Large differences in reanalyses of diabatic heating in the tropical upper troposphere and lower stratosphere

摘要

We present the time mean heat budgets of the tropical upper troposphere (UT)and lower stratosphere (LS) as simulated by five reanalysis models:the Modern-Era Retrospective Analysis for Research and Applications (MERRA),European Reanalysis (ERA-Interim), Climate Forecast System Reanalysis (CFSR),Japanese 25-yr Reanalysis and Japan Meteorological Agency Climate Data Assimilation System (JRA-25/JCDAS),and National Centers for Environmental Prediction/National Center for AtmosphericResearch (NCEP/NCAR) Reanalysis 1. The simulated diabatic heatbudget in the tropical UTLS differs significantly from model to model, withsubstantial implications for representations of transport and mixing. Largedifferences are apparent both in the net heat budget and in all comparableindividual components, including latent heating, heating due to radiativetransfer, and heating due to parameterised vertical mixing. We describe anddiscuss the most pronounced differences. Discrepancies in latent heatingreflect continuing difficulties in representing moist convection in models.Although these discrepancies may be expected, their magnitude is stilldisturbing. We pay particular attention to discrepancies in radiative heating(which may be surprising given the strength of observational constraints ontemperature and tropospheric water vapour) and discrepancies in heating dueto turbulent mixing (which have received comparatively little attention). Thelargest differences in radiative heating in the tropical UTLS areattributable to differences in cloud radiative heating, but importantsystematic differences are present even in the absence of clouds. Localmaxima in heating and cooling due to parameterised turbulent mixing occur inthe vicinity of the tropical tropopause.