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Natalie P. Thomas, Michael G. Bosilovich, Allison B. Marquardt Collow, Randal D. Koster, Siegfried D. Schubert, Amin Dezfuli, and Sarith P. Mahanama

heat waves over the Pacific Northwest United States, Bumbaco et al. (2013) also noted a greater role of precipitable water in nighttime heat waves, compared with a stronger 500-hPa ridge and increased subsidence during daytime heat waves. Over the Korean Peninsula, nighttime heat events were found to be associated with a baroclinic atmospheric structure and increased cloud cover ( Hong et al. 2018 ). A comprehensive analysis of mechanisms driving nighttime heat waves for different regions of the

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Richard I. Cullather and Sophie M. J. Nowicki

these data. Previous studies have focused on the presence of intense North Atlantic atmospheric blocking events (e.g., Rajewicz and Marshall 2014 ; Häkkinen et al. 2014 ; McLeod and Mote 2016 ). These conditions may preferentially allow for an enhanced solar radiative flux to reach the ice sheet surface and allow for albedo feedback processes to promote large-scale melting. Alternatively, Bennartz et al. (2013) identified the importance of warm air advection and the role of clouds in

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Allison B. Marquardt Collow and Mark A. Miller

reaching the surface with a reduction in insolation of 125 W m −2 at the diurnal maximum observed around local noon ( Hahmann and Dickinson 1997 ; Culf et al. 1998 ; Malhi et al. 2002 ). Simulations of cloud radiative forcing suggest that almost triple the amount of SW radiation can reach the surface in the absence of clouds ( Culf et al . 1998 ), although clouds are not the only feature within the atmosphere that can impact downwelling SW radiation in this region. The aerosol single scattering

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Laura M. Hinkelman

-D-14-00165.1 Shekhar , R. , and W. R. Boos , 2017 : Weakening and shifting of the Saharan shallow meridional circulation during wet years of the West African monsoon . J. Climate , 30 , 7399 – 7422 , . 10.1175/JCLI-D-16-0696.1 Sohn , B. J. , T. Nakajima , M. Satoh , and H.-S. Jang , 2010 : Impact of different definitions of clear-sky flux on the determination of longwave cloud radiative forcing: NICAM simulation results . Atmos. Chem

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

Halpert 1987 ; Dai and Wigley 2000 ; Gu et al. 2007 ; Robertson et al. 2014 ). Midlatitude storm-track changes embodying teleconnections with tropical forcing also have significant variations at higher latitudes. Over longer time scales Pacific decadal variability [PDV or Pacific decadal oscillation (PDO); e.g., Power et al. 1999 ; Dai 2013 ; Lyon et al. 2014 ] and other basin-scale phenomena [e.g., the Atlantic multidecadal oscillation (AMO); Enfield et al. 2001 ; Sutton and Hodson 2005

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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

( Heidinger et al. 2014 ), AOD retrievals from the Multiangle Imaging SpectroRadiometer (MISR) over bright surfaces ( Kahn et al. 2005 ), and ground-based Aerosol Robotic Network (AERONET) direct measurements of AOD (Level 2; Holben et al. 1998 ). Despite their rapid increase in complexity, aerosol models remain uncertain due to poorly constrained emissions and physical process parameterizations such as hygroscopic growth, mixing, and aerosol–cloud interactions ( Textor et al. 2006 ; Kinne et al. 2006

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Young-Kwon Lim, Robin M. Kovach, Steven Pawson, and Guillaume Vernieres

from the observations of SST, cloud, and precipitation and with the European Centre for Medium-Range Weather Forecasts (ECMWF) interim reanalysis (ERA-Interim; Dee et al. 2011 ) to demonstrate the capability of the GEOS data assimilation system and robustness of our conclusions. Having characterized the El Niño events including their intercomparison in section 3 , a closer examination of transience is presented in section 4 . A particular focus is on exploring the time evolution of SST

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

than for air temperature. Feedbacks on solar radiation are subject to questionable links in the model between the surface energy balance and the simulation of clouds. We note again, though, that MERRA-2, through improvements in its radiation physics, does show increased consistency between its precipitation and solar radiation fields ( Fig. 9 ). The presence of an overall increased consistency among the land surface forcing variables can be seen, in conjunction with the imposed realism of 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

both the MERRA-Land precipitation and the (uncorrected) AGCM-generated precipitation from MERRA-2 and MERRA. Moreover, in MERRA-2 the precipitation is corrected within the coupled atmosphere–land modeling system, allowing the near-surface air temperature and humidity to respond to the improved precipitation forcing. MERRA-2 thus provides more self-consistent surface meteorological data than were used for MERRA-Land ( Reichle et al. 2017 ). This enhanced self-consistency in the forcing data also

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

boundary forcing. 2. Data a. Reanalyses Presently there are several contemporary reanalysis datasets and different configurations of reanalyses that can provide context for the changes in the water cycle from MERRA to MERRA-2. ERA-Interim is the latest from ECMWF ( Dee et al. 2011 ), and it supersedes their previous reanalysis (ERA-40; all acronyms are listed in appendix B ). Likewise, The Japanese 55-year Reanalysis ( Ebita et al. 2011 ; Kobayashi et al. 2015 ) supersedes the previous JRA-25

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