Eyewall evolution for typhoons crossed the terrains

Based on the best-track data from 1945 to 2006, the eyewall evolution induced by the landfall process over Luzon is studied. In average there are 3 typhoons per year originated from the western North Pacific that cross the Philippines. Since 1997, the evolution of the eyewall structure can be depicted by the microwave images of the Special Sensor Microwave Imager (SSM/I) and Tropical Rainfall Measuring Mission Microwave Imager (TMI). By examining the available microwave images of typhoons during the landfall period between 1997 and 2006, we show that most typhoons experienced similar eyewall evolution processes, i.e., the radius of the eyewall expands during landfall for 85% of the landfalling typhoons, while the radius of eyewall shrink when typhoon reenter to the ocean for 50% of the cases. This result shows how the terrain of suitable size may naturally modulate the eyewall evolution. The dynamics of this eyewall evolution processes is worth of further investigation by the idealized numerical experiments. The dynamics for such eyewall evolution processes would be discussed while compared with results from numerical experiments.