New estimates of the large-scale Arctic atmospheric energy budget

摘要

New estimates of the current energy budget of the north polar cap (the region north of70°N) are synthesized by combining data from new atmospheric reanalyses and satelliteretrievals. For the period 2000-2005, monthly means from the Clouds and the Earth'sRadiant Energy System (CERES) satellite data set are considered to provide the mostreliable top-of-atmosphere (TOA) radiation budget. The remaining components of theenergy budget, comprising of the energy storage, horizontal convergence of energy, andthe net surface flux between the atmospheric and subsurface columns, are compiled usingdata from the Japanese 25 Year Reanalysis Project (JRA) and the National Centers forEnvironmental Prediction (NCEP) /National Center for Atmospheric Research (NCAR)Reanalysis (NRA). The annual cycles of energy budget components for the polar cap arefairly consistent between the JRA and NRA, but with some systematic differences.JRA depicts an annual mean surface flux of 14 W IT1-2 (upward), compared to only 5 W –2 . mNRA. Most of this disparity appears to be due to differences in sea ice and albedo.Horizontal atmospheric energy flux divergence calculated using mass-corrected fluxvalues contains artifacts leading to unphysical results. We argue that backing out theenergy flux convergence as a residual from the net surface heat flux and time change inenergy storage from each reanalysis, and the TOA radiation budget from CERES, providesfor more physically realistic results in the Arctic. Monthly mean anomalies of budgetterms, used to examine conditions leading to the extreme seasonal sea ice extent minimumof September 2005, point to the importance of albedo feedback.