Effects of the Atmosphere and Sea-Surface Waves on Current and Temperature/Salinity Variations in a Shallow Water Environment

Abstract : A shallow water experiment (d 10 m) was carried out to measure the contribution of wind, precipitation and sea surface wave effects on current, pressure and temperature/salinity variations. It is found that during heavy rainfall (precipitation exceeding 5 mm), there is a corresponding salinity decrease of approximately 1 psu at 5.8 m depth. Analysis of wind data shows that the cross-shore winds exhibit 24 h periodicity associated with land/sea breezes as a result of land cooling and heating. The 24 h periodicity of cross-shore winds is reflected in temperature and salinity variations leading to the conclusion that advection by wind is the primary cause of low frequency variations. Sea surface wave data show predominantly Mediterranean swell (mean period 4 5 and significant wave heights less than 1 m). During the passage of a storm, significant wave heights exceeded 3 m and so the theory of Stokes finite amplitude waves in conjunction with linear theory is used to model particle motion, pressure, temperature/salinity and sound speed variations. Observations and models are compared for six different days and conditions: a local storm event, a calm period, during the peak of a major storm, the post-storm stage, during swell-dominated seas and finally when the sea was calm again. The velocity field shows current oscillations characteristic of a wave boundary layer. The temperature/salinity and hence sound speed variations show that when the orbital particle motions are strong, there is a low frequency spectral power law 0f-(5/3 to the left of the surface wave peak and a high frequency spectral power attenuation of approximately f-3.5 to the right.