The Role of Stratospheric Variability in the Leading Intraseasonal Variability Modes of Surface Air Temperature in Boreal Winter

Abstract:

Sudden stratospheric warmings (SSWs) are typically followed by the negative phase of Arctic Oscillation (AO) on the intraseasonal time scale, with a high pressure anomaly centered near Greenland and a cold anomaly over northern Eurasia. In contrast, the two leading intraseasonal variability modes of surface air temperature (SAT) are associated with high pressure anomalies over the Alaskan region and central Eurasia, respectively, corresponding to the so-called “warm Arctic, cold continents” pattern over the respective regions. The local circulation anomalies in the SAT modes indicate distinct atmospheric dynamics from more zonal circulation anomalies associated with the AO. Here we evaluate the intraseasonal SAT modes and the role of stratospheric variability in SAT modes in reanalyses and climate models in comparison with the more familiar AO. We will also investigate the mechanisms of local planetary wave dynamics in the downward influence of the stratosphere on the SAT modes as compared to planetary wave-zonal flow interactions that are typical for the AO. As the interannual variability in SAT often exhibits a similar spatial pattern to the intraseasonal variability in SAT, understanding the influence of the stratosphere on intraseasonal surface temperature variability could have important implications for the temperature variability on interannual or longer time scales.