ALBERT

Description: 〈b〉Dynamic changes in optical and chemical properties of tar ball aerosols by atmospheric photochemical aging〈/b〉〈br〉 Chunlin Li, Quanfu He, Julian Schade, Johannes Passig, Ralf Zimmermann, Daphne Meidan, Alexander Laskin, and Yinon Rudich〈br〉 Atmos. Chem. Phys., 19, 139-163, https://doi.org/10.5194/acp-19-139-2019, 2019〈br〉 〈p〉Following wood pyrolysis, tar ball aerosols were laboratory generated from wood tar separated into polar and nonpolar phases. Chemical information of fresh tar balls was obtained from a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and single-particle laser desorption/resonance enhanced multiphoton ionization mass spectrometry (SP-LD-REMPI-MS). Their continuous refractive index (RI) between 365 and 425 nm was retrieved using a broadband cavity enhanced spectroscopy (BBCES). Dynamic changes in the optical and chemical properties for the nonpolar tar ball aerosols in 〈span〉NO〈sub〉〈i〉x〈/i〉〈/sub〉〈/span〉-dependent photochemical process were investigated in an oxidation flow reactor (OFR). Distinct differences in the chemical composition of the fresh polar and nonpolar tar aerosols were identified. Nonpolar tar aerosols contain predominantly high-molecular weight unsubstituted and alkyl-substituted polycylic aromatic hydrocarbons (PAHs), while polar tar aerosols consist of a high number of oxidized aromatic substances (e.g., methoxy-phenols, benzenediol) with higher O : C ratios and carbon oxidation states. Fresh tar balls have light absorption characteristics similar to atmospheric brown carbon (BrC) aerosol with higher absorption efficiency towards the UV wavelengths. The average retrieved RI is 〈span〉1.661+0.020〈i〉i〈/i〉〈/span〉 and 〈span〉1.635+0.003〈i〉i〈/i〉〈/span〉 for the nonpolar and polar tar aerosols, respectively, with an absorption Ångström exponent (AAE) between 5.7 and 7.8 in the detected wavelength range. The RI fits a volume mixing rule for internally mixed nonpolar/polar tar balls. The RI of the tar ball aerosols decreased with increasing wavelength under photochemical oxidation. Photolysis by UV light (254 nm), without strong oxidants in the system, slightly decreased the RI and increased the oxidation state of the tar balls. Oxidation under varying OH exposure levels and in the absence of 〈span〉NO〈sub〉〈i〉x〈/i〉〈/sub〉〈/span〉 diminished the absorption (bleaching) and increased the O : C ratio of the tar balls. The photobleaching via OH radical initiated oxidation is mainly attributed to decomposition of chromophoric aromatics, nitrogen-containing organics, and high-molecular weight components in the aged particles. Photolysis of nitrous oxide (〈span〉N〈sub〉2〈/sub〉O〈/span〉) was used to simulate 〈span〉NO〈sub〉〈i〉x〈/i〉〈/sub〉〈/span〉-dependent photochemical aging of tar balls in the OFR. Under high-〈span〉NO〈sub〉〈i〉x〈/i〉〈/sub〉〈/span〉 conditions with similar OH exposure, photochemical aging led to the formation of organic nitrates, and increased both oxidation degree and light absorption for the aged tar ball aerosols. These observations suggest that secondary organic nitrate formation counteracts the bleaching by OH radical photooxidation to eventually regain some absorption of the aged tar ball aerosols. The atmospheric implication and climate effects from tar balls upon various oxidation processes are briefly discussed.〈/p〉

Description: 〈b〉A Double ITCZ Phenomenology of Wind Errors in the Equatorial Atlantic in Seasonal Forecasts with ECMWF Models〈/b〉〈br〉 Jonathan K. P. Shonk, Teferi D. Demissie, and Thomas Toniazzo〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1316,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Modern climate models are affected by systematic biases that harm their ability to produce reliable seasonal forecasts and climate projections. In this study, we investigate causes of biases in wind patterns over the tropical Atlantic during northern spring in three related models. We find that the wind biases are associated with an increase in excess rainfall and convergence in the tropical western Atlantic at the start of April, leading to the redirection of trade winds away from the equator.

Description: 〈b〉New particle formation in the marine atmosphere during seven cruise campaigns〈/b〉〈br〉 Yujiao Zhu, Kai Li, Yanjie Shen, Yang Gao, Xiaohuan Liu, Yang Yu, Huiwang Gao, and Xiaohong Yao〈br〉 Atmos. Chem. Phys., 19, 89-113, https://doi.org/10.5194/acp-19-89-2019, 2019〈br〉 In this paper, we investigate new particle formation (NPF) events during seven cruises. NPF events were observed on 25 days and were most likely associated with the long-range transport of anthropogenic air pollutants. The relationship between the net generated amount of new particles and their apparent formation rate is established and explained in terms of the roles of different vapor precursors. The survival probability of new particles to CCN size is also discussed.

Description: 〈b〉Aircraft-based measurements of High Arctic springtime aerosol show evidence for vertically varying sources, transport and composition〈/b〉〈br〉 Megan D. Willis, Heiko Bozem, Daniel Kunkel, Alex K. Y. Lee, Hannes Schulz, Julia Burkart, Amir A. Aliabadi, Andreas B. Herber, W. Richard Leaitch, and Jonathan P. D. Abbatt〈br〉 Atmos. Chem. Phys., 19, 57-76, https://doi.org/10.5194/acp-19-57-2019, 2019〈br〉 The vertical distribution of Arctic aerosol is an important driver of its climate impacts. We present vertically resolved measurements of aerosol composition and properties made in the High Arctic during spring on an aircraft platform. We explore how aerosol properties are related to transport history and show evidence of vertical trends in aerosol sources, transport mechanisms and composition. These results will help us to better understand aerosol–climate interactions in the Arctic.

Description: 〈b〉Aerosol radiative effects with MACv2〈/b〉〈br〉 Stefan Kinne〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-949,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉onthly global maps for aerosol properties of the MACv2 climatology are applied in an off-line radiative transfer model to determine aerosol radiative effects. For details beyond global averages in most cases global maps are presented to visualize regional and seasonal details. Aside from the direct radiative (aerosol presence) effect, including those for aerosol components as extracted from MACv2 aerosol optics, also the major aerosol indirect radiative effect is covered. Hereby, the impact of smaller drops in water clouds due to added anthropogenic aerosol was simulated by applying a satellite retrieval based fit from locally associations between aerosol and drop concentrations over oceans. Present-day anthropogenic aerosols of MACv2 – on a global average basis – reduce the radiative net-fluxes at the top of the atmosphere (TOA) by −1.0 W/m〈sup〉2〈/sup〉 and at the surface by −2.1 W/m〈sup〉2〈/sup〉. Direct cooling contributions are only about half of indirect contributions (−.35 vs −.65) at TOA, but about twice at the surface (−1.45 vs −.65), as solar absorption of the direct effect warms the atmosphere by +1.1 W/m〈sup〉2〈/sup〉. Natural aerosols are on average less absorbing (for a relatively larger solar TOA cooling) and larger in size (now contributing with IR greenhouse warming). Thus, average TOA direct forcing efficiencies for total and anthropogenic aerosol happen to be similar: −11 W/m〈sup〉2〈/sup〉/AOD at all-sky and −24 W/m〈sup〉2〈/sup〉/AOD at clear-sky conditions. The present-day direct impact by all soot (BC) is globally averaged +0.55W/m〈sup〉2〈/sup〉 and at least half of it should be attributed to anthropogenic sources. Hereby any accuracy of anthropogenic impacts, not just for soot, suffers from the limited access to a pre-industrial reference. Anthropogenic uncertainty has a particular strong impact on aerosol indirect effects, which dominate the (TOA) forcing. Accounting for uncertainties in the anthropogenic definition, present-day aerosol forcing is estimated to stay within the −0.7 to −1.6 W/m〈sup〉2〈/sup〉 range, with a best estimate at −1 W/m〈sup〉2〈/sup〉. Calculations with model predicted temporal changes to anthropogenic AOD indicate that qualitatively the anthropogenic aerosol forcing has not changed much over the last decades and is not likely to increase over the next decades, despite strong regional shifts. These regional shifts explain most solar insolation (brightening or dimming) trends that have been observed by ground-based radiation data.〈/p〉

Description: 〈b〉Thermal structure of the mesopause region during the WADIS-2 rocket campaign〈/b〉〈br〉 Raimund Wörl, Boris Strelnikov, Timo P. Viehl, Josef Höffner, Pierre-Dominique Pautet, Michael J. Taylor, Yucheng Zhao, and Franz-Josef Lübken〈br〉 Atmos. Chem. Phys., 19, 77-88, https://doi.org/10.5194/acp-19-77-2019, 2019〈br〉 Simultaneous temperature measurements during the WADIS-2 rocket campaign are used to investigate the thermal structure of the mesopause region. Vertically and horizontally resolved in situ and remote measurements are in good agreement and show dominating long-term and large-scale waves with periods of 24 h and higher tidal harmonics. Only a few gravity waves with periods shorter than 6 h and small amplitudes are there.

Description: 〈b〉Classification of aerosol population type and cloud condensation nuclei properties in a coastal California littoral environment using an unsupervised cluster model〈/b〉〈br〉 Samuel A. Atwood, Sonia M. Kreidenweis, Paul J. DeMott, Markus D. Petters, Gavin C. Cornwell, Andrew C. Martin, and Kathryn A. Moore〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1297,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 This paper presents measurements of aerosol particles at a coastal location. The particles were classified into distinct aerosol types using both microphysical measurements and meteorological information, allowing rapid changes between the aerosol types to be reliably identified. These particles can alter cloud and precipitation processes, and inclusion of the differences between types can improve atmospheric models and remote sensing retrievals in littoral zones.

Description: 〈b〉Develop a coupled agent-based modeling approach for uncertain water management decisions〈/b〉〈br〉 Jin-Young Hyun, Shih-Yu Huang, Y. C. Ethan Yang, Vincent Tidwell, and Jordan Macknick〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2018-555,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 This study applies a 〈q〉two-way〈/q〉 coupled agent-based model (ABM) with a River-Reservoir management model (RiverWare) to address the interaction between human and natural systems using Bayesian Inference (BI) mapping joined with Cost-Loss (CL). The calibration results show that this methodology can capture the historical pattern of both human activities and natural dynamics and outperforms those without using BI and CL.

Description: 〈b〉Detection of Outflow of Formaldehyde and Glyoxal from the African continent to the Atlantic Ocean with a MAX-DOAS Instrument〈/b〉〈br〉 Lisa K. Behrens, Andreas Hilboll, Andreas Richter, Enno Peters, Leonardo M. A. Alvarado, Anna B. Kalisz Hedegaard, Folkard Wittrock, John P. Burrows, and Mihalis Vrekoussis〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1286,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 MAX-DOAS measurements were conducted on the research vessel Maria S. Merian during a cruise from the Azores to South Africa in October 2016. The measurements indicate enhanced levels of HCHO and CHOCHO over the remote Atlantic Ocean, which is unexpected due to their short lifetime. Precursors of these gases or gas-aerosol combinations might be transported. Model simulations indicate potential source regions over the African continent, probably related to biomass burning or biogenic emissions.

