Diurnal Convection-Wind Coupling in the Bay of Bengal

Kilpatrick, T, Xie SP, Nasuno T.  2017.  Diurnal Convection-Wind Coupling in the Bay of Bengal. Journal of Geophysical Research-Atmospheres. 122:9705-9720.

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atmospheric model, cycle, linear-theory, madden-julian oscillation, maritime continent, monsoon, precipitation, scale interactions, sea-breeze, summer, trmm-pr


Satellite observations of infrared brightness temperature and rainfall have shown offshore propagation of diurnal rainfall signals in some coastal areas of the tropics, suggesting that diurnal rainfall is coupled to land-sea breeze circulations. Here we utilize satellite observations of surface winds and rainfall to show the offshore copropagation of land breeze and diurnal rainfall signals for 300-400 km from the east coast of India into the Bay of Bengal. The wind observations are from the 2003 Quick Scatterometer (QuikSCAT)-SeaWinds "tandem mission" and from 17 years of the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI); the rainfall observations are from the TRMM 3B42 product and from TMI. The surface wind convergence maximum leads the rainfall maximum by 1-2 h in the western part of the bay, implying that the land breeze forces the diurnal cycle of rainfall. The phase speed of the offshore propagation is approximately 18 m s(-1), consistent with a deep hydrostatic gravity wave forced by diurnal heating over India. Comparisons with a cloud system-resolving atmospheric model and the ERA-Interim reanalysis indicate that the models realistically simulate the surface land breeze but greatly underestimate the amplitude of the rainfall diurnal cycle. The satellite observations presented in this study therefore provide a benchmark for model representation of this important atmosphere-ocean-land surface interaction. Plain Language Summary Satellite rainfall observations show a strong diurnal cycle in the Bay of Bengal during the summer monsoon. Here for the first time we utilize concurrent satellite observations of surface winds and rainfall to demonstrate the interaction between the land-sea breeze, forced by the diurnal cycle of solar heating over India, and diurnal rainfall over the Bay of Bengal. The observations are consistent with the land breeze acting as a forcing mechanism for the diurnal cycle of rainfall over the bay and, therefore, illuminate an important atmosphere-ocean-land surface interaction that is poorly represented in many climate models.