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Abstract:
The intensity of the stratospheric polar vortex (iSPV) is predicted less than 2 weeks ahead. However, low-frequency components of the climate system, such as large-scale sea surface temperature anomalies (SSTAs) e.g. El Niño–Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO), extend the period of stratospheric dynamics’ prediction.
In this work, the response of iSPV anomalies to large-scale SSTAs is evaluated using idealized modeling on ISCA platform.
It is shown that SSTAs in the mid-latitudes of the Pacific Ocean on their own do not significantly influence the formation of iSPV. With positive SSTAs in the Niño-3 region (CEN), a weakening of the polar vortex by 40% is observed. The weakening of the vortex with positive SSTAs in the central part of the tropical Pacific Ocean (ENM) is comparable to the effect of the CEN. During La Niña (LN) years the vortex weakened by no more than 20%.
The positive PDO phase significantly increases the effect of EN, while the negative phase of the PDO decreases. The LN effect is weakened by both PDO phases.
An analysis of the large-scale pressure field structure in the middle troposphere showed that CEN leads to increased PNA pattern, and during LN, the spatial structure of pressure anomalies corresponds to an increase in the AO. In contrast to some recent studies, it is shown that the pressure field response in the middle troposphere to ENM is similar to the response to CEN. This study proposes the mechanisms for the formation of these observed anomalies.