Description: 〈b〉Primary and secondary sources of ambient formaldehyde in the Yangtze River Delta based on OMPS observation〈/b〉〈br〉 Wenjing Su, Cheng Liu, Qihou Hu, Shaohua Zhao, Youwen Sun, Wei Wang, Yizhi Zhu, Jianguo Liu, and Jhoon Kim〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1192,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 For a better understanding of the pollution and atmospheric chemistry of HCHO, we evaluated its primary and secondary sources in the Yangtze River Delta based on HCHO column density from Ozone Mapping and Profiler Suite (OMPS) and combining with surface in-situ measurements. We found that secondary formation contributed most to ambient HCHO for a long time, but primary emission could be dominant in the winter. The usability of total HCHO as the proxy of VOCs reactivity depends on time scale.

Description: 〈b〉Insights into the O : C dependent mechanisms controlling the evaporation of α-pinene secondary organic aerosol particles〈/b〉〈br〉 Angela Buchholz, Andrew T. Lambe, Arttu Ylisirniö, Zijun Li, Olli-Pekka Tikkanen, Celia Faiola, Eetu Kari, Liqing Hao, Olli Luoma, Wei Huang, Claudia Mohr, Douglas R. Worsnop, Sergey A. Nizkorodov, Taina Yli-Juuti, Siegfried Schobesberger, and Annele Virtanen〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1305,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 We studied the evaporation of α-pinene secondary organic aerosol particles in clean air to derive their volatility from the observed size changes. We found that the particles became more resilient to evaporation with increased oxidative age, possibly increasing their lifetime in the atmosphere. Also, increased relative humidity increased the particle evaporation. Mass spectrometry measurements of the particles at different stages of evaporation revealed some water-induced composition changes.

Description: 〈b〉Analyses of temperature and precipitation in the Indian Jammu and Kashmir region for the 1980–2016 period: implications for remote influence and extreme events〈/b〉〈br〉 Sumira Nazir Zaz, Shakil Ahmad Romshoo, Ramkumar Thokuluwa Krishnamoorthy, and Yesubabu Viswanadhapalli〈br〉 Atmos. Chem. Phys., 19, 15-37, https://doi.org/10.5194/acp-19-15-2019, 2019〈br〉 This paper is of first of its kind for the Jammu and Kashmir (western Himalayas) region, India. It shows the clear relation between the upper tropospheric Rossby wave activity (potential vorticity at the 350 K potential temperature and 200 mb level surface pressure) and the surface weather parameters (e.g., precipitation) over a period of 3 decades during 1980–2016. This indicates that the climatic weather pattern over the Kashmir region is influenced mostly by global climate change processes.

Description: 〈b〉Large increases in N〈sub〉cn〈/sub〉 and N〈sub〉ccn〈/sub〉 together with a nucleation-modeparticle pool over the northwestern Pacific Ocean in the spring of 2014〈/b〉〈br〉 Juntao Wang, Yanjie Shen, Kai Li, Yang Gao, Huiwang Gao, and Xiaohong Yao〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1089,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 In this paper, we studied the spatiotemporal variability of N〈sub〉cn〈/sub〉 and particle number size distributions, as well as N〈sub〉ccn〈/sub〉 and CCN activities over the NWPO in the spring of 2014. Several new findings have been revealed and discussed, e.g., large increases of N〈sub〉cn〈/sub〉 and N〈sub〉ccn〈/sub〉, against historical data and small contributions of dust and BB aerosols to N〈sub〉cn〈/sub〉 and N〈sub〉ccn〈/sub〉 on the monthly time scale, etc. This work may help understand the influence of the current outflow from the Asian continent on the climate.

Description: 〈b〉On what scales can GOSAT flux inversions constrain anomalies in terrestrial ecosystems?〈/b〉〈br〉 Brendan Byrne, Dylan B. A. Jones, Kimberly Strong, Saroja M. Polavarapu, Anna B. Harper, David F. Baker, and Shamil Maksyutov〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-909,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Spatial and temporal variations in atmospheric CO〈sub〉2〈/sub〉 are driven by fluxes of CO〈sub〉2〈/sub〉 at Earth's surface. Therefore, measurements of variations in atmospheric CO〈sub〉2〈/sub〉 from satellites, such as the Greenhouse Gases Observing Satellite (GOSAT), inform the spatiotemporal variations in CO〈sub〉2〈/sub〉 fluxes at Earth's surface. In this study, we examine how well interannual variations in CO〈sub〉2〈/sub〉 surface fluxes can be estimated from GOSAT measurements. We show estimated CO〈sub〉2〈/sub〉 anomalies are correlated with temperature anomalies.

Description: 〈b〉A simple model for local-scale sensible and latent heat advection contributions to snowmelt〈/b〉〈br〉 Phillip Harder, John W. Pomeroy, and Warren D. Helgason〈br〉 Hydrol. Earth Syst. Sci., 23, 1-17, https://doi.org/10.5194/hess-23-1-2019, 2019〈br〉 As snow cover becomes patchy during snowmelt, energy is advected from warm snow-free surfaces to cold snow-covered surfaces. This paper proposes a simple sensible and latent heat advection model for snowmelt situations that can be coupled to one-dimensional energy balance snowmelt models. The model demonstrates that sensible and latent heat advection fluxes can compensate for one another, especially in early melt periods.

Description: 〈b〉Quantitative precipitation estimation with weather radar using a data- and information-based approach〈/b〉〈br〉 Malte Neuper and Uwe Ehret〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2018-606,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 In our study we apply a data-driven approach to estimate precipitation quantitatively with the use of weather radar data. The method is based on Information theory concepts. It uses predictive relations expressed by empirical discrete probability distributions directly derived from data rather than the standard deterministic functions.

Description: 〈b〉Time-variability of the fraction of young water in a small headwater catchment〈/b〉〈br〉 Michael P. Stockinger, Heye R. Bogena, Andreas Lücke, Christine Stumpp, and Harry Vereecken〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2018-604,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 Precipitation moves through the soil to become streamwater. The fraction of precipitation that became streamwater after 3 months (Fyw) can be calculated with the stable isotopes of water. Previously this was done for all the isotope data available, e.g., for several years. We used one year of data to calculate Fyw and moved this calculation time window over the time series. Results highlight that Fyw varies in time. Comparison studies of different regions should take this into account.

Description: 〈b〉Stochastic modeling of flow and conservative transport in three-dimensional discrete fracture networks〈/b〉〈br〉 I-Hsien Lee, Chuen-Fa Ni, Fang-Pang Lin, Chi-Ping Lin, and Chien-Chung Ke〈br〉 Hydrol. Earth Syst. Sci., 23, 19-34, https://doi.org/10.5194/hess-23-19-2019, 2019〈br〉 Few studies focused on the direct solution of the ADE for 3-D DFNs. The study is the first to solve the ADE and focus on assessing the velocity uncertainty in 3-D DFNs. The velocity uncertainty shows a limited range of influence close to the mean diameter of a fracture. The information is useful for engineering designs at sites with fractured rocks. We quantified that the tracer test in wells might lead to the overestimation of mean concentration and induce high uncertainty in fractured media.

Description: 〈b〉The importance of crystalline phases in ice nucleation by volcanic ash〈/b〉〈br〉 Elena C. Maters, Donald B. Dingwell, Corrado Cimarelli, Dirk Müller, Thomas F. Whale, and Benjamin J. Murray〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1326,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 This experimental study investigates the influence of volcanic ash chemical composition, crystallinity, and mineralogy on its ability to promote freezing of supercooled water. The results indicate that crystals in ash play a key role in this process, and suggest that alkali and plagioclase feldspars in ash may be highly ice-active. These findings contribute to improving understanding of the potential of ash emissions from different explosive eruptions to impact ice formation in the atmosphere.

Description: 〈b〉Local and regional contributions to fine particulate matter in the 18 cities of Sichuan Basin, southwestern China〈/b〉〈br〉 Xue Qiao, Hao Guo, Ya Tang, Pengfei Wang, Wenye Deng, Xing Zhao, Jianlin Hu, Qi Ying, and Hongliang Zhang〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1214,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 A source-oriented version of the CMAQ model was used to quantify contributions from nine regions to PM〈sub〉2.5〈/sub〉 and its components in the 18 cities within the Sichuan Basin. Non-local emissions contribute to 39~66 % and 25~52 % to the citywide average PM〈sub〉2.5〈/sub〉 concentrations of 45~126 and 14~31 μg m〈sup〉−3〈/sup〉 in the winter and summer, respectively. This study demonstrates the importance of joint emission control efforts among cities within the SCB and neighbor regions to the east.

Description: 〈b〉The significant contribution of HONO to secondary pollutants during a severe winter pollution event in southern China〈/b〉〈br〉 Xiao Fu, Tao Wang, Li Zhang, Qinyi Li, Zhe Wang, Men Xia, Hui Yun, Weihao Wang, Chuan Yu, Dingli Yue, Yan Zhou, Junyun Zheng, and Rui Han〈br〉 Atmos. Chem. Phys., 19, 1-14, https://doi.org/10.5194/acp-19-1-2019, 2019〈br〉 This study has identified the major contributors to the observed high HONO levels during a severe winter pollution episode and highlighted the importance of HONO chemistry in the combined photochemical and haze pollution in a subtropical region. It also highlighted the critical need to include and update HONO sources in regional air quality models in order to predict ozone and other secondary pollutants better during heavy pollution events in southern China and similar regions.

Description: 〈b〉On the fine vertical structure of the low troposphere over the coastal margins of East Antarctica〈/b〉〈br〉 Étienne Vignon, Olivier Traullé, and Alexis Berne〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1197,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 The sea-level rise associated to climate change will depend on how much the Antarctic ice sheet gain – viz precipitation – or loose mass. The precipitation simulation by climate models used for projections depends on the representation of the atmospheric circulation over and around Antarctica. Using daily measurements from balloon soundings at nine stations, this study characterizes the structure of the atmosphere over the Antarctic coast and assess its representation in a climate model.

Description: 〈b〉Is water vapor a key player of the wintertime haze in North China Plain?〈/b〉〈br〉 Jiarui Wu, Naifang Bei, Bo Hu, Suixin Liu, Meng Zhou, Qiyuan Wang, Xia Li, Lang Liu, Tian Feng, Zirui Liu, Yichen Wang, Junji Cao, Xuexi Tie, Jun Wang, Luisa T. Molina, and Guohui Li〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1289,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 The near-surface PM〈sub〉2.5〈/sub〉 contribution of the ALW total effect is 17.5 % in NCP, indicating that ALW plays an important role in the PM〈sub〉2.5〈/sub〉 formation during the wintertime haze pollution. Moreover, the ALW-HET overwhelmingly dominates the PM〈sub〉2.5〈/sub〉 enhancement due to the ALW. The ALW does not consistently enhance near-surface [PM〈sub〉2.5〈/sub〉] with increasing RH. When the RH exceeds 80 %, the contribution of the ALW commences to decrease caused by the high occurrence frequencies of precipitation.

