Adjoint sensitivity studies of a semi-permanent eddy in the central Red Sea

Adjoint model sensitivity analyses are conducted on a semi-permanent eddy in the Red Sea using the MIT general circulation model (MITgcm). A semi-permanent anti-cyclonic eddy, occasionally replaced by a cyclonic eddy, is captured in the middle basin of the Red Sea at about 23^oN by using satellite measurements of sea surface height (SSH), sea surface temperature (SST), in-situ observation, and glider measurements. The eddy activities were also reproduced by the model. To understand the governing factors that control the formation and evolution of this eddy, forward and adjoint sensitivities with respect to previous model state and atmospheric forcing were computed using the MITgcm and its adjoint. Since the validity of the adjoint model sensitivities depends on the capability of the forward model to simulate the eddy’s formation and evolution, a 14-year (2000-2013) forward model simulation was performed using realistic atmospheric forcing, initial and boundary conditions. The outputs have been validated with remote sensing data and in-situ observations. The model was found successfully reproduced the eddy and can therefore be utilized for studying and examining the mechanisms that can possibly trigger and strengthen the eddy, and that may influence the formation of eddies in different types. We examine and analyze the effects of wind stress, intensity of the boundary current and net heat flux, and estimating to what extent these factors could modulate the eddies.