Improved Detection Using Negative Elevation Angles for Mountaintop WSR-88Ds: Simulation of KMSX near Missoula, Montana

Abstract

KMSX, near Missoula, Montana, is one of the Weather Surveillance Radars-1988 Doppler (WSR-88Ds) that are located on the top of a mountain. Because all WSR-88Ds employ scanning strategies that were developed for flatland radars, mountaintop radars send signals well above the populated valleys and terrain surrounding the radars. Forecasters who use mountaintop WSR-88Ds are at a distinct disadvantage in not being able to detect crucial weather phenomena near the earth's surface. The use of negative elevation angles has been proposed as a solution to this problem. This type of radar operation poses no public radiation hazard, because the microwave radiation exposure level is about two orders of magnitude below the acceptable guideline near the radar and rapidly decreases with increasing distance. The feasibility of KMSX using negative elevation angles is simulated using several different weather situations. The simulations show the potential for improved detections of low-altitude weather conditions in the surrounding valleys and improved estimates of precipitation amounts throughout the coverage area. For example, using the lowest elevation angle (+0.5°) of the current WSR-88D scanning strategies, simulated rainfall rates detected in the valleys progressively decrease from about 80% of the surface value near the radar to only 1% of the surface value at 220 km. However, using an elevation angle of ?0.8°, simulated rainfall rates detected at all ranges out to 220 km are about 80%?95% of the surface values.