Dissipative Energization of Baroclinic Waves by Surface Ekman Pumping

A two-layer quasi-geostrophic model is used to study the effect of lower boundary Ekman pumping on the energetics of baroclinic waves. Although the direct impact of the Ekman pumping is to damp the total eddy energy, either the eddy available potential energy (EAPE) or the eddy kinetic energy (EKE), individually, can grow due to the Ekman pumping. Growth of EAPE is favored if the phase difference between the upper and lower wave fields is less than a quarter wave length, and EKE is favored if the phase difference is greater than a quarter wave length. A numerical model calculation shows that the EAPE growth occurs directly through the Ekman pumping, and that the increased EAPE can in turn lead to further growth by strengthening the baroclinic energy conversion from zonal available potential energy to the EAPE. Through this indirect effect, the Ekman pumping can increase the net production of total eddy energy.