The precipitation regime in the region surrounding Guam has two distinct seasons, a dry and wet season. Typically, the wet season encompasses the months of July through December. On the other hand, the dry season occupies the months of January through June. Dry season precipitation generally consists of trade wind showers and very little organized convection. During the wet season, much of the precipitation that falls in the region of Guam originates from organized convection such as squall lines, mesoscale convective systems and typhoons.
Guam has been selected as one of the Ground Validation (GV) sites for the NASA Tropical Rainfall Measuring Mission (TRMM). TRMM is unique in that it is carrying the first spaceborne precipitation radar. In order to understand and validate the measurements made from the spaceborne precipitation radar (and for the other instruments aboard the satellite (see Simpson et al., 1988 details of the instrumentation)) a detailed study of the echo characteristics from the ground based radars must be made. The data collected by the Anderson Air Force Base WSR-88D radar located on Guam has been made available for TRMM.
The data used in this study focuses on the wet season precipitation during the months of July through October for years 1995 and 1996. A total of about eight months of data were in used the analysis. To understand the characteristics of the precipitation, a variety of statistics were examined. To compare with a study of tropical precipitation from TOGA COARE, radar echoes were categorized by size, duration, orientation, and linearity using similar techniques that were applied by Rickenbach (1998). Also, statistical information was examined such as conditional averages, fractional time in rain, fractional areal coverage, and temporal and spatial correlation. These results will be used to develop a climatology of echo characteristics for Guam. This information will be used to understand and validate the measurements collected by instruments deployed on the TRMM satellite.