The Role of Downward Infrared Radiation in the Recent Arctic Winter Warming Trend

During the past three decades, the most rapid warming at the surface has occurred during the Arctic winter. By analyzing daily ERA-Interim data, it was found that the majority of the winter warming trend north of 70^oN can be explained by the trend in the downward infrared radiation (IR). This downward IR trend can be attributed to an enhanced poleward flux of moisture and sensible heat into the Arctic by poleward propagating Rossby waves, which increases the total column water, clouds and temperature within this region. This enhanced moisture flux is mostly due to changes in the planetary-scale atmospheric circulation rather than an increase in moisture in lower latitudes. An examination of the anomalous surface sensible and latent heat fluxes show that these fluxes are downward at the beginning of the moisture intrusion and become positive afterwards. The results of this study suggest Arctic amplification has mostly arisen through an increase in the frequency and/or strength of moisture intrusions, and the accompany increase in downward IR, rather than through a sea ice/albedo feedback.