Lawrence Berkeley National Laboratory

Reanalyses have proven to be convenient tools for studying the Arctic climate system, but their uncertainties should first be identified. In this study, five reanalyses (JRA-55, 20CRv2c, CFSR, ERA-Interim, and MERRA-2) are compared with NASA CERES-MODIS (CM)-derived cloud fractions (CFs), cloud water paths (CWPs), topof- atmosphere (TOA) and surface longwave (LW) and shortwave (SW) radiative fluxes over theArctic (708-908N) over the period of 2000-12, and CloudSat-CALIPSO (CC)-derived CFs from2006 to 2010. Themonthlymean CFs in all reanalyses except JRA-55 are close to or slightly higher than the CC-derived CFs from May to September. However, wintertime CF cannot be confidently evaluated until instrument simulators are implemented in reanalysis products. The comparison betweenCMandCCCFs indicates thatCM-derived CFs are reliable in summer but not in winter. Although the reanalysisCWPs follow the general seasonal variations ofCMCWPs, their annual means are only half or even less than the CM-retrieved CWPs (126 gm-2). The annual mean differences in TOA and surface SW and LWfluxes between CERES EBAF and reanalyses are less than 6Wm-2 for TOA radiative fluxes and 16Wm-2 for surface radiative fluxes. All reanalyses show positive biases along the northern and eastern coasts of Greenland as a result of model elevation biases or possible CMclear-sky retrieval issues. The correlations between the reanalyses and CERES satellite retrievals indicate that all five reanalyses estimate radiative fluxes better than cloud properties, and MERRA-2 and JRA-55 exhibit comparatively higher correlations for Arctic cloud and radiation properties.