An Examination of the Saharan Air Layer Using Radio Occultation

The Saharan Air Layer (SAL) is an elevated layer of dry, warm, and dusty air between 500-850 hPa that originates in the Sahara and maintains its characteristics as it travels westward over the Atlantic Ocean. This atmospheric phenomenon plays an important role in determining hurricane formation, deterioration, and intensity, but there is still much that is unknown. With the exception of various field campaigns (it would be good to give one or two examples, names.dates only), the vertical structure of the SAL has not been studied with continuous high-resolution observations. Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Global Positioning System (GPS) radio occultation (RO) data provide the opportunity to examine the vertical and temporal structures of the SAL with high resolution. In this study, we examine vertical profiles of temperature, relative humidity, and refractivity over an east-to-west cross-section from Miami to eastern Africa. We evaluate data spanning from late spring to early summer, when the SAL is most active. SAL outbreaks are identified by Geostationary Operational Environmental Satellite (GOES)-16 split-window imagery, and the RO data are geographically and temporally collocated with the outbreaks. The vertical RO profiles are then analyzed and compared with European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA) Interim model and radiosonde data. Preliminary results indicate that RO, ERA-Interim, and radiosonde profiles are generally in good agreement, and that RO is adept at detecting the dry SAL, with relative humidity decreasing by almost 40% between the altitudes of 3-4 km in one case.