Tracking Dry Air Sources That Affect Atlantic Tropical Storm Debby (2006)

Increasing attention has been paid to the impact of dry air on Atlantic tropical cyclone activity. And the Saharan air layer (SAL) has received considerable attention in recent years as a potential influence on the formation and development of Atlantic tropical cyclones. However, how the SAL affects tropical cyclone intensity is still an issue in debate.Using numerical simulation data, we simulate the SAL activity and tropical cyclone activites,such as tropical stom Debby(2006),and the sources of dry air that affects Tropical Storm Debby are tracked through calculating the trajectories of the dry that penetrates into the inner areas of the storm at its middle levels. The results suggest that Debby was coming from a warm-core disturbance. The maximum warming is located at400hPa. At the early stage, the dry air was around the southeast side of the tropical cyclone. Through calculating the trajectories of the dry, four sources of the dry air are identified based on the trajectory calculation. In agreement with previous studies, the dry air can come from the subsidence associated with the subtropical high over West Africa and the Saharan air layer (SAL). In addition, we find that considerable dry air can come from mid-latitudes lower and middle troposphere. At the early stage of Debby, dry air accounts for35.7%of the total air at middle levels, among which51.9%dry air is from the SAL. As Debby moves northwestward, the influence of the SAL dry air decreases, while the dry air from middle latitudes becomes important.