Modelling the effects of dry air intrusion on hurricane intensification and development

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Robert Pasken (Saint Louis University)
Michael Folmer (Center for Weather and Climate Prediction)
Jason Dunion (NOAA/AOML/Hurricane Research Division)
Jeffery Halversion (Department of Geography and Enviromental Systems University of Maryland Baltimore County)

Each year, about 50 African Easterly Waves (AEWs) move off the West African coast and traverse the tropical Atlantic. Of these 50 AEWs, ten to fifteen may develop into tropical storms and half of that number may develop into hurricanes. Questions have arisen on the role that the Saharan Air Layer (SAL) plays in tropical cyclogenesis as the SAL is an environment that is hostile to maintaining deep convection or organization due to a low moisture content, and an abundance of cloud condensation nuclei. When tropical cyclones move away from the SAL, rapid intensification has been noted. To better understand the role of the SAL and the interactions between the SAL and AEWs, numerical simulations using WRF in concert with NAMMA dropsonde data were conducted . Simulations of hurricane Helene with and without the dropsonde data with obs-nudging and 3-DVAR are compared against observations. Although there are only small differences between the obs-nudging and 3-DVAR assimulations, incorporation of the dropsonde data significantly improved the simulation results. These simulations a better understanding of the role the SAL plays is possible.

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