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 70 degrees N and 65 degrees S 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 70 degrees N, F-strat is found to be important to the climatology and variability of F-wall, contributing 20.9 W m(-2) 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.

Automated summary

The study examines the vertical structure of moist static energy flux into polar regions using NASA-MERRA-2 reanalysis data from 1980 to 2016. It finds a bimodal distribution of climatological flux in the middle to lower troposphere and middle to upper stratosphere, with a near-zero flux at the tropopause. Especially at 70 degrees N, the contribution of F-strat to F-wall is significant during winter, impacting the variability of F-wall.