Role of low-frequency wind variability in inducing WWBs during the onset of super El Niños

Abstract

In this study, the effect of multiple timescale wind fields on the westerly wind burst (WWB) was investigated during the onset of super (1982, 1997, and 2015) and regular El Niño events. The results revealed that extreme WWBs during the onset of the super El Niño group were attributed to low-frequency westerly (≥ 90 days, LFW), medium-frequency westerly (20–90 days, MFW, or intraseasonal) and high-frequency westerly (≤ 20 days, HFW) components, accounting for approximately 56, 22 and 22%, respectively. Thus, the extreme WWBs during the onset of super El Niños were primarily contributed by LFWs. By contrast, the WWBs during the onset of regular El Niños were determined primarily by MFWs (37%) and HFWs (35%), whereas the LFW contribution is relatively small (28%). Further analysis indicated that LFWs during the onset of the super El Niños were primarily a response to a positive SST anomaly in the tropical to eastern North Pacific resembling the Pacific Meridional Mode (PMM), which had persisted during the preceding 9–12 months in the extratropical eastern North Pacific. A significant lagged correlation between the tropical and extratropical North Pacific SST was identified, and their correlation has become stronger since the late 1980s. MFWs during the onset of the super El Niños were primarily associated with the Madden–Julian Oscillation.