WILBERT

Description: Regional scaling of annual mean precipitation and water availability with global temperature change Peter Greve, Lukas Gudmundsson, and Sonia I. Seneviratne Earth Syst. Dynam., 9, 227-240, https://doi.org/10.5194/esd-9-227-2018, 2018 Assessing projected hydroclimatological changes is crucial, but associated with large uncertainties. We statistically assess here the response of precipitation and water availability to global temperature change, enabling us to estimate the significance of drying/wetting tendencies under anthropogenic climate change. We further show that opting for a 1.5 K warming target just slightly influences the mean response but could substantially reduce the risk of experiencing extreme changes.

Description: Advanced design and characterization methodologies for memory-aware CMOS power-amplifier implementation Martin Schleyer, Dominic Maurath, Heinrich Klar, and Friedel Gerfers Adv. Radio Sci., 15, 49-54, https://doi.org/10.5194/ars-15-49-2017, 2017 This paper reports on an effective root-cause analysis method of memory effects in power amplifiers, as well as introduces compensation techniques on a circuit design level. Despite conventional memory-effect approaches, the discussed method uses a two-tone scan over a wide operation and modulation range. The approach is demonstrated on a 65-nm CMOS power amplifier with an OIP1 of 27 dBm and a PAE of over 30 % using WCDMA and LTE signals.

Description: An interoperable research data infrastructure to support climate service development Tiziana De Filippis, Leandro Rocchi, and Elena Rapisardi Adv. Sci. Res., 14, 335-340, https://doi.org/10.5194/asr-14-335-2018, 2018 Accessibility, availability, re-use and re-distribution of scientific data are prerequisites to build climate services across Europe. The proposed architecture uses open-source tools and interoperable standards to ensure sustainability in the development and deployment of Web applications. The availability of structured raw data as customized information paves the way for building climate service purveyors to support adaptation, mitigation and risk management at different scales.

Description: Wind regimes and their relation to synoptic variables using self-organizing maps Sigalit Berkovic Adv. Sci. Res., 15, 1-9, https://doi.org/10.5194/asr-15-1-2018, 2018 This study exemplifies the ability of the self-organizing maps method to directly define well known wind regimes over Israel during the entire year, except summer, period at 12:00 UTC. This procedure may be applied at other hours and is highly relevant to future automatic climatological analysis and applications. The investigation is performed by analysing surface wind measurements. The relation between the synoptic variables and the wind regimes is revealed from composite calculations.

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: 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: 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 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: Increasing persistent haze in Beijing: potential impacts of weakening East Asian winter monsoons associated with northwestern Pacific sea surface temperature trends Lin Pei, Zhongwei Yan, Zhaobin Sun, Shiguang Miao, and Yao Yao Atmos. Chem. Phys., 18, 3173-3183, https://doi.org/10.5194/acp-18-3173-2018, 2018 This paper demonstrates the increasing frequency of persistent haze events (PHE) in Beijing based on updated observations and explores the associated changes in large-scale atmospheric circulations with possible links to the large-scale warming trend. We propose a more concrete observation-based mechanism for explaining how the local PHE in Beijing change with large-scale climate warming via the sea surface temperature anomaly in the northwestern Pacific.

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: 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: 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: 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: 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: A high-resolution inventory of air pollutant emissions from crop residue burning in China Xiaohui Zhang, Yan Lu, Qin'geng Wang, and Xin Qian Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2017-1113,2018 Manuscript under review for ACP (discussion: open, 0 comments) Activity data at prefectural-city level combined with high-resolution land use data were adopted to improve spatial resolution and detailed crop rotations and harvest times in different regions were considered in determining temporal distribution. Also, MODIS fire products were applied to verify the spatial and temporal variations of the emissions. Results showed that high emissions were generally located in Eastern, Central and Northeastern China, and temporally peaking in June and October.

