The connection between the second leading mode of the winter North Pacific sea surface temperature anomalies and stratospheric sudden warming events

Using the Hadley Center HadISST dataset and the NCEP/NCAR reanalysis dataset over the winters (December-February) from 1948 to 2014, this paper investigates the connections between the first two primary components of the sea surface temperature (SST) anomalies over the North Pacific and the stratospheric sudden warmings (SSWs) in the Northern Hemisphere winter. The results show that the winter SSW duration is more correlated to the second primary component (PC2) than the first primary component (PC1). The SSW event occurs more frequently and the winter SSW duration is longer during the positive phases of PC2 than the negative phases of PC2. The analysis also reveals that there are 10-20 year oscillations in the SSW duration after 1980, which are related to the decadal variation of PC2. The positive phases of PC2 are marked by more positive Pacific-North America (PNA) and western Pacific (WP) teleconnections in the upper troposphere. Consequently, wavenumber-1 planetary waves in the upper troposphere are strengthened and the upward Eliassen-Palm fluxes (EP fluxes) in the extratropical stratosphere are enhanced. The enhanced upward EP fluxes into the stratosphere result in SSWs persisting longer. The negative phase of PC2 has the opposite effect on the SSW duration to the positive phase of PC2. Although the SST anomalies associated with PC2 are mainly driven by the atmosphere, our model simulations show that SST anomalies of PC2 are capable of producing a feedback on the PNA and the WP and modulating the variability of SSWs.