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Texas A&M University (2019)

A Study of Hydrodynamics in the Northern Arabian Gulf

Li, Dapeng

Titre : A Study of Hydrodynamics in the Northern Arabian Gulf

Auteur : Li, Dapeng

Université de soutenance : Texas A&M University

Grade : Doctor of Philosophy (PhD) 2019

In this study, we characterize hydrodynamics induced by winds (winter Shamals), tides and baroclinic tides in the Northern Arabian Gulf (NAG) based on observational data. Winter Shamals (strong, dry, northwesterly winds) are unique surface meteorological phenomena 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/m^2 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 six-fold increase in latent heat loss (from 27.9 to 182.9 W/m^2 ) at the air-sea interface. Such Shamal events were found to significantly enhance turbulent mixing, as exemplified by a fivefold increase in mean turbulence kinetic energy (TKE) dissipation rates from 2.3x10^-7 to 1.2x10^-6 W/kg, and an almost complete homogenization of the water temperature. Small-scale (time < 24 h and horizontal length < 10 km) hydrodynamics are significantly influenced by tides in the NAG. During the deployment between 14-28 July, 2017, measurements in the near bottom layer ( 1.5-6.5 meter above bottom) showed : (1) semi-diurnal upwelling and downwelling induced by tides, with a maximum vertical speed of 10 mm/s ; (2) positive vertical velocity gradients during the ebb tides, indicating horizontal convergence ; (3) quarter-diurnal cycles in TKE dissipation rates, with inequalities between the daily two floods and two ebbs ; (4) well-correlated relations between turbulent diffusivity and gradient Richardson number. Interactions between barotropic tides, stratifications, and varying topography usually generate baroclinic tides. Measurements between 22-29 January, 2013 showed : (1) the maximum isopycnal displacement induced by baroclinic tides was 8 m, 30 % of the overall water depth of 27 m ; (2) the peak baroclinic tidal parameters (baroclinic velocity, pressure anomaly, horizontal kinetic energy, and horizontal energy flux) occurred near the surface and bottom ; (3) vertical oscillations of stratified water within the entire water column ; (4) most of the time the gradient Richardson number was less than 0.25, suggesting shear instability.

Sujets : Hydrodynamics Northern Arabian Gulf


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