Tropospheric water vapour above Switzerland over the last 12 years J. Morland1, M. Collaud Coen2, K. Hocke1,3, P. Jeannet2, and C. Mätzler1,3 1Institute of Applied Physics, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland 2MétéoSuisse, Station aérologique, 1530 Payerne, Switzerland 3Oeschger Centre for Climate Change Research, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
Abstract. Integrated Water vapour (IWV) has been measured since 1994 by the
TROWARA microwave radiometer in Bern, Switzerland. Homogenization
techniques were used to identify and correct step changes in IWV
related to instrument problems. IWV from radiosonde, GPS and
sun photometer (SPM) was used in the homogenisation process as well as partial IWV columns
between valley and mountain weather stations. The average
IWV of the homogenised TROWARA time series was 14.4 mm over
the 1996–2007 period, with maximum and minimum monthly average values
of 22.4 mm and 8 mm occurring in August and January,
respectively. A weak diurnal cycle in TROWARA IWV was detected with an
amplitude of 0.32 mm, a maximum at 21:00 UT and a minimum at
11:00 UT. For 1996–2007, TROWARA trends were compared with those
calculated from the Payerne radiosonde and the closest ECMWF grid
point to Bern.
Using least squares analysis, the IWV time series of
radiosondes at Payerne, ECMWF, and TROWARA showed consistent
positive trends from 1996 to 2007. The radiosondes measured an IWV trend of
0.45±0.29%/y, the TROWARA radiometer observed a trend of 0.39±0.44%/y,
and ECMWF operational analysis gave a trend of
Since IWV has a strong and variable annual cycle, a seasonal
trend analysis (Mann-Kendall analysis) was also performed.
The seasonal trends are stronger by a factor 10 or so compared to the full year trends above.
The positive IWV trends of the summer months are partly compensated by the
negative trends of the winter months. The strong seasonal trends of
IWV on regional scale underline the necessity of
long-term monitoring of IWV for detection,understanding, and forecast
of climate change effects in the Alpine region.
Citation: Morland, J., Collaud Coen, M., Hocke, K., Jeannet, P., and Mätzler, C.: Tropospheric water vapour above Switzerland over the last 12 years, Atmos. Chem. Phys., 9, 5975-5988, doi:10.5194/acp-9-5975-2009, 2009.