Description: 〈b〉Towards an advanced observation system for the marine Arctic in the framework of the Pan-Eurasian Experiment (PEEX)〈/b〉〈br〉 Timo Vihma, Petteri Uotila, Stein Sandven, Dmitry Pozdnyakov, Alexander Makshtas, Alexander Pelyasov, Roberta Pirazzini, Finn Danielsen, Sergey Chalov, Hanna K. Lappalainen, Vladimir Ivanov, Ivan Frolov, Anna Albin, Bin Cheng, Sergey Dobrolyubov, Viktor Arkhipkin, Stanislav Myslenkov, Tuukka Petäjä, and Markku Kulmala〈br〉 Atmos. Chem. Phys., 19, 1941-1970, https://doi.org/10.5194/acp-19-1941-2019, 2019〈br〉 The Arctic marine climate system, ecosystems, and socio-economic systems are changing rapidly. This calls for the establishment of a marine Arctic component of the Pan-Eurasian Experiment (MA-PEEX), for which we present a plan. The program will promote international collaboration; sustainable marine meteorological, sea ice, and oceanographic observations; advanced data management; and multidisciplinary research on the marine Arctic and its interaction with the Eurasian continent.

Description: 〈b〉Multi-decadal Hydrologic Change and Variability in the Amazon River Basin: Understanding Terrestrial Water Storage Variations and Drought Characteristics〈/b〉〈br〉 Suyog Chaudhari, Yadu Pokhrel, Emilio Moran, and Gonzalo Miguez-Macho〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2019-57,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉We investigate the interannual and interdecadal hydrological changes in the Amazon river basin and its sub-basins during 1980–2015 period, using GRACE satellite data and a physically-based, 2-km grid continental scale hydrological model (Leaf-Hydro-Flood) that incorporates a prognostic groundwater scheme and the effects of land use land cover change (LULC). The analyses focus on the dominant mechanisms that modulate terrestrial water storage (TWS) variations and droughts. Our results indicate that (1) the model simulates the basin-averaged TWS variations remarkably well, however, disagreements are observed in spatial patterns of temporal trends for post-2008 period, (2) the 2010s is the driest period since 1980, characterized by a major shift in decadal mean compared to 2000s due to the increased frequency of droughts, (3) long-term trends in TWS suggests that the Amazon as a whole is getting wetter (1.13 mm/y), but its southern and south-eastern sub-basins are facing significant negative TWS trends, caused primarily by intensified LULC changes, (4) increasing divergence between dry season total water deficit (TWD) and TWS release (TWS-R) suggest a strengthening dry season, especially in the southern and south-eastern sub-basins, and (5) the sub-surface storage regulates the propagation of meteorological droughts into hydrological droughts by strongly modulating TWS release with respect to its storage preceding the drought condition. Our simulations provide crucial insight on the importance of sub-surface storage in alleviating surface water deficit across Amazon and open pathways for improving prediction and mitigation of extreme droughts under changing climate and increasing hydrologic alterations due to human activities (e.g., LULC change).〈/p〉

Description: 〈b〉Toward high-spatial resolution hydrological modeling for China: Calibrating the VIC model〈/b〉〈br〉 Bowen Zhu, Xianhong Xie, Chuiyu Lu, Shanshan Meng, Yi Yao, and Yibing Wang〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2019-72,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 The hydrological modeling of China have been limited to spatial resolutions of 10 km or greater, rendering it impossible to assess local conditions. In our study, we developed a hydrological modeling based on VIC model at a much finer spatial scale (~ 6 km). The simulated runoff, SM and ET were extensively evaluated using observations and remote sensing data. This high-resolution modeling is capable of capturing flood and drought events with respect to their timing, duration, and spatial extent.

Description: 〈b〉Faulting patterns in the Lower Yarmouk Gorge potentially influence groundwater flow paths〈/b〉〈br〉 Nimrod Inbar, Eliahu Rosenthal, Fabien Magri, Marwan Alraggad, Peter Möller, Akiva Flexer, Joseph Guttman, and Christian Siebert〈br〉 Hydrol. Earth Syst. Sci., 23, 763-771, https://doi.org/10.5194/hess-23-763-2019, 2019〈br〉 In areas of enigmatic hydrology, water scarcity, and transboundary water resources, management strategies should rely on comprehensive modeling which must be based on realistic geometry, including all relevant structural features. Based on available geophysical and geological data, a new faulting pattern in the Lower Yarmouk Gorge is suggested as a basis for hydrogeological modeling. Furthermore, unexpected pull-apart basin rim fault evolution is discussed in the context of tectonic collision.

Description: 〈b〉MICS-Asia III: Multi-model comparison and evaluation of aerosol over East Asia〈/b〉〈br〉 Lei Chen, Yi Gao, Meigen Zhang, Joshua S. Fu, Jia Zhu, Hong Liao, Jialin Li, Kan Huang, Baozhu Ge, Xuemei Wang, Yun Fat LAM, Chuan Yao Lin, Syuichi Itahashi, Tatsuya Nagashima, Mizuo Kajino, Kazuyo Yamaji, Zifa Wang, and Jun-ichi Kurokawa〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1346,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Simulated aerosol concentrations from 14 CTMs within the framework of MICS–Asia III are detailedly evaluated with an extensive set of measurements in East Asia. Similarities and differences among model performances are also analyzed. Although more considerable capacities for reproducing the aerosol concentrations and their variations are shown in current CTMs than those in MICS–Asia II, more efforts are needed to reduce diversities of simulated aerosol concentrations among air quality models.

Description: 〈b〉Systematic comparison of five machine-learning methods in classification and interpolation of soil particle size fractions using different transformed data〈/b〉〈br〉 Mo Zhang and Wenjiao Shi〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2018-584,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 1 comment)〈br〉 We systematically analyzed both direct (or indirect) soil texture classification and soil particle size fractions (psf) interpolation using five machine learning methods combined with untransformed and log ratio transformed data. The results showed that random forest had notable consequences for soil psf interpolation and soil texture classification (indirect performed better). Our systematic comparison helps to elucidate the processing and selection of compositional data in spatial simulation.

Description: 〈b〉Contributions of different anthropogenic volatile organic compound sources to ozone formation at a receptor site in the Pearl River Delta region and its policy implications〈/b〉〈br〉 Zhuoran He, Xuemei Wang, Zhenhao Ling, Jun Zhao, Hai Guo, Min Shao, and Zhe Wang〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1293,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 In this study, source apportionment of volatile organic compounds (VOCs) and their contributions to photochemical O〈sub〉3〈/sub〉 formation was analyzed by the Positive Matrix Factorization model and an observation-based model for data collected at a receptor site in the Pearl River Delta (PRD) region. Furthermore, the policies for controlling VOC were brief reviewed. The findings could provide quantitative information on devising appropriate measures on the VOCs, NOx, and O〈sub〉3〈/sub〉 pollution in PRD.

Description: 〈b〉Characterisation and source identification of biofluorescent aerosol emissions over winter and summer periods in the United Kingdom〈/b〉〈br〉 Elizabeth Forde, Martin Gallagher, Virginia Foot, Roland Sarda-Esteve, Ian Crawford, Paul Kaye, Warren Stanley, and David Topping〈br〉 Atmos. Chem. Phys., 19, 1665-1684, https://doi.org/10.5194/acp-19-1665-2019, 2019〈br〉 The abundance and diversity of airborne biological particles in different environments remains poorly constrained. Measurements of such particles were conducted at four sites in the United Kingdom, using real-time fluorescence instrumentation. Using local land cover types, sources of suspected particle types were identified and compared. Most sites exhibited a wet-discharged fungal spore dominance, with the exception of one site, which was inferred to be influenced by a local dairy farm.

Description: 〈b〉Evidence for a major missing source in the global chloromethane budget from stable carbon isotopes〈/b〉〈br〉 Enno Bahlmann, Frank Keppler, Julian Wittmer, Markus Greule, Heinz Friedrich Schöler, Richard Seifert, and Cornelius Zetzsch〈br〉 Atmos. Chem. Phys., 19, 1703-1719, https://doi.org/10.5194/acp-19-1703-2019, 2019〈br〉 Chloromethane is the most important natural carrier of chlorine to the stratosphere. From a newly determined carbon isotope effect of −11.2 ‰ for the tropospheric loss of CH〈sub〉3〈/sub〉Cl we derive a tropical rainforest CH〈sub〉3〈/sub〉Cl source of 670 ± 200 Gg a〈sup〉−1〈/sup〉, 60 % smaller than previous estimates. A revision of previous bottom-up estimates using above-ground biomass instead of rainforest area strongly supports this lower estimate. Our results suggest a large unknown tropical value of 1530 ± 200 Gg a〈sup〉−1〈/sup〉.

Description: 〈b〉New particle formation in the active volcanic plume of the Piton de la Fournaise: specific features from a long-term dataset〈/b〉〈br〉 Clémence Rose, Brice Foucart, David Picard, Aurélie Colomb, Jean-Marc Metzger, Pierre Tulet, and Karine Sellegri〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-100,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 New particle formation (NPF) is a significant climate-relevant source of aerosols in the atmosphere. We show that during the eruptive period of the Piton de la Fournaise in 2015, NPF was favoured compared to regular days. Using the largest data set ever reported in volcanic plume conditions, we quantify the emission rates of particles over a broad size range and provide a new statistically robust parameterization to take into account this important source of atmospheric particles in models.

Description: 〈b〉Turbulent enhancement of radar reflectivity factor for polydisperse cloud droplets〈/b〉〈br〉 Keigo Matsuda and Ryo Onishi〈br〉 Atmos. Chem. Phys., 19, 1785-1799, https://doi.org/10.5194/acp-19-1785-2019, 2019〈br〉 This paper presents a parameterization to predict the influence of microscale turbulent clustering of cloud droplets on the radar reflectivity factor, based on a direct numerical simulation (DNS) of turbulence. The proposed parameterization takes account of the turbulent clustering structure of droplets with arbitrary size distributions. This paper also discusses quantitative influences on realistic radar observations, applying the parameterization to high-resolution cloud-simulation data.

Description: 〈b〉Parameter-state ensemble thinning for short-term hydrological prediction〈/b〉〈br〉 Bruce Davison, Vincent Fortin, Alain Pietroniro, Man K. Yau, and Robert Leconte〈br〉 Hydrol. Earth Syst. Sci., 23, 741-762, https://doi.org/10.5194/hess-23-741-2019, 2019〈br〉 This paper explores a new method of predicting streamflow using a complex model. It makes use of streamflow observations to reduce an existing ensemble of model runs for predictive purposes. The study illustrated that the method could work given the proper constraints, which were only possible if there was enough knowledge about how the river responded to precipitation in the previous months. Ideas were discussed to allow the method to be used in a way to predict future streamflow.

Description: 〈b〉The influence of wind and land evapotranspiration on the variability of moisture sources and precipitation of the Yangtze River Valley〈/b〉〈br〉 Astrid Fremme and Harald Sodemann〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2018-629,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 This study examines the evaporation sources of precipitation falling over the Yangtze River Valley on China's East coast. The summer monsoon rainfall causes large seasonal and interannual variations which affect a large population. We found that evaporation from surrounding land regions is important, supplying more than half of the summertime precipitation. Extreme dry and wet summers are connected to contributions from specific land and ocean regions.

Description: 〈b〉Kinetic mass-transfer calculation of water isotope fractionation due to cloud microphysics in a regional meteorological model〈/b〉〈br〉 I-Chun Tsai, Wan-Yu Chen, Jen-Ping Chen, and Mao-Chang Liang〈br〉 Atmos. Chem. Phys., 19, 1753-1766, https://doi.org/10.5194/acp-19-1753-2019, 2019〈br〉 In conventional models, isotope exchange between liquid and gas phases is usually assumed to be in equilibrium, and the highly kinetic phase transformation processes inferred in clouds are yet to be fully investigated. We show that different factors controlling isotopic composition, including water vapor sources, atmospheric transport, phase transition pathways of water in clouds, and kinetic-versus-equilibrium mass transfer, contributed significantly to the variations in isotope composition.

