Coupled Atmosphere–Ocean Variations on Timescales of Days Observed in the Western Tropical Pacific Warm Pool During Mid‐March 2020

Abstract

Waters with very high sea surface temperature (SST) occupy the western tropical Pacific Ocean (Figure 1); this high SST region is called the tropical Pacific warm pool. Due to high precipitation (rainfall) in the western equatorial region, sea surface salinity (SSS) in the western Pacific warm pool is substantially lower than that to the eastern and central Pacific. Because of the high SST, the equatorial atmosphere and ocean are likely to be coupled with each other associated with substantial heat flux from the ocean to the atmosphere as well as momentum flux from the atmosphere to the ocean. In other words, the favorable conditions for the occurrence of the air-sea interaction are satisfied in the western equatorial region. In particular, the warm pool extends (shrinks) during El Niño (La Niño) in association with the anomalous eastward (westward) shift of the warm pool eastern edge (Delcroix & Picaut, 1998;Picaut et al., 1996). The zonal displacement of the eastern edge of the warm pool related to the El Niño-Southern Oscillation (ENSO) reaches approximately 8,000 km (e.g., Philander, 1990;Rasmusson & Carpenter, 1982).In addition to the ENSO timescale, the eastern edge of the warm pool is displaced zonally on seasonal (Ando & Hasegawa, 2009;Mignot et al., 2007) and shorter timescales. Atmospheric and oceanic disturbances on timescales of days (with spectral peaks between 4 and 5 days) have been observed in the western equatorial Pacific