygra-CD campaign Lev D. Labzovskii, Alexandros Papayannis, Ioannis Binietoglou, Robert F. Banks, Jose M. Baldasano, Florica Toanca, Chris G. Tzanis, and John Christodoulakis Ann. Geophys., 36, 213-229, https://doi.org/10.5194/angeo-36-213-2018, 2018 This study aims to evaluate synergetic methods for relative humidity vertical profiling based on lidar–radiometer and lidar–simulation combinations. We demonstrate the effectiveness of combined lidar-based methods for relative humidity profiling in comparison with radiometer observations or WRF simulations and assess temperature-related uncertainties in resulting relative humidity profiles. All results are acquired during the HygrA-CD campaign in Athens (Greece) in 2014.

Description: Monitoring potential ionosphere changes caused by Van earthquake (Mw 7.2) using GNSS measurements Selcuk Peker, Samed Inyurt, and Cetin Mekik Ann. Geophys. Discuss., https//doi.org/10.5194/angeo-2018-11,2018 Manuscript under review for ANGEO (discussion: open, 0 comments) Several scientists from different disciplines have studied earthquakes for many years. As a result of these studies, it has been proposed that some changes take place in the ionosphere layer before, during or after earthquakes, and the ionosphere should be monitored in earthquake prediction studies. This study investigates the changes in the ionosphere created by the earthquake with magnitude of Mw=7.2 in the northwest of the Lake Erçek which is located to the north of the province of Van in Turkey on 23 October 2011 and at 1.41 pm local time (−3 UT) with the epicenter of 38.758° N, 43.360° E using the TEC values obtained by the Global Ionosphere Models (GIM) created by IONOLAB-TEC and CODE. In order to see whether the ionospheric changes obtained by the study in question were caused by the earthquake or not, the ionospheric conditions were studied by utilizing indices providing information on solar and geomagnetic activities (F10.7 cm, Kp, Dst). As a result of the statistical test on the TEC values obtained from the both models, positive and negative anomalies were obtained for the times before, on the day of and after the earthquake, and the reasons for these anomalies are discussed in detail in the last section of the study. As the ionospheric conditions in the analyzed days were highly vibrant, it was thought that the anomalies were caused by geomagnetic effects, solar activity and the earthquake. The authors believe that interdisciplinary studies are needed to distinguish the earthquake-related part of the anomalies in question.

Description: Cross-correlation and cross-wavelet analyses of the solar wind IMF B z and auroral electrojet index AE coupling during HILDCAAs Adriane Marques de Souza, Ezequiel Echer, Mauricio José Alves Bolzan, and Rajkumar Hajra Ann. Geophys., 36, 205-211, https://doi.org/10.5194/angeo-36-205-2018, 2018 Cross-wavelet and classical cross-correlation analyses were used in order to study solar-wind–magnetosphere coupling during HILDCAAs. Cross-correlation analyses results show that the coupling between the solar wind and the magnetosphere during HILDCAAs occurs mainly in the period ≤ 8 h. Classical correlation analysis indicates that the correlation between IMF B z and AE may be classified as moderate (0.4–0.7) and that more than 80 % of the HILDCAAs exhibit a lag of 20–30 min.

Description: The geomagnetic coast effect at two 80° S stations in Antarctica, observed in the ULF range Mauro Regi, Marcello De Lauretis, Patrizia Francia, Stefania Lepidi, Andrea Piancatelli, and Stefano Urbini Ann. Geophys., 36, 193-203, https://doi.org/10.5194/angeo-36-193-2018, 2018 Our results suggest that sea–land interface affects the polarization parameters at coastal stations. We proposed a method for directly estimating, in the frequency domain, the normal field variations at coastal stations, by inverting the linear relationship between horizontal field measurements at coastal and reference stations. Our techniques could also be used to detect possible anomalous effects due to sporadic changes in ground conductivity.

Description: Aircraft Observations of Aerosol in the Manaus Urban Plume and Surrounding Tropical Forest during GoAmazon 2014/15 John E. Shilling, Mikhail S. Pekour, Edward C. Fortner, Paulo Artaxo, Suzane de Sá, John M. Hubbe, Karla M. Longo, Luiz A. T. Machado, Scot T. Martin, Stephen R. Springston, Jason Tomlinson, and Jian Wang Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-193,2018 Manuscript under review for ACP (discussion: open, 0 comments) We report aircraft observations of the evolution of organic aerosol in the Manaus urban plume as it ages. We observe dynamic changes in the organic aerosol. The mean carbon oxidation state of the OA increases from −0.6 to −0.45. Hydrocarbon-like organic aerosol (HOA) mass is lost and is balanced out by formation of oxygenated organic aerosol (OOA). Because HOA loss is balanced by OOA formation, we observe little change in the net Δorg/ΔCO values with aging.

Description: Influence of anthropogenic emissions and boundary conditions on multi-model simulations of major air pollutants over Europe and North America in the framework of AQMEII3 Ulas Im, Jesper Heile Christensen, Camilla Geels, Kaj Mantzius Hansen, Jørgen Brandt, Efisio Solazzo, Ummugulsum Alyuz, Alessandra Balzarini, Rocio Baro, Roberto Bellasio, Roberto Bianconi, Johannes Bieser, Augustin Colette, Gabriele Curci, Aidan Farrow, Johannes Flemming, Andrea Fraser, Pedro Jimenez-Guerrero, Nutthida Kitwiroon, Peng Liu, Uarporn Nopmongcol, Laura Palacios-Peña, Guido Pirovano, Luca Pozzoli, Marje Prank, Rebecca Rose, Ranjeet Sokhi, Paolo Tuccella, Alper Unal, Marta G. Vivanco, Greg Yarwood, Christian Hogrefe, and Stefano Galmarini Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2017-1231,2018 Manuscript under review for ACP (discussion: open, 0 comments) We evaluate the impact of global and regional anthropogenic emission reductions on major air pollutant levels over Europe and North America, using a multi-model ensemble of regional chemistry and transport models. Results show that ozone levels are largely driven by long-range transport over both continents while other pollutants such as carbon monoxide or aerosols are mainly controlled by domestic sources. Use of multi model ensembles can help to reduce the uncertainties in individual models.

Description: Nighttime wind and scalar variability within and above an Amazonian canopy Pablo E. S. Oliveira, Otávio C. Acevedo, Matthias Sörgel, Anywhere Tsokankunku, Stefan Wolff, Alessandro C. Araújo, Rodrigo A. F. Souza, Marta O. Sá, Antônio O. Manzi, and Meinrat O. Andreae Atmos. Chem. Phys., 18, 3083-3099, https://doi.org/10.5194/acp-18-3083-2018, 2018 Carbon dioxide and latent heat fluxes within the canopy are dominated by low-frequency (nonturbulent) processes. There is a striking contrast between fully turbulent and intermittent nights, such that turbulent processes dominate the total nighttime exchange during the former, while nonturbulent processes are more relevant in the latter. In very stable nights, during which intermittent exchange prevails, the stable boundary layer may be shallower than the highest observational level at 80 m.

Description: Lower tropospheric ozone over India and its linkage to the South Asian monsoon Xiao Lu, Lin Zhang, Xiong Liu, Meng Gao, Yuanhong Zhao, and Jingyuan Shao Atmos. Chem. Phys., 18, 3101-3118, https://doi.org/10.5194/acp-18-3101-2018, 2018 Deteriorating tropospheric ozone pollution over India may not only affect local human health and vegetation but also perturb global ozone distribution. This study analyzes the processes controlling lower tropospheric ozone over India using OMI satellite observations (2006–2014) and model simulations (1990–2010). We show that the South Asian monsoon largely controls the seasonal cycle and interannual variability of Indian lower tropospheric ozone via changes in ozone production and transport.