Description: 〈b〉Biomass-burning smoke heights over the Amazon observed from space〈/b〉〈br〉 Laura Gonzalez-Alonso, Maria Val Martin, and Ralph A. Kahn〈br〉 Atmos. Chem. Phys., 19, 1685-1702, https://doi.org/10.5194/acp-19-1685-2019, 2019〈br〉 The vertical distribution of fire smoke and factors that control its rise had not yet been quantified across the Amazon. We developed a satellite-based long record of smoke plume heights. We find that smoke heights are driven by many factors: vegetation, seasonality, time of day, fire intensity, and atmospheric and drought conditions. Also, drought increases fire pollution, with implications for air quality. Policies to control fires may be crucial in the future as more droughts are projected.

Description: 〈b〉Retrieving the age of air spectrum from tracers: principle and method〈/b〉〈br〉 Aurélien Podglajen and Felix Ploeger〈br〉 Atmos. Chem. Phys., 19, 1767-1783, https://doi.org/10.5194/acp-19-1767-2019, 2019〈br〉 The age spectrum (distribution of transit times) provides a compact description of transport from the surface to a given point in the atmosphere. It also determines the surface-emitted tracer content of an air parcel. We propose a method to invert this relation in order to retrieve age spectra from tracer concentrations and demonstrate its feasibility in idealized and model setups. Applied to observations, the approach might help to better constrain atmospheric transport timescales.

Description: 〈b〉Impact of a nitrogen emission control area (NECA) on the future air quality and nitrogen deposition to seawater in the Baltic Sea region〈/b〉〈br〉 Matthias Karl, Johannes Bieser, Beate Geyer, Volker Matthias, Jukka-Pekka Jalkanen, Lasse Johansson, and Erik Fridell〈br〉 Atmos. Chem. Phys., 19, 1721-1752, https://doi.org/10.5194/acp-19-1721-2019, 2019〈br〉 Air emissions of nitrogen oxides from ship traffic in the Baltic Sea are a health concern in coastal areas of the Baltic Sea region. We find that the introduction of the nitrogen emission control area (NECA) is critical for reducing ship emissions of nitrogen oxides to levels that are low enough to sustainably dampen ozone production. The decline of the ship-related nitrogen deposition to the Baltic Sea between 2012 and 2040 varies between 46 % and 78 % in different regulation scenarios.

Description: 〈b〉Physical properties of secondary photochemical aerosol from OH oxidation of a cyclic siloxane〈/b〉〈br〉 Nathan J. Janechek, Rachel F. Marek, Nathan Bryngelson, Ashish Singh, Robert L. Bullard, William H. Brune, and Charles O. Stanier〈br〉 Atmos. Chem. Phys., 19, 1649-1664, https://doi.org/10.5194/acp-19-1649-2019, 2019〈br〉 Cyclic volatile methyl siloxanes (cVMSs) are widely used chemicals in personal care products which can undergo oxidation to generate secondary organic aerosol. In this work, cVMS oxidation aerosols were generated using a photochemical chamber and the physical properties characterized. The aerosol yield, volatility, hygroscopicity, morphology, elemental composition, and proposed parameters for treatment as secondary organic aerosol in atmospheric models are provided.

Description: 〈b〉Local air pollution from oil rig emissions observed during the airborne DACCIWA campaign〈/b〉〈br〉 Vanessa Brocchi, Gisèle Krysztofiak, Adrien Deroubaix, Greta Stratmann, Daniel Sauer, Hans Schlager, Konrad Deetz, Guillaume Dayma, Claude Robert, Stéphane Chevrier, and Valéry Catoire〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-27,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 This study reports the first flaring in-situ measurements in southern West Africa. According to the measurements, oil rig flaring plumes in Ghana lead to increases in NO〈sub〉2〈/sub〉 and aerosols but not always in CO and not in SO〈sub〉2〈/sub〉. Flaring measurements can be reproduced using FLEXPART model, adjusting both the emission flux and the injection height. The DACCIWA satellite flaring inventory provides a reasonable estimate of flaring emission.

Description: 〈b〉A new uncertainty estimation technique for multiple datasets and its application to various precipitation products〈/b〉〈br〉 Xudong Zhou, Jan Polcher, Tao Yang, and Ching-Sheng Huang〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2019-49,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 This article proposes a new uncertainty estimation technique for multiple datasets. The new uncertainty estimation method considers all the variations in time and space dimensions, so that it avoids the averaging variation in either of the dimension which is necessary in classic uncertainty estimations. Comparisons with classic and new uncertainty metrics demonstrate that classic metrics may underestimate the uncertainties among datasets.

Description: 〈b〉Consistency of satellite-based precipitation products in space and over time compared with gauge observations and snow- hydrological modelling in the Lake Titicaca region〈/b〉〈br〉 Frédéric Satgé, Denis Ruelland, Marie-Paule Bonnet, Jorge Molina, and Ramiro Pillco〈br〉 Hydrol. Earth Syst. Sci., 23, 595-619, https://doi.org/10.5194/hess-23-595-2019, 2019〈br〉 This paper assesses the potential of satellite precipitation estimates (SPEs) for precipitation measurement and hydrological and snow modelling. A total of 12 SPEs is considered to provide a global overview of available SPE accuracy for users interested in such datasets. Results show that, over poorly monitored regions, SPEs represent a very efficient alternative to traditional precipitation gauges to follow precipitation in time and space and for hydrological and snow modelling.

Description: 〈b〉Monitoring snowpack outflow volumes and their isotopic composition to better understand streamflow generation during rain-on-snow events〈/b〉〈br〉 Andrea Rücker, Stefan Boss, James W. Kirchner, and Jana von Freyberg〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2019-11,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 To better understand how rain-on-snow (ROS) events affect snowpack outflow volumes and streamflow generation, we measured snowpack outflow volumes and isotopic composition during ten ROS events with automated snowmelt lysimeters at three locations in a pre-Alpine catchment. We quantified the spatiotemporal variability of snowpack outflow and its relative contribution to streamflow, and identified rainfall characteristics and initial snow depth as major controls on snow hydrological processes.

Description: 〈b〉Using the Maximum Entropy Production approach to integrate energy budget modeling in a hydrological model〈/b〉〈br〉 Audrey Maheu, Islem Hajji, François Anctil, Daniel F. Nadeau, and René Therrien〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2018-636,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 We tested a new method to simulate terrestrial evaporation in a hydrological model. Given physical constraints imposed by this model, it should help avoid the overestimation of terrestrial evaporation in climate change assessments. We show the good performance of the model by comparing simulated terrestrial evaporation to observations at three sites with different climates and vegetation. Overall, this research proposes a method that will improve our ability to make stream flow projections.

Description: 〈b〉Atmospheric band fitting coefficients derived from a self-consistent rocket-borne experiment〈/b〉〈br〉 Mykhaylo Grygalashvyly, Martin Eberhart, Jonas Hedin, Boris Strelnikov, Franz-Josef Lübken, Markus Rapp, Stefan Löhle, Stefanos Fasoulas, Mikhail Khaplanov, Jörg Gumbel, and Ekaterina Vorobeva〈br〉 Atmos. Chem. Phys., 19, 1207-1220, https://doi.org/10.5194/acp-19-1207-2019, 2019〈br〉 Based on rocket-borne true common volume observations of atomic oxygen, atmospheric band emission (762 nm), and background atmosphere density and temperature, one-step, two-step, and combined mechanisms of O〈sub〉2〈/sub〉(〈i〉b〈/i〉〈sup〉1〈/sup〉Σg〈sup〉+〈/sup〉) formation were analyzed. We found new coefficients for the fit function based on self-consistent temperature, atomic oxygen, and volume emission observations. This can be used for atmospheric band volume emission modeling or the estimation of atomic oxygen by known volume emission.

Description: 〈b〉Effects of organic coating on the nitrate formation by suppressing the N〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 heterogeneous hydrolysis: A case study during wintertime in Beijing-Tianjin-Hebei (BTH)〈/b〉〈br〉 Lang Liu, Jiarui Wu, Suixin Liu, Xia Li, Jiamao Zhou, Tian Feng, Yang Qian, Junji Cao, Xuexi Tie, and Guohui Li〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-25,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉Although stringent emission mitigation strategies have been carried out since 2013 in Beijing-Tianjin-Hebei (BTH), China, heavy haze with high levels of fine particulate matters (PM〈sub〉2.5〈/sub〉) still frequently engulfs the region during wintertime and the nitrate contribution to PM〈sub〉2.5〈/sub〉 mass has progressively increased. The N〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 heterogeneous hydrolysis is referred to as the most important pathway of the nitrate formation at nighttime. In the present study, the WRF-CHEM model is applied to simulate a heavy haze episode from 10 to 27 February 2014 in BTH to evaluate the contribution of the N〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 heterogeneous hydrolysis and the effect of organic coating to the nitrate formation. The model generally performs reasonably well in simulating meteorological parameters, air pollutants and aerosol species against observations in BTH. The N〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 heterogeneous hydrolysis with all the secondary organic aerosol assumed to be involved in coating considerably improves the nitrate simulations compared to the measurements in Beijing. On average, organic coating decreases nitrate concentrations by 8.4 % in BTH during the episode, and the N〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 heterogeneous hydrolysis with organic coating contributes about 30.1 % of nitrate concentrations. Additionally, the reaction also plays a considerable role in the heavy haze formation, with a PM〈sub〉2.5〈/sub〉 contribution of about 11.6 % in BTH. Sensitivity studies also reveal that future studies need to be conducted to predict the organic aerosol hygroscopicity for accurately representing the organic coating effect on the N〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 heterogeneous hydrolysis.〈/p〉

Description: 〈b〉Cloud feedbacks in extratropical cyclones: insight from long-term satellite data and high-resolution global simulations〈/b〉〈br〉 Daniel T. McCoy, Paul R. Field, Gregory S. Elsaesser, Alejandro Bodas-Salcedo, Brian H. Kahn, Mark D. Zelinka, Chihiro Kodama, Thorsten Mauritsen, Benoit Vanniere, Malcolm Roberts, Pier L. Vidale, David Saint-Martin, Aurore Voldoire, Rein Haarsma, Adrian Hill, Ben Shipway, and Jonathan Wilkinson〈br〉 Atmos. Chem. Phys., 19, 1147-1172, https://doi.org/10.5194/acp-19-1147-2019, 2019〈br〉 The largest single source of uncertainty in the climate sensitivity predicted by global climate models is how much low-altitude clouds change as the climate warms. Models predict that the amount of liquid within and the brightness of low-altitude clouds increase in the extratropics with warming. We show that increased fluxes of moisture into extratropical storms in the midlatitudes explain the majority of the observed trend and the modeled increase in liquid water within these storms.

Description: 〈b〉Long-range-transported Canadian smoke plumes in the lower stratosphere over northern France〈/b〉〈br〉 Qiaoyun Hu, Philippe Goloub, Igor Veselovskii, Juan-Antonio Bravo-Aranda, Ioana Elisabeta Popovici, Thierry Podvin, Martial Haeffelin, Anton Lopatin, Oleg Dubovik, Christophe Pietras, Xin Huang, Benjamin Torres, and Cheng Chen〈br〉 Atmos. Chem. Phys., 19, 1173-1193, https://doi.org/10.5194/acp-19-1173-2019, 2019〈br〉 Smoke plumes generated in Canadian fire activities were elevated to the lower stratosphere and transported from North America to Europe. The smoke plumes were observed by three lidar systems in northern France. This study provides a comprehensive characterization for aged smoke aerosols at high altitude using lidar observations. It presents that fire activities on the Earth's surface can be an important contributor of stratospheric aerosols and impact the Earth's radiation budget.

