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Mohar Chattopadhyay, Will McCarty, and Isaac Moradi

1. Introduction Microwave temperature sounders provide key information on global temperature to the initial conditions of numerical weather prediction models via the assimilation of their radiance measurements. These observations are core to the global observing system, as they fill in key observing gaps that would otherwise exist. They are complementary to conventional observations of temperature, which are spatially sparse over much of the globe—particularly over oceans. The bulk of

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Mohar Chattopadhyay, Will McCarty, and Isaac Moradi

Abstract

Microwave temperature sounders provide key observations in data assimilation, both in the current and historical global observing systems, as they provide the largest amount of horizontal and vertical temperature information due to their insensitivity to clouds. In the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), microwave sounder radiances from the Advanced Microwave Sounding Unit-A (AMSU-A) are assimilated beginning with NOAA-15 and continuing through the current period. The time series of observation minus background statistics for AMSU-A channels sensitive to upper stratosphere and lower mesosphere show variabilities due to changes in AMSU-A constellation in the early AMSU-A period. Noted discrepancies are seen at the onset and exit of AMSU-A observations on the NOAA-15, NOAA-16, NOAA-17, and NASA EOS Aqua satellites. This effort characterizes the sensitivity, both in terms of the observations and the MERRA-2 analysis. Furthermore, it explores the use of reprocessed and inter-calibrated datasets to evaluate whether these homogenized observations can reduce the disparity due to change in instrumental biases against the model background. The results indicate that the AMSU-A radiances used in MERRA-2 are the fundamental cause of this inter-platform sensitivity which can be mitigated by using reprocessed data. The results explore the importance of the reprocessing of the AMSU-A radiances as well as their inter-calibration.

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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

also capable of assimilating microwave and hyperspectral infrared radiances from planned future satellites, including MetOp-C and JPSS. The temporary spike in the number of QuikSCAT data assimilated in MERRA-2 in late 2000 is due to an error in preprocessing, which led to observations beyond the midswath “sweet spot” being used in the analysis. This has no discernible impact on the quality of the analyzed fields or on the use of other observations in the assimilation system. Fig . 1. Observations

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Allison B. Marquardt Collow and Mark A. Miller

the MPL cloud mask is available for the entire year of 2014. Liquid water path and integrated water vapor were measured by a line-of-sight microwave radiometer every 20 s, and these data have undergone extensive quality control ( Cadeddu 1993 ). Aerosols are assessed using observations from a cloud condensation nuclei counter ( Jefferson et al. 2010 ). Quality control through the ARM data stream protocol has been applied to all AMF1 observations. A true analysis of the energy budget must include

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

an added value brought to satellite observations of ozone through data assimilation. In particular, work done at the GMAO over the past decade has shown that assimilation of retrieved ozone data from the Microwave Limb Sounder (MLS) along with total ozone observations from the Ozone Monitoring Instrument (OMI), both onboard the Earth Observing System (EOS) Aura satellite, produces realistic global distributions of ozone in the stratosphere and upper troposphere ( Stajner et al. 2008 ; Wargan

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Michael G. Bosilovich, Franklin R. Robertson, Lawrence Takacs, Andrea Molod, and David Mocko

present. While several uncertainties exist, including greater uncertainty before routine microwave observations were included in late 1987 and also some variations when those become limited, the estimates are as reliable as we have for the entire globe. Remote Sensing Systems (2016) provides total precipitable water observations using SSM/I instruments over ice-free ocean areas. Mears and Wentz (2009) describe the RSS observations of the temperature of the lower troposphere, available globally

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Richard I. Cullather and Sophie M. J. Nowicki

during the day of largest melt area, in agreement with observations ( Bennartz et al. 2013 ). Fig . 10. MERRA-2 fields of (a) sea level pressure and 10-m winds and (b) total cloud fraction for 0000 UTC 11 Jul 2012. Sea level pressure is contoured every 1 hPa, and wind vectors are shown in m s −1 . Cloud fraction is contoured for every 0.05. MEaSUREs surface melt from passive microwave data is indicated with hatching. A significant event occurred over the period 14–19 July 1989, in which roughly 35

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Krzysztof Wargan and Lawrence Coy

warm winters in the Arctic stratosphere since the late 1990s . J. Geophys. Res. , 110 , D04107 , doi: 10.1029/2004JD005367 . Manney , G. L. , and Coauthors , 2008 : The evolution of the stratopause during the 2006 major warming: Satellite data and assimilated meteorological analyses . J. Geophys. Res. , 113 , D11115 , doi: 10.1029/2007JD009097 . Manney , G. L. , and Coauthors , 2009 : Aura Microwave Limb Sounder observations of dynamics and transport during the record-breaking 2009

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Rolf H. Reichle, Q. Liu, Randal D. Koster, Clara S. Draper, Sarith P. P. Mahanama, and Gary S. Partyka

/ ). MERRA-2 replaces the original MERRA reanalysis ( Rienecker et al. 2011 ) and includes updates to the AGCM ( Molod et al. 2012 , 2015 ) and to the Global Statistical Interpolation atmospheric analysis scheme of Wu et al. (2002) . In addition to the atmospheric in situ and remotely sensed observations used in MERRA, the MERRA-2 system also ingests observations from newer microwave sounders and hyperspectral infrared radiance instruments, and other new data types. Moreover, MERRA-2 preserves the

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Rolf H. Reichle, Clara S. Draper, Q. Liu, Manuela Girotto, Sarith P. P. Mahanama, Randal D. Koster, and Gabrielle J. M. De Lannoy

1. Introduction Retrospective analysis (reanalysis) data products are based on the assimilation of a vast number of in situ and remote sensing observations into an atmospheric general circulation model (AGCM) and provide global, subdaily estimates of atmospheric and land surface conditions across several decades. The recent Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2; Gelaro et al. 2016, manuscript submitted to J. Climate ), provides data beginning in

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