Description: Technical Note: Atmospheric CO 2 inversions on the mesoscale using data-driven prior uncertainties: methodology and system evaluation Panagiotis Kountouris, Christoph Gerbig, Christian Rödenbeck, Ute Karstens, Thomas Frank Koch, and Martin Heimann Atmos. Chem. Phys., 18, 3027-3045, https://doi.org/10.5194/acp-18-3027-2018, 2018 Atmospheric inversions are widely used in the optimization of surface carbon fluxes on a regional scale using information from atmospheric CO 2 dry mole fractions. In many studies the prior flux uncertainty applied to the inversion schemes does not directly reflect the true flux uncertainties but is used to regularize the inverse problem. Here, we aim to implement an inversion scheme using the Jena inversion system and applying a prior flux error structure derived from a model–data residual analysis using high spatial and temporal resolution over a full year period in the European domain. We analyzed the performance of the inversion system with a synthetic experiment, in which the flux constraint is derived following the same residual analysis but applied to the model–model mismatch. The synthetic study showed a quite good agreement between posterior and true fluxes on European, country, annual and monthly scales. Posterior monthly and country-aggregated fluxes improved their correlation coefficient with the known truth by 7 % compared to the prior estimates when compared to the reference, with a mean correlation of 0.92. The ratio of the SD between the posterior and reference and between the prior and reference was also reduced by 33 % with a mean value of 1.15. We identified temporal and spatial scales on which the inversion system maximizes the derived information; monthly temporal scales at around 200 km spatial resolution seem to maximize the information gain.

Description: Atmospheric CO 2 inversions on the mesoscale using data-driven prior uncertainties: quantification of the European terrestrial CO 2 fluxes Panagiotis Kountouris, Christoph Gerbig, Christian Rödenbeck, Ute Karstens, Thomas F. Koch, and Martin Heimann Atmos. Chem. Phys., 18, 3047-3064, https://doi.org/10.5194/acp-18-3047-2018, 2018 Optimized biogenic carbon fluxes for Europe were estimated from high-resolution regional-scale inversions, utilizing atmospheric CO 2 measurements at 16 stations for the year 2007. Additional sensitivity tests with different data-driven error structures were performed. As the atmospheric network is rather sparse and consequently contains large spatial gaps, we use a priori biospheric fluxes to further constrain the inversions. The biospheric fluxes were simulated by the Vegetation Photosynthesis and Respiration Model (VPRM) at a resolution of 0.1° and optimized against eddy covariance data. Overall we estimate an a priori uncertainty of 0.54 GtC yr −1 related to the poor spatial representation between the biospheric model and the ecosystem sites. The sink estimated from the atmospheric inversions for the area of Europe (as represented in the model domain) ranges between 0.23 and 0.38 GtC yr −1 (0.39 and 0.71 GtC yr −1 up-scaled to geographical Europe). This is within the range of posterior flux uncertainty estimates of previous studies using ground-based observations.

Description: Contrasting the co-variability of daytime cloud and precipitation over tropical land and ocean Daeho Jin, Lazaros Oreopoulos, Dongmin Lee, Nayeong Cho, and Jackson Tan Atmos. Chem. Phys., 18, 3065-3082, https://doi.org/10.5194/acp-18-3065-2018, 2018 To what degree can precipitation be predicted given information about clouds? Or, conversely, with precipitation information at hand, can we provide good guesses about the clouds responsible? To answer these questions, we performed joint analysis of rainfall and cloud data, which are significantly decoupled. We find that only for the deepest and thickest clouds does cloud amount relate strongly with the intensity of rainfall, and that the details are different over oceans and land.

