Radiative Feedbacks from Dry Environmental Air Accelerate Tropical Cyclogenesis

A number of recent studies have highlighted that the key process of cloud radiative feedback in accelerating tropical cyclone (TC) development is by enhancing spatial gradients in radiative heating. Building on this, this study further examines how spatial gradients in free tropospheric moisture influence TC development via their impact on radiative heating. We conducted a series of idealized model simulations modifying longwave radiative heating contributed by water vapor in the environmental region outside TC. Sensitivity experiments reveal that a vortex in drier environmental moisture tends to undergo faster growth. Moreover, weak vortices require a dry environmental free troposphere to develop. Further analyses indicate that this faster genesis process primarily arises from a stronger contrast in moisture-induced radiative heating. These findings highlight the potentially important yet overlooked role of dry air in facilitating TC genesis.