Description: 〈b〉In-cloud formation of secondary species in iron-containing particles〈/b〉〈br〉 Qinhao Lin, Xinhui Bi, Guohua Zhang, Yuxiang Yang, Long Peng, Xiufeng Lian, Yuzhen Fu, Mei Li, Duohong Chen, Mark Miller, Ji Ou, Mingjin Tang, Xinming Wang, Ping'an Peng, Guoying Sheng, and Zhen Zhou〈br〉 Atmos. Chem. Phys., 19, 1195-1206, https://doi.org/10.5194/acp-19-1195-2019, 2019〈br〉 〈p〉The increase in secondary species through cloud processing potentially increases aerosol iron (Fe) bioavailability. In this study, a ground-based counterflow virtual impactor coupled with a real-time single-particle aerosol mass spectrometer was used to characterize the formation of secondary species in Fe-containing cloud residues (dried cloud droplets) at a mountain site in southern China for nearly 1 month during the autumn of 2016. Fe-rich, Fe-dust, Fe-elemental carbon (Fe-EC), and Fe-vanadium (Fe-V) cloud residual types were obtained in this study. The Fe-rich particles, related to combustion sources, contributed 84 % (by number) to the Fe-containing cloud residues, and the Fe-dust particles represented 12 %. The remaining 4 % consisted of the Fe-EC and Fe-V particles. It was found that above 90 % (by number) of Fe-containing particles had already contained sulfate before cloud events, leading to no distinct change in number fraction (NF) of sulfate during cloud events. Cloud processing contributed to the enhanced NFs of nitrate, chloride, and oxalate in the Fe-containing cloud residues. However, the in-cloud formation of nitrate and chloride in the Fe-rich type was less obvious relative to the Fe-dust type. The increased NF of oxalate in the Fe-rich cloud residues was produced via aqueous oxidation of oxalate precursors (e.g., glyoxylate). Moreover, Fe-driven Fenton reactions likely increase the formation rate of aqueous-phase OH, improving the conversion of the precursors to oxalate in the Fe-rich cloud residues. During daytime, the decreased NF of oxalate in the Fe-rich cloud residues was supposed to be due to the photolysis of Fe-oxalate complexes. This work emphasizes the role of combustion Fe sources in participating in cloud processing and has important implications for evaluating Fe bioavailability from combustion sources during cloud processing.〈/p〉

Description: 〈b〉Long-term simulation of the boundary layer flow over the double-ridge site during the Perdigão 2017 field campaign〈/b〉〈br〉 Johannes Wagner, Thomas Gerz, Norman Wildmann, and Kira Gramitzky〈br〉 Atmos. Chem. Phys., 19, 1129-1146, https://doi.org/10.5194/acp-19-1129-2019, 2019〈br〉 Long-term WRF-LES simulations were performed with a horizontal resolution of 200 m for a period of 49 days during the Perdigão campaign. Simulation results were used to characterize the meteorological conditions and to analyse characteristic flow patterns. It could be shown that thermally driven flows including low-level jets frequently occurred during the observation period. Model results were in very good agreement with observations in spite of the long simulation time.

Description: 〈b〉Perspectives and ambitions of interdisciplinary connectivity researchers〈/b〉〈br〉 Eva Nora Paton, Anna Smetanová, Tobias Krueger, and Anthony Parsons〈br〉 Hydrol. Earth Syst. Sci., 23, 537-548, https://doi.org/10.5194/hess-23-537-2019, 2019〈br〉 We reviewed research perspectives and ambitions of connectivity scientists in order to improve joint connectivity research across disciplinary boundaries. We demonstrated the wide diversity of approaching science in the community. We introduced a shared mental model approach with an exploratory case study as a way to overcome persistent barriers in understanding by identifying gaps and overlaps of individual researchers' perspectives, which improves collaboration in interdisciplinary science.

Description: 〈b〉New particle formation from sulfuric acid and ammonia: nucleation and growth model based on thermodynamics derived from CLOUD measurements for a wide range of conditions〈/b〉〈br〉 Andreas Kürten〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1323,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 New particle formation and growth are important processes affecting climate and air quality. A significant fraction of the newly-formed particles is thought to originate from sulfuric acid, water and ammonia. The present study introduces a process model for the calculation of aerosol nucleation and growth rates for this chemical system. The thermodynamic parameters enabling these calculations are derived from laboratory (CLOUD chamber) measurements.

Description: 〈b〉Hydrogeological conceptual model of andesitic watersheds revealed by high-resolution geophysics〈/b〉〈br〉 Benoit Vittecoq, Pierre-Alexandre Reninger, Frédéric Lacquement, Guillaume Martelet, and Sophie Violette〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2018-637,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 Water resources management on volcanic islands is challenging and faces several issues. Taking the advantage of new airborne geophysical technology, correlated with boreholes and springs data, we develop a watershed scale conceptual model and demonstrate that permeability increase with age for the studied formations. Moreover, complex geological structures lead to preferential flow circulations and to discrepancy between topographical and hydrogeological watershed, influencing rivers flowrates.

Description: 〈b〉Development and Validation of a Dense 18-Year Time Series of Surface Water Fraction Estimates from MODIS for the Mediterranean Region〈/b〉〈br〉 Linlin Li, Andrew Skidmore, Anton Vrieling, and Tiejun Wang〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2019-5,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 We derived an 8-day 500 m resolution surface water fraction product over the Mediterranean for 2000–2017 based on MODIS and SRTM data. Our dataset could serve as a tool for (a) monitoring the seasonal, inter-annual and long-term dynamics of surface water extent especially in arid and semi-arid areas; (b) updating and refining of existing wetland and habitat databases; and (c) evaluating ecosystem services and biodiversity assessments.

Description: 〈b〉Effects of turbulence structure and urbanization on the heavy haze pollution process〈/b〉〈br〉 Yan Ren, Hongsheng Zhang, Wei Wei, Bingui Wu, Xuhui Cai, and Yu Song〈br〉 Atmos. Chem. Phys., 19, 1041-1057, https://doi.org/10.5194/acp-19-1041-2019, 2019〈br〉 During the heavy pollution process, there are overestimations regarding the exchange between the atmosphere and surface since the normal calculation of turbulent fluxes includes the impact of sub-mesoscale motion. The intermittent turbulence intensity is closely related to the concentration of PM2.5. The intermittency is weaker over the complex surface condition than over the flat terrain, and urbanization reduces the degree of weakening in turbulent exchange during the heavy pollution process.

Description: 〈b〉Insight into the Composition of Organic Compounds (≥ C〈sub〉6〈/sub〉) in PM〈sub〉2.5〈/sub〉 in Wintertime in Beijing, China〈/b〉〈br〉 Ruihe Lyu, Zongbo Shi, Mohammed Salim Alam, Xuefang Wu, Di Liu, Tuan V. Vu, Christopher Stark, Pingqing Fu, Yinchang Feng, and Roy M. Harrison〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1273,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Severe pollution of the Beijing atmosphere is a frequent occurrence. The airborne particles which characterise the episodes of haze contain a wide range of chemical constituents but organic compounds make up a substantial proportion. In this study individual compounds have been analysed under both haze and non-haze conditions and the measurements are compared with samples collected in London where the air pollution climate and sources are very different.

Description: 〈b〉Photochemical impacts of haze pollution in an urban environment〈/b〉〈br〉 Michael Hollaway, Oliver Wild, Ting Yang, Yele Sun, Weiqi Xu, Conghui Xie, Lisa Whalley, Eloise Slater, Dwayne Heard, and Dantong Liu〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-29,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 This study, for the first time, uses combinations of aerosol and lidar data to drive an offline photolysis scheme. Absorbing species are shown to have the greatest impact on photolysis rate constants in the winter and scattering aerosol are shown to dominate responses in the summer. During haze episodes, aerosols are shown to produce a greater impact than cloud cover. The findings demonstrate the potential photochemical impacts of haze pollution in a highly polluted urban environment.

Description: 〈b〉Heterogeneous ice nucleation on dust particles sourced from nine deserts worldwide – Part 2: Deposition nucleation and condensation freezing〈/b〉〈br〉 Yvonne Boose, Philipp Baloh, Michael Plötze, Johannes Ofner, Hinrich Grothe, Berko Sierau, Ulrike Lohmann, and Zamin A. Kanji〈br〉 Atmos. Chem. Phys., 19, 1059-1076, https://doi.org/10.5194/acp-19-1059-2019, 2019〈br〉 The role non-mineral components play in the freezing behavior of atmospheric desert dust is not well known. In this study, we use chemical imaging methods to investigate this for airborne and surface-collected desert dust samples. We find that in most cases the ice nucleation behavior is determined by the dust mineralogical composition. However, volatile organic material can coat active sites and decrease the dust ice nucleation ability, while biological particles can significantly increase it.

Description: 〈b〉Estimation of ground-level particulate matter concentrations through the synergistic use of satellite observations and process-based models over South Korea〈/b〉〈br〉 Seohui Park, Minso Shin, Jungho Im, Chang-Keun Song, Myungje Choi, Jhoon Kim, Seungun Lee, Rokjin Park, Jiyoung Kim, Dong-Won Lee, and Sang-Kyun Kim〈br〉 Atmos. Chem. Phys., 19, 1097-1113, https://doi.org/10.5194/acp-19-1097-2019, 2019〈br〉 This study proposed machine-learning-based models to estimate ground-level particulate matter concentrations using satellite observations and numerical model-derived data. Aerosol optical depth was identified as the most significant for estimating ground-level PM concentrations, followed by wind speed and solar radiation. The results show that the proposed models produced better performance than the existing approaches, particularly in improving on the biases of the process-based models.

