Enhanced Hadley and Walker Circulation and ENSO Signals in GSSTF2 Oceanic Evaporation

An Empirical Orthogonal Function (EOF) analysis of monthly oceanic evaporation using data from the version 2 of the GSFC Sea Surface Turbulent Flux (GSSTF2) data set for the period July 1987-December 2000 shows two significant distinct modes that characterized the interannual variations. The first EOF, which explains 9.2% of the variance, is characterized by large increase in the subtropics accompanied by small decrease in the eastern equatorial Pacific and the Pacific warm pool region. An Empirical mode decomposition of the time series associated with the first EOF shows an increasing trend that started around the early 1990s. This EOF pattern and the associated time series is consistent with an enhanced tropical Hadley and Walker circulation, which is also suggested from remote sensing observations of cloudiness, top of the atmosphere radiation budget, and tropical water vapor variations. The second EOF, explaining 5.7% of the variance, shows a similar pattern to the ENSO mode found in oceanic precipitation. Its associated time series shows a correlation of 0.74 with the Southern Oscillation Index (SOI), significant at the 95% level.