Description: Ozone impacts of gas–aerosol uptake in global chemistry transport models Scarlet Stadtler, David Simpson, Sabine Schröder, Domenico Taraborrelli, Andreas Bott, and Martin Schultz Atmos. Chem. Phys., 18, 3147-3171, https://doi.org/10.5194/acp-18-3147-2018, 2018 The impact of six heterogeneous gas–aerosol uptake reactions on tropospheric ozone and nitrogen species was studied using two chemical transport models, the Meteorological Synthesizing Centre-West of the European Monitoring and Evaluation Programme (EMEP MSC-W) and the European Centre Hamburg general circulation model combined with versions of the Hamburg Aerosol Model and Model for Ozone and Related chemical Tracers (ECHAM-HAMMOZ). Species undergoing heterogeneous reactions in both models include N 2 O 5 , NO 3 , NO 2 , O 3 , HNO 3 , and HO 2 . Since heterogeneous reactions take place at the aerosol surface area, the modelled surface area density ( S a ) of both models was compared to a satellite product retrieving the surface area. This comparison shows a good agreement in global pattern and especially the capability of both models to capture the extreme aerosol loadings in east Asia. The impact of the heterogeneous reactions was evaluated by the simulation of a reference run containing all heterogeneous reactions and several sensitivity runs. One reaction was turned off in each sensitivity run to compare it with the reference run. The analysis of the sensitivity runs confirms that the globally most important heterogeneous reaction is the one of N 2 O 5 . Nevertheless, NO 2 , HNO 3 , and HO 2 heterogeneous reactions gain relevance particularly in east Asia due to the presence of high NO x concentrations and high S a in the same region. The heterogeneous reaction of O 3 itself on dust is of minor relevance compared to the other heterogeneous reactions. The impacts of the N 2 O 5 reactions show strong seasonal variations, with the biggest impacts on O 3 in springtime when photochemical reactions are active and N 2 O 5 levels still high. Evaluation of the models with northern hemispheric ozone surface observations yields a better agreement of the models with observations in terms of concentration levels, variability, and temporal correlations at most sites when the heterogeneous reactions are incorporated. Our results are loosely consistent with results from earlier studies, although the magnitude of changes induced by N 2 O 5 reaction is at the low end of estimates, which seems to fit a trend, whereby the more recent the study the lower the impacts of these reactions.

Description: Aerosol–cloud interactions in mixed-phase convective clouds – Part 1: Aerosol perturbations Annette K. Miltenberger, Paul R. Field, Adrian A. Hill, Phil Rosenberg, Ben J. Shipway, Jonathan M. Wilkinson, Robert Scovell, and Alan M. Blyth Atmos. Chem. Phys., 18, 3119-3145, https://doi.org/10.5194/acp-18-3119-2018, 2018 Changes induced by perturbed aerosol conditions in moderately deep mixed-phase convective clouds (cloud top height  ∼  5 km) developing along sea-breeze convergence lines are investigated with high-resolution numerical model simulations. The simulations utilise the newly developed Cloud–AeroSol Interacting Microphysics (CASIM) module for the Unified Model (UM), which allows for the representation of the two-way interaction between cloud and aerosol fields. Simulations are evaluated against observations collected during the COnvective Precipitation Experiment (COPE) field campaign over the southwestern peninsula of the UK in 2013. The simulations compare favourably with observed thermodynamic profiles, cloud base cloud droplet number concentrations (CDNC), cloud depth, and radar reflectivity statistics. Including the modification of aerosol fields by cloud microphysical processes improves the correspondence with observed CDNC values and spatial variability, but reduces the agreement with observations for average cloud size and cloud top height. Accumulated precipitation is suppressed for higher-aerosol conditions before clouds become organised along the sea-breeze convergence lines. Changes in precipitation are smaller in simulations with aerosol processing. The precipitation suppression is due to less efficient precipitation production by warm-phase microphysics, consistent with parcel model predictions. In contrast, after convective cells organise along the sea-breeze convergence zone, accumulated precipitation increases with aerosol concentrations. Condensate production increases with the aerosol concentrations due to higher vertical velocities in the convective cores and higher cloud top heights. However, for the highest-aerosol scenarios, no further increase in the condensate production occurs, as clouds grow into an upper-level stable layer. In these cases, the reduced precipitation efficiency (PE) dominates the precipitation response and no further precipitation enhancement occurs. Previous studies of deep convective clouds have related larger vertical velocities under high-aerosol conditions to enhanced latent heating from freezing. In the presented simulations changes in latent heating above the 0°C are negligible, but latent heating from condensation increases with aerosol concentrations. It is hypothesised that this increase is related to changes in the cloud field structure reducing the mixing of environmental air into the convective core. The precipitation response of the deeper mixed-phase clouds along well-established convergence lines can be the opposite of predictions from parcel models. This occurs when clouds interact with a pre-existing thermodynamic environment and cloud field structural changes occur that are not captured by simple parcel model approaches.

Description: Regional uncertainty of GOSAT XCO 2 retrievals in China: quantification and attribution Nian Bie, Liping Lei, ZhaoCheng Zeng, Bofeng Cai, Shaoyuan Yang, Zhonghua He, Changjiang Wu, and Ray Nassar Atmos. Meas. Tech., 11, 1251-1272, https://doi.org/10.5194/amt-11-1251-2018, 2018 The results imply that XCO 2 from satellite observations could be reliably applied in the assessment of atmospheric CO 2 enhancements induced by anthropogenic CO 2 emissions. The large inconsistency among different algorithms presented in western deserts with a high albedo and dust aerosols demonstrates that further improvement is still necessary in such regions, even though many algorithms have endeavored to minimize the effects of aerosols and albedo.

Description: The First Evaluation of Formaldehyde Column Observations by Pandora Spectrometers during the KORUS-AQ Field Study Elena Spinei, Andrew Whitehill, Alan Fried, Martin Tiefengraber, Travis N. Knepp, Scott Herndon, Jay R. Herman, Moritz Müller, Nader Abuhassan, Alexander Cede, Petter Weibring, Dirk Richter, James Walega, James Crawford, James Szykman, Lukas Valin, David J. Williams, Russell Long, Robert J. Swap, Youngjae Lee, Nabil Nowak, and Brett Poche Atmos. Meas. Tech. Discuss., https//doi.org/10.5194/amt-2018-57,2018 Manuscript under review for AMT (discussion: open, 0 comments) Formaldehyde is toxic to humans and is formed in the atmosphere in the presence of air pollution, but the measurements are sparse. Pandora global network instruments measure total formaldehyde column from the surface to the top of troposphere and will be widely available. This study compared formaldehyde Pandora columns with the surface and aircraft integrated columns near Seoul, South Korea. Relatively good agreement was observed between the three datasets with some overestimation by Pandoras.

Description: Halo ratio from ground based all-sky imaging Paolo Dandini, Zbigniew Ulanowski, David Campbell, and Richard Kaye Atmos. Meas. Tech. Discuss., https//doi.org/10.5194/amt-2018-3,2018 Manuscript under review for AMT (discussion: open, 0 comments) The halo ratio indicates the strength of the 22° cirrus halo, and gives valuable information on cloud properties. We propose to obtain it from all-sky images by applying a range of transformations and corrections and averaging brightness azimuthally over sun-centred images. The ratio is then taken at two angles from the sun, 20° and 23°, in variance from previous suggestions. While we find ratios 〉 1 to be linked to halos, they can occur under scattered cumuli as artefacts due to cloud edges.

Description: Chemical characterization of laboratory-generated tar ball particles Ádám Tóth, András Hoffer, Mihály Pósfai, Tibor Ajtai, Zoltán Kónya, Marianne Blazsó, Zsuzsanna Czégény, Gyula Kiss, Zoltán Bozóki, and András Gelencsér Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-132,2018 Manuscript under review for ACP (discussion: open, 0 comments) Atmospheric tar balls are abundant particles in biomass smoke and were shown to be strongly light-absorbing. Being able to synthesize pure tar balls in the laboratory we deployed various analytical techniques to determine the chemical characteristics of tar balls and to compare them with those of other light-absorbing particle types such as soot (black carbon, BC). The results have relevance in better representing these specific smoke particles in global climate models.

Description: Results from the Fourth WMO Filter Radiometer Comparison for aerosol optical depth measurements Stelios Kazadzis, Natalia Kouremeti, Henri Diémoz, Julian Gröbner, Bruce W. Forgan, Monica Campanelli, Victor Estellés, Kathleen Lantz, Joseph Michalsky, Thomas Carlund, Emilio Cuevas, Carlos Toledano, Ralf Becker, Stephan Nyeki, Panagiotis G. Kosmopoulos, Viktar Tatsiankou, Laurent Vuilleumier, Frederick M. Denn, Nozomu Ohkawara, Osamu Ijima, Philippe Goloub, Panagiotis I. Raptis, Michael Milner, Klaus Behrens, Africa Barreto, Giovanni Martucci, Emiel Hall, James Wendell, Bryan E. Fabbri, and Christoph Wehrli Atmos. Chem. Phys., 18, 3185-3201, https://doi.org/10.5194/acp-18-3185-2018, 2018 Aerosol optical depth measured from ground-based sun photometers is the most important parameter for studying the changes in the Earth's radiation balance due to aerosols. Representatives for various sun photometer types belonging to individual institutions or international aerosol networks gather every 5 years, for 3 weeks, in Davos, Switzerland, in order to compare their aeorosol optical depth retrievals. This work presents the results of the latest (fourth) filter radiometer intercomparison.

