Thesis (M.Sc.) - Cairo University - Faculty of Science - Department of Astronomy and Meteorology

Precipitable water vapor (PWV) is an essential factor for weather prediction and climate research due to its influence on delaying radio signals that, in turn, affects the navigation systems. This study introduces the first attempt to estimate the amount of PWV in Egypt using the available data from the ground-based Global positioning system (GPS) data at two cities; Helwan and Alexandria. One of the key parameters extracted from the GPS data is the zenith wet delay (ZWD). We found that the ZWD range is 5.25 to 269.75 mm for Helwan and 7.125 to 319.56 mm for Alexandria. This leads to a variation in the calculated PWV values between (0.84 - 43.16 mm) for Helwan and (1.14 - 51.13 mm) for Alexandria. Throughout the year, PWV reaches its maximum at late summer and early autumn while its minimum is reached at the winter. Results were validated using the Weather Research and Forecasting (WRF) model. The difference in the estimated PWV from the two different GPS stations in Helwan and Alexandria has a maximum value of around 8.1 mm. This difference is due to the different meteorological conditions at the two sites. On the other hand, for both stations, the PWV results show good agreement with those from the WRF model with the correlation coefficient (r) up to 0.95. The average difference of the estimated PWV between GPS and WRF are 9.16 and 8.55 mm for Helwan and Alexandria respectively. Therefore, we conclude that the methodology used to compute the PWV over Egypt using the available GPS data is accurate and can be used for different Egyptian cities

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