Secondary Eyewall Formation in Tropical Cyclones by Outflow-Jet-Interaction

Abstract

his study uses idealized numerical simulations to show that the interaction between tropical cyclones and a mid-latitude jet can result in secondary eyewall formation. It is argued that the eddy activity by the outflow-jet interaction can enhance the upper-level outflow, thereby creating an asymmetric stratiform region outside of the primary eyewall. Numerous long-lasting deep convective cells are able to form in the stratiform cloud, creating forcing necessary for the secondary eyewall. The low-level inflow and the TC?s primary circulation advect the deep convective cells inward and cyclonically. The secondary eyewall forms after the deep convection has surrounded the TC. In contrast, numerical simulations without the jet do not show secondary eyewall formation. For moderately strong jets of wind speed 15-30 m s?1, there is little sensitivity to the jet strength. There is sensitivity to the distance between the jet and the TC, with secondary eyewall formation evident when their separation is 15 degrees latitude, but not when the separation exceeds 20 degrees.