Description: Aircraft Observations of Aerosol in the Manaus Urban Plume and Surrounding Tropical Forest during GoAmazon 2014/15 John E. Shilling, Mikhail S. Pekour, Edward C. Fortner, Paulo Artaxo, Suzane de Sá, John M. Hubbe, Karla M. Longo, Luiz A. T. Machado, Scot T. Martin, Stephen R. Springston, Jason Tomlinson, and Jian Wang Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-193,2018 Manuscript under review for ACP (discussion: open, 0 comments) We report aircraft observations of the evolution of organic aerosol in the Manaus urban plume as it ages. We observe dynamic changes in the organic aerosol. The mean carbon oxidation state of the OA increases from −0.6 to −0.45. Hydrocarbon-like organic aerosol (HOA) mass is lost and is balanced out by formation of oxygenated organic aerosol (OOA). Because HOA loss is balanced by OOA formation, we observe little change in the net Δorg/ΔCO values with aging.

Description: Influence of anthropogenic emissions and boundary conditions on multi-model simulations of major air pollutants over Europe and North America in the framework of AQMEII3 Ulas Im, Jesper Heile Christensen, Camilla Geels, Kaj Mantzius Hansen, Jørgen Brandt, Efisio Solazzo, Ummugulsum Alyuz, Alessandra Balzarini, Rocio Baro, Roberto Bellasio, Roberto Bianconi, Johannes Bieser, Augustin Colette, Gabriele Curci, Aidan Farrow, Johannes Flemming, Andrea Fraser, Pedro Jimenez-Guerrero, Nutthida Kitwiroon, Peng Liu, Uarporn Nopmongcol, Laura Palacios-Peña, Guido Pirovano, Luca Pozzoli, Marje Prank, Rebecca Rose, Ranjeet Sokhi, Paolo Tuccella, Alper Unal, Marta G. Vivanco, Greg Yarwood, Christian Hogrefe, and Stefano Galmarini Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2017-1231,2018 Manuscript under review for ACP (discussion: open, 0 comments) We evaluate the impact of global and regional anthropogenic emission reductions on major air pollutant levels over Europe and North America, using a multi-model ensemble of regional chemistry and transport models. Results show that ozone levels are largely driven by long-range transport over both continents while other pollutants such as carbon monoxide or aerosols are mainly controlled by domestic sources. Use of multi model ensembles can help to reduce the uncertainties in individual models.

Description: Nighttime wind and scalar variability within and above an Amazonian canopy Pablo E. S. Oliveira, Otávio C. Acevedo, Matthias Sörgel, Anywhere Tsokankunku, Stefan Wolff, Alessandro C. Araújo, Rodrigo A. F. Souza, Marta O. Sá, Antônio O. Manzi, and Meinrat O. Andreae Atmos. Chem. Phys., 18, 3083-3099, https://doi.org/10.5194/acp-18-3083-2018, 2018 Carbon dioxide and latent heat fluxes within the canopy are dominated by low-frequency (nonturbulent) processes. There is a striking contrast between fully turbulent and intermittent nights, such that turbulent processes dominate the total nighttime exchange during the former, while nonturbulent processes are more relevant in the latter. In very stable nights, during which intermittent exchange prevails, the stable boundary layer may be shallower than the highest observational level at 80 m.

Description: Lower tropospheric ozone over India and its linkage to the South Asian monsoon Xiao Lu, Lin Zhang, Xiong Liu, Meng Gao, Yuanhong Zhao, and Jingyuan Shao Atmos. Chem. Phys., 18, 3101-3118, https://doi.org/10.5194/acp-18-3101-2018, 2018 Deteriorating tropospheric ozone pollution over India may not only affect local human health and vegetation but also perturb global ozone distribution. This study analyzes the processes controlling lower tropospheric ozone over India using OMI satellite observations (2006–2014) and model simulations (1990–2010). We show that the South Asian monsoon largely controls the seasonal cycle and interannual variability of Indian lower tropospheric ozone via changes in ozone production and transport.

Description: Investigating the yield of H 2 O and H 2 from methane oxidation in the stratosphere Franziska Frank, Patrick Jöckel, Sergey Gromov, and Martin Dameris Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-170,2018 Manuscript under review for ACP (discussion: open, 0 comments) Previously, it was assumed that one molecule of methane produces two water molecules. Applying various modeling concepts, we find that this overestimates the production in some areas of the atmosphere and underestimate it in other. Additionally, the chemical loss of water influences the actual abundance of it, especially in the upper atmosphere. We question the assumption of a vertically constant chemical production of water vapor and rather encourage to apply a sophisticated vertical profile.

Description: Ozone impacts of gas–aerosol uptake in global chemistry transport models Scarlet Stadtler, David Simpson, Sabine Schröder, Domenico Taraborrelli, Andreas Bott, and Martin Schultz Atmos. Chem. Phys., 18, 3147-3171, https://doi.org/10.5194/acp-18-3147-2018, 2018 The impact of six heterogeneous gas–aerosol uptake reactions on tropospheric ozone and nitrogen species was studied using two chemical transport models, the Meteorological Synthesizing Centre-West of the European Monitoring and Evaluation Programme (EMEP MSC-W) and the European Centre Hamburg general circulation model combined with versions of the Hamburg Aerosol Model and Model for Ozone and Related chemical Tracers (ECHAM-HAMMOZ). Species undergoing heterogeneous reactions in both models include N 2 O 5 , NO 3 , NO 2 , O 3 , HNO 3 , and HO 2 . Since heterogeneous reactions take place at the aerosol surface area, the modelled surface area density ( S a ) of both models was compared to a satellite product retrieving the surface area. This comparison shows a good agreement in global pattern and especially the capability of both models to capture the extreme aerosol loadings in east Asia. The impact of the heterogeneous reactions was evaluated by the simulation of a reference run containing all heterogeneous reactions and several sensitivity runs. One reaction was turned off in each sensitivity run to compare it with the reference run. The analysis of the sensitivity runs confirms that the globally most important heterogeneous reaction is the one of N 2 O 5 . Nevertheless, NO 2 , HNO 3 , and HO 2 heterogeneous reactions gain relevance particularly in east Asia due to the presence of high NO x concentrations and high S a in the same region. The heterogeneous reaction of O 3 itself on dust is of minor relevance compared to the other heterogeneous reactions. The impacts of the N 2 O 5 reactions show strong seasonal variations, with the biggest impacts on O 3 in springtime when photochemical reactions are active and N 2 O 5 levels still high. Evaluation of the models with northern hemispheric ozone surface observations yields a better agreement of the models with observations in terms of concentration levels, variability, and temporal correlations at most sites when the heterogeneous reactions are incorporated. Our results are loosely consistent with results from earlier studies, although the magnitude of changes induced by N 2 O 5 reaction is at the low end of estimates, which seems to fit a trend, whereby the more recent the study the lower the impacts of these reactions.

Description: Exploring the relationship between surface PM 2.5 and meteorology in Northern India Jordan L. Schnell, Vaishali Naik, Larry W. Horowitz, Fabien Paulot, Jingqiu Mao, Paul Ginoux, Ming Zhao, and Kirpa Ram Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-24,2018 Manuscript under review for ACP (discussion: open, 0 comments) We evaluate the ability of a developmental version of the NOAA GFDL Atmospheric Model, version 4 to simulate observed wintertime pollution and its relationship to weather over Northern India, one of the most densely populated and polluted regions in world. We also compare two emission inventories and find that the newest version dramatically improves our simulation. Observed and modeled pollution is the highest within the Indo-Gangetic Plain, where it is closely related to near-surface weather.

