Marine boundary layer simulation and verification during BOBMEX-Pilot using NCMRWF model

A global spectral model (T80L18) that is operational at NCMRWF is utilized to study the structure of the marine boundary layer over the Bay of Bengal during the BOBMEX-Pilot period. The vertical profiles of various meteorological parameters within the boundary layer are studied and verified against the available observations. The diurnal variation of various surface fields are also studied. The impact of non-local closure scheme for the boundary layer parameterisation is seen in simulation of the flow pattern as well as on the boundary layer structure over the oceanic region. Analysis of the marine boundary layer structure and the air sea interaction processes are crucial and very important in understanding the general flow pattern over the Indian subcontinent including the genesis of lows and depressions. It remains then essential that the boundary layer structure as simulated by the numerical models should be reproduced in the most realistic manner. The marine boundary layer plays a key role in the atmospheric energy exchange pro- cesses. As distinguished from most land surfaces, open sea and ocean surfaces are characterized by a remarkable temporal and spatial homogeneity of temperature. This is primarily due to the large heat capacity and efficient mixing processes in the upper oceanic mixed layer. Thus, over much of the ocean, the surface heat flux does not play a large role in determining the boundary layer structure. Observa- tional validation of boundary layer theory, details of boundary layer structure rely heavily on data which is relatively sparse and especially rare in the case of marine boundary layer. Few observational studies are available on the marine boundary layer over the Indian Ocean. BOBMEX offered an opportunity to explore the structure of the marine boundary layer and its evolution over the Bay of Bengal.