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Gloria L. Manney, Michelle L. Santee, Zachary D. Lawrence, Krzysztof Wargan, and Michael J. Schwartz

that have been shown to provide robust results for UTLS studies. Reanalysis datasets are one of the most powerful tools available to characterize large-scale dynamical processes, but they must be used with care since the underlying forecast models and data assimilation systems they rely on have limitations (e.g., Fujiwara et al. 2017 ). Numerous studies highlight the importance of comparing results from multiple reanalyses for UTLS studies (e.g., Manney et al. 2017 ; Manney and Hegglin 2018

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C. A. Randles, A. M. da Silva, V. Buchard, P. R. Colarco, A. Darmenov, R. Govindaraju, A. Smirnov, B. Holben, R. Ferrare, J. Hair, Y. Shinozuka, and C. J. Flynn

operational aerosol optical depth data assimilation over global oceans . J. Geophys. Res. , 113 , D10208 , doi: 10.1029/2007JD009065 . 10.1029/2007JD009065 Zhang , Y. , M. Bocquet , V. Mallet , C. Seigneur , and A. Baklanov , 2012 : Real-time air quality forecasting. Part I: History, techniques, and current status . Atmos. Environ. , 60 , 632 – 655 , doi: 10.1016/j.atmosenv.2012.06.031 . 10.1016/j.atmosenv.2012.06.031

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Kevin Hodges, Alison Cobb, and Pier Luigi Vidale

loss of life and disruption in vulnerable societies ( ECLAC 2009 ). It is therefore important to utilize the available data and new analysis techniques to better understand their properties and behavior, with the aim of mitigating their societal, economic, and environmental impacts. Because of the relatively short observational record of TCs, and problems with sampling within the record, there is considerable uncertainty in the variability of TCs in terms of frequency over climate time scales of

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V. Buchard, C. A. Randles, A. M. da Silva, A. Darmenov, P. R. Colarco, R. Govindaraju, R. Ferrare, J. Hair, A. J. Beyersdorf, L. D. Ziemba, and H. Yu

geographical and temporal coverage due to cloud contamination, uncertainties in aerosol retrievals, and sensor-specific data gaps. Although they provide continuity, aerosol models experience uncertainties due to emissions and physical parameterizations. One approach to provide a better representation of aerosols in the atmosphere is to take advantage of both models and sparse observations using data assimilation techniques. By combining the high temporal and spatial coverage of a global model with

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Bin Guan, Duane E. Waliser, and F. Martin Ralph

different aspects of the phenomenon, a number of techniques have been previously developed for objective identification of ARs. For example, the technique based on the integrated water vapor (IWV) signature of ARs was developed associated with the availability of high-quality satellite retrievals of IWV over the northeastern Pacific ( Ralph et al. 2004 ; Neiman et al. 2008 ; Wick et al. 2013 ). The technique based on point observations of IWV and surface wind was designed to best take advantage of

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Mohar Chattopadhyay, Will McCarty, and Isaac Moradi

, changes to the instrument calibration, changes in the position of the instruments, as well as human error in collecting observations from instruments such as radiosondes. These reprocessing techniques have largely improved the quality of sonde data. Additionally, there are microwave data from scanning instruments that are reliable in their vertical coverage (due to uniform spectral resolution) and horizontal coverage (due to uniform orbital and scan geometry). The microwave (MW) temperature sounders

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Franklin R. Robertson, Michael G. Bosilovich, and Jason B. Roberts

; Kobayashi et al. 2015 ) that blend diverse measurements of wind, moisture, and temperature as well as other observations with first-guess estimates from model short-term forecasts. While reanalyses effectively reconcile observations with physically based dynamical models, there are a number of practical problems that result in moisture transport fields typically having substantial systematic time-dependent biases ( Trenberth et al. 2011 ; Robertson et al. 2011 ; Lorenz and Kunstmann 2012 ; Trenberth

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Ronald Gelaro, Will McCarty, Max J. Suárez, Ricardo Todling, Andrea Molod, Lawrence Takacs, Cynthia A. Randles, Anton Darmenov, Michael G. Bosilovich, Rolf Reichle, Krzysztof Wargan, Lawrence Coy, Richard Cullather, Clara Draper, Santha Akella, Virginie Buchard, Austin Conaty, Arlindo M. da Silva, Wei Gu, Gi-Kong Kim, Randal Koster, Robert Lucchesi, Dagmar Merkova, Jon Eric Nielsen, Gary Partyka, Steven Pawson, William Putman, Michele Rienecker, Siegfried D. Schubert, Meta Sienkiewicz, and Bin Zhao

applications ranging from air quality forecasting to studies of aerosol–climate and aerosol–weather interactions (e.g., Bocquet et al. 2015 ). An analysis splitting technique ( Randles et al. 2017 ) is used to assimilate AOD at 550 nm, in which a two-dimensional analysis is performed first using error covariances derived from innovation data, and then the horizontal increments are projected vertically and across species using an ensemble method. AOD observations are derived from several sources, including

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Allison B. Marquardt Collow, Michael G. Bosilovich, and Randal D. Koster

extreme precipitation events and how they will change in the future will help enable the precautions needed to protect society from such events, for example, through more accurate forecasts. While it is quite possible that the increasing trend in extreme precipitation events will continue into the future, there is considerable uncertainty ( IPCC 2013 ; Janssen et al. 2014 ). The frequency of extreme precipitation events in the Northeast varies by season, and this frequency has changed over time

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Krzysztof Wargan, Gordon Labow, Stacey Frith, Steven Pawson, Nathaniel Livesey, and Gary Partyka

quality of these fields has not encouraged the atmospheric ozone community to use them in scientific research. Typically, researchers prefer to utilize satellite and in situ ozone data along with assimilated meteorological variables. To our knowledge, the only comprehensively validated reanalysis ozone fields are those from two European Centre for Medium-Range Weather Forecasts (ECMWF) reanalyses: ERA-40 ( Dethof and Hólm 2004 ) and ERA-Interim ( Dragani 2011 ). On the other hand, a large body of

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