Description: Extraction of wind and temperature information from hybrid 4D-Var assimilation of stratospheric ozone using NAVGEM Douglas R. Allen, Karl W. Hoppel, and David D. Kuhl Atmos. Chem. Phys., 18, 2999-3026, https://doi.org/10.5194/acp-18-2999-2018, 2018 This study examines whether ozone data in the stratosphere (10–50 km altitude) can be used to benefit weather forecasts. The approach involves creating simulated ozone data and assimilating these into the US Navy's global weather model. Key findings are that assimilation of dense and accurate ozone data markedly benefits winds and temperature. However, the benefit is small when realistic ozone data are assimilated along with currently available microwave and infrared sounding measurements.

Description: Establishing the Impact of Model Surfactants on Cloud Condensation Nuclei Activity of Sea Spray Aerosols Sara D. Forestieri, Sean M. Staudt, Thomas M. Kuborn, Katharine Faber, Christopher R. Ruehl, Timothy H. Bertram, and Christopher D. Cappa Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-207,2018 Manuscript under review for ACP (discussion: open, 0 comments) Our work establishes how surface tension reduction influences droplet growth and activation of simple sea spray mimics, i.e. NaCl coated with fatty acids. Fatty acids can substantially reduce droplet surface tension near activation, but have limited impact on activation. Coating of NaCl by stearic acid (a wax) impedes water uptake, but this impedance is removed if oleic acid (a liquid) is mixed in. The properties that surface active compounds need to impact activation are theoretically examined.

Description: Source apportionment of atmospheric aerosol in a marine dusty environment by Ionic/composition Mass Balance (IMB) João Cardoso, Susana M. Almeida, Teresa Nunes, Marina Almeida-Silva, Mário Cerqueira, Célia Alves, Fernando Rocha, Paula Chaves, Miguel Reis, Pedro Salvador, Begoña Artiñano, and Casimiro Pio Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-10,2018 Manuscript under review for ACP (discussion: open, 0 comments) Atmospheric aerosol was sampled in Cape Verde islands and analysed for chemical composition. Very high levels of dust were measured during the winter months, as a result of transport from Africa. Mass Balances were applied to the particulate material, permitting the determination of 7 different source contributions to the aerosol loading. The balance methodology compared well with Standard Source Apportionment methods, showing its capability for the source apportionment of aerosol particles.

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: Field calibration of electrochemical NO 2 sensors in a citizen science context Bas Mijling, Qijun Jiang, Dave de Jonge, and Stefano Bocconi Atmos. Meas. Tech., 11, 1297-1312, https://doi.org/10.5194/amt-11-1297-2018, 2018 Although in many cities the population is exposed to air pollution, real-time air quality is usually only measured at a few locations. New low-cost sensor technology has the potential to extend the monitoring network significantly. We show that citizen science campaigns using the current generations of electrochemical NO 2 sensors may provide useful complementary data on local air quality in an urban setting, provided that experiments are properly set up and the data are carefully analysed.

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: 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: Calibration and field testing of cavity ring-down laser spectrometers measuring CH 4 , CO 2 , and δ 13 CH 4 deployed on towers in the Marcellus Shale region Natasha L. Miles, Douglas K. Martins, Scott J. Richardson, Christopher W. Rella, Caleb Arata, Thomas Lauvaux, Kenneth J. Davis, Zachary R. Barkley, Kathryn McKain, and Colm Sweeney Atmos. Meas. Tech., 11, 1273-1295, https://doi.org/10.5194/amt-11-1273-2018, 2018 Analyzers measuring methane and methane isotopic ratio were deployed at four towers in the Marcellus Shale natural gas extraction region of Pennsylvania. The methane isotopic ratio is helpful for differentiating emissions from natural gas activities from other sources (e.g., landfills). We describe the analyzer calibration. The signals observed in the study region were generally small, but the instrumental performance demonstrated here could be used in regions with stronger enhancements.