Description: Aerosol–cloud interactions in mixed-phase convective clouds – Part 1: Aerosol perturbations Annette K. Miltenberger, Paul R. Field, Adrian A. Hill, Phil Rosenberg, Ben J. Shipway, Jonathan M. Wilkinson, Robert Scovell, and Alan M. Blyth Atmos. Chem. Phys., 18, 3119-3145, https://doi.org/10.5194/acp-18-3119-2018, 2018 Changes induced by perturbed aerosol conditions in moderately deep mixed-phase convective clouds (cloud top height  ∼  5 km) developing along sea-breeze convergence lines are investigated with high-resolution numerical model simulations. The simulations utilise the newly developed Cloud–AeroSol Interacting Microphysics (CASIM) module for the Unified Model (UM), which allows for the representation of the two-way interaction between cloud and aerosol fields. Simulations are evaluated against observations collected during the COnvective Precipitation Experiment (COPE) field campaign over the southwestern peninsula of the UK in 2013. The simulations compare favourably with observed thermodynamic profiles, cloud base cloud droplet number concentrations (CDNC), cloud depth, and radar reflectivity statistics. Including the modification of aerosol fields by cloud microphysical processes improves the correspondence with observed CDNC values and spatial variability, but reduces the agreement with observations for average cloud size and cloud top height. Accumulated precipitation is suppressed for higher-aerosol conditions before clouds become organised along the sea-breeze convergence lines. Changes in precipitation are smaller in simulations with aerosol processing. The precipitation suppression is due to less efficient precipitation production by warm-phase microphysics, consistent with parcel model predictions. In contrast, after convective cells organise along the sea-breeze convergence zone, accumulated precipitation increases with aerosol concentrations. Condensate production increases with the aerosol concentrations due to higher vertical velocities in the convective cores and higher cloud top heights. However, for the highest-aerosol scenarios, no further increase in the condensate production occurs, as clouds grow into an upper-level stable layer. In these cases, the reduced precipitation efficiency (PE) dominates the precipitation response and no further precipitation enhancement occurs. Previous studies of deep convective clouds have related larger vertical velocities under high-aerosol conditions to enhanced latent heating from freezing. In the presented simulations changes in latent heating above the 0°C are negligible, but latent heating from condensation increases with aerosol concentrations. It is hypothesised that this increase is related to changes in the cloud field structure reducing the mixing of environmental air into the convective core. The precipitation response of the deeper mixed-phase clouds along well-established convergence lines can be the opposite of predictions from parcel models. This occurs when clouds interact with a pre-existing thermodynamic environment and cloud field structural changes occur that are not captured by simple parcel model approaches.

Description: Atmospheric QBO and ENSO indices with high vertical resolution from GNSS radio occultation temperature measurements Hallgeir Wilhelmsen, Florian Ladstädter, Barbara Scherllin-Pirscher, and Andrea K. Steiner Atmos. Meas. Tech., 11, 1333-1346, https://doi.org/10.5194/amt-11-1333-2018, 2018 Tropical atmospheric variability is often described using proxy indices of the Quasi-Biennial Oscillation and the El Niño–Southern Oscillation. We introduce new proxies derived from GNSS radio occultation (RO) satellite measurements. Using the high vertical resolution of the RO temperature fields we obtain altitude-resolved indices which can improve the description of atmospheric variability patterns and can be used in climate studies where a detailed knowledge of these patterns is required.

Description: Unraveling hydrometeor mixtures in polarimetric radar measurements Nikola Besic, Josué Gehring, Christophe Praz, Jordi Figueras i Ventura, Jacopo Grazioli, Marco Gabella, Urs Germann, and Alexis Berne Atmos. Meas. Tech. Discuss., https//doi.org/10.5194/amt-2018-58,2018 Manuscript under review for AMT (discussion: open, 0 comments) In this paper we propose an innovative approach for hydrometeor de-mixing, i.e. to identify and quantify the presence of mixtures of different hydrometeor types in a radar sampling volume. It is a bin-based approach, inspired by conventional decomposition methods, and evaluated using C and X band radar measurements compared with synchronous ground observations. The paper also investigates the potential influence of incoherency in the backscattering from hydrometeor mixtures in a radar volume.

Description: The SPARC water vapour assessment II: Comparison of stratospheric and lower mesospheric water vapour time series observed from satellites Farahnaz Khosrawi, Stefan Lossow, Gabriele P. Stiller, Karen H. Rosenlof, Joachim Urban, John P. Burrows, Robert P. Damadeo, Patrick Eriksson, Maya García-Comas, John C. Gille, Yasuko Kasai, Michael Kiefer, Gerald E. Nedoluha, Stefan Noël, Piera Raspollini, William G. Read, Alexei Rozanov, Christopher E. Sioris, Kaley A. Walker, and Katja Weigel Atmos. Meas. Tech. Discuss., https//doi.org/10.5194/amt-2018-33,2018 Manuscript under review for AMT (discussion: open, 0 comments) Time series of stratospheric and lower mesospheric water vapour using 33 data sets were compared in the framework of the second SPARC water vapour assessment. We find that all data sets can be considered in observational and modelling studies addressing e.g. stratospheric and lower mesospheric water vapour variability and trends when data set specific characteristics (e.g. a drift) and restrictions (e.g. temporal and spatial coverage) are taken into account.

Description: Shipborne Wind Measurement and Motion-induced Error Correction of a Coherent Doppler Lidar over the Yellow Sea in 2014 Xiaochun Zhai, Songhua Wu, Bingyi Liu, Xiaoquan Song, and Jiaping Yin Atmos. Meas. Tech., 11, 1313-1331, https://doi.org/10.5194/amt-11-1313-2018, 2018 A Doppler wind lidar attitude correction method is presented. This algorithm-based method relaxes the requirements for mechanical stability and active compensation mechanisms. A shipborne wind measurement campaign was carried out in the Yellow Sea, 2014. Comparison between lidar and radiosonde wind measurements shows good consistency, indicating that the method can provide continuous and high spatio-temporal resolution measurement of atmospheric turbulence processes in the marine boundary layer.

Description: Evaluation of linear regression techniques for atmospheric applications: the importance of appropriate weighting Cheng Wu and Jian Zhen Yu Atmos. Meas. Tech., 11, 1233-1250, https://doi.org/10.5194/amt-11-1233-2018, 2018 A new data generation scheme that employs the Mersenne twister (MT) pseudorandom number generator is proposed to conduct benchmark tests on a variety of linear regression techniques. With an appropriate weighting, Deming regression (DR), weighted ODR (WODR), and York regression (YR) are recommended for atmospheric studies when both x and y data have measurement errors. An Igor-based program (Scatter Plot) is developed to facilitate the regression implementation.

Description: Comparisons of the tropospheric specific humidity from GPS radio occultations with ERA-Interim, NASA MERRA, and AIRS data Panagiotis Vergados, Anthony J. Mannucci, Chi O. Ao, Olga Verkhoglyadova, and Byron Iijima Atmos. Meas. Tech., 11, 1193-1206, https://doi.org/10.5194/amt-11-1193-2018, 2018 This study cross-compares the 10-year record of GPS radio occultation (GPS-RO) specific humidity product against independent databases (e.g., AIRS satellite, NASA/MERRA, and ERA-Interim). Our objective is to investigate the suitability of the GPS-RO humidity as a climate variable, which the science community could use in climate research. GPS-RO offers high vertical resolution, low sensitivity to clouds, and long-term stability making GPS-RO humidity a valuable complementary data set.

Description: A full-mission data set of H 2 O and HDO columns from SCIAMACHY 2.3 μm reflectance measurements Andreas Schneider, Tobias Borsdorff, Joost aan de Brugh, Haili Hu, and Jochen Landgraf Atmos. Meas. Tech. Discuss., https//doi.org/10.5194/amt-2017-489,2018 Manuscript under review for AMT (discussion: open, 0 comments) A new data set of vertical column densities of the water vapour isotopologues H 2 O and HDO retrieved from shortwave infrared measurements (2339 nm to 2383 nm) by the SCIAMACHY satellite instrument for the whole mission period from 2003 to 2012 is presented. The data are validated against ground-based Fourier transform infrared measurements. High-altitude stations observe different air columns, thus in this case collocated scenes with clouds around station height are needed for agreement.

Description: Reflected ray retrieval from radio occultation data using radio holographic filtering of wave fields in ray space Michael E. Gorbunov, Estel Cardellach, and Kent B. Lauritsen Atmos. Meas. Tech., 11, 1181-1191, https://doi.org/10.5194/amt-11-1181-2018, 2018 We apply linear and non-linear representations of wave fields, based on Fourier integral operators and Wigner distribution function, to the retrieval of reflected rays from radio occultation observations. We introduce a reflection index that characterizes the relative intensity of the reflected ray. A comparison of indices evaluated for a large base of events including the visual identification of reflections indicated a good agreement with our definition of reflection index.

Description: The Effect of Instrumental Stray Light on Brewer and Dobson Total Ozone Measurements Omid Moeini, Zahra Vaziri, C. Thomas McElroy, David W. Tarasick, Robert D. Evans, Irina Petropavlovskikh, and Keh-Harng Feng Atmos. Meas. Tech. Discuss., https//doi.org/10.5194/amt-2018-2,2018 Manuscript under review for AMT (discussion: open, 0 comments) This study documents the error caused by the effect of stray light in the Brewer and Dobson total ozone measurements using a mathematical model for each instrument. The errors caused by stray light are particularly significant at high latitudes in the late winter and early spring when measurements are made at large solar zenith angles and large total ozone column. It is considerable importance if those data are to be used for trend analysis or satellite data validation.

