Exploring the Tropically Excited Arctic Warming Mechanism with Station Data: Links between Tropical Convection and Arctic Downward Infrared Radiation

Abstract:

The Tropically Excited Arctic Warming (TEAM) mechanism ascribes Arctic surface warming to tropical convection, which excites poleward propagating Rossby wave trains that transport water vapor and heat into the Arctic. A crucial component of the TEAM mechanism is the increase in downward infrared radiation (IR) that precedes the Arctic warming. Previous studies have examined the downward IR associated with the TEAM mechanism with reanalysis data. To corroborate previous findings, we examine the linkage between tropical convection, Rossby wave trains, and downward IR with Baseline Surface Radiation Network (BSRN) downward IR station data. The physical processes that drive changes in the downward IR are also investigated by regressing 300-hPa geopotential height, outgoing longwave radiation, water vapor flux, ERA-Interim downward IR, and other key variables, against the BSRN downward IR at Barrow, Alaska and Ny-Alesund, Spitsbergen.

Both the Barrow and the Ny-Alesund station downward IR anomalies are preceded by anomalous tropical convection and poleward propagating Rossby wave trains. The wave train associated with Barrow resembles the Pacific/North American teleconnection pattern and that for Ny-Alesund corresponds to a northwest Atlantic wave train. It is found that both wave trains promote warm and moist advection from the midlatitudes into the Arctic. The resulting water vapor flux convergence, multiplied by the latent heat of vaporization, closely resembles the regressed ERA-Interim downward IR. These results suggest that the combination of warm advection, latent heat release, and increased cloudiness all contribute toward an increase in downward IR.