Turbulent characteristics of momentum flux in the marine atmospheric boundary layer of North Bay of Bengal

We use a 16-month-long, 20 Hz wind data from a mooring deployed in the Bay of Bengal (BoB) to study the characteristics of turbulent wind stress (u(sic)w(sic)) events in the marine atmospheric boundary layer (MABL). Quadrant analysis of the motion-corrected u(sic) and w(sic) suggests that sweep and ejections, representing downward stress transfer into the ocean, dominate the u(sic)w(sic) (similar to 140%). In comparison, outward and inward interactions representing an upward stress transfer into the atmosphere provide the counter-contribution (similar to 40%). We found a wind speed (ws) dependency on stress transfer for ws > 3 m/s, while for low ws, the swell-dominated ocean state modulates the u(sic)w(sic) with a significant reverse stress transfer into the atmosphere, especially during intermonsoon periods. It is found that for weak winds (ws< 3 m/s), the number of turbulent events (N) is less, but they frequently repeat with more considerable flux per event (<(f)over cap>), with outward and inward interactions (sweeps and ejections) dominating during intermonsoon periods (monsoon periods). For medium to strong winds, sweeps and ejections dominate u(sic)w(sic). Ejections are found to be the most efficient method of stress transfer in the BoB, contributing 80% of u(sic)w(sic), compared to sweeps contributing similar to 60% and interaction processes contributing similar to - 20% each to the u(sic)w(sic). Though the duration of sweep events is larger than ejections and with comparable flux energy per event ((f) over cap), the larger number N of ejection events makes it the dominant stress transfer mechanism in the Bay in all seasons.