Precipitable water vapor from ground based GPS observations over Southwestern North American: Summer 2002 and 2003

Abstract

For the first time in North American monsoon related research, ground-based GPS measurements have been used. Two years (2002 and 2003) of precipitable water vapor data estimated for the region of southern Arizona and northern Sonora were studied. Through an examination of PWV differences we found retrievals are approximately lO" = 1.9 mm as good as those calculated by the radiosonde and approximately 3 mm for GOES. Based on the GPS-PWV time series behavior we propose a new definition of the monsoon onset as an alternative to the one used by the NWS. With this definition and thanks to the high GPS time resolution we can contribute to the monsoon onset moisture source discussion since, as shown in Chapter 3, differences of about 1 hour were detected between Douglas and Tucson AZ sites. Using GPS-ET A comparisons we estimated the ETA analysis errors for the Arizona and Sonora GPS sites. The difference Standard deviations obtained for the Sonora sites are up to 1.65 mm greater than those obtained for the Arizona sites, in part as a result of the lack of upper air measurements in Sonora. In the future, these results can help in estimating the impact of errors in the analyses in Sonora on the weather forecasts in Arizona. Furthermore, on a much smaller, local scale, it is shown that the GPS can detect convective activity near the GPS surface site, a strength unknown before this study. We conclude with a perspective on future uses of this technique for the monsoon region of Arizona and Sonora.