Description: 〈b〉Observational evidence of particle condensational growth in the UTLS over Tibetan Plateau〈/b〉〈br〉 Qianshan He, Jianzhong Ma, Xiangdong Zheng, Xiaolu Yan, Holger Vömel, Frank G. Wienhold, Wei Gao, Dongwei Liu, Guangming Shi, and Tiantao Cheng〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-6,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 An enhanced aerosol layer in the upper troposphere/lower stratosphere was observed by a COBALD over the Tibetan Plateau, in the summer of 2014. The Color Index of the enhanced aerosol layer indicates the prevalence of dominant fine particles with mode radius less than 0.1 μm. Except for the very small particles at low relative humidity (RHi 

Description: 〈b〉Subgrid variations of the cloud water and droplet number concentration over the tropical ocean: satellite observations and implications for warm rain simulations in climate models〈/b〉〈br〉 Zhibo Zhang, Hua Song, Po-Lun Ma, Vincent E. Larson, Minghuai Wang, Xiquan Dong, and Jianwu Wang〈br〉 Atmos. Chem. Phys., 19, 1077-1096, https://doi.org/10.5194/acp-19-1077-2019, 2019〈br〉 〈p〉One of the challenges in representing warm rain processes in global climate models (GCMs) is related to the representation of the subgrid variability of cloud properties, such as cloud water and cloud droplet number concentration (CDNC), and the effect thereof on individual precipitation processes such as autoconversion. This effect is conventionally treated by multiplying the resolved-scale warm rain process rates by an enhancement factor (〈span〉〈i〉E〈/i〉〈sub〉〈i〉q〈/i〉〈/sub〉〈/span〉) which is derived from integrating over an assumed subgrid cloud water distribution. The assumed subgrid cloud distribution remains highly uncertain. In this study, we derive the subgrid variations of liquid-phase cloud properties over the tropical ocean using the satellite remote sensing products from Moderate Resolution Imaging Spectroradiometer (MODIS) and investigate the corresponding enhancement factors for the GCM parameterization of autoconversion rate. We find that the conventional approach of using only subgrid variability of cloud water is insufficient and that the subgrid variability of CDNC, as well as the correlation between the two, is also important for correctly simulating the autoconversion process in GCMs. Using the MODIS data which have near-global data coverage, we find that 〈span〉〈i〉E〈/i〉〈sub〉〈i〉q〈/i〉〈/sub〉〈/span〉 shows a strong dependence on cloud regimes due to the fact that the subgrid variability of cloud water and CDNC is regime dependent. Our analysis shows a significant increase of 〈span〉〈i〉E〈/i〉〈sub〉〈i〉q〈/i〉〈/sub〉〈/span〉 from the stratocumulus (Sc) to cumulus (Cu) regions. Furthermore, the enhancement factor 〈span〉〈i〉E〈/i〉〈sub〉〈i〉N〈/i〉〈/sub〉〈/span〉 due to the subgrid variation of CDNC is derived from satellite observation for the first time, and results reveal several regions downwind of biomass burning aerosols (e.g., Gulf of Guinea, east coast of South Africa), air pollution (i.e., East China Sea), and active volcanos (e.g., Kilauea, Hawaii, and Ambae, Vanuatu), where the 〈span〉〈i〉E〈/i〉〈sub〉〈i〉N〈/i〉〈/sub〉〈/span〉 is comparable to or even larger than 〈span〉〈i〉E〈/i〉〈sub〉〈i〉q〈/i〉〈/sub〉〈/span〉, suggesting an important role of aerosol in influencing the 〈span〉〈i〉E〈/i〉〈sub〉〈i〉N〈/i〉〈/sub〉〈/span〉. MODIS observations suggest that the subgrid variations of cloud liquid water path (LWP) and CDNC are generally positively correlated. As a result, the combined enhancement factor, including the effect of LWP and CDNC correlation, is significantly smaller than the simple product of 〈span〉〈i〉E〈/i〉〈sub〉〈i〉q〈/i〉〈/sub〉⋅〈i〉E〈/i〉〈sub〉〈i〉N〈/i〉〈/sub〉〈/span〉. Given the importance of warm rain processes in understanding the Earth's system dynamics and water cycle, we conclude that more observational studies are needed to provide a better constraint on the warm rain processes in GCMs.〈/p〉

Description: 〈b〉Aerosol indirect effects on the temperature-precipitation scaling〈/b〉〈br〉 Nicolas Da Silva, Sylvain Mailler, and Philippe Drobinski〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1334,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 1 comment)〈br〉 Mycrophysical effects of aerosols were found to weaken precipitation in an Euro-Mediterranean area. The present numerical study quantify the processes that may be involved through the use of the temperature-precipitation relationship. It shows larger aerosol effects at low temperatures. At these temperatures, the most contributing process is the increase of atmospheric stability through an enhanced aerosol cooling effect in the lower troposphere compared to the upper troposphere.

Description: 〈b〉Observationally constrained analysis of sea salt aerosol in the marine atmosphere〈/b〉〈br〉 Huisheng Bian, Karl Froyd, Daniel M. Murphy, Jack Dibb, Mian Chin, Peter R. Colarco, Anton Darmenov, Arlindo da Silva, Tom L. Kucsera, Gregory Schill, Hongbin Yu, Paul Bui, Maximillan Dollner, Bernadett Weinzierl, and Alexander Smirnov〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-18,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 We address the GEOS-GOCART sea salt simulations constrained by NASA EVS ATom measurements, as well as those by MODIS and AERONET MAN. The study covers remote regions over the Pacific, Atlantic, and Southern Oceans from near surface to ~ 12 km altitude and covers both summer and winter seasons. Important sea salt fields, e.g. mass mixing ratio, vertical distribution, size distribution, and marine aerosol AOD, as well as their relationship to relative humidity and emissions, are examined.

Description: 〈b〉Niger discharge from radar altimetry: Bridging gaps between gauge and altimetry time series〈/b〉〈br〉 Stefan Schröder, Anne Springer, Jürgen Kusche, Bernd Uebbing, Luciana Fenoglio-Marc, Bernd Diekkrüger, and Thomas Poméon〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2019-36,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 1 comment)〈br〉 We propose to derive altimetric rating curves by 〈q〉bridging〈/q〉 gaps between time series from gauge and altimeter measurements using hydrological model simulations. We investigate several stations at the Niger river, which is a challenging region. We show that altimetry reproduces discharge well and enables continuing the gauge time series, albeit at lower temporal resolution.

Description: 〈b〉Statistical approaches for identification of low-flow drivers: temporal aspects〈/b〉〈br〉 Anne Fangmann and Uwe Haberlandt〈br〉 Hydrol. Earth Syst. Sci., 23, 447-463, https://doi.org/10.5194/hess-23-447-2019, 2019〈br〉 Low-flow events are little dynamic in space and time. Thus, it is hypothesized that models can be found, based on simple statistical relationships between low-flow metrics and meteorological states, that can help identify potential low-flow drivers. In this study we assess whether such relationships exist and whether they can be applied to predict future low flow within regional climate change impact assessment in the northwestern part of Germany.

Description: 〈b〉Integrating multiple satellite observations into a coherent dataset to monitor the full water cycle – application to the Mediterranean region〈/b〉〈br〉 Victor Pellet, Filipe Aires, Simon Munier, Diego Fernández Prieto, Gabriel Jordá, Wouter Arnoud Dorigo, Jan Polcher, and Luca Brocca〈br〉 Hydrol. Earth Syst. Sci., 23, 465-491, https://doi.org/10.5194/hess-23-465-2019, 2019〈br〉 This study is an effort for a better understanding and quantification of the water cycle and related processes in the Mediterranean region, by dealing with satellite products and their uncertainties. The aims of the paper are 3-fold: (1) developing methods with hydrological constraints to integrate all the datasets, (2) giving the full picture of the Mediterranean WC, and (3) building a model-independent database that can evaluate the numerous regional climate models (RCMs) for this region.

Description: 〈b〉Speciated and total emission factors of particulate organics from burning western US wildland fuels and their dependence on combustion efficiency〈/b〉〈br〉 Coty N. Jen, Lindsay E. Hatch, Vanessa Selimovic, Robert J. Yokelson, Robert Weber, Arantza E. Fernandez, Nathan M. Kreisberg, Kelley C. Barsanti, and Allen H. Goldstein〈br〉 Atmos. Chem. Phys., 19, 1013-1026, https://doi.org/10.5194/acp-19-1013-2019, 2019〈br〉 Wildfires in the western US are occurring more frequently and burning larger land areas. Smoke from these fires will play a greater role in regional air quality and atmospheric chemistry than in the past. To help fire and climate modelers and atmospheric experimentalists better understand how smoke impacts the environment, we have separated, identified, classified, and quantified the thousands of organic compounds found in smoke and related their amounts emitted to fire conditions.

Description: 〈b〉Enhanced ice nucleation activity of coal fly ash aerosol particles initiated by ice-filled pores〈/b〉〈br〉 Nsikanabasi Silas Umo, Robert Wagner, Romy Ullrich, Alexei Kiselev, Harald Saathoff, Peter G. Weidler, Daniel J. Cziczo, Thomas Leisner, and Ottmar Möhler〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-7,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Annually, over 600 Tg of coal fly ash (CFA) are produced; and a significant proportion of this amount is injected into the atmosphere, which could significantly contribute to heterogeneous ice formation in clouds. This study presents an improved understanding of CFA particles' behaviour in forming ice in clouds, especially when exposed to lower temperatures before being re-circulated in the upper troposphere or entrained into the lower troposphere.

Description: 〈b〉Contrail cirrus radiative forcing for future air traffic〈/b〉〈br〉 Lisa Bock and Ulrike Burkhardt〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1294,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 The climate impact of air traffic is to a large degree caused by changes in cirrus cloudiness resulting from the formation of contrails. We use an atmospheric climate model with a contrail cirrus parameterization to investigate the climate impact of contrail cirrus for the year 2050. The strong increase in contrail cirrus radiative forcing due to the projected increase in air traffic volume cannot be compensated for by the reduction of soot emissions and by improvements in propulsion efficiency.

Description: 〈b〉Ice nucleating particles in the marine boundary layer in the Canadian Arctic during summer 2014〈/b〉〈br〉 Victoria E. Irish, Sarah J. Hanna, Megan D. Willis, Swarup China, Jennie L. Thomas, Jeremy J. B. Wentzell, Ana Cirisan, Meng Si, W. Richard Leaitch, Jennifer G. Murphy, Jonathan P. D. Abbatt, Alexander Laskin, Eric Girard, and Allan K. Bertram〈br〉 Atmos. Chem. Phys., 19, 1027-1039, https://doi.org/10.5194/acp-19-1027-2019, 2019〈br〉 Ice nucleating particles (INPs) are atmospheric particles that catalyse the formation of ice crystals in clouds. INPs influence the Earth's radiative balance and hydrological cycle. In this study we measured the concentrations of INPs in the Canadian Arctic marine boundary layer. Average INP concentrations fell within the range measured in other marine boundary layer locations. We also found that mineral dust is a more important contributor to the INP population than sea spray aerosol.

Description: 〈b〉On the diurnal, weekly, and seasonal cycles and annual trends in atmospheric CO〈sub〉2〈/sub〉 at Mount Zugspitze, Germany, during 1981–2016〈/b〉〈br〉 Ye Yuan, Ludwig Ries, Hannes Petermeier, Thomas Trickl, Michael Leuchner, Cédric Couret, Ralf Sohmer, Frank Meinhardt, and Annette Menzel〈br〉 Atmos. Chem. Phys., 19, 999-1012, https://doi.org/10.5194/acp-19-999-2019, 2019〈br〉 In this study, we presented a time series analysis of a 36-year composite CO〈sub〉2〈/sub〉 measurement record at Mount Zugspitze in Germany. Compared with other GAW observatories, Zugspitze proves to be a highly suitable site for monitoring the background levels of air components using proper data selection procedures. Detailed analyses of long-term trends and seasonality, as well as a thorough study of combined weekly periodicity and diurnal cycles, were conducted.

Description: 〈b〉Simulation of the radiative effect of haze on urban hydrological cycle using reanalysis data in Beijing〈/b〉〈br〉 Tom V. Kokkonen, Susan B. Grimmond, Sonja Murto, Huizhi Liu, Anu-Maija Sundström, and Leena Järvi〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1226,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 This is the first study to evaluate and correct the WATCH WFDEI reanalysis product in highly polluted urban environment. It gives important understanding of the uncertainties in reanalysis products in local scale urban modelling in polluted environments and identifies and corrects the most important variables in hydrological modelling. This is also the first study to examine the effects of haze on local scale urban hydrological cycle.

