GPS observations of daily variations in the atmospheric water vapor content

Abstract

Estimates of the atmospheric Integrated Water Vapor (IWV) for 30 GPS sites in Europe, covering the period from January 1997 until August 1999 are analyzed. For every month the diurnal cycle in the IWV is estimated by averaging the data referred to that particular hour for that month. The average peak-to-peak value of the diurnal cycle during the winter months is between 0.6 mm and 1.5 mm, while during the summer months the peak-to-peak value is between 0.8 mm and 3.2 mm. The GPS results at the Onsala Space Observatory are compared to those obtained from a co-located microwave radiometer and nearby (distance 37 km) radiosonde launches. We find that the estimated diurnal variations are comparable to the uncertainties in the measurements and the models used. However, a clear dependence between the peak-to-peak value and latitude of the observations is seen during the summer months. No such dependence is detected for the winter period.