Abstract
The NCEP–NCAR reanalysis dataset and the HadISST dataset (1959–2014) are used to analyze the impact of two types of El Niño events, i.e., eastern Pacific El Niño (EP-El Niño) and central Pacific El Niño (CP-El Niño) events, on the duration of major and minor sudden stratospheric warmings (SSWs) in Northern Hemisphere winter (November to February). Although the frequency of major and minor SSWs during different types of El Niño shows no distinct differences, the duration of both major and minor SSWs during CP-El Niño is shorter than that during EP-El Niño. The spatial distribution of geopotential height anomalies preceding major SSWs resembles the western Pacific (WP) teleconnection pattern, while the spatial distribution of geopotential height anomalies preceding minor SSWs bears similarity to the Pacific–North America (PNA) teleconnection pattern. An enhancement of the strength of both wavenumber 1 and wavenumber 2 is found before major SSWs. Before minor SSWs, wavenumber 1 is also strengthened, but wavenumber 2 is weakened. The analysis also reveals that EP-El Niño tends to induce positive phases of PNA and WP teleconnections, while CP-El Niño induces negative-phase WP teleconnection. As the positive phases of the PNA and WP teleconnections are related to the strengthening of wavenumber 1, EP-El Niño causes an enhancement of wavenumber 1 in the high-latitude upper troposphere and an enhancement of the upward wave flux in the high-latitude stratosphere, accompanied by a negative anomaly in Eliassen–Palm flux divergence in the subpolar stratosphere, which accounts for the longer SSW duration during EP-El Niño than during CP-El Niño.
Highlights
Sudden stratospheric warmings (SSWs) are large-scale warmings of the polar stratosphere accompanied by a weakening of westerly wind around the polar vortex (Andrews et al, 1987)
It is apparent that the duration of minor SSWs increases with the strength of minor SSWs as the duration of positive meridional temperature gradient increases with the maximum meridional temperature gradient, the linearity between them is less justified, i.e., for a given minor SSW strength, some minor SSWs last longer while some others have a shorter duration
This study uses NCEP–NCAR reanalysis data to investigate the different impact of EP-El Nino and CP-El Nino on the duration of SSWs
Summary
Sudden stratospheric warmings (SSWs) are large-scale warmings of the polar stratosphere accompanied by a weakening of westerly wind around the polar vortex (Andrews et al, 1987). Graf and Zanchettin (2012) and Garfinkel et al (2013) reported that both CP-El Nino and EP-El Nino induce a weakened stratospheric polar vortex in late winter. It is apparent from the above-mentioned studies that the responses of the northern stratospheric polar vortex to different types of El Nino events remain debatable. Iza and Calvo (2015) found that SSWs play a significant role in explaining the different responses of the northern stratospheric polar vortex to the two types of El Nino events. The responses of SSWs in the Northern Hemisphere, including both major and minor SSWs, to CP-El Nino and EP-El Nino, are compared
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