[AOS17-09] The Role of Pacific Subtropical High Belts in the ENSO Cycle
Keywords:ENSO theory, Subtropical high belts, Extratropical forcing, ENSO phase-lock, Combination of Walker Circulation and Hadley Cell
This article conducted statistical analyses on the formation of El Niño and Southern Oscillation (ENSO) from several angles by using conventional data. We found that both El Niño and La Niña are closely associated with the preliminary activity of the Pacific Subtropical High (PSH) belts on both sides of equator if bringing an assumption of the influence of annual cycle on ENSO cycle into our calculations. The PSH belts, especially in their eastern sides, tended to have been continuous weakening for months before El Niño maturing. Oppositely, the continuous enhancing of the PSH belts might be regarded as a prelude of a La Niña. This signal the PSH belts send to omen ENSO’s coming appeared about two months earlier than the one from the elements in tropical regions. We found that the strengthening or weakening of the PSH belts could act as a more original force for driving the ENSO cycle than the elements in tropics through controlling the variation of trade winds. Since the southern PSH belt appeared more powerful than the northern one in the situation, the phase lock of the ENSO cycle might be explained by this clue. Because the southern PSH belt that approaches the nearest area of the equator every June-August in a calendar year can exert a more powerful impact on equatorial elements, SST in Eastern Equatorial Pacific will be significantly affected 3-4 months later, i.e. the general ENSO mature phase happening around the end of a calendar year. We proposed a plausible mechanism for the ENSO formation based on the results and conducted a targeted discussion on this new mechanism that could explain the problems the current conceptual ENSO models left.