Precipitable water vapor (PWV) is a meteorological variable that impacts the major atmospheric processes.
It is a non-homogeneous variable that differs spatially and temporally. The spatial and temporal
variability of the PWV in Egypt is investigated in this study using Global Navigation Satellite Systems
(GNSS) Radio Occultation (RO) from 2006 to 2021. The GNSS RO technique was used to obtain PWV values;
the validation results agree with the radiosonde technique. From the statistical results, the mean
bias is 0.1846 mm. The PWV has a latitudinal style in which it is inversely proportional to latitude. So,
it is evident that higher PWV occurs at low latitudes. However, some PWV values are higher over sites
near the coast of the Mediterranean Sea. No clear and direct relationship is found between PWV and longitude.
So, PWV is mainly dependent on latitude. The annual mean PWV values over Egypt range from
9.23 mm to 13.51 mm. The higher values of PWV are in the summer season between 10.74 mm and
21.55 mm. While the PWV values are in the winter season range from 6.84 mm to 9.94 mm. The highest
values of PWV occur in August between 12.35 mm and 23.35 mm and the lowest values of PWV are in
January and February ranging from 5.62 mm to 11.05 mm. PWV values are higher during the day and
lower at night.
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