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: Interlaboratory comparison of δ 13 C and δ D measurements of atmospheric CH 4 for combined use of data sets from different laboratories Taku Umezawa, Carl A. M. Brenninkmeijer, Thomas Röckmann, Carina van der Veen, Stanley C. Tyler, Ryo Fujita, Shinji Morimoto, Shuji Aoki, Todd Sowers, Jochen Schmitt, Michael Bock, Jonas Beck, Hubertus Fischer, Sylvia E. Michel, Bruce H. Vaughn, John B. Miller, James W. C. White, Gordon Brailsford, Hinrich Schaefer, Peter Sperlich, Willi A. Brand, Michael Rothe, Thomas Blunier, David Lowry, Rebecca E. Fisher, Euan G. Nisbet, Andrew L. Rice, Peter Bergamaschi, Cordelia Veidt, and Ingeborg Levin Atmos. Meas. Tech., 11, 1207-1231, https://doi.org/10.5194/amt-11-1207-2018, 2018 Isotope measurements are useful for separating different methane sources. However, the lack of widely accepted standards and calibration methods for stable carbon and hydrogen isotopic ratios of methane in air has caused significant measurement offsets among laboratories. We conducted worldwide interlaboratory comparisons, surveyed the literature and assessed them systematically. This study may be of help in future attempts to harmonize data sets of isotopic composition of atmospheric methane.

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: Cloud fraction determined by thermal infrared and visible all-sky cameras Christine Aebi, Julian Gröbner, and Niklaus Kämpfer Atmos. Meas. Tech. Discuss., https//doi.org/10.5194/amt-2018-68,2018 Manuscript under review for AMT (discussion: open, 0 comments) A newly developed hemispherical thermal infrared cloud camera (IRCCAM) is presented. The IRCCAM allows to detect clouds automatically during day and nighttime. The cloud fraction determined from the IRCCAM is compared with the cloud fraction determined from other instruments over a time period of two years. The IRCCAM has an agreement of ±2 oktas cloud fraction in 90 % of the data compared to other instruments. There are no significant differences between seasons or different times of day.

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 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: 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: 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: 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: 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: Field calibration of electrochemical NO 2 sensors in a citizen science context Bas Mijling, Qijun Jiang, Dave de Jonge, and Stefano Bocconi Atmos. Meas. Tech., 11, 1297-1312, https://doi.org/10.5194/amt-11-1297-2018, 2018 Although in many cities the population is exposed to air pollution, real-time air quality is usually only measured at a few locations. New low-cost sensor technology has the potential to extend the monitoring network significantly. We show that citizen science campaigns using the current generations of electrochemical NO 2 sensors may provide useful complementary data on local air quality in an urban setting, provided that experiments are properly set up and the data are carefully analysed.

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: 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: Calibration and field testing of cavity ring-down laser spectrometers measuring CH 4 , CO 2 , and δ 13 CH 4 deployed on towers in the Marcellus Shale region Natasha L. Miles, Douglas K. Martins, Scott J. Richardson, Christopher W. Rella, Caleb Arata, Thomas Lauvaux, Kenneth J. Davis, Zachary R. Barkley, Kathryn McKain, and Colm Sweeney Atmos. Meas. Tech., 11, 1273-1295, https://doi.org/10.5194/amt-11-1273-2018, 2018 Analyzers measuring methane and methane isotopic ratio were deployed at four towers in the Marcellus Shale natural gas extraction region of Pennsylvania. The methane isotopic ratio is helpful for differentiating emissions from natural gas activities from other sources (e.g., landfills). We describe the analyzer calibration. The signals observed in the study region were generally small, but the instrumental performance demonstrated here could be used in regions with stronger enhancements.

