Water vapor characterization and trends in the UTLS measured by the Swiss Raman Lidar for Meteorological Observation (RALMO).

An overview of the MeteoSwiss Raman Lidar for Meteorological Observation (RALMO) system is provided along with the procedure to calibrate the retrieved humidity profiles. The different error contributions stemming from RALMO acquisition system and from the atmospheric disturbances to the measured humidity signal are also defined. The systematic and random error components are combined into the overall error of the retrieved humidity $(q)$. The overall $q$ error and profiles are validated via direct comparison with the co-located Vaisala RS41 radiosounding at 23:00 UTC. The calibrated and validated $q$-profiles are then used to calculate the trends of humidity in the Upper Troposphere/Lower Stratosphere (UTLS) region above Payerne, Switzerland. The trends over the entire timeseries since 2008 are calculated at three levels in the UTLS, i.e. at 7-8.5 km, 8.5-10 km and 10-11.5 km and compared with the trends calculated using the Vaisala RS41 for the same period. The trend analysis shows that the mean bias between RALMO and the RS41 increases with height in a range of 0-20% and that the yearly trends at the three levels in the UTLS are flat within their uncertainty.