Description: 〈b〉Charactersing spatio-temporal variability in seasonal snow cover at a regional scale from MODIS data: The Clutha Catchment, New Zealand〈/b〉〈br〉 Todd A. N. Redpath, Pascal Sirguey, and Nicolas J. Cullen〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2019-30,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 Spatio-temporal variability of seasonal snow cover is characterised from 16 years of MODIS data for the Clutha Catchment, New Zealand. No trend was detected in snow covered area. Spatial modes of variability reveal the role of anomalous winter airflow. The sensitivity of snow cover duration to temperature and precipitation variability is found to vary spatially across the catchment. These findings provide new insight into seasonal snow processes in New Zealand and guidance for modelling efforts.

Description: 〈b〉Evaluation and comparison of MAIAC, DT and DB aerosol products over China〈/b〉〈br〉 Ning Liu, Bin Zou, Huihui Feng, Yuqi Tang, and Yu Liang〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1339,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 The first systematic validation and comparison of MAIAC, DT and DB AOD products across China during 2000 to 2017 is presented. In this process, the overall accuracy, land type dependence, view geometry dependence, spatiotemporal retrieval accuracy, spatial variation pattern and spatiotemporal completeness of three products are analyzed in details. In general, MAIAC achieves higher accuracy than DT and DB, but DT or DB may perform better than MAIAC under some specific land cover types or seasons.

Description: 〈b〉Multi-timescale variations of modelled stratospheric water vapor derived from three modern reanalysis products〈/b〉〈br〉 Mengchu Tao, Paul Konopka, Felix Ploeger, Xiaolu Yan, Jonathon S. Wright, Mohamadou Diallo, Stephan Fueglistaler, and Martin Riese〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-39,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 This paper examines the annual and inter-annual variations as well as long-term trend of modelled stratospheric water vapor with a Lagrangian chemical transport model driven by ERA-I, MERRA-2 and JRA-55. We find reasonable consistency among the annual cycle, QBO and the variabilities induced by ENSO and volcanic aerosols. The main discrepancies are linked to the differences in reanalysis upwelling rates in the lower stratosphere. The trends are sensitive to the reanalyses that drives the model.

Description: 〈b〉Common volume satellite studies of polar mesospheric clouds with Odin/OSIRIS tomography and AIM/CIPS nadir imaging〈/b〉〈br〉 Lina Broman, Susanne Benze, Jörg Gumbel, Ole-Martin Christensen, and Cora E. Randall〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1035,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Combining satellite observations of Polar Mesospheric Clouds are complicated due to satellite geometry and measurement technique. In this study, tomographic limb observations are compared to observations from a nadir viewing satellite using a common volume approach. We present a technique that overcomes differences in scattering conditions and observation geometry. The satellites show excellent agreement, which lays the basis for future insights into horizontal and vertical cloud processes.

Description: 〈b〉Spatially distributed sensitivity of simulated global groundwater heads and flows to hydraulic conductivity, groundwater recharge and surface water body parameterization〈/b〉〈br〉 Robert Reinecke, Laura Foglia, Steffen Mehl, Jonathan D. Herman, Alexander Wachholz, Tim Trautmann, and Petra Döll〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2019-10,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 Recently, the first global groundwater models were developed to better understand surface water-groundwater interactions, and human water use impacts. However, the reliability of model outputs is limited by a lack of data as well as model assumptions required due to the necessarily coarse spatial resolution. In this study we present first global maps of model sensitivity to their parameterization and build a foundation to improve data sets and model design as well as model understanding.

Description: 〈b〉Urban population exposure to NO〈sub〉x〈/sub〉 emissions from local shipping in three Baltic Sea harbour cities – a generic approach〈/b〉〈br〉 Martin Otto Paul Ramacher, Matthias Karl, Johannes Bieser, Jukka-Pekka Jalkanen, and Lasse Johansson〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-127,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 We simulated the impact of NO〈sub〉x〈/sub〉 shipping emissions on air quality and exposure in the Baltic Sea harbour cities Rostock (Germany), Riga (Latvia) and Gdansk-Gdynia (Poland) for 2012. We found that local shipping affects total NO〈sub〉2〈/sub〉 with 22 %, 11 %, and 16 % in Rostock, Riga and Gdansk-Gdynia. Exposure to NO〈sub〉2〈/sub〉 from all emission sources was highest at home addresses (54–59 %). Emissions from shipping have a high impact on NO〈sub〉2〈/sub〉 exposure in the port area (50–80 %).

Description: 〈b〉Rate constant and secondary organic aerosol formation from the gas-phase reaction of eugenol with hydroxyl radicals〈/b〉〈br〉 Changgeng Liu, Yongchun Liu, Tianzeng Chen, Jun Liu, and Hong He〈br〉 Atmos. Chem. Phys., 19, 2001-2013, https://doi.org/10.5194/acp-19-2001-2019, 2019〈br〉 The rate constant and SOA formation for the OH-initiated reaction of eugenol were studied for the first time in an oxidation flow reactor. Significant SOA formation was observed, and SOA yield depended on precursor concentration and OH exposure. SO〈sub〉2〈/sub〉 and NO〈sub〉2〈/sub〉 both enhanced SOA yields. In addition, NO〈sub〉2〈/sub〉 participated in OH-initiated reaction and produced organic nitrates. The results could be helpful for further understanding SOA formation from the atmospheric oxidation of methoxyphenols.

Description: 〈b〉Evaluating solar radiation forecast uncertainty〈/b〉〈br〉 Minttu Tuononen, Ewan J. O'Connor, and Victoria A. Sinclair〈br〉 Atmos. Chem. Phys., 19, 1985-2000, https://doi.org/10.5194/acp-19-1985-2019, 2019〈br〉 Many applications require accurate forecasts of the amount of solar radiation reaching the surface, such as solar energy and UV radiation forecasts. This also means that cloud must be correctly forecast. We investigated the skill of these forecasts over Helsinki, Finland, using cloud and solar radiation observations. We found that there were errors in the model radiation forecast even when the clouds were correctly forecast, which we attribute to incorrect representation of the cloud properties.

Description: 〈b〉Spatiotemporal patterns and driving factors of flood disaster in China〈/b〉〈br〉 Pan Hu, Qiang Zhang, Chong-Yu Xu, Shao Sun, and Jiayi Fang〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2019-73,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 China is the country highly sensitive to flood disasters. Here we investigated flood disasters and relevant driving factors using meteorological disaster records s and also hourly rainfall data. We used the GeoDetector method to analyze potential driving factors behind flood disasters. We found increased rainstorm-induced flood disasters and increase in flood disaster frequency. Meanwhile, reduced flood-related death rates imply enhanced flood-mitigation infrastructure and facilities.

Description: 〈b〉Variability of Bulk Water Vapor Content in the Marine Cloudy Boundary Layers from Microwave and Near-Infrared Imagery〈/b〉〈br〉 Luis F. Millán, Matthew D. Lebsock, and Joao Teixeira〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-4,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 The synergy of the collocated Advanced Microwave Scanning Radiometer (AMSR) and the Moderate Resolution Imaging Spectroradiometer (MODIS) provides daily global estimates of marine boundary layer water vapor. AMSR provides the total column water vapor, while MODIS provides the water vapor above the cloud layers. The difference between the two gives the vapor between the surface and the cloud top, which may be interpreted as the boundary layer water vapor.

Description: 〈b〉Mapping rainfall hazard based on rain gauge data: an objective cross-validation framework for model selection〈/b〉〈br〉 Juliette Blanchet, Emmanuel Paquet, Pradeebane Vaittinada Ayar, and David Penot〈br〉 Hydrol. Earth Syst. Sci., 23, 829-849, https://doi.org/10.5194/hess-23-829-2019, 2019〈br〉 We propose an objective framework for estimating rainfall cumulative distribution functions in a region when data are only available at rain gauges. Our methodology allows us to assess goodness-of-fit of the full distribution, but with a particular focus on its tail. It is applied to daily rainfall in the Ardèche catchment in the south of France. Results show a preference for a mixture of Gamma distribution over seasons and weather patterns, with parameters interpolated with a thin plate spline.

Description: 〈b〉Quantifying projected changes in runoff variability and flow regimes of the Fraser River Basin, British Columbia〈/b〉〈br〉 Siraj Ul Islam, Charles L. Curry, Stephen J. Déry, and Francis W. Zwiers〈br〉 Hydrol. Earth Syst. Sci., 23, 811-828, https://doi.org/10.5194/hess-23-811-2019, 2019〈br〉 〈p〉In response to ongoing and future-projected global warming, mid-latitude, nival river basins are expected to transition from a snowmelt-dominated flow regime to a nival–pluvial one with an earlier spring freshet of reduced magnitude. There is, however, a rich variation in responses that depends on factors such as the topographic complexity of the basin and the strength of maritime influences. We illustrate the potential effects of a strong maritime influence by studying future changes in cold season flow variability in the Fraser River Basin (FRB) of British Columbia, a large extratropical watershed extending from the Rocky Mountains to the Pacific Coast. We use a process-based hydrological model driven by an ensemble of 21 statistically downscaled simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5), following the Representative Concentration Pathway 8.5 (RCP 8.5).〈/p〉 〈p〉Warming under RCP 8.5 leads to reduced winter snowfall, shortening the average snow accumulation season by about one-third. Despite this, large increases in cold season rainfall lead to unprecedented cold season peak flows and increased overall runoff variability in the VIC simulations. Increased cold season rainfall is shown to be the dominant climatic driver in the Coast Mountains, contributing 60 % to mean cold season runoff changes in the 2080s. Cold season runoff at the outlet of the basin increases by 70 % by the 2080s, and its interannual variability more than doubles when compared to the 1990s, suggesting substantial challenges for operational flow forecasting in the region. Furthermore, almost half of the basin (45 %) transitions from a snow-dominated runoff regime in the 1990s to a primarily rain-dominated regime in the 2080s, according to a snowmelt pulse detection algorithm. While these projections are consistent with the anticipated transition from a nival to a nival–pluvial hydrologic regime, the marked increase in FRB cold season runoff is likely linked to more frequent landfalling atmospheric rivers in the region projected in the CMIP5 models, providing insights for other maritime-influenced extratropical basins.〈/p〉

Description: 〈b〉A proxy for atmospheric daytime gaseous sulfuric acid concentration in urban Beijing〈/b〉〈br〉 Yiqun Lu, Chao Yan, Yueyun Fu, Yan Chen, Yiliang Liu, Gan Yang, Yuwei Wang, Federico Bianchi, Biwu Chu, Ying Zhou, Rujing Yin, Rima Baalbaki, Olga Garmash, Chenjuan Deng, Weigang Wang, Yongchun Liu, Tuukka Petäjä, Veli-Matti Kerminen, Jingkun Jiang, Markku Kulmala, and Lin Wang〈br〉 Atmos. Chem. Phys., 19, 1971-1983, https://doi.org/10.5194/acp-19-1971-2019, 2019〈br〉 Gaseous sulfuric acid is one of the key precursors for atmospheric new particle formation processes, but its measurement remains challenging. This work develops an estimation method for the gaseous sulfuric acid concentration in an urban environment in China using multiple atmospheric variables that are easier to measure. The consideration of the heterogeneous formation of HONO and the subsequent photo-production of OH radicals improves the performance of the estimation method.