Description: Information content analysis: the potential for methane isotopologue retrieval from GOSAT-2 Edward Malina, Yukio Yoshida, Tsuneo Matsunaga, and Jan-Peter Muller Atmos. Meas. Tech., 11, 1159-1179, https://doi.org/10.5194/amt-11-1159-2018, 2018 We present an assessment of the predicted information content and retrieval errors for 13 CH 4 retrieval from the planned GOSAT-2 satellite, assuming a wide range of land surface conditions. Retrieval of this quantity may allow for estimation of methane source types (e.g. biological or non-biological) based on the δ 13 C metric. We conclude that GOSAT-2 can be used for this purpose (to an accuracy of 10 ‰) assuming sufficient spatial (regional) and temporal (at least monthly) averaging.

Description: Retrieval of health-related UV doses from PAR measurements Marcelo de Paula Corrêa, Sophie Godin-Beekmann, Fabrina Bolzan Martins, Kátia Mendes, Martial Haeffelin, Miguel Rivas, and Elisa Rojas Atmos. Meas. Tech. Discuss., https//doi.org/10.5194/amt-2017-466,2018 Manuscript under review for AMT (discussion: open, 0 comments) This paper provides a very simple method for UV index estimation from PAR measurements. These latter are generally performed by cheaper instruments and commonly found in any ordinary meteorological station. A large dataset collected in South America and Europe was used to test this method and thes results are comparable to the instrumental errors. For this reason, the method is a useful tool for UV index evaluations in regions lacking adequate instrumentation.

Description: Water vapour retrieval using the Precision Solar Spectroradiometer Panagiotis-Ioannis Raptis, Stelios Kazadzis, Julian Gröbner, Natalia Kouremeti, Lionel Doppler, Ralf Becker, and Constantinos Helmis Atmos. Meas. Tech., 11, 1143-1157, https://doi.org/10.5194/amt-11-1143-2018, 2018 The purpose of this work is to retrieve integrated water vapour using spectral measurements from Precision Solar Spectroradiometer (PSR). Two different approaches were developed one using single-channel direct sun irradiance measurements, and the second one integrating at a certain spectral region. The results of the spectral approach are closer to the retrievals of non-photometric techniques (GPS, microwave radiometer and radiosondes), suggesting this method provide more accurate IWV product.

Description: Potential of INSAT-3D Sounder Derived Total Precipitable Water Product for Weather Forecast Shailesh Parihar, Ashim Kumar Mitra, and Rajiv Bhatla Atmos. Meas. Tech. Discuss., https//doi.org/10.5194/amt-2018-8,2018 Manuscript under review for AMT (discussion: open, 0 comments) Current work is based on operational work carried out at IMD, New Delhi using INSAT-3D satellite derived sounder product TPW for the weather events such as rainfall and thunderstorm. The INSAT-3D TPW is being used by forecasters as well as many user community from last 2 years. This work is mainly bring out the in-depth validation with in-situ ground measurement data as well as GNSS system for its suitability in weather prediction. This paper can be utilized operationally for weather purpose.

Description: Eolian dust dispersal patterns since the last glacial period in eastern Central Asia: insights from a loess-paleosol sequence in the Ili Basin Yue Li, Yougui Song, Kathryn E. Fitzsimmons, Hong Chang, Rustam Orozbaev, and Xinxin Li Clim. Past, 14, 271-286, https://doi.org/10.5194/cp-14-271-2018, 2018 This paper finds a close tie between loess magnetic susceptibility and wind strength in the Ili Basin, eastern Central Asia, and identifies three distinct aerodynamic environments with end-member modeling analysis of grain size. The Siberian High is the dominant influence on wind dynamics, resulting in loess deposition, and acts as a teleconnection between the climatic systems of the North Atlantic and East Asia in the high northern latitudes, but not for the mid-latitude westerlies.

Description: Climate impact on the development of Pre-Classic Maya civilization Kees Nooren, Wim Z. Hoek, Brian J. Dermody, Didier Galop, Sarah Metcalfe, Gerald Islebe, and Hans Middelkoop Clim. Past Discuss., https//doi.org/10.5194/cp-2018-15,2018 Manuscript under review for CP (discussion: open, 0 comments) We present two new palaeoclimatic records for the Central Maya Lowlands, adding valuable new insights into the impact of climate change on the development of Maya civilization. Lake Tuspan's diatom record is indicative of precipitation changes at a local scale, while a beach ridge elevation record from world’s largest late Holocene beach ridge plain provides a regional picture.

Description: Astronomical tunings of the Oligocene–Miocene transition from Pacific Ocean Site U1334 and implications for the carbon cycle Helen M. Beddow, Diederik Liebrand, Douglas S. Wilson, Frits J. Hilgen, Appy Sluijs, Bridget S. Wade, and Lucas J. Lourens Clim. Past, 14, 255-270, https://doi.org/10.5194/cp-14-255-2018, 2018 We present two astronomy-based timescales for climate records from the Pacific Ocean. These records range from 24 to 22 million years ago, a time period when Earth was warmer than today and the only land ice was located on Antarctica. We use tectonic plate-pair spreading rates to test the two timescales, which shows that the carbonate record yields the best timescale. In turn, this implies that Earth’s climate system and carbon cycle responded slowly to changes in incoming solar radiation.

Description: Random and externally controlled occurrence of Dansgaard-Oeschger events Johannes Lohmann and Peter D. Ditlevsen Clim. Past Discuss., https//doi.org/10.5194/cp-2018-3,2018 Manuscript under review for CP (discussion: open, 0 comments) The climate of the last glacial period has been frequently interrupted by rapid warming events, the cause of which is still unknown. One open question is whether the occurrence of events is random or externally controlled. We studied the temporal characteristics of warm and cold phases using statistical null models and find that they are well described as random processes modulated by two different external climate factors. This may help distinguish physical mechanisms for rapid climate change.

Description: The Ross Sea Dipole – temperature, snow accumulation and sea ice variability in the Ross Sea region, Antarctica, over the past 2700 years Nancy A. N. Bertler, Howard Conway, Dorthe Dahl-Jensen, Daniel B. Emanuelsson, Mai Winstrup, Paul T. Vallelonga, James E. Lee, Ed J. Brook, Jeffrey P. Severinghaus, Taylor J. Fudge, Elizabeth D. Keller, W. Troy Baisden, Richard C. A. Hindmarsh, Peter D. Neff, Thomas Blunier, Ross Edwards, Paul A. Mayewski, Sepp Kipfstuhl, Christo Buizert, Silvia Canessa, Ruzica Dadic, Helle A. Kjær, Andrei Kurbatov, Dongqi Zhang, Edwin D. Waddington, Giovanni Baccolo, Thomas Beers, Hannah J. Brightley, Lionel Carter, David Clemens-Sewall, Viorela G. Ciobanu, Barbara Delmonte, Lukas Eling, Aja Ellis, Shruthi Ganesh, Nicholas R. Golledge, Skylar Haines, Michael Handley, Robert L. Hawley, Chad M. Hogan, Katelyn M. Johnson, Elena Korotkikh, Daniel P. Lowry, Darcy Mandeno, Robert M. McKay, James A. Menking, Timothy R. Naish, Caroline Noerling, Agathe Ollive, Anaïs Orsi, Bernadette C. Proemse, Alexander R. Pyne, Rebecca L. Pyne, James Renwick, Reed P. Scherer, Stefanie Semper, Marius Simonsen, Sharon B. Sneed, Eric J. Steig, Andrea Tuohy, Abhijith Ulayottil Venugopal, Fernando Valero-Delgado, Janani Venkatesh, Feitang Wang, Shimeng Wang, Dominic A. Winski, V. Holly L. Winton, Arran Whiteford, Cunde Xiao, Jiao Yang, and Xin Zhang Clim. Past, 14, 193-214, https://doi.org/10.5194/cp-14-193-2018, 2018 Temperature and snow accumulation records from the annually dated Roosevelt Island Climate Evolution (RICE) ice core show that for the past 2 700 years, the eastern Ross Sea warmed, while the western Ross Sea showed no trend and West Antarctica cooled. From the 17th century onwards, this dipole relationship changed. Now all three regions show concurrent warming, with snow accumulation declining in West Antarctica and the eastern Ross Sea.

Description: Signal detection in global mean temperatures after “Paris”: an uncertainty and sensitivity analysis Hans Visser, Sönke Dangendorf, Detlef P. van Vuuren, Bram Bregman, and Arthur C. Petersen Clim. Past, 14, 139-155, https://doi.org/10.5194/cp-14-139-2018, 2018 In December 2015, 195 countries agreed in Paris to hold the increase in global temperature well below 2.0 °C. However, the Paris Agreement is not conclusive as regards methods to calculate it. To find answers to these questions we performed an uncertainty and sensitivity analysis where datasets, model choices, choices for pre-industrial and warming definitions have been varied. Based on these findings we propose an estimate for signal progression in global temperature since pre-industrial time.