Description: Interlaboratory comparison of δ 13 C and δ D measurements of atmospheric CH 4 for combined use of data sets from different laboratories Taku Umezawa, Carl A. M. Brenninkmeijer, Thomas Röckmann, Carina van der Veen, Stanley C. Tyler, Ryo Fujita, Shinji Morimoto, Shuji Aoki, Todd Sowers, Jochen Schmitt, Michael Bock, Jonas Beck, Hubertus Fischer, Sylvia E. Michel, Bruce H. Vaughn, John B. Miller, James W. C. White, Gordon Brailsford, Hinrich Schaefer, Peter Sperlich, Willi A. Brand, Michael Rothe, Thomas Blunier, David Lowry, Rebecca E. Fisher, Euan G. Nisbet, Andrew L. Rice, Peter Bergamaschi, Cordelia Veidt, and Ingeborg Levin Atmos. Meas. Tech., 11, 1207-1231, https://doi.org/10.5194/amt-11-1207-2018, 2018 Isotope measurements are useful for separating different methane sources. However, the lack of widely accepted standards and calibration methods for stable carbon and hydrogen isotopic ratios of methane in air has caused significant measurement offsets among laboratories. We conducted worldwide interlaboratory comparisons, surveyed the literature and assessed them systematically. This study may be of help in future attempts to harmonize data sets of isotopic composition of atmospheric methane.

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: 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: 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: Cloud fraction determined by thermal infrared and visible all-sky cameras Christine Aebi, Julian Gröbner, and Niklaus Kämpfer Atmos. Meas. Tech. Discuss., https//doi.org/10.5194/amt-2018-68,2018 Manuscript under review for AMT (discussion: open, 0 comments) A newly developed hemispherical thermal infrared cloud camera (IRCCAM) is presented. The IRCCAM allows to detect clouds automatically during day and nighttime. The cloud fraction determined from the IRCCAM is compared with the cloud fraction determined from other instruments over a time period of two years. The IRCCAM has an agreement of ±2 oktas cloud fraction in 90 % of the data compared to other instruments. There are no significant differences between seasons or different times of day.

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: 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: 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: 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: 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: Increasing persistent haze in Beijing: potential impacts of weakening East Asian winter monsoons associated with northwestern Pacific sea surface temperature trends Lin Pei, Zhongwei Yan, Zhaobin Sun, Shiguang Miao, and Yao Yao Atmos. Chem. Phys., 18, 3173-3183, https://doi.org/10.5194/acp-18-3173-2018, 2018 This paper demonstrates the increasing frequency of persistent haze events (PHE) in Beijing based on updated observations and explores the associated changes in large-scale atmospheric circulations with possible links to the large-scale warming trend. We propose a more concrete observation-based mechanism for explaining how the local PHE in Beijing change with large-scale climate warming via the sea surface temperature anomaly in the northwestern Pacific.

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: Fire intensity impacts on post-fire temperate coniferous forest net primary productivity Aaron M. Sparks, Crystal A. Kolden, Alistair M. S. Smith, Luigi Boschetti, Daniel M. Johnson, and Mark A. Cochrane Biogeosciences, 15, 1173-1183, https://doi.org/10.5194/bg-15-1173-2018, 2018 Through landscape-scale satellite observations we demonstrate that fire intensity has a dose–response relationship with temperate forest net primary productivity. Increasing fire intensity resulted in persisting step-wise reductions in post-fire net primary productivity. Forests with higher proportions of fire-resistant species generally had lower reductions in post-fire net primary productivity. A conceptual framework for assessing spatiotemporal post-fire effects is presented.

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: 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: 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: 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: Ice-nucleating efficiency of aerosol particles and possible sources at three coastal marine sites Meng Si, Victoria E. Irish, Ryan H. Mason, Jesús Vergara-Temprado, Sarah Hanna, Luis A. Ladino, Jacqueline D. Yakobi-Hancock, Corinne L. Schiller, Jeremy J. B. Wentzell, Jonathan P. D. Abbatt, Ken S. Carslaw, Benjamin J. Murray, and Allan K. Bertram Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-81,2018 Manuscript under review for ACP (discussion: open, 0 comments) Using the concentrations of ice-nucleating particles (INPs) and total aerosol particles measured at three coastal marine sites, the ice-nucleating efficiency of aerosol particles as a function of size was determined. The ice-nucleating efficiency was strongly dependent on size, with larger particles being more efficient. This type of information can help determine or rule out the sources of INPs, and constrain future modeling of INPs and mixed-phase clouds.