Description: 〈b〉On the sources and sinks of atmospheric VOCs: An integrated analysis of recent aircraft campaigns over North America〈/b〉〈br〉 Xin Chen, Dylan B. Millet, Hanwant B. Singh, Armin Wisthaler, Eric C. Apel, Elliot L. Atlas, Donald R. Blake, Steven S. Brown, John D. Crounse, Joost A. de Gouw, Frank Flocke, Alan Fried, Brian G. Heikes, Rebecca S. Hornbrook, Tomas Mikoviny, Kyung-Eun Min, Markus Müller, J. Andrew Neuman, Daniel W. O'Sullivan, Jeff Peischl, Gabriele G. Pfister, Dirk Richter, James M. Roberts, Thomas B. Ryerson, Stephen Shertz, Victoria Treadaway, Patrick R. Veres, James Walega, Carsten Warneke, Rebecca A. Washenfelder, Petter Weibring, and Bin Yuan〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-115,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Volatile organic compounds (VOCs) affect air quality and modify the lifetimes of other pollutants. We combine a high-resolution 3D atmospheric model with an ensemble of aircraft observations to perform an integrated analysis of the VOC budget over North America. We find that biogenic emissions provide the main source of VOC reactivity even in most major cities. Our findings point to key gaps in current models related to oxygenated VOCs and to the distribution of VOCs in the free troposphere.

Description: 〈b〉Characterization of Transport Regimes and the Polar Dome during Arctic Spring and Summer using in-situ Aircraft Measurements〈/b〉〈br〉 Heiko Bozem, Peter Hoor, Daniel Kunkel, Franziska Köllner, Johannes Schneider, Andreas Herber, Hannes Schulz, W. Richard Leaitch, Amir A. Aliabadi, Megan D. Willis, Julia Burkart, and Jonathan P. D. Abbatt〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-70,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 We present airborne trace gas measurements in the European and Canadian Arctic for July 2014 and April 2015. Based on CO and CO〈sub〉2〈/sub〉 in-situ data as well as 10-day kinematic back trajectories we characterize the prevailing transport regimes and derive a tracer based diagnostic for the determination of the polar dome boundary. Using the tracer derived boundary the analysis of the recent transport history of air masses within the polar dome reveals significant differerences between spring and summer.

Description: 〈b〉Importance of biogenic volatile organic compounds to acyl peroxy nitrates (APN) production in the southeastern US during SOAS 2013〈/b〉〈br〉 Shino Toma, Steve Bertman, Christopher Groff, Fulizi Xiong, Paul B. Shepson, Paul Romer, Kaitlin Duffey, Paul Wooldridge, Ronald Cohen, Karsten Baumann, Eric Edgerton, Abigail R. Koss, Joost de Gouw, Allen Goldstein, Weiwei Hu, and Jose L. Jimenez〈br〉 Atmos. Chem. Phys., 19, 1867-1880, https://doi.org/10.5194/acp-19-1867-2019, 2019〈br〉 Acyl peroxy nitrates (APN) were measured near the ground in Alabama using GC in summer 2013 to study biosphere–atmosphere interactions. APN were lower than measured in the SE USA over the past 2 decades. Historical data showed APN in 2013 was limited by NO〈sub〉〈i〉x〈/i〉〈/sub〉 and production was dominated by biogenic precursors more than in the past. Isoprene-derived MPAN correlated with isoprene hydroxynitrates as NO〈sub〉〈i〉x〈/i〉〈/sub〉-dependent products. MPAN varied with aerosol growth, but not with N-containing particles.

Description: 〈b〉Detection and classification of laminae in balloon-borne ozonesonde profiles: application to the long-term record from Boulder, Colorado〈/b〉〈br〉 Kenneth Minschwaner, Anthony T. Giljum, Gloria L. Manney, Irina Petropavlovskikh, Bryan J. Johnson, and Allen F. Jordan〈br〉 Atmos. Chem. Phys., 19, 1853-1865, https://doi.org/10.5194/acp-19-1853-2019, 2019〈br〉 We analyzed balloon measurements of ozone between the surface and 25 km altitude above Boulder, Colorado, and developed an algorithm to detect and classify layers of either unusually high or unusually low ozone. These layers range in vertical thickness from a few hundred meters to a few kilometers. We found that these laminae are an important contributor to the overall variability in ozone, especially in the transition region between the troposphere and stratosphere.

Description: 〈b〉A Review and Synthesis of Future Earth System Change in the Interior of Western Canada: Part I – Climate and Meteorology〈/b〉〈br〉 Ronald E. Stewart, Kit K. Szeto, Barrie R. Bonsal, John M. Hanesiak, Bohdan Kochtubajda, Yanping Li, Julie M. Thériault, Chris M. DeBeer, Benita Y. Tam, Zhenhua Li, Zhuo Liu, Jennifer A. Bruneau, Sébastien Marinier, and Dominic Matte〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2019-51,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 This article examines future atmospheric-related phenomena across the interior of western Canada. Changes in large scale atmospheric circulation and extent of warming vary with season and these generally lead to increases in factors associated with extremes such as spring and early summer floods and drought, although not necessarily summer convection. The northward movement of the 0 °C isotherm will furthermore be associated with changes to hazardous conditions such as freezing rain.

Description: 〈b〉Long-term groundwater recharge rates across India by in situ measurements〈/b〉〈br〉 Soumendra N. Bhanja, Abhijit Mukherjee, R. Rangarajan, Bridget R. Scanlon, Pragnaditya Malakar, and Shubha Verma〈br〉 Hydrol. Earth Syst. Sci., 23, 711-722, https://doi.org/10.5194/hess-23-711-2019, 2019〈br〉 Groundwater depletion in India has been a much-debated issue in recent years. Here we investigate long-term, spatiotemporal variation in prevailing groundwater recharge rates across India. Groundwater recharge rates have been estimated based on field-scale groundwater-level measurements and the tracer injection approach; recharge rates from the two estimates compared favorably. The role of precipitation in controlling groundwater recharge is studied.

Description: 〈b〉Winter 2018 major sudden stratospheric warming impact on midlatitude mesosphere from microwave radiometer measurements〈/b〉〈br〉 Yuke Wang, Valery Shulga, Gennadi Milinevsky, Aleksey Patoka, Oleksandr Evtushevsky, Andrew Klekociuk, Wei Han, Asen Grytsai, Dmitry Shulga, Valery Myshenko, and Oleksandr Antyufeyev〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1361,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 1 comment)〈br〉 The major sudden stratospheric warming (SSW) dramatically changed atmospheric conditions from mesosphere to troposphere. This event is accompanied by a sharp increase in the stratosphere temperature and zonal wind reverse producing strong changes in surface weather. These changes affect even the midlatitude mesosphere, which is not widely covered by observations. Our newly installed microwave radiometer allowed studying mesospheric zonal wind to understand the SSW 2018 behavior at mid-latitudes.

Description: 〈b〉In-situ constraints on the vertical distribution of global aerosol〈/b〉〈br〉 Duncan Watson-Parris, Nick Schutgens, Carly Reddington, Kirsty J. Pringle, Dantong Liu, James D. Allan, Hugh Coe, Ken S. Carslaw, and Philip Stier〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1337,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 The vertical distribution of aerosol in the atmosphere affects its ability to act as cloud condensation nuclei, and changes the amount of sunlight it absorbs or reflects. Common global measurements of aerosol provide no information about this vertical distribution. Using a global collection of in-situ aircraft measurements to compare with an aerosol-climate model (ECHAM-HAM) we explore the key processes controlling this distribution and find that wet removal plays a key role.

Description: 〈b〉The role of low-level clouds in the West African monsoon system〈/b〉〈br〉 Anke Kniffka, Peter Knippertz, and Andreas H. Fink〈br〉 Atmos. Chem. Phys., 19, 1623-1647, https://doi.org/10.5194/acp-19-1623-2019, 2019〈br〉 The role of low-level clouds in the southern West Africa (SWA) energy balance and the West African monsoon system is assessed via targeted sensitivity studies with the NWP model ICON. We show for the first time that rainfall over SWA depends logarithmically on the optical thickness of low clouds, as these control the diurnal evolution of the planetary boundary layer, vertical stability and finally convection. Small variations in clouds or aerosol have a substantial impact on precipitation.

Description: 〈b〉Snow-darkening versus direct radiative effects of mineral dust aerosol on the Indian summer monsoon onset: role of temperature change over dust sources〈/b〉〈br〉 Zhengguo Shi, Xiaoning Xie, Xinzhou Li, Liu Yang, Xiaoxun Xie, Jing Lei, Yingying Sha, and Xiaodong Liu〈br〉 Atmos. Chem. Phys., 19, 1605-1622, https://doi.org/10.5194/acp-19-1605-2019, 2019〈br〉 Asian dust is one of the important components in modern and past climate change via its effects, including snow-darkening and direct radiation. We employed model experiments to evaluate these effects on Indian monsoon and found that the monsoon onset responds significantly to both. Snow-darkening effect weakens the monsoon, but direct radiative effect intensifies it. Besides the previous Tibetan Plateau studies proposed, our work highlights the importance of temperature change over dust sources.

Description: 〈b〉Influence of cloud microphysical processes on black carbon wet removal, global distributions, and radiative forcing〈/b〉〈br〉 Jiayu Xu, Jiachen Zhang, Junfeng Liu, Kan Yi, Songlin Xiang, Xiurong Hu, Yuqing Wang, Shu Tao, and George Ban-Weiss〈br〉 Atmos. Chem. Phys., 19, 1587-1603, https://doi.org/10.5194/acp-19-1587-2019, 2019〈br〉 In this study, we fully describe black carbon wet removal coupled with all cloud processes from a cloud microphysics scheme in a climate model and conduct sensitivity simulations that turn off each cloud process one at a time. We find that convective scavenging, aerosol activation, ice nucleation, evaporation of rain–snow, and below-cloud scavenging dominate wet deposition of BC. In addition, the range of direct radiative forcing derived from sensitivity simulations is large, 0.09–0.33 W m〈sup〉−2〈/sup〉.

Description: 〈b〉Using GRACE in a streamflow recession to determine drainable water storage in the Mississippi River Basin〈/b〉〈br〉 Heloisa Ehalt Macedo, Ralph Edward Beighley, Cedric H. David, and John T. Reager〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2019-65,2019〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 The water stored under surface is very important to define the amount of water available for human and environmental applications. However, it is still a challenge to obtain measurements. NASA’s GRACE satellites provide information on total terrestrial water storage based on observations of gravity changes. Here, we relate GRACE data with streamflow measurements, providing estimations of the fraction of baseflow and total drainable storage for the Mississippi River Basin.

Description: 〈b〉A conceptual model of organochlorine fate from a combined analysis of spatial and mid- to long-term trends of surface and ground water contamination in tropical areas (FWI)〈/b〉〈br〉 Philippe Cattan, Jean-Baptiste Charlier, Florence Clostre, Philippe Letourmy, Luc Arnaud, Julie Gresser, and Magalie Jannoyer〈br〉 Hydrol. Earth Syst. Sci., 23, 691-709, https://doi.org/10.5194/hess-23-691-2019, 2019〈br〉 We investigated the management of long-term environmental pollution by organochlorine pesticides. We selected the case of chlordecone on the island of Martinique. We propose a conceptual model of organochlorine fate accounting for physical conditions relative to soils and geology. This model explains pollution variability in water but also the dynamics of pollution trends. It helps to identify risky areas where pollution will last for a long time and where more attention is needed.