Abstract
The development of GPS (Global Positioning System) meteorology has recently enabled us to infer the amount of precipitable water vapor (PWV) using GPS networks. In the present study an analysis is done to the data of GPS-derived PWV and vapor pressure near the ground obtained in a plain located in the northern part of Kyushu Island, Japan. They are shown to change seasonally and highly correlate each other. Theoretical relation is investigated between PWV and vapor pressure under the assumption that vapor density decreases exponetially with height. A linear relation is analytically derived between them, which is consistent with the result from observations. We calculate a representative height for vapor density on the basis of neighboring upper-air observations. Using the representative height a convenient formula is proposed to estimate monthly-averaged vapor pressure near the ground. The estimated vapor pressure showed a good agreement with observed one.
