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

The Tropically Excited Arctic Warming (TEAM) mechanism ascribes Arctic Amplification to tropical convection, which excites poleward propagating Rossby wave trains that transport moisture 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 in this study, we examine the linkage between tropical convection, Rossby wave trains, and downward IR through the use of Baseline Surface Radiation Network (BSRN) downward IR station data. The physical processes that drive changes in the downward IR are also investigated. Lagged regressions are performed between 300 hPa geopotential height, outgoing longwave radiation, moisture flux and moisture flux convergence, ERA-Interim downward IR, and other key variables, against the BSRN downward IR at Barrow, Alaska and NyÅlesund, Spitsbergen.

Both the Barrow and the NyÅlesund station downward IR 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 NyÅlesund corresponds to a northwest Atlantic wave train. Furthermore, for Barrow, the tropical convection is associated with the Madden-Julian Oscillation. It is found that both wave trains advect water vapor from the midlatitudes into the Arctic. The resulting moisture flux convergence, multiplied by the latent heat of vaporization, closely resembles the regressed ERA-Interim downward IR. These results suggest that the water vapor advected into the Arctic undergoes condensation, with most of the latent heat release being realized in an increase in downward IR rather than a warming of the clouds.