PNNL

Abstract

Tropical cyclones (TC) often induce strong mixing in the upper ocean that generates a trail of cooler sea surface temperature (Twake) in their wakes. The Twake can affect TC intensity, so its prediction is important, especially in coastal regions where TCs can make landfall. Coastal Twakes are often more complex compared to those in the open ocean due to the influence from coastline geometry, highly variable water depth, continental runoff and shelf processes. Using observational data since 1982, here we show a significantly stronger global mean Twake in coastal regions compared to offshore regions. Temperature stratification and mixed layer depth are the main drivers of the stronger coastal Twakes in the Northern Hemisphere. The North Indian Ocean stands out as an exception in the Northern Hemisphere because of its weaker coastal Twake that is driven by stronger coastal salinity stratification. In the Southern Hemisphere, TC intensity and translation speed are more important than ocean stratification in driving coastal-offshore Twake differences. The South Indian Ocean is the only basin with a stronger coastal Twake that is supported by weaker coastal salinity stratification. The findings suggest that coastal-offshore differences in ocean stratification need to be properly represented in models in order to capture changes in TC-induced ocean cooling as storms approach landfall.