Carefully calibrated and quality-controlled Raman water vapour lidars can be used to make frequent measurements of tropospheric and lower stratospheric water vapour at high vertical resolution of (< 1 km). The RAman Lidar for Meteorological Observation (RALMO), located in Payerne, Switzerland, was designed for operational water vapour measurements and has one of the longest quality-controlled data sets available. The data set ranges from 2008-2019 with an average of 50% uptime over the entire period. We processed the entire data set using an optimal estimation retrieval technique providing a complete uncertainty budget on a profile per profile basis. The lidar was calibrated combining external calibration against co-located radiosoundings from the GCOS Reference Upper Air Network (GRUAN) and internal calibration based on the lidar's solar background measurements. Tropospheric profiles are retrived from raw data integrated over an entire night, while UTLS profiles are retrieved from monthly integrated data. We will show that the monthly UTLS profiles are an accurate estimate of the monthly mean water vapor profiles, and hence suited for trend analyses.
For the first time, we show non-uniform increases in water vapour through the troposphere with trends ranging from +7% specific humidity per decade to +20% specific humidity per decade depending on the altitude. Almost all of the water vapour trends in the troposphere are statistically significant at the 95% Level. Combining these results with temperature measurements from the co-located operational radiosonde record leads to the conclusion that relative humidity is increasing from 2008 to 2019 throughout the troposphere.