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David H. Bromwich, Julien P. Nicolas, and Andrew J. Monaghan

1. Introduction Over the last decade, there has been increasing evidence of a positive contribution of the Antarctic Ice Sheet to global sea level rise ( Allison et al. 2009 ). The corresponding ice mass loss is mainly driven by enhanced ice discharge into the ocean from West Antarctica and the Antarctic Peninsula ( Rignot et al. 2008 ; Pritchard et al. 2009 ); see geographic names in Fig. 1 . There is, however, considerable uncertainty as to how the ice sheet’s surface mass balance (SMB) has

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Behnjamin J. Zib, Xiquan Dong, Baike Xi, and Aaron Kennedy

be random overlapped ( Xu and Randall, 1996 ). A more accurate system description and evaluation of R2 is documented in Kanamitsu et al. (2002) . 3) 20CR reanalysis NOAA's 20CR dataset uses a new version of the NCEP atmosphere–land model along with an Ensemble Kalman Filter data assimilation technique ( Whitaker and Hamill 2002 ) that assimilates only surface pressure reports and observations while using observed the Hadley Centre Sea Ice and SST dataset (HadISST) sea surface temperatures and

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Michael A. Brunke, Zhuo Wang, Xubin Zeng, Michael Bosilovich, and Chung-Lin Shie

TOVS (ATOVS) instruments, the Atmospheric Infrared Sounder (AIRS), the Microwave Sounding Unit (MSU), the Advanced Microwave Sounding Unit-A (AMSU-A), and SSM/I; and ozone retrievals from the Solar Backscatter Ultraviolet instrument (SBUV) ( Rienecker et al. 2011 ). SST was taken from the Hadley Centre Sea Ice and Sea Surface Temperature (HadISST; Rayner et al. 2003 ) and the Reynolds et al. (2007) products. Used here are the surface turbulent flux (tavg1_2d_flx_Nx) and single-level atmospheric

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J. Brent Roberts, Franklin R. Robertson, Carol A. Clayson, and Michael G. Bosilovich

72 vertical levels from the surface to 0.01 hPa. Sea surface temperature and sea ice are prescribed from the Reynolds dataset ( Reynolds et al. 2002 ). Surface winds are assimilated over the ocean using data from Special Sensor Microwave Imager (SSM/I) and scatterometer retrievals. Atmospheric temperature and moisture at the lowest model level are prognostic variables used for computing the vertical gradients in moisture and temperature needed for calculation of the latent and sensible heat

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Tiffany A. Shaw, Judith Perlwitz, Nili Harnik, Paul A. Newman, and Steven Pawson

simulations of the recent past (P1, P2, and P-Cl1960) and two twenty-first-century simulations (C21 and C21-Cl1960). These five simulations were also analyzed by Perlwitz et al. (2008) . The P1 (P2) simulations cover the period from 1950 (1951) to 2004. These reference simulations for the recent past are forced with observed changes in sea surface temperature (SST) and the Hadley Centre sea ice and SST (HadISST; Rayner et al. 2003 ), greenhouse gas concentrations, and halogens. The P2 simulation is

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Franklin R. Robertson and Jason B. Roberts

convection and sea surface temperature on intraseasonal timescales . J. Climate , 13 , 2086 – 2104 . Yu , L. , and R. A. Weller , 2007 : Objectively analyzed air–sea heat fluxes for the global ice-free oceans (1981–2005) . Bull. Amer. Meteor. Soc. , 88 , 527 – 539 . Yu , L. , X. Jin , and R. A. Weller , 2008 : Multidecade global flux datasets from the Objectively Analyzed Air-sea Fluxes (OAFlux) Project: Latent and sensible heat fluxes, ocean evaporation, and related surface

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Brian E. Mapes and Julio T. Bacmeister

the wrong level, near 700 hPa instead of 550 hPa in the tropics. In the model code, freezing and melting were both assigned a time scale of 5000 s, a time chosen to express ice nucleation delays in the freezing process. For melting, 5000 s is so long (5-km fall at a typical snowfall speed of 1 m s −1 ) that a secondary cleanup line of code is actually handling most snow melting, at the first altitude (going downward) where T exceeds 5°C. Thus melting is, indeed, occurring too low in the MERRA

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Michele M. Rienecker, Max J. Suarez, Ronald Gelaro, Ricardo Todling, Julio Bacmeister, Emily Liu, Michael G. Bosilovich, Siegfried D. Schubert, Lawrence Takacs, Gi-Kong Kim, Stephen Bloom, Junye Chen, Douglas Collins, Austin Conaty, Arlindo da Silva, Wei Gu, Joanna Joiner, Randal D. Koster, Robert Lucchesi, Andrea Molod, Tommy Owens, Steven Pawson, Philip Pegion, Christopher R. Redder, Rolf Reichle, Franklin R. Robertson, Albert G. Ruddick, Meta Sienkiewicz, and Jack Woollen

generated by the DAS. The sea surface temperature and sea ice concentration boundary conditions are derived from the weekly 1° sea surface temperature product of Reynolds et al. (2002) , linearly interpolated in time to each model time step. The MERRA system also nudges the stratospheric water vapor to zonal-mean climatological values based on data from the Halogen Occultation Experiment (HALOE; Randel et al. 1998 ) and the Microwave Limb Sounder (MLS) on the Aura satellite. c. Production MERRA was

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Michael G. Bosilovich, Franklin R. Robertson, and Junye Chen

monthly analysis based on gauge observations, satellite estimates, and numerical model outputs . Bull. Amer. Meteor. Soc. , 78 , 2539 – 2558 . Yu , L. , and R. A. Weller , 2007 : Objectively analyzed air–sea heat fluxes for the global ice-free oceans (1981–2005) . Bull. Amer. Meteor. Soc. , 88 , 527 – 539 .

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Franklin R. Robertson, Michael G. Bosilovich, Junye Chen, and Timothy L. Miller

-American seas). These are preferred areas of deep moisture and frequent convection ( Adler et al. 2003 ), and the added moisture from the increments acts to systematically increase precipitation (not shown). There are also positive values in oceanic subtropical ridge locations in eastern ocean basins where precipitation is quite small but the transition from stratocumulus to trade wind cumulus regimes are found. In the eastern Pacific a region of negative increments (drying) just south of the equator forms

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