Has There Been a Recent Shallowing of Tropical Cyclones?

Abstract

Many aspects of tropical cyclone (TC) properties at the surface have been changing but any systematic vertical changes are unknown. Here, we document a recent trend of high thick clouds of TCs. The global inner-core high thick cloud fraction measured by satellite has decreased from 2002 to 2021 by about 10% per decade. The TC inner-core surface rain rate is also found to have decreased during the same period by a similar percentage. This suppression of high thick clouds and rain has been largest during the intensification phase of the strongest TCs. Hence, these two independent and consistent observations suggest that the TC inner-core convection has weakened and that TCs have become shallower recently at least. For this period, the lifetime maximum intensity of major TCs has not changed and this suggests an increased efficiency of the spin-up of TCs. Plain Language SummaryAs the atmosphere is becoming warmer under the climate change, many aspects of tropical cyclone (TC) have been changing or are expected to change, for example, TC intensity and TC height. The height of stronger TCs is expected to become taller. We present the first satellite observations of TC clouds near the TC top and demonstrate that the thick clouds of the inner part of TC, which is the part with the most intense winds and rain, has actually decreased during the period between 2002 and 2021. The decrease of high thick clouds within the inner part of TC is also consistent with the observed decreased rain there. However, the lifetime maximum intensity has not changed for this period. This all suggests that the strongest convection of a TC has weakened, and become shallower. TC may also have been spinning up more efficiently converting less energy to similar maximum intensities.