Abstract
Using reanalysis and the sea surface temperature (SST) analysis, the combined impact of El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) on the northern winter stratosphere is investigated. The warm and weak stratospheric polar vortex response to El Niño simply appears during positive PDO, whereas the cold and strong stratospheric polar vortex response to La Niña is preferable during negative PDO in the reanalysis. Two mechanisms may account for the enhanced stratospheric response when ENSO and PDO are in phase. First, the asymmetries of the intensity and frequency between El Niño and La Niña can be identified for the two PDO phases. Second, the extratropical SST anomalies in the North Pacific may also play a role in the varying extratropical response to ENSO. The North Pacific SST anomalies related to PDO superimpose ENSO SST anomalies when they are in phase but undermine them when they are out of phase. The superimposed North Pacific SST anomalies help to increase SST meridional gradient anomalies between tropical and extratropics, as well as to lock the local height response to ENSO. Therefore, the passages for the upward propagation of waves from the troposphere is more unimpeded when positive PDO is configured with El Niño, and vice versa when negative PDO is configured with La Niña.
Highlights
The significant response of the northern winter stratosphere to El Niño–Southern Oscillation (ENSO) has been widely reported in a large number of observational [1,2,3,4,5] and modeling [6,7,8,9,10,11,12,13,14]studies
Pacific–North America (PNA)-like height pattern induced by El Niño is usually stronger than the negative positivePacific–North America (PNA) pattern induced by La Niña
We find polar nightthan jet in winters seemingly exhibits case number is relatively small than other configurations, and the strong a southward shift and the response is much stronger than other configurations of El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO)
Summary
The significant response of the northern winter stratosphere to El Niño–Southern Oscillation (ENSO) has been widely reported in a large number of observational [1,2,3,4,5] and modeling [6,7,8,9,10,11,12,13,14]. It was demonstrated that the European wintertime rainfall response to ENSO is stronger and more significant during the positive PDO than during the negative PDO [44] Another example is the modulation of the ENSO–China precipitation relationship by PDO [45,46]. Considering that the forced PNA teleconnection in the troposphere can bridge the ENSO SST and the stratospheric response in the extratropics, the decadal changes in its structure and intensity may have led to the unstable relationship between the stratospheric response and ENSO [47,48]. The observed tropospheric responses to El Niño and La Niña under different PDO phases are discussed, and the stratospheric responses to different ENSO/PDO configurations are provided.
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