Physical response of the Northern Arabian Gulf to winter Shamals

Abstract

Abstract Winter Shamals (strong northwesterly winds) are unique surface meteorological phenomena in the Northern Arabian Gulf (NAG). Here we report results from the first observational study designed to investigate the effects of winter Shamals on the hydrodynamics in the NAG. During the Shamal event of 24–26 March 2013, surface wind stress was observed to increase from 0.01 to 0.11 N/m2 and was followed by a decrease in relative humidity from 66.6 to 47.2%. The increase in wind speed and decrease in humidity resulted in a sixfold increase in latent heat loss (from 27.9 to 182.9 W/m2) at the air-sea interface. Such Shamal events were found to affect the hydrodynamics in four aspects: 1. increase of mean surface wave heights and periods, which are fetch limited, from 0.4 to 0.7 m and from 2.8 to 3.8 s, respectively; 2. residual (after removal of tides) surface elevation decrease of 0.6 m and change of residual cross-shore and along-shore velocity fields; 3. Significant increase in turbulent mixing as exemplified by a fivefold increase in mean turbulence kinetic energy dissipation rates from 2.3 × 10−7 to 1.2 × 10−6 W/kg; 4. An almost complete homogenization of the thermal structure.