Coupled Atmosphere–Ocean Variations on Timescales of Days Observed in the Western Tropical Pacific Warm Pool During Mid-March 2020
October 04,2022

Akira Nagano, Biao Geng, Kelvin J. Richards, Meghan F. Cronin, Kyoko Taniguchi, Masaki Katsumata, Iwao Ueki

Published in Journal of Geophysical Research: Oceans, September 2022

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.

Fig. Hovmöller (time–longitude) diagrams of daily (a) sea surface temperature (SST; °C) and (b) outgoing longwave radiation (OLR; W m−2) at the equator from 140°E to 160°W during 1–25 March 2020. The 30°C and 210 W m−2 isotherms are indicated by the solid contours in panels (a) and (b), respectively. Vertical dotted lines show locations of the R/V Mirai and the Wave Gliders. Periods except for the observation are meshed.

Nagano, A., Geng, B., Richards, K. J., Cronin, M. F., Taniguchi, K., Katsumata, M., & Ueki, I. (2022). Coupled atmosphere–ocean variations on timescales of days observed in the western tropical Pacific warm pool during mid-March 2020. Journal of Geophysical Research: Oceans, 127, e2022JC019032.

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