92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Wednesday, 25 January 2012
The Impact of the Saharan Air Layer on the Development of Eastern Atlantic Tropical Cyclones
Room 244 (New Orleans Convention Center )
Michael J. Folmer, University of Maryland, College Park, MD; and R. W. Pasken, T. Eichler, G. Chen, J. Dunion, and J. Halverson

Approximately 50 African Easterly Waves (AEWs) move off the West African coast and traverse the tropical Atlantic, each year. Of these 50 AEWs, ten to fifteen may develop into tropical storms and half of that number may develop into hurricanes. In the last decade, questions have arisen on the effects of the Saharan Air Layer (SAL) and its interaction with tropical cyclogenesis. The SAL has been hypothesized to introduce dry air, vertical wind shear, and an abundance of cloud condensation nuclei that disrupt a TC circulation. When TCs move away from the SAL, rapid intensification has been noted. Numerical simulations, using the Weather and Research Forecasting (WRF) model in concert with GPS dropsondes released during the NASA African Monsoon Multidisciplinary Analyses (NAMMA) 2006 Field Campaign, were conducted to better study the interaction between SAL and AEW/TCs. Using GFS Re-Analysis (FNL) datasets to initialize the WRF, a sensitivity test was performed on the assimilated GPS dropsondes to understand the effects of individual variables on the simulation and determine the extent of improvement in the model analysis fields when compared to available observations. The temperature observations provided the most significant difference in the modeled storm organization, storm strength, and synoptic environment, but all of the variables assimilated at the same time gave a more representative mesoscale and synoptic picture. An analysis of the SAL was performed using all GPS dropsondes to determine the most significant impacts on the structure and strength of Wave 6 and Wave 7 from the NAMMA 2006 Field Campaign. Model simulations were compared to available satellite imagery and backward trajectories were performed using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HySPLIT) model.

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