Description: Eolian dust dispersal patterns since the last glacial period in eastern Central Asia: insights from a loess-paleosol sequence in the Ili Basin Yue Li, Yougui Song, Kathryn E. Fitzsimmons, Hong Chang, Rustam Orozbaev, and Xinxin Li Clim. Past, 14, 271-286, https://doi.org/10.5194/cp-14-271-2018, 2018 This paper finds a close tie between loess magnetic susceptibility and wind strength in the Ili Basin, eastern Central Asia, and identifies three distinct aerodynamic environments with end-member modeling analysis of grain size. The Siberian High is the dominant influence on wind dynamics, resulting in loess deposition, and acts as a teleconnection between the climatic systems of the North Atlantic and East Asia in the high northern latitudes, but not for the mid-latitude westerlies.

Description: Holocene climate aridification trend and human impact interrupted by millennial- and centennial-scale climate fluctuations from a new sedimentary record from Padul (Sierra Nevada, southern Iberian Peninsula) María J. Ramos-Román, Gonzalo Jiménez-Moreno, Jon Camuera, Antonio García-Alix, R. Scott Anderson, Francisco J. Jiménez-Espejo, and José S. Carrión Clim. Past, 14, 117-137, https://doi.org/10.5194/cp-14-117-2018, 2018 In this study we carried out a multiproxy high-resolution analysis on a sediment record from the Padul Basin in the Sierra Nevada (southern Iberian Peninsula). Padul is a classical and very unique site from the Mediterranean area as it contains a very long and continuous Quaternary sedimentary record. However, the uppermost part of the record was never recovered. In this study we focus on the last 4700 cal yr BP of Holocene climate variability and human activity in the Mediterranean area.

Description: Climate impact on the development of Pre-Classic Maya civilization Kees Nooren, Wim Z. Hoek, Brian J. Dermody, Didier Galop, Sarah Metcalfe, Gerald Islebe, and Hans Middelkoop Clim. Past Discuss., https//doi.org/10.5194/cp-2018-15,2018 Manuscript under review for CP (discussion: open, 0 comments) We present two new palaeoclimatic records for the Central Maya Lowlands, adding valuable new insights into the impact of climate change on the development of Maya civilization. Lake Tuspan's diatom record is indicative of precipitation changes at a local scale, while a beach ridge elevation record from world’s largest late Holocene beach ridge plain provides a regional picture.

Description: Technical note: Optimizing the utility of combined GPR, OSL, and LiDAR (GOaL) to extract paleoenvironmental records and decipher shoreline evolution Amy J. Dougherty, Jeong-Heon Choi, Chris S. M. Turney, and Anthony Dosseto Clim. Past Discuss., https//doi.org/10.5194/cp-2018-4,2018 Manuscript under review for CP (discussion: open, 2 comments) Records of past sea levels, storms, and their impacts on coastline are crucial in forecasting future changes resulting from anthropogenic global warming. Coastal barriers that have prograded over the Holocene preserve within their accreting sands history of storm erosion and changes in sea level. High-resolution geophysics, geochronology, and remote sensing techniques offer an optimal way to extract these records and decipher shoreline evolution: Light Detection and Ranging (LiDAR) images the lateral extent of relict shoreline dune morphology; Ground Penetrating Radar (GPR) data records paleo-dune, beach and nearshore stratigraphy; Optically Stimulated Luminescence (OSL) dates when sand grains were deposited that form these shorelines. Utilization of these technological advances has recently become more prevalent in coastal research. The resolution and sensitivity of these methods offer unique insights on coastal environments and their relationship to past climate change. However, discrepancies in analysis and presentation of the data can result in erroneous interpretations. When utilized correctly on prograded barriers these methods (independently or in various combinations) have produced storm records, constructed sea-level curves, quantified sediment budgets, and deciphered coastal evolution. Therefore, combining the application of GPR, OSL, and LiDAR (GOaL) on one prograded barrier has the potential to generate detailed records of storms, sea level, and sediment supply for that coastline. Obtaining this GOaL hat-trick can provide valuable insights into how these three factors influenced past and future barrier evolution. Here we argue that systematically achieving GOaL hat-tricks on some of the 300+ prograded barriers worldwide would allow us to disentangle local patterns of sediment supply from regional effects of storms or global changes in sea level, allowing direct comparison to climate proxy records. To fully realize this aim requires standardization of methods to optimize results. The impetus for this initiative is to establish a framework for consistent data analysis that maximizes the potential of GOaL to contribute to climate change research and assist coastal communities in mitigating future impacts of global warming.

Description: Astronomical tunings of the Oligocene–Miocene transition from Pacific Ocean Site U1334 and implications for the carbon cycle Helen M. Beddow, Diederik Liebrand, Douglas S. Wilson, Frits J. Hilgen, Appy Sluijs, Bridget S. Wade, and Lucas J. Lourens Clim. Past, 14, 255-270, https://doi.org/10.5194/cp-14-255-2018, 2018 We present two astronomy-based timescales for climate records from the Pacific Ocean. These records range from 24 to 22 million years ago, a time period when Earth was warmer than today and the only land ice was located on Antarctica. We use tectonic plate-pair spreading rates to test the two timescales, which shows that the carbonate record yields the best timescale. In turn, this implies that Earth’s climate system and carbon cycle responded slowly to changes in incoming solar radiation.

Description: Glacial Inception on Baffin Island: The Interaction of Ice Flow and Meteorology Leah Birch, Timothy Cronin, and Eli Tziperman Clim. Past Discuss., https//doi.org/10.5194/cp-2018-5,2018 Manuscript under review for CP (discussion: open, 1 comment) Over the past 0.8 million years, 100 kyr ice ages have dominated Earth's climate with geological evidence suggesting the last glacial inception began in the mountains of Baffin Island. Currently, state-of-the-art global climate models (GCMs) have difficulty simulating glacial inception, possibly due in part to their coarse horizontal resolution and the neglect of ice flow dynamics in some models. We attempt to address the initial inception problem on Baffin Island by asynchronously coupling the Weather Research and Forecast model (WRF), configured as a high resolution inner domain over Baffin and an outer domain incorporating much of North America, to an ice flow model using the shallow ice approximation. The mass balance is calculated from WRF simulations, and used to drive the ice model, which updates the ice extent and elevation, that then serve as inputs to the next WRF run. We drive the regional WRF configuration using atmospheric boundary conditions from 1986 that correspond to a relatively cold summer, and with 115 kya insolation. Initially, ice accumulates on mountain glaciers, driving downslope ice flow which expands the size of the ice caps. However, continued iterations of the atmosphere and ice models reveal a stagnation of the ice sheet on Baffin Island, driven by melting due to warmer temperatures at the margins of the ice caps. This warming is caused by changes in the larger-scale circulation that are forced by elevation changes due to the ice growth. A stabilizing feedback between ice elevation and atmospheric circulation thus prevents full inception from occurring.

Description: Climate information preserved in seasonal water isotope at NEEM: relationships with temperature, circulation and sea ice Minjie Zheng, Jesper Sjolte, Florian Adolphi, Bo Møllesøe Vinther, Hans Christian Steen-Larsen, Trevor James Popp, and Raimund Muscheler Clim. Past Discuss., https//doi.org/10.5194/cp-2018-8,2018 Manuscript under review for CP (discussion: open, 0 comments) Analyzing seasonally resolved δ 18 O ice core data can aid the interpretation of the climate information in ice cores, providing also insights into factors governing the δ 18 O signal that cannot be deciphered by investigating the annual δ 18 O data only. However, the seasonal isotope signal has not yet to be investigated in northern Greenland, e.g. at the NEEM (North Greenland Eemian Ice Drilling) ice core drill site. Here we analyze seasonally resolved δ 18 O data from four shallow NEEM ice cores covering the last 150 years. Based on correlation analysis with observed temperature, we attribute about 70 % and 30 % of annual accumulation to summer and winter respectively. The NEEM summer δ 18 O signal correlates strongly with summer western Greenland coastal temperature and with the first principal component (PC1) of summer δ 18 O from multiple seasonally resolved ice cores from central/southern Greenland. However, there are no significant correlations between NEEM winter δ 18 O data and western Greenland coastal winter temperature, or southern/central Greenland winter δ 18 O PC1. The stronger correlation with temperature during summer and the dominance of summer precipitation skew the annual δ 18 O signal in NEEM. The strong footprint of temperature in NEEM summer δ 18 O record also suggests that the summer δ 18 O record, rather than the winter δ 18 O record, is a better temperature proxy at the NEEM site. Despite dominant signal of North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation (AMO) in the central-southern ice cores data, both NAO and AMO exert weak influences on NEEM seasonal δ 18 O variations. The NEEM seasonal δ 18 O is found to be highly correlated with Baffin Bay sea ice concentration (SIC) in satellite observation period (1979–2004), suggesting a connection of the sea ice extent with δ 18 O at NEEM. NEEM winter δ 18 O significantly correlates with SIC even for the period prior to satellite observation (1901–1978). The NEEM winter δ 18 O may reflect sea ice variations of Baffin Bay rather than temperature itself. This study shows that seasonally resolved δ 18 O records, especially for sites with seasonal precipitation bias such as NEEM, provide a better understanding of how changing air temperature and circulation patterns are associated with the variability of the δ 18 O records.

