Does Cooler Air Near the Top of the Saharan Air Layer (SAL) Play a Role in Hurricane Intensity Change during Hurricane-SAL Interactions?

Ensemble WRF simulations of Hurricane Nadine (2012), observed during the NASA Hurricane and Severe Storm Sentinel (HS3) campaign, are used to examine the impact of the Saharan Air Layer (SAL) on the storm. HS3 observations suggested that the SAL air generally remained outside the outermost convection of the storm on its eastern side during its mature stage (~14-15 September 2012). However, it was not possible from the observations to quantify the SAL’s impact. In this study, the Goddard version of the Weather Research and Forecasting (WRF) model with interactive aerosol-cloud-radiation physics is used to identify the role of SAL using a 30-member ensemble of Nadine. Most studies of SAL-hurricane interactions typically focus on the warm and dry air at lower-to-middle levels within the SAL. At the top of the SAL, the air is typically cooler and often more moist than the surrounding environment. The ensembles indicate that the warmth of the SAL plays a role in storm intensity (weaker storms for greater SAL warmth) during early stages of storm intensification on 10-11 September, but not so much at later stages. In contrast, air near the top of the SAL and at its leading edge is generally positively correlated with storm intensity, particularly at later stages of the storm, suggesting that cooler air is associated with weaker intensification. The possible role of this cooler air and the mechanism by which it may impact storm intensity will be presented.