Ph.D. Topic

Boundary layer wind balances and their influence on equatorial sea-surface temperatures

At the equator, over the ocean, pressure gradients are weak so that vertical momentum fluxes and horizontal eddies are required to maintain near equatorial surface winds.  Two strong  feedback mechanisms are hypothesized: one by which a stronger vertical flux of momentum leads to colder surface temperatures which stabilizes the boundary layer and reduces the downward momentum flux, a negative feedback; another whereby stronger winds at the equator maintain larger near equatorial surface temperature gradients, which drive off-equatorial zonal winds, whose momentum is carried by eddies to help maintain the winds, a positive feedback.  This is a tightly coupled system that is not well represented in existing climate models. Its dynamics will be investigated in coupled storm resolving global models, something that has only now become feasible, to better understand how the interplay of turbulent momentum fluxes and sea-surface temperature influence the pattern of convection and the structure of the global tropics.

Supervisors: Prof. Dr. Bjorn Stevens and Dr. Christian Wengel