Observations of Gusty Wind Effect to Turbulence in the Ocean Surface Boundary Layer

Turbulence in the ocean surface boundary layer (OSBL) plays a key role in the momentum and heat transfer in the upper oceans. Under low wind conditions, higher gustiness from stronger anisotropic turbulence increases vertical wind fluctuations and injects additional momentum across the air-sea interface. As light winds cover a larger fraction of tropical oceans, observations of the gustier atmospheric surface layer to the OSBL turbulence are of great importance and interest. Near-surface turbulence measurements were conducted during the Couple Air-Sea Processes and Electromagnetic Ducting Research project east coast field campaign (CASPER-EAST) over a 15-day period with winds varying between 1 m/s to 10 m/s. During the three low-wind events (less than 3 m/s), the measured OSBL turbulence kinetic energy (TKE) increases as wind speed decreases. This increase in TKE is associated with larger wind gusts measured from a nearby surface buoy. The increasing TKE is correlated with decreasing wind speed. This study shows that the gusty atmospheric surface layer under low wind conditions enhances both wind stress and OSBL turbulence and the impact can be parametrized by a wind speed-dependent formulation.