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 ( $u\text{'}w\text{'})$ events in the marine atmospheric boundary layer (MABL). Quadrant analysis of the motion-corrected $u\text{'}$ and $w\text{'}$ suggests that sweep and ejections, representing downward stress transfer into the ocean, dominate the $u\text{'}w\text{'}$ (~ 140%). In comparison, outward and inward interactions representing an upward stress transfer into the atmosphere provide the counter-contribution (~ 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 $u\text{'}w\text{'}$ with a significant reverse stress transfer into the atmosphere, especially during intermonsoon periods. It is found that for weak winds ( $\mathrm{ws}$ < 3 m/s), the number of turbulent events (N) is less, but they frequently repeat with more considerable flux per event ( $\hat{f})$ , with outward and inward interactions (sweeps and ejections) dominating during intermonsoon periods (monsoon periods). For medium to strong winds, sweeps and ejections dominate $u\text{'}w\text{'}.$ Ejections are found to be the most efficient method of stress transfer in the BoB, contributing 80% of $u\text{'}w\text{'}$ , compared to sweeps contributing ~ 60% and interaction processes contributing ~ - 20% each to the $u\text{'}w\text{'}$ . Though the duration of sweep events is larger than ejections and with comparable flux energy per event ( $\hat{f}$ ), the larger number N of ejection events makes it the dominant stress transfer mechanism in the Bay in all seasons.