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Seasonally stratified correlations of the 200 mb tropical wind field to the Southern Oscillation
Author(s) -
Selkirk Rennie
Publication year - 1984
Publication title -
journal of climatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.58
H-Index - 166
eISSN - 1097-0088
pISSN - 0196-1748
DOI - 10.1002/joc.3370040403
Subject(s) - equator , climatology , geology , westerlies , northern hemisphere , madden–julian oscillation , subtropics , sea surface temperature , atmospheric sciences , latitude , southern hemisphere , forcing (mathematics) , prevailing winds , atmospheric circulation , convection , oceanography , geography , meteorology , geodesy , fishery , biology
The response of the 200 mb tropical wind field to the Southern Oscillation and central equatorial Pacific sea surface temperature is examined with correlation and regression analyses on a seasonally stratified basis. Although there are differences in magnitude, all seasons are found to exhibit the following set of responses: during periods of low Southern Oscillation Index and high equatorial sea surface temperature there are easterly anomalies of the equatorial zonal wind and westerly anomalies in the adjacent subtropics. These anomalies are consistent with the circulations in simple models of the Walker circulation in which the longitudinal scale of equatorial heating is increased, resulting in reduced zonal overturning at the equator (weakened Walker circulation) and increased meridional overturning and acceleration of the subtropical westerlies in a region slightly to the west of the anomalous heating centre. The correlation and regression results also show that central Pacific equatorial sea surface temperature is an excellent index of the heating anomalies. Theoretical results have predicted that the importance of remote forcing from the tropics in higher latitudes is dependent upon the strength of the intervening zonal wind field. Season‐to‐season differences are particularly apparent in the northern hemisphere responses of the zonal wind field to the Southern Oscillation: remote responses are relatively strong when the mean zonal winds over the Pacific region and corresponding values of standing wave group velocity are relatively large and vice versa. A similar correspondence is not found south of the equator as the correlation results do not vary as strongly with season. This may be due to greater equatorial trapping of Southern Oscillation anomalies in the same season when subtropical winds are more favourable for meridional coupling.