Observation of long term trends in the amount of atmospheric water vapor by space geodesy and remote sensing techniques

We present long term trends in the amount of atmospheric water vapor at the Swedish West Coast. These trends are derived from geodetic Very Long Baseline Interferometry (VLBI), ground based microwave radiometry, and radiosonde observations. The time span of observations covers 25 years and the data were collected at the Onsala Space Observatory (VLBI and microwave radiometry) and the Gothenburg-Landvetter Airport (radiosondes). The three techniques detect positive trends in the integrated precipitable water vapor (IPWV) on the order of 0.4 to 0.6 kg/m² per decade. The IPWV data derived from the three techniques have correlation coefficients on the order of 0.95 and better. However, there is no perfect agreement between the IPWV trends derived by the three techniques. This might partly be explained by different temporal sampling and data gaps.