Sudden Stratospheric Warmings - The Role of Radiation Revealed Through an Energy Budget Analysis

Sudden stratospheric warmings (SSWs) are impressive events that occur in the winter hemisphere's polar stratosphere and are capable of producing temperature anomalies upwards of +50 degrees within a matter of days. While much work has been dedicated towards determining how SSWs occur and their ability to interact with the underlying troposphere, one under-explored aspect of SSWs is the role of radiation. Using a radiative transfer model and an energy budget analysis for distinct layers of the stratosphere, this work accounts for the radiative contribution to the removal of the anomalous energy associated with SSWs. In total, 19 events are investigated over the 1979-2016 period. This work reveals that in the absence of dynamical heating following major SSWs, longwave radiative cooling dominates and often results in a strong negative temperature anomaly. The stratospheric temperature change driven by the radiative cooling is characterized by an exponential decay of the temperature anomaly with an increasing e-folding time of 6.3 ± 2.6 to 21.6 ± 8.3 days from the upper to lower stratosphere. This work also demonstrates a negligible impact that water vapour and ozone have on the longwave and shortwave radiative heating rates during SSWs when the concentrations of these gases are perturbed from their climatological state.