Temperature inversions and their influence on the mixed layer heat budget during the winters of 2006-2007 and 2007-2008 in the Bay of Bengal

Time series measurements of temperature, salinity and surface meteorological parameters recorded at 8 degrees N, 90 degrees E in the southern central Bay of Bengal (BoB) from a Research Moored Array for African-Asian-Australian Monsoon Analysis and predication (RAMA) buoy are used to document temperature inversions and their influence on the mixed layer heat budget during the winters, defined as October to March, of 2006-2007 (W67) and 2007-2008 (W78). There is a marked difference in the frequency and amplitude of temperature inversion between these two winters, with variations much stronger in W78 compared to W67. The formation of temperature inversions is favored by the existence of thick barrier layers, which are also more prominent in W78 compared to W67. Inversions occur when heating in the barrier layer below the mixed layer by penetrative shortwave radiation is greater than heating of the mixed layer by net surface heat flux and horizontal advection. Our analysis further demonstrates that intraseasonal and year-to-year variability in the frequency and magnitude of temperature inversions during winter have substantial influence on mixed layer temperature through the modulation of vertical heat flux at the base of mixed layer.