Abstract
Continuous meteorological examination of the Pre-Alpine zones in Northern Italy (Po Valley) is important for determination of atmospheric water cycles connected with floods and rainfalls. During a special meteorological observing period (MAP-SOP), radiosounding and other measurements were made in the site of Verona (Italy). This paper deals with Zenith Total Delay (ZTD) and Precipitable Water (PW) comparisons obtained by GPS, radiosounding and other meteorological measurements. PW and ZTD from ground-based GPS data in comparison with classical techniques (e.g., WVR, radiosounding) from recent literature present an accurate tool for use in meteorology applications (e.g., assimilation in Numerical Weather Prediction (NWP) models on short-range precipitation forecasts). Comparison of such ZTD for MAP-SOP showed a standard deviation of 16.1 mm and PW comparison showed a standard deviation of 2.7 mm, confirming the accuracy of GPS measurements for meteorology applications. In addition, PW data and its time variation are also matched with time series of meteorological situations. Those results indicate that changes in PW values could be connected to changes in air masses, i.e. to passages of both cold and warm fronts. There is also a correlation between precipitation, forthcoming increase and the following decrease of PW. A good agreement between oscillation of PW and precipitation and strong cyclonic activities is found.
Highlights
During MAP-SOP (Bougeault at al., 2001) field experiments (Mesoscale Alpine Program/ Special Observing Period, September-November1999), the special observation station in Verona was set up mainly for inflow probing, and upstream-measurements related to gap-flow studies in connection with neighbouring Alpine valleys
Zenith Wet Delay (ZWD, non-hydrostatic) is mainly due to the permanent dipole moment of water vapor, which is highly variable in space and time: the ZWD is fully attributed with the content of water vapor along the signal path
Due to large local radio interference with the GPS signal at Verona radiosounding site, GPSZTD were retrieved for the GPS permanent site in Padua (Italy), which belongs to IGS Network, as the nearest one to the Verona; the distance of approximately 70 km, inside the range of baselines used by other authors, e.g., 50 km (Vedel et al, 2001); 100 km (Emardson et al, 1998)
Summary
During MAP-SOP (Bougeault at al., 2001) field experiments Signals are delayed in the neutral atmosphere because of the refraction, which is a function of temperature, pressure and water content. The induced dipole moment of the atmosphere is associated with the Zenith Hydrostatic Delay (ZHD). Zenith Wet Delay (ZWD, non-hydrostatic) is mainly due to the permanent dipole moment of water vapor, which is highly variable in space and time: the ZWD is fully attributed with the content of water vapor along the signal path. GPS data may serve for the estimation of integrated water vapor in the atmosphere (Bevis et al, 1992), using their Zenith Total Delay (ZTD). The principal aim of this work was to compare radiosounding-based ZTD and PW (precipitable water) with delays and PW obtained from GPS analyses. The second aim of the work was to examine variations in PW estimates obtained from GPS with respect to the occurrence of significant meteorological events, followed in detail during MAP-SOP, in order to determine possible regularities in meteorological perspective
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