Observed sub-daily variability of latent and sensible heat fluxes in the Bay of Bengal during the summer

The sub-daily variability of latent (LHF) and sensible heat flux (SHF) in the Bay of Bengal (BoB) during the summer (May–September) is examined using moored buoys data at 8° N (2008 and 2011), 12° N (2010, 2011, 2012, 2013, 2014, and 2015), and 15° N (2009, 2013, 2014, and 2015) along 90° E. In the weak wind regime (< 6 ms⁻¹), LHF loss from the ocean shows semi-diurnal variability with a higher range at 8° N (~ 21 Wm⁻²) than at 12° N (~ 13 Wm⁻²) and 15° N (~ 8 Wm⁻²). However, LHF depicts a diurnal variability in the strong wind regime (> 6 ms⁻¹) with a range of ~ 13 Wm⁻² at 8° N and ~ 17 Wm⁻² at 12° N and 15° N. In the strong wind regime, SHF shows heat gain by the ocean with a maximum (minimum) value during the daytime (night), while it shows heat loss from the ocean in the weak wind regime with maximum (minimum) value during the night (daytime). The diurnal range of SHF does not show significant meridional variation in the strong (~ 3.5 Wm⁻²) and weak (~ 2 Wm⁻²) wind regime. The difference in sub-daily evolution of air-temperature, air-specific humidity, and wind speed determines distinct evolutions of LHF and SHF in different wind regimes, which appears to be driven by atmospheric boundary layer processes and eastward propagating land-sea breeze signals over the BoB. Finally, we also establish the relationship between sub-daily evolutions of turbulent heat fluxes in the different wind regimes with synoptic conditions associated with the active and break phases of the Indian summer monsoon.