Precipitable Water Vapor Retrieval Technology Research And Appliactions Of Ground Based GPS Observations

GPS meteorology theory has made it possible to detect the atmospheric water vapor by the Gorund based GPS, whose network provides the good conditions for the high-altitude atmospheric observations. GPS meteorology is stepping into the operational application stage from the research. The purpose of this paper is to provide the new methods and improve the methods to obtain the high-precision water vapor products by the high resolution GPS observations and use them effectively in the rainstorm forecasting and other meteorological services. The study is composed of the GPS PWV (Precipitable Water Vapor) retrieval technique improvement and localization, one new tomography algorithm of the GPS3D water vapor by the oberservations constraint, the quasi-real-time ground-based GPS atmospheric water vapor automatic calculation system development and the application of GPS observations in nowcasting, assimilation and regional climate analysis. The methods and results follow:1. The hydrostatic delay calculation models suiting for the PWV calculated in the middle reaches of the Yangtze River area is improved from the three traditional hydrostatic delay models with the regression algorithm based on radiosonde, microwave radiometer data in2years. The PWV bias between by GPS and radiosonde (RS) decreased4-8mm. The atmospheric weighted mean temperature in this area has been localized by9radiosonde stations data with the regression algorithm too. The PWV bias between GPS and RS decased6-10mm by using the above optimization methods.2. Gaussian horizontal restriction and sounding vertical restriction are used in the tomography algorithm as well as the observations at the ground to increase the condtions for solving the lack rank equations of3D water vapor. Not only the wet refraction but the regional water vapor density can be retrieved by the above algorithms. The density average bias of water vapor by GPS is-0.63g/m3and the standard bias1.22g/m3, and the correlation coefficient0.98in comparison to that by RS. With the the observation at the ground, the three-dimensional water vapor density accuracy has been improved in the total space, even in the lower layer and the edge area.3. Based on the above algorithms, the quasi-real-time automatic calculation system for the ground-based GPS atmospheric water vapor has been established and can output the products per30minutes. System functions contains the timing start, the downloading data including rapid IGS ephemeris, GPS network data and meteorological data, providing the products of precipitable water vapor, slant water vapor in Hubei province with59GPS stations and three-dimensional water vapor distribution in easten Hubei area with22GPS stations. 4. The tests of GPS data assimilation in LAPS system show that GPS water vapor observations improve the precipitation forecast quality of precipitation area and intensity. The humidity central area of precipitation is agreed with the actual rain area by the GPS assimilation. GPS water vapor assimilation improves the troposphere moisture and temperature field above the500hPa, and has a good performance on the heavy rain forecast.5. According to the statistics of the GPS water vapor observations in2006-2008, the characteristics of PWV varations are in approximate agreement with that of site’s rainfall but also the reginal ones. PWV threshold in the middle reaches of the Yangtze River for rain and heavy rain has been provided, such as that the precipitation PWV threshold is35mm, heavy precipitation PWV threshold50mm before the Meiyu season, precipitation threshold48mm, heavy precipitation55mm in the Meiyu season. The threshold values of precipitation are closer to the heavy precipitation thresholds in summer than in winter. Tests show that the threshold values is useful to rainfall prediction, the average critical success index of thresholds in24hours precipitation forecasting, which is22.7%, is even better than the index of comprehensive forecasting22%.6. Based on the observations in2000-2004by GPS network in the Three Gorges Reservoir, the regional water vapor changes before and after impoundment of reservoir follow:PWV peak in2003after the impoundment is more than that before impoundment with3-5mm, the PWV changes abnormally in the winter of2003and spring (January-April2004); diurnal variation shows that the water vapor changes become more stable than before. After the impoundment, PWV average is6mm more than the value before impoundment. The numerical model simulations also show that the growth of the underlying surface water bodies enhanced the regional water vapor and precipitation.