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