Description: Response of the carbon cycle in an intermediate complexity model to the different climate configurations of the last nine interglacials Nathaelle Bouttes, Didier Swingedouw, Didier M. Roche, Maria F. Sanchez-Goni, and Xavier Crosta Clim. Past, 14, 239-253, https://doi.org/10.5194/cp-14-239-2018, 2018 Atmospheric CO 2 is key for climate change. CO 2 is lower during the oldest warm period of the last million years, the interglacials, than during the most recent ones (since 430 000 years ago). This difference has not been explained yet, but could be due to changes of ocean circulation. We test this hypothesis and the role of vegetation and ice sheets using an intermediate complexity model. We show that only small changes of CO 2 can be obtained, underlying missing feedbacks or mechanisms.

Description: A model-data comparison of the Last Glacial Maximum surface temperature changes Akil Hossain, Xu Zhang, and Gerrit Lohmann Clim. Past Discuss., https//doi.org/10.5194/cp-2018-9,2018 Manuscript under review for CP (discussion: open, 0 comments) Over the Last Glacial Maximum (LGM, ~ 21 ka BP), the presence of vast Northern Hemisphere ice-sheets caused abrupt changes in surface topography and background climatic state. While the ice-sheet extent is well known, several conflicting ice-sheet topography reconstructions suggest that there is uncertainty in this boundary condition. The terrestrial and sea surface temperature (SST) of the LGM as simulated with six different Laurentide Ice Sheet (LIS) reconstructions in a fully coupled Earth System Model (COSMOS) have been compared with the subfossil pollen and plant macrofossil based and marine temperature proxies reconstruction. The terrestrial reconstruction shows a similar pattern and in good agreement with model data. The SST proxy dataset comprises a global compilation of planktonic foraminifera, diatoms, radiolarian, dinocyst, alkenones and planktonic foraminifera Mg / Ca-derived SST estimates. Significant mismatches between modeled and reconstructed SST have been observed. Among the six LIS reconstructions, Tarasov’s LIS reconstruction shows the highest correlation with reconstructed terrestrial and SST. In the case of radiolarian, Mg / Ca, diatoms and foraminifera show a positive correlation while dinocyst and alkenones show very low and negative correlation with the model. Dinocyst-based SST records are much warmer than reconstructed by other proxies as well as Pre-industrial (PI) temperature. However, there are large discrepancies between model temperatures and temperature recorded by different proxies. Eight different PMIP3 models also compared with temperature proxies reconstruction which show mismatches with the proxy records might be due to misinterpreted and/or biased proxy records. Therefore, it has been speculated that considering different habitat depths and growing seasons of the planktonic organisms used for SST reconstruction could provide a better agreement of proxy data with model results on a regional scale. Moreover, it can reduce model-data misfits. It is found that shifting in the habitat depth and living season can remove parts of the observed model-data mismatches in SST anomalies.

Description: Sedproxy: a forward model for sediment archived climate proxies Andrew M. Dolman and Thomas Laepple Clim. Past Discuss., https//doi.org/10.5194/cp-2018-13,2018 Manuscript under review for CP (discussion: open, 0 comments) Climate proxies from marine sediments provide an important record of past temperatures, but contain noise from many sources. These include mixing by burrowing organisms, seasonal and habitat biases, measurement error and small sample size effects. We have created a forward model that simulates the creation of proxy records and provide it as a user-friendly R package. It allows multiple sources of uncertainty to be considered together when interpreting proxy climate records.

Description: The ENSO teleconnections to the Indian summer monsoon climate through the Last Millennium as simulated by the PMIP3 Charan Teja Tejavath, Karumuri Ashok, Supriyo Chakraborty, and Rengaswamy Ramesh Clim. Past Discuss., https//doi.org/10.5194/cp-2018-7,2018 Manuscript under review for CP (discussion: open, 1 comment) Analysing multiple CMIP5/PMIP3 Last Millennium simulations, we find that the Indian region was warmer and wetter during the medieval warm period, and cooler and drier in the little ice age, as compared to the last millennium mean conditions. This supports findings from the few available proxy findings. The Indian summer monsoon-ENSO association is robust through the last millennium, but varied on centennial time scales.

Description: Evidence for increased expression of the Amundsen Sea Low over the South Atlantic during the late Holocene Zoë Thomas, Richard T. Jones, Chris Fogwill, Jackie Hatton, Alan Williams, Alan Hogg, Scott Mooney, Philip Jones, David Lister, Paul Mayewski, and Chris Turney Clim. Past Discuss., https//doi.org/10.5194/cp-2018-11,2018 Manuscript under review for CP (discussion: open, 0 comments) We report a high-resolution study of a 5000 year-long peat record from the Falkland Islands, an area sensitive to the dynamics of the Amundsen Sea Low, which plays a major role in modulating the Southern Ocean climate. We find wetter, colder conditions between 5000 and 2500 years ago due to enhanced southerly airflow, with the establishment of drier and warmer conditions from 2500 years to present, implying more westerly airflow and increased projection of the ASL onto the South Atlantic.

Description: Sensitivity of the Eocene climate to CO 2 and orbital variability John S. Keery, Philip B. Holden, and Neil R. Edwards Clim. Past, 14, 215-238, https://doi.org/10.5194/cp-14-215-2018, 2018 In the Eocene (~ 55 million years ago), the Earth had high levels of atmospheric CO 2 , so studies of the Eocene can provide insights into the likely effects of present-day fossil fuel burning. We ran a low-resolution but very fast climate model with 50 combinations of CO 2 and orbital parameters, and an Eocene layout of the oceans and continents. Climatic effects of CO 2 are dominant but precession and obliquity strongly influence monsoon rainfall and ocean–land temperature contrasts, respectively.

Description: On the mechanisms of warming the mid-Pliocene and the inference of a hierarchy of climate sensitivities with relevance to the understanding of climate futures Deepak Chandan and W. Richard Peltier Clim. Past Discuss., https//doi.org/10.5194/cp-2018-18,2018 Manuscript under review for CP (discussion: open, 0 comments) We infer the physical mechanisms by which the mid-Pliocene could have sustained a warm climate. We also provide a mid-Pliocene perspective on a range of climate sensitivities applicable on several timescales. Warming inferred on the basis of these sensitivity parameters is compared to forecasted levels of warming. This leads us to conclude that projections for 300–500 years into the future underestimate the potential for warming because they do not account for long timescale feedback processes.

Description: The effect of high dust amount on the surface temperature during the Last Glacial Maximum: A modelling study using MIROC-ESM Rumi Ohgaito, Ayako Abe-Ouchi, Ryouta O'ishi, Toshihiko Takemura, Akinori Ito, Tomohiro Hajima, Shingo Watanabe, and Michio Kawamiya Clim. Past Discuss., https//doi.org/10.5194/cp-2018-2,2018 Manuscript under review for CP (discussion: open, 1 comment) The behaviour of dust on climate can be investigated using past climate. The Last Glacial Maximum (LGM, 21 000 years before present) is known to be dustier. We investigated the impact of plausible dust distribution on the climate of the LGM using an Earth System Model and found that the effect of the LGM dust results in less cooling over the polar regions. Main finding is that the radiative perturbation by the high dust loading in the troposphere acts to warm the surface surrounding Antarctica.

Description: 300 years of hydrological records and societal responses to droughts and floods on the Pacific coast of Central America Alvaro Guevara-Murua, Caroline A. Williams, Erica J. Hendy, and Pablo Imbach Clim. Past, 14, 175-191, https://doi.org/10.5194/cp-14-175-2018, 2018 This study reconstructs a new semi-quantitative rainfall index for the Pacific coast of Central America using documentary sources for the period 1640 to 1945. In addition, we explore the various mechanisms and processes that may explain inter-annual and inter-decadal rainfall variability over the Pacific coast of Central America.

Description: Random and externally controlled occurrence of Dansgaard-Oeschger events Johannes Lohmann and Peter D. Ditlevsen Clim. Past Discuss., https//doi.org/10.5194/cp-2018-3,2018 Manuscript under review for CP (discussion: open, 0 comments) The climate of the last glacial period has been frequently interrupted by rapid warming events, the cause of which is still unknown. One open question is whether the occurrence of events is random or externally controlled. We studied the temporal characteristics of warm and cold phases using statistical null models and find that they are well described as random processes modulated by two different external climate factors. This may help distinguish physical mechanisms for rapid climate change.

