Abstract
Abstract. The Mediterranean hydrometeorological observatory Cévennes-Vivarais (OHM-CV) coordinates hydrometeorological observations (radars, rain gauges, water level stations) on a regional scale in southeastern France. In the framework of OHM-CV, temporary GPS measurements have been carried out for 2 months in autumn 2002, when the heaviest rainfall are expected. These measurements increase the spatial density of the existing permanent GPS network, by adding three more receivers between the Mediterranean coast and the Cévennes-Vivarais range to monitor maritime source of water vapour flow feeding the precipitating systems over the Cévennes-Vivarais region. In addition, a local network of 18 receivers covered an area of 30 by 30 km within the field of view of the meteorological radar. These regional and local networks of permanent and temporary stations are used to monitor the precipitable water vapour (PWV) with high temporal resolution (15 min). Also, the dense local network provided data which have been inverted using tomographic techniques to obtain the 3-D field of tropospheric water vapour content. This study presents methodological tests for retrieving GPS tropospheric observations from dense networks, with the aim of assessing the uncertainties of GPS retrievals. Using optimal tropospheric GPS retrieval methods, high resolution measurements of PWV on a local scale (a few kilometres) are discussed for rain events. Finally, the results of 3-D fields of water vapour densities from GPS tomography are analysed with respect to precipitation fields derived from a meteorological radar, showing a good correlation between precipitation and water vapour depletion areas.
Highlights
Water vapour is a very variable thermodynamic quantity in the atmosphere which influences atmospheric dynamics on very different temporal and spatial scales
They will be later converted into slant precipitable water vapour following a similar conversion strategy as the conversion zenith wet delays (ZWD) to PWV mentioned in Sect
We conducted a sensitivity study of GPS tropospheric parameters zenith total delay (ZTD) and horizontal gradients estimated from our dense network
Summary
Water vapour is a very variable thermodynamic quantity in the atmosphere which influences atmospheric dynamics on very different temporal and spatial scales (from a climatic scale to a mesoscale). For this study and to obtain a good regional coverage (see Fig. 1), we have added 3 temporary stations to the permanent GPS stations network (8 stations4)5of the CévennesVivarais region Such a regional network enables us to describe the incoming water vapour flow before it impinges on the Cévennes-Vivarais mountain range. The major products of GPS meteorological solutions are the time series and 2-D maps of the PWV (Precipitable Water Vapour) distribution as well as the 3-D water vapour fields through tomographic inversion. The main applications of tropospheric water vapour estimates from ground-based GPS data are:
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