Observation on anisotropy in moisture distribution with GPS during the passage of a squall line

Slant water vapor (SWV) measurements from a ground-based global positioning system (GPS) instrument can provide accurate, high temporal-resolution and multi-directional water vapor information for moisture variation analysis. In this study, the preliminary comparison for GPS SWV measurements against water vapor radiometer (WVR) shows that GPS SWV measurements are accurate. We compared vertical SWV (VSWV) observations against precipitable water vapor (PWV) measurements from a GPS receiver located at the south of Beijing (54511 station) during the passage of a squall line. We found that VSWV observations display more variations than PWV measurements in moisture distribution. We also compared the temporal difference of VSWV observations between individual GPS satellites. We found obvious spatial anisotropy in moisture distribution during the passage of the squall line. These results suggest that SWV observations are very valuable in the analysis and construction of accurate moisture distribution.