Tropical Pacific Wind Research Articles

Empirical Orthogonal Function Analysis of Wind Vectors over the Tropical Pacific Region

Abstract The method of empirical orthogonal function analysis is applied to wind stress vectors over the tropical Pacific Ocean from 1961 through 1978. It is determined that this vector analysis enables a more thorough analysis of wind components than do comparable scalar analyses. The method is presented and discussed. By partitioning the spatial variance of the data into many patterns, each modulated by a complex time series, this technique provided further insight into the variability of the tropical Pacific wind field. The trade winds in each hemisphere are strongest during the respective winter and early spring. In addition, the northeast trades are more variable and stronger than the southeast trades. The 1960s more characterized by a relatively flat interannual signal, but the 1970s were more variable and were characterized by an equatorial convergent zone in the western and middle Pacific. The El Nino signal also indicates a difference between the '60s and the '70s. The Los Ninos of 1972 and 1976 ...

Associations among the tropical pacific wind and sea surface temperature fields and higher latitude circulation

AbstractAn empirical study was conducted examining associations between seasonal trade wind and sea surface temperature (SST) fields in the eastern half of the tropical Pacific Ocean for the period 1949‐1979. In addition, the tropical fields were statistically related to the extratropical circulation of the Northern Hemisphere (i.e. 700 mb heights). This study differs from most prior studies in that the trade wind field was examined primarily in terms of the horizontal trade wind divergence and seasonally stratified lag relationships were computed.Seasonally stratified autocorrelations of empirical orthogonal function (EOF) amplitudes (out to four seasons) indicated significant persistence of EOF1 of SST and divergence until spring‐summer for any initial season; accordingly, spring and summer (summer and autumn) EOF1 for SST (divergence) exhibited the greatest persistence. For divergence some tendency for a reversal of sign was seen from the autumn, winter, or spring seasons to the following autumn, which may imply negative air‐sea feedback mechanisms operating.Seasonally stratified cross correlations betwen the first EOF for SST and divergence indicated a significant contemporaneous relationship. When divergence leads SST, the relationship is significant at short lags (1‐3 seasons) until spring as a target season is reached. The same is true when SST leads divergence except that a significant relationship returns with opposite sign in the subsequent summer and auiumn. Winter SST and divergence, in particular, are well correlated with prior values of the other parameter.When the tropical parameters were related to the extratropical circulation through correlation with gridded 700 mb heights, significant patterns were found only when winter 700 mb heights were the target parameter (i.e. tropical parameter leading winter 700 mb heights). Summer through winter tropical SST and divergence (EOF1) displays a good association with subsequent winter extratropical circulation in the form of an expanded/contracted circumpolar vortex. The relationship between trade wind divergence and subsequent winter circulation is significant using the prior winter (4 season lag), vanishes during spring, and returns with the opposite sign for summer through winter (lags 0‐2). Using either SST or divergence, the observed relationships are stronger at lags 1 and 2 than at lag 0.

Interannual Fluctuations of the Tropical Pacific Wind Field and the Southern Oscillation

Abstract Linear regression analysis of tropical Pacific winds versus a Southern Oscillation Index (SOI) show departures from the seasonal mean wind associated with the phase of SOI. When the SOI is low the largest departures are westerlies on the equator and in the subtropics west of the dateline. The Intertropical Convergence Zone (ITCZ) and the South Pacific Convergence Zone (SPCZ) shift equatorward. Departures from mean wind are strongest from September through February and weakest from March to May. The usual pattern of cyclonic wind stress curl in the tropics and anticyclonic wind stress curl in the subtropics intensifies when the SOI is low. Effects of these changes on ocean circulation are discussed and compared to changes in ocean circulation data.

Time and Space Variability of Tropical Pacific Wind Stress

Abstract The results of a spectral analysis of a new, subjectively analyzed data set of tropical Pacific wind stress are presented. The monthly data for the 10-year period, 1961–70, allow a detailed inspection of the distributions of frequency and zonal wavenumber spectra from 29°N to 29°S. In addition, the results obtained using the subjective analysis technique are briefly compared with those obtained using two objective methods. The frequency spectra vary greatly throughout the tropical Pacific. There also are differences between the spectra for the wind-stress magnitude and its components. The only statistically significant peaks are for the annual and semiannual cycles. Differences between the frequency spectra for the wind-stress magnitude and the wind-stress components are discussed. Plots of the spatial distributions of the power in the annual and semiannual signals are presented and related to seasonal climatological features in the tropical Pacific wind field. Other plots are introduced which sh...