Tracking the Saharan Air Layer with Satellite Data

The Saharan Air Layer (SAL) is an elevated layer of air that is warm, dry, and sometimes contains sand and dust particles that are lifted by the winds over the Saharan desert. Knowing the location of the SAL is helpful to weather forecasters to better predict if a tropical system will weaken or strengthen. Developing tropical waves located within the SAL will likely weaken due to the stabilizing effect of the dry air, and the increased wind shear; both of which prevent strong convection from occurring. Tropical waves located to the west or south of the SAL have the potential to rapidly intensify. In the absence of good in situ measurements, the use of satellite data to detect and monitor the SAL is critical to tropical storm forecasting. Currently there are several products that can help monitor the SAL. The infrared split-window difference product, detects elevated temperature inversions over the ocean during the day and night, but often over-determines the SAL areal coverage. Multiple channel image combinations in the form of red-green-blue (RGB) color composites can be used to highlight the sand and dust associated with the SAL. Useful experimental RGB color composite products include the EUMETSAT “dust”, “pseudo natural color”, and “aerosol tracking” products. In this research study the experimental products were compared to determine how well each product detected the SAL. The results were varied, and each product had its own advantages and disadvantages for the detection of the SAL.