Patchy layered structure of tropical troposphere as seen by Indian MST radar

The MST radar observations at Gadanki (13.47° N, 79.18° E) show, almost every day throughout the year, stratified layers of intense reflectivity near the tropopause level (17 km) and also at a couple of levels between 4 km and 10 km. Highest individual reflectivity values occur near 17 km, but they occur for a short while. The region between 11 km and 15 km shows the lowest values of reflectivity alongwith vertical downward motion almost on all days of the year. High values of reflectivity are attributed to the existence of visible or sub-visible clouds; the layered structure of clouds is attributed to inertio-gravity waves with vertical wavelength of 2-3 km. It is suggested that each high reflectivity layer consists mainly of thin sheets and patches of visible and sub-visible cloud material. Hydrometeors inside the cloud material go up and down due to gravity, precipitation-loading, Brunt-Vaisala oscillations, and Kelvin-Helmholtz waves. In these small-scale motions, thin air sheets and patches get formed with sharp temperature and humidity discontinuities through contact cooling, melting, evaporation, condensation and freezing. Also, melting and freezing at low temperatures generate electrical charges in these thin sheets and patches. These thin sheets and patches have vertical dimensions ranging from a few centimetres to several metres and horizontal dimensions of the order of 1km. These thin sheets and patches have corresponding vertical and horizontal discontinuities and sharp gradients in refractive index for the MST radar beam. These show up as regions of high values of reflectivity

The First PPP-Based GPS Water Vapor Real-Time Monitoring System in Pearl-River-Delta Region, China

China Satellite Navigation Conference (CSNC) 2013, Wuhan, China, 15-17 May 2013The first Precipitable Water Vapor Real-Time Monitoring System (PWVRMS) based on Global Positioning System Precise Point Positioning (PPP) technique has been developed for the Pearl-River-Delta region. This PWVRMS system estimates GPS satellite clock error data in real-time while using International GNSS Service (IGS) predicted precise satellite orbit directly. Currently it processes GPS data every 10 min on a daily basis from three networks in Pearl-River-Delta region: Hong Kong SatRef GPS network, Macao MoSRef GPS network and Guangdong CORS network. Compared to traditional double-differencing technique, the advantage of using PPP technique is that (1) the PWV estimation at each station is completely independent and is not affected by data quality at other stations; (2) the computation is much faster and simpler. This PWVRMS system is evaluated using radiosonde water vapor data. The GPS PWV accuracy is about 2.20 mm though the GPS station is 4.1 km away from the radiosonde. It is expected the actual GPS PWV accuracy should be higher if the GPS station is collocated with the radiosonde station. The real-time PWV products can be widely used in weather forecasts, climate researches, and water vapor correction for remote sensing images such as SAR applications. Currently the PWVRMS supplies real-time water vapor data to several meteorological agencies in Pearl-River-Delta region including Hong Kong Observatory, Macao Meteorological and Geophysical Bureau, Shenzhen Meteorological Bureau and Guangdong Meteorological Bureau for their weather forecasting service and research.Department of Land Surveying and Geo-Informatic