Application of global positioning systems (GPS) data for atmospheric water vapour variation in Thailand

Abstract

The purpose of this research is to identify the period of southwest monsoon season in Thailand by using IWV value obtained from GPS together with other meteorological data. In addition, the obtained IWV value are used to study the effect of high pressure area and the transfer of confluence wind in the winter and summer season. A new application of GPS in Thailand is the GPS-Meteorology. GPS signal propagation delayed by atmospheric water vapour is conversed into the term of zenith wet delay (ZWD), the retrieved ZWD can be transformed to the integrated water vapour (IWV) over that GPS receiver by using Bernese GPS software version 4.2 (B-GPS_IWV). The accuracy of B-GPS_IWV can be measured by the difference between B-GPS_IWV value and the IWV obtained from the Water vapour Microwave Radiometer (MWR_IWV). The result shows that the difference is 1.34 mm and its correlation coefficient is 0.81. The southwest monsoon period can be identified by the relationship of B-GPS_IWV, wind direction change, and rainfall where the onset and withdrawal are represented by the increase and decrease of B-GPS_IWV, respectively. In addition, the passage of high pressure area can be explained by decreasing of B-GPS_IWV in 3-5 days before the high pressure area move down. Moreover, it is found that the occurrent spike of B-GPS_IWV in the day of the dominative confluence wind can be used to explain the transfer of moist air into the land.