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Abstract: Spatial and temporal variabilities in the vertical structure of Marine Atmospheric Boundary Layer (MABL) over the Bay of Bengal (BoB) are investigated through a ship-borne field experiment measurements pertaining to three different classes, namely: night, morning and afternoon conditions. High-resolution vertical profiles of meteorological parameters obtained through balloon-borne GPS Sondes during the Winter phase of Integrated Campaign for Aerosols, gases and Radiation Budget (W-ICARB) formed the primary database for the present investigation. The study advocates usage of wind shear profiles in association with virtual potential temperature (θ v ) and specific humidity (q) profiles for determination of the mixed layer heights (MLH). The mean values of turbulent flow thickness (TFT) obtained from the vertical profiles of Bulk Richardson Number (Ri B ) and MLH magnitudes for the entire cruise did not show any appreciable variations for three classes. During the entire cruise period, the MLH varied in a range from 450m to 1500m with a mean of about 900m, whereas the TFT variations were confined between 125m and 1475m with a mean of about 581m. The statistical means of TFT and MLH were similar for nighttime profiles, whereas they showed significant differences in the morning and afternoon conditions. Spatio-temporal variability in the MLH showed good correlation with the surface-layer sensible heat flux which is one of the driving mechanisms in mixing processes. [Copyright &y& Elsevier]