Horizontal-Humidity Gradient From One Single-Scanning Microwave Radiometer

We present a method for deriving horizontal-humidity variability from a single-scanning passive microwave radiometer (MWR). The MWR used has full scanning capabilities in azimuth and elevation and is sensitive to the path of integrated water vapor as well as cloud liquid water. Applying a simple linear-gradient model together with an assumed vertical profile derived from the closest radiosonde ascent, the strength and direction of the horizontal-humidity gradient can be determined with a temporal resolution on the order of 15-20 min. For the case of an approaching frontal system, the derived humidity field can explain up to 88% of the measured humidity variance-the missing variance can most probably be attributed to convective activity.