The Coastal Effect on Ahead-of-Eye-Center Cooling Induced by Tropical Cyclones

Abstract

Abstract The characteristics of in-storm cooling occurring ahead of the eye center are investigated based on a combination of observations and numerical simulations, as well as its sensitivity to tropical cyclone (TC) characteristics and oceanic climatological conditions. A composite of drifter and remote sensing observations from 1979 to 2020 in the Northern Hemisphere statistically evidences that the percentage of TC-induced ahead-of-eye-center cooling is enhanced remarkably over the coastal ocean compared with that over the open sea, no matter what the TC intensity, translation speed, and prestorm SST conditions are. Results are statistically similar when the actual ahead-of-eye SST cooling is used. Idealized numerical simulation results show that as the TC center approaches the coastline, the percentage of ahead-of-eye-center cooling increases steadily with the water depth shallowing below 100 m. This phenomenon may not be caused by strong stratification of the coastal ocean, as previous studies suggested. An ocean heat balance analysis reveals a new mechanism responsible for the enhanced percentage of ahead-of-eye-center cooling near the coast: although the vertical mixing dominates in the surface cooling process over the open sea, broad and intense advection is largely responsible for the rapid increase of the percentage of ahead-of-eye-center cooling over the coastal ocean, owing to less cold-water entrainment from below. A series of sensitivity experiments are conducted by varying TC characteristics in terms of intensity, translation speed, radius of maximum wind speed, and ocean characteristics in terms of temperature profiles and slope rates of the shelf. The percentage of ahead-of-eye-center cooling is dependent on the intensity and translation speed of TCs but shows little sensitivity to other parameters.