Description: Aerosol optical properties over Europe: an evaluation of the AQMEII Phase 3 simulations against satellite observations Laura Palacios-Peña, Pedro Jiménez-Guerrero, Rocío Baró, Alessandra Balzarini, Roberto Bianconi, Gabriele Curci, Tony Christian Landi, Guido Pirovano, Marje Prank, Angelo Riccio, Paolo Tuccella, and Stefano Galmarini Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2017-1119,2018 Manuscript under review for ACP (discussion: open, 0 comments) The main uncertainties in estimates of changes in the Earth's energy budget are related to the role of atmospheric aerosols. These changes are caused mainly by aerosol-radiation (ARI) and aerosol-cloud interactions (ACI), which heavily depend on aerosol properties. From the 1980s, many international modelling initiatives have studied atmospheric aerosols and their climate effects. Phase 3 of the Air Quality Model Evaluation International Initiative (AQMEII) focuses on evaluating and intercomparing regional and linked global/regional modelling systems by collaborating with the Task Force on the Hemispheric Transport of Air Pollution Phase 2 (HTAP2) initiative. Within this framework, the main aim of this work was to evaluate the representation of aerosol optical depth (AOD) and the Ångström exponent (AE) by the AQMEII Phase 3 simulations over Europe. The evaluation was made using satellite data from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors on board the Terra and Aqua platforms. The results indicated that the skills of AQMEII simulations in the AOD representation produced fewer errors than in the AE. Regardless of the models and emissions used, models were skilful at representing the low and medium AOD values observed (below 0.5). However, high values (close to 1.0) were underestimated for biomass burning episodes, and were overestimated for desert dust contributions, related mainly to emission and boundary conditions. Despite this behaviour, the spatial and temporal variability of this variable was well-represented by all the models. Generally, the AE evaluation showed more serious errors than the AOD evaluation. Moreover, the observed variability of this parameter was strongly underestimated in all the simulations.

Description: A high-resolution inventory of air pollutant emissions from crop residue burning in China Xiaohui Zhang, Yan Lu, Qin'geng Wang, and Xin Qian Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2017-1113,2018 Manuscript under review for ACP (discussion: open, 0 comments) Activity data at prefectural-city level combined with high-resolution land use data were adopted to improve spatial resolution and detailed crop rotations and harvest times in different regions were considered in determining temporal distribution. Also, MODIS fire products were applied to verify the spatial and temporal variations of the emissions. Results showed that high emissions were generally located in Eastern, Central and Northeastern China, and temporally peaking in June and October.

Description: Atmospheric CO 2 inversions on the mesoscale using data-driven prior uncertainties: quantification of the European terrestrial CO 2 fluxes Panagiotis Kountouris, Christoph Gerbig, Christian Rödenbeck, Ute Karstens, Thomas F. Koch, and Martin Heimann Atmos. Chem. Phys., 18, 3047-3064, https://doi.org/10.5194/acp-18-3047-2018, 2018 Optimized biogenic carbon fluxes for Europe were estimated from high-resolution regional-scale inversions, utilizing atmospheric CO 2 measurements at 16 stations for the year 2007. Additional sensitivity tests with different data-driven error structures were performed. As the atmospheric network is rather sparse and consequently contains large spatial gaps, we use a priori biospheric fluxes to further constrain the inversions. The biospheric fluxes were simulated by the Vegetation Photosynthesis and Respiration Model (VPRM) at a resolution of 0.1° and optimized against eddy covariance data. Overall we estimate an a priori uncertainty of 0.54 GtC yr −1 related to the poor spatial representation between the biospheric model and the ecosystem sites. The sink estimated from the atmospheric inversions for the area of Europe (as represented in the model domain) ranges between 0.23 and 0.38 GtC yr −1 (0.39 and 0.71 GtC yr −1 up-scaled to geographical Europe). This is within the range of posterior flux uncertainty estimates of previous studies using ground-based observations.

