Researches On Interdecadal Variation Of Relationship Between ENSO And The Northern Hemisphere Atmospheric Circulation

According to the correlation between the SSTA of Nifio3.4 area and geopotential height anomaly of 500hPa in the winter Northern Hemisphere, a key region of high coherence coefficient in the eastern North Asia is selected. The switch of the relationship between ENSO and the winter Northern Hemispheric atmospheric circulation in recent 50 years is fixed, by calculating running correlation coefficient between the SSTA of Nino3.4 area and the standard anomaly of geopotential height anomaly of 500hPa in the key region. Then the relationship between ENSO phases and the winter Northern Hemispheric circulation in different periods pre- and post-switch is researched. After that, by the same means, the relationship between ENSO phase and the summer Northern Hemispheric circulation is studied. In the end, the analysis of the winter time is proved by numerical simulation. The results show:1. In the 50 years, the relationship between ENSO phases and the winter Northern Hemispheric circulation is switched in the late 1970s, and so as the summer Northern Hemispheric circulation. Before late 1970s, the impact of ENSO on near-equatorial circulation can reach to mid-latitude Asia, while its impacts are localized to tropical-subtropical after that time.2. After late 1970s, the ENSO phases have evidently faint impact on the winter mid-high latitude Eastern Hemispheric atmospheric circulation, but obviously strongly on the Western Hemispheric atmospheric circulation.The summer Northern Hemispheric circulation's reponse to the ENSO events varies in different latitudes. In the mid-high latitudes, relationship between atmospheric circulation and ENSO events in the Eastern Hemisphere improves, but that in the Western Hemisphere diminishes distinctly.3. All the selected elements simulated in the numerical model are consistent with the diagnosis analysis in the 3rd chapter. The numerical simulation shows the coherent results thatthe institute region in low latitude moves southward and the Eastern Hemispheric mid-high latitude atmospheric circulation has diminishing influence by the ENSO phases, while the Western Hemispheric mid-high latitude circulation responds to the ENSO events evidently.5. The most important reasons that may make the inter-decadal characteristic of the relationship between ENSO phases and the winter Northern Hemispheric atmospheric circulation come into being are the change of the background SST and the increase of the strength of ENSO phases, which changes from cold to warm near the end of 1970s. The background SST shift to warm state, while the strength, influence areas of the ENSO phases and the tropical convection are increased, which inprove the strength of Walker circulation, and ascending branch site of it moves eastward. Then the Hadley circulation in the Eastern Hemisphere is weakened and that in the Western Hemisphere is enhanced, followed with the moment of momentum taken by its ascending branch increased in the Western Hemisphere while weakened in the Eastern Hemisphere. The PNA pattern is enhanced and the Pacific-East Asian teleconnection is weakened. As a result, the atmospheric circulation's response to the ENSO events in the Eastern Hemisphere is weakened and that in the Western Hemisphere is enhanced.