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

From 11 to 12 March 2020, we observed atmosphere and ocean variations during a temporal warming of the western tropical Pacific warm pool and the associated active convection on the equator by the R/V Mirai and unmanned surface vehicles, known as Wave Gliders. The warming, which extended the warm pool eastward at a speed of approximately 2.9 m s(-1), was found to be caused mainly by high sensitivity of the temperature of the thin mixed layer to shortwave and longwave radiation flux. During the warming, westward-propagating inertia-gravity wave disturbances in addition to intensified northerly wind intermittently enhanced turbulent latent heat release into the atmosphere (>150 W m(-2)), leading to heavy rainfall from midnight to morning, so-called diurnal dancing, in the eastern region of the warm pool. The strong air-sea coupling was related to the zonal wind variation trapped near the sea level, which caused their convergences, also intensified atmospheric convection. Subsequently (13-14 March), due to the atmospheric density stratification and wind speed changes, atmospheric disturbances radiated upward and ceased to be coupled with the ocean.