Description: Technical Note: Atmospheric CO 2 inversions on the mesoscale using data-driven prior uncertainties: methodology and system evaluation Panagiotis Kountouris, Christoph Gerbig, Christian Rödenbeck, Ute Karstens, Thomas Frank Koch, and Martin Heimann Atmos. Chem. Phys., 18, 3027-3045, https://doi.org/10.5194/acp-18-3027-2018, 2018 Atmospheric inversions are widely used in the optimization of surface carbon fluxes on a regional scale using information from atmospheric CO 2 dry mole fractions. In many studies the prior flux uncertainty applied to the inversion schemes does not directly reflect the true flux uncertainties but is used to regularize the inverse problem. Here, we aim to implement an inversion scheme using the Jena inversion system and applying a prior flux error structure derived from a model–data residual analysis using high spatial and temporal resolution over a full year period in the European domain. We analyzed the performance of the inversion system with a synthetic experiment, in which the flux constraint is derived following the same residual analysis but applied to the model–model mismatch. The synthetic study showed a quite good agreement between posterior and true fluxes on European, country, annual and monthly scales. Posterior monthly and country-aggregated fluxes improved their correlation coefficient with the known truth by 7 % compared to the prior estimates when compared to the reference, with a mean correlation of 0.92. The ratio of the SD between the posterior and reference and between the prior and reference was also reduced by 33 % with a mean value of 1.15. We identified temporal and spatial scales on which the inversion system maximizes the derived information; monthly temporal scales at around 200 km spatial resolution seem to maximize the information gain.

Description: Contrasting the co-variability of daytime cloud and precipitation over tropical land and ocean Daeho Jin, Lazaros Oreopoulos, Dongmin Lee, Nayeong Cho, and Jackson Tan Atmos. Chem. Phys., 18, 3065-3082, https://doi.org/10.5194/acp-18-3065-2018, 2018 To what degree can precipitation be predicted given information about clouds? Or, conversely, with precipitation information at hand, can we provide good guesses about the clouds responsible? To answer these questions, we performed joint analysis of rainfall and cloud data, which are significantly decoupled. We find that only for the deepest and thickest clouds does cloud amount relate strongly with the intensity of rainfall, and that the details are different over oceans and land.

Description: Extraction of wind and temperature information from hybrid 4D-Var assimilation of stratospheric ozone using NAVGEM Douglas R. Allen, Karl W. Hoppel, and David D. Kuhl Atmos. Chem. Phys., 18, 2999-3026, https://doi.org/10.5194/acp-18-2999-2018, 2018 This study examines whether ozone data in the stratosphere (10–50 km altitude) can be used to benefit weather forecasts. The approach involves creating simulated ozone data and assimilating these into the US Navy's global weather model. Key findings are that assimilation of dense and accurate ozone data markedly benefits winds and temperature. However, the benefit is small when realistic ozone data are assimilated along with currently available microwave and infrared sounding measurements.

Description: Establishing the Impact of Model Surfactants on Cloud Condensation Nuclei Activity of Sea Spray Aerosols Sara D. Forestieri, Sean M. Staudt, Thomas M. Kuborn, Katharine Faber, Christopher R. Ruehl, Timothy H. Bertram, and Christopher D. Cappa Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-207,2018 Manuscript under review for ACP (discussion: open, 0 comments) Our work establishes how surface tension reduction influences droplet growth and activation of simple sea spray mimics, i.e. NaCl coated with fatty acids. Fatty acids can substantially reduce droplet surface tension near activation, but have limited impact on activation. Coating of NaCl by stearic acid (a wax) impedes water uptake, but this impedance is removed if oleic acid (a liquid) is mixed in. The properties that surface active compounds need to impact activation are theoretically examined.

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: 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: 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 goo