Thermohaline convection in a couple stress fluid layer under varying gravity conditions

Thermohaline convection in a couple stress fluid layer under variable gravity conditions is analyzed using both linear theory and energy methods to gain insight into fluid behavior relevant to geophysical and space science applications. The normal mode technique applied to the linearized system yields critical values consistent with those obtained via the energy approach across all considered boundary conditions. The presence of couple stresses and solute gradients counteracts the destabilizing thermal gradient, thereby delaying the onset of convection. Variations in the gravity parameter significantly influence the stability threshold. These findings provide a unified framework that combines double diffusion, couple stresses, and variable gravity, with practical relevance to modeling stratified fluid layers in Earth's mantle, subsurface geothermal circulation, and biological or fluid transport processes under low-gravity environments such as space missions.