Influence of Tropical Pacific Winds at Different Timescales on ENSO Evolution

Winds play a key role in the onset, evolution, and decay of El Niño Southern Oscillation (ENSO) events. Low-frequency anomalous westerlies accompany tropical Pacific interannual sea surface temperature (SST) anomalies, while high-frequency wind variations in the form of Westerly Wind Events (WWEs) can trigger El Niños through the excitation of oceanic equatorial Kelvin waves. Previous studies have indicated that high-frequency wind variations are not purely stochastic atmospheric noise, but are energized and strengthened by the SST anomalies themselves, effectively behaving as a state dependent multiplicative noise. The relative sparsity of long term in situ observations, and the limited duration of satellite retrievals have until recently hampered a systematic and comprehensive analysis of tropical Pacific winds across all these timescales. In this study we use the newly reprocessed cross-calibrated multi-platform (CCMP V2) wind vector data set, which combines intercalibrated satellite and buoy winds over the period 1988-2015. We first illustrate how CCMP V2 is a reliable, continuous, and homogeneous blend of satellite and in situ data that provides speed and direction from sub-daily to interannual scales over the global ocean. We then use this data set to examine the interplay of interannual and subseasonal time scales at different longitudes during El Niño, La Niña, and neutral conditions. The seasonal and longitudinal distribution of WWEs is also estimated for different definitions of the WWEs, and the dependency of the WWEs characteristics upon the local SST conditions is re-examined and discussed.