Description: The Ross Sea Dipole – temperature, snow accumulation and sea ice variability in the Ross Sea region, Antarctica, over the past 2700 years Nancy A. N. Bertler, Howard Conway, Dorthe Dahl-Jensen, Daniel B. Emanuelsson, Mai Winstrup, Paul T. Vallelonga, James E. Lee, Ed J. Brook, Jeffrey P. Severinghaus, Taylor J. Fudge, Elizabeth D. Keller, W. Troy Baisden, Richard C. A. Hindmarsh, Peter D. Neff, Thomas Blunier, Ross Edwards, Paul A. Mayewski, Sepp Kipfstuhl, Christo Buizert, Silvia Canessa, Ruzica Dadic, Helle A. Kjær, Andrei Kurbatov, Dongqi Zhang, Edwin D. Waddington, Giovanni Baccolo, Thomas Beers, Hannah J. Brightley, Lionel Carter, David Clemens-Sewall, Viorela G. Ciobanu, Barbara Delmonte, Lukas Eling, Aja Ellis, Shruthi Ganesh, Nicholas R. Golledge, Skylar Haines, Michael Handley, Robert L. Hawley, Chad M. Hogan, Katelyn M. Johnson, Elena Korotkikh, Daniel P. Lowry, Darcy Mandeno, Robert M. McKay, James A. Menking, Timothy R. Naish, Caroline Noerling, Agathe Ollive, Anaïs Orsi, Bernadette C. Proemse, Alexander R. Pyne, Rebecca L. Pyne, James Renwick, Reed P. Scherer, Stefanie Semper, Marius Simonsen, Sharon B. Sneed, Eric J. Steig, Andrea Tuohy, Abhijith Ulayottil Venugopal, Fernando Valero-Delgado, Janani Venkatesh, Feitang Wang, Shimeng Wang, Dominic A. Winski, V. Holly L. Winton, Arran Whiteford, Cunde Xiao, Jiao Yang, and Xin Zhang Clim. Past, 14, 193-214, https://doi.org/10.5194/cp-14-193-2018, 2018 Temperature and snow accumulation records from the annually dated Roosevelt Island Climate Evolution (RICE) ice core show that for the past 2 700 years, the eastern Ross Sea warmed, while the western Ross Sea showed no trend and West Antarctica cooled. From the 17th century onwards, this dipole relationship changed. Now all three regions show concurrent warming, with snow accumulation declining in West Antarctica and the eastern Ross Sea.

Description: Insights into Atlantic multidecadal variability using the Last Millennium Reanalysis framework Hansi K. A. Singh, Gregory J. Hakim, Robert Tardif, Julien Emile-Geay, and David C. Noone Clim. Past, 14, 157-174, https://doi.org/10.5194/cp-14-157-2018, 2018 The Atlantic Multidecadal Oscillation (AMO) is prominent in the climate system. We study the AMO over the last 2000 years using a novel proxy framework, the Last Millennium Reanalysis. We find that the AMO is linked to continental warming, Arctic sea ice retreat, and an Atlantic precipitation shift. Low clouds decrease globally. We find no distinct multidecadal spectral peak in the AMO over the last 2 millennia, suggesting that human activities may have enhanced the AMO in the modern era.

Description: Signal detection in global mean temperatures after “Paris”: an uncertainty and sensitivity analysis Hans Visser, Sönke Dangendorf, Detlef P. van Vuuren, Bram Bregman, and Arthur C. Petersen Clim. Past, 14, 139-155, https://doi.org/10.5194/cp-14-139-2018, 2018 In December 2015, 195 countries agreed in Paris to hold the increase in global temperature well below 2.0 °C. However, the Paris Agreement is not conclusive as regards methods to calculate it. To find answers to these questions we performed an uncertainty and sensitivity analysis where datasets, model choices, choices for pre-industrial and warming definitions have been varied. Based on these findings we propose an estimate for signal progression in global temperature since pre-industrial time.

Description: Glacial Inception on Baffin Island: The Interaction of Ice Flow and Meteorology Leah Birch, Timothy Cronin, and Eli Tziperman Clim. Past Discuss., https//doi.org/10.5194/cp-2018-5,2018 Manuscript under review for CP (discussion: open, 1 comment) Over the past 0.8 million years, 100 kyr ice ages have dominated Earth's climate with geological evidence suggesting the last glacial inception began in the mountains of Baffin Island. Currently, state-of-the-art global climate models (GCMs) have difficulty simulating glacial inception, possibly due in part to their coarse horizontal resolution and the neglect of ice flow dynamics in some models. We attempt to address the initial inception problem on Baffin Island by asynchronously coupling the Weather Research and Forecast model (WRF), configured as a high resolution inner domain over Baffin and an outer domain incorporating much of North America, to an ice flow model using the shallow ice approximation. The mass balance is calculated from WRF simulations, and used to drive the ice model, which updates the ice extent and elevation, that then serve as inputs to the next WRF run. We drive the regional WRF configuration using atmospheric boundary conditions from 1986 that correspond to a relatively cold summer, and with 115 kya insolation. Initially, ice accumulates on mountain glaciers, driving downslope ice flow which expands the size of the ice caps. However, continued iterations of the atmosphere and ice models reveal a stagnation of the ice sheet on Baffin Island, driven by melting due to warmer temperatures at the margins of the ice caps. This warming is caused by changes in the larger-scale circulation that are forced by elevation changes due to the ice growth. A stabilizing feedback between ice elevation and atmospheric circulation thus prevents full inception from occurring.

Description: Holocene climate aridification trend and human impact interrupted by millennial- and centennial-scale climate fluctuations from a new sedimentary record from Padul (Sierra Nevada, southern Iberian Peninsula) María J. Ramos-Román, Gonzalo Jiménez-Moreno, Jon Camuera, Antonio García-Alix, R. Scott Anderson, Francisco J. Jiménez-Espejo, and José S. Carrión Clim. Past, 14, 117-137, https://doi.org/10.5194/cp-14-117-2018, 2018 In this study we carried out a multiproxy high-resolution analysis on a sediment record from the Padul Basin in the Sierra Nevada (southern Iberian Peninsula). Padul is a classical and very unique site from the Mediterranean area as it contains a very long and continuous Quaternary sedimentary record. However, the uppermost part of the record was never recovered. In this study we focus on the last 4700 cal yr BP of Holocene climate variability and human activity in the Mediterranean area.

Description: Technical note: Optimizing the utility of combined GPR, OSL, and LiDAR (GOaL) to extract paleoenvironmental records and decipher shoreline evolution Amy J. Dougherty, Jeong-Heon Choi, Chris S. M. Turney, and Anthony Dosseto Clim. Past Discuss., https//doi.org/10.5194/cp-2018-4,2018 Manuscript under review for CP (discussion: open, 2 comments) Records of past sea levels, storms, and their impacts on coastline are crucial in forecasting future changes resulting from anthropogenic global warming. Coastal barriers that have prograded over the Holocene preserve within their accreting sands history of storm erosion and changes in sea level. High-resolution geophysics, geochronology, and remote sensing techniques offer an optimal way to extract these records and decipher shoreline evolution: Light Detection and Ranging (LiDAR) images the lateral extent of relict shoreline dune morphology; Ground Penetrating Radar (GPR) data records paleo-dune, beach and nearshore stratigraphy; Optically Stimulated Luminescence (OSL) dates when sand grains were deposited that form these shorelines. Utilization of these technological advances has recently become more prevalent in coastal research. The resolution and sensitivity of these methods offer unique insights on coastal environments and their relationship to past climate change. However, discrepancies in analysis and presentation of the data can result in erroneous interpretations. When utilized correctly on prograded barriers these methods (independently or in various combinations) have produced storm records, constructed sea-level curves, quantified sediment budgets, and deciphered coastal evolution. Therefore, combining the application of GPR, OSL, and LiDAR (GOaL) on one prograded barrier has the potential to generate detailed records of storms, sea level, and sediment supply for that coastline. Obtaining this GOaL hat-trick can provide valuable insights into how these three factors influenced past and future barrier evolution. Here we argue that systematically achieving GOaL hat-tricks on some of the 300+ prograded barriers worldwide would allow us to disentangle local patterns of sediment supply from regional effects of storms or global changes in sea level, allowing direct comparison to climate proxy records. To fully realize this aim requires standardization of methods to optimize results. The impetus for this initiative is to establish a framework for consistent data analysis that maximizes the potential of GOaL to contribute to climate change research and assist coastal communities in mitigating future impacts of global warming.