Different Impact of Central Pacific and Eastern Pacific El Nio on the Duration of Sudden Stratospheric Warming

The NCEP–NCAR reanalysis dataset and the Had ISST dataset(1959–2014) are used to analyze the impact of two types of El Nio events, i.e., eastern Pacific El Nio(EP-El Nio) and central Pacific El Nio(CP-El Nio) 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 Nio shows no distinct differences, the duration of both major and minor SSWs during CP-El Nio is shorter than that during EP-El Nio. 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 Nio tends to induce positive phases of PNA and WP teleconnections, while CP-El Nio 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 Nio 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 Nio than during CP-El Nio.

Different Impact of Central Pacific and Eastern Pacific El Niño on the Duration of Sudden Stratospheric Warming

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.