Stratospheric and tropospheric flux contributions to the polar cap energy budgets

The flux of moist static energy into the polar regions plays a key role in the energy budget and climate of the polar regions. While usually studied from a vertically integrated perspective (F_wall), this analysis examines its vertical structure, using the NASA-MERRA-2 reanalysis to compute climatological and anomalous fluxes of sensible, latent, and potential energy across 708N and 658S for the period 1980–2016. The vertical structure of the climatological flux is bimodal, with peaks in the middle to lower troposphere and middle to upper stratosphere. The near-zero flux at the tropopause defines the boundary between stratospheric (F_strat) and tropospheric (F_trop) contributions to F_wall. Especially at 708N, F_strat is found to be important to the climatology and variability of F_wall, contributing 20.9 W m²² to F_wall (19% of F_wall) during the winter and explaining 23% of the variance of F_wall. During winter, an anomalous poleward increase in F_strat preceding a sudden stratospheric warming is followed by an increase in outgoing longwave radiation anomalies, with little influence on the surface energy budget of the Arctic. Conversely, a majority of the energy input by an anomalous poleward increase in F_trop goes toward warming the Arctic surface. Overall, F_trop is found to be a better metric than F_wall for evaluating the influence of atmospheric circulations on the Arctic surface climate.