The Impact of Tropical Sea Surface Temperature on the Arctic Stratospheric Polar Vortex Trend

Abstract

The changes in the Arctic stratospheric polar vortex are influenced by various factors and exert impacts on both the weather and climate of the troposphere and the surface. In this study, we analysed the trends of the stratospheric polar vortex using the self-organising map (SOM) method. There is a decreasing trend in the occurrence of strong polar vortices, while there is an increasing trend in the occurrence of weak polar vortices. The analysis revealed that nine nodes (3 × 3) of SOMs can explain approximately one-third (the trend contribution ratio is 33.4%) of the significant increase in the geopotential height field, in which two nodes (Nodes 3 and 7) amount to approximately three-quarters (25.23%) of the total contribution (33.4%). Significantly positive sea surface temperature (SST) anomalies in the tropical western Pacific and the southwestern Pacific Ocean associated with Node 3 enhanced convective activity in these areas, resulting in negative Rossby wave sources (RWS) and divergent winds, triggering a Rossby wave train. This wave train generates positive geopotential height anomalies over the Arctic Ocean in the stratosphere, which helps weaken the Arctic polar vortex. A wave train excited by suppressed convective activity in the tropical West Pacific and South China Sea related to Node 7 propagates northeastward along a similar path to middle and high latitudes. However, this wave train induces geopotential height anomalies opposite in sign over the Arctic Ocean, which favours the strengthening of the polar vortex. The EP flux in the high-latitude lower stratosphere associated with the two above wave trains can explain the Arctic polar vortex anomalies. Our results show that the influence of SST in the warm pool region on the stratospheric polar vortex is greater than in other ocean regions.