Future changes in Atlantic hurricanes with the rotated-stretched ARPEGE-Climat at very high resolution

Chauvin, Fabrice ; Pilon, Romain ; Palany, Philippe ; Belmadani, Ali

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<p align=justify>The new CNRM-CM6 release of the CNRM/CERFACS atmospheric general circulation model has been used in a rotated/stretched configuration that allows a local horizontal resolution of less than 15 km over the tropical North Atlantic basin. Sea surface temperatures (SST) arise from a previous lower resolution simulation of the Coupled Model Intercomparison Project-5 exercise and corrected through a quantile-quantile method. Moreover, five-member ensemble simulations have been performed for both present and RCP8.5 scenario climates. For validation purposes, another five-member ensemble simulation has been performed with prescribed observed SST. Tracking of tropical cyclones (TCs) in these simulations reveals that the intensity of the simulated TCs are quite realistic and may reach the strongest hurricane ever observed, allowing to distinguish between TC categories in the analysis. Although the model tends to underestimate the occurrence of TCs over low latitudes, the realism of simulated TCs has nevertheless improved compared to previous versions of the model, due to both increased resolution and changes in the parameterizations used in the model. Changes observed in the simulations between present and future climates confirm previous results stating that there is no clear change in the overall number of TCs but an increase in the intensity of major hurricanes as well as an increase of rainfall in all TC categories. A new result suggests that TC activity response to climate warming may be significantly different from 1 month of the hurricane season to another. In our simulations we observe a robust decrease of TCs in the tropics in July while August and September experience a large increase of TCs over the mid-latitudes. Finally, we find a relation between a large increase in TC activity near the African coast and changes in the African atmospheric dynamics and rainfall in September.</p>
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