|TITLE||ON THE RELATIONSHIP BETWEEN ENSO, STRATOSPHERIC SUDDEN WARMINGS AND BLOCKING|
|AUTHORS||David / Barriopedro (1,2)|Natalia / Calvo (1)|
- Universidad Complutense de Madrid, Madrid, Spain
- Instituto de Geociencias (IGEO), CSIC-UCM, Madrid, Spain
|ABSTRACT||Major Stratospheric Sudden Warmings (SSWs) are foremost disruptions of the polar vortex accompanied by a reversal of the westerly wind and a dramatic warming of the polar stratosphere. These anomalies progress downwards into the troposphere, where they persist from weeks to months. Thus, SSWs provide a potential source for more skilful seasonal forecasts of tropospheric winter weather in the northern extratropics. However, little attention has been paid to identify the tropospheric precursors of SSWs.
In this study, we examine the influence of El Niño-Southern Oscillation (ENSO) on different aspects of Stratospheric Sudden Warmings (SSWs) and atmospheric blocking, including the blocking precursors of SSWs, for the 1958-2010 period of the ERA-40 and ERA-I reanalyses.
It is found that SSWs are preceded by blocking patterns over different regions depending on the ENSO phase. Euro-Atlantic and western Atlantic blocks tend to precede SSWs during El Niño (EN), whereas Eastern Pacific and Siberian blocks are the preferred precursors of SSWs during La Niña (LN) winters.
Our results also reveal that the regional blocking precursors of SSWs during each ENSO phase have different impacts on the upward propagation of planetary-scale wave number 1 and 2, and hence determine ENSO differences in the wave number signatures of SSWs. SSWs occurring during EN are preceded by amplification of wave number 1, whereas LN SSWs are predominantly associated to wave number 2 amplification. This leads to an unbalanced frequency of wave-1 and wave-2 SSWs between opposite ENSO phases.|