On the Long-term Trend of Changes in Integrated Water Vapor Based on the Results of Continuous GPS Measurements at the Observation Point IRKM (Irkutsk)

The results of long-term observations of the total water vapor of the troposphere (IWV) at the permanent GPS measurement station IRKM (Irkutsk) are presented. When modeling the total zenith tropospheric delay (ZTD), a simplified formula based on a bi-square height model of the refractive index was used. For a more accurate determination of IWV, local values of the regression model for the weighted “mean temperature” of the troposphere which is determined using radiosonde data in Angarsk are determined. Small differences in the regression models showed that there are minor annual changes in air temperature over the city of Angarsk. For the reliability of the measurements of IWV by means of GPS, the results of observations were compared with the data of observations by the water vapor radiometer (WVR). According to permanent GPS observations, a very weak negative linear trend of the total humidity for the IRKM point (-0.04 mm per decade) was established. At the same time, the change in the temperature values on the Earth's surface at the same point was + 0.7 K per decade. In this work, long-term predicted changes in the total moisture content of the troposphere for the city of Irkutsk are confirmed.