Tropical cyclogenesis in warm climates simulated by a cloud-system resolving model
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Here we investigate tropical cyclogenesis in warm climates, focusing on the effect of reduced equator-to-pole temperature gradient relevant to past equable climates and, potentially, to future climate change. Using a cloud-system resolving model that explicitly represents moist convection, we conduct idealized experiments on a zonally periodic equatorial β-plane stretching from nearly pole-to-pole and covering roughly one-fifth of Earth’s circumference. To improve the representation of tropical cyclogenesis and mean climate at a horizontal resolution that would otherwise be too coarse for a cloud-system resolving model (15 km), we use the hypohydrostatic rescaling of the equations of motion, also called reduced acceleration in the vertical. The simulations simultaneously represent the Hadley circulation and the intertropical convergence zone, baroclinic waves in mid-latitudes, and a realistic distribution of tropical cyclones (TCs), all without use of a convective parameterization. Using this model, we study the dependence of TCs on the meridional sea surface temperature gradient. When this gradient is significantly reduced, we find a substantial increase in the number of TCs, including a several-fold increase in the strongest storms of Saffir–Simpson categories 4 and 5. This increase occurs as the mid-latitudes become a new active region of TC formation and growth. When the climate warms we also see convergence between the physical properties and genesis locations of tropical and warm-core extra-tropical cyclones. While end-members of these types of storms remain very distinct, a large distribution of cyclones forming in the subtropics and mid-latitudes share properties of the two.
KeywordsTropical cyclones Climate change Atmospheric modeling Paleoclimate
We thank two anonymous reviewers for their constructive comments on the paper. Financial support was provided by grants to AVF from the David and Lucile Packard Foundation, NSF (AGS-0163807), and NOAA (NA14OAR4310277). WRB was supported by Office of Naval Research award N000141512531. JS was supported by the Russian Foundation for Basic Research (grant #17-05-00509) and the Russian Science Foundation (grant #14-50-00095). Support from the Yale University Faculty of Arts and Sciences High Performance Computing facility is acknowledged.
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