A 10-year integrated atmospheric water vapor record using precision filter radiometers at two high-alpine sites

Measurements of integrated water vapor (IWV) density using precision filter radiometers (PFRs) at two high-alpine, mid-latitude stations in the Swiss Alps are reported. Both sites, Davos ( 1590 m asl) and Jungfraujoch (JFJ; 3580 m asl), exhibited a maximum IWV in summer and minimum in winter. Annual mean IWV was 6.7 (+/- 3.9; 1 std) kg m(-2) from 1995 to 2005 and 2.2 (+/- 1.5) kg m(-2) from 1999 to 2005, respectively. Co-located GPS measurements exhibited a small positive IWV bias (GPS-PFR) at Davos (0.4 kg m(-2)) and a large negative bias at JFJ (-1.5 kg m(-2)). Microwave radiometer IWV at JFJ agreed well with PFR IWV suggesting that GPS IWV suffers from unmodeled effects. Linear IWV trend analysis indicated no significant trend at either Davos or JFJ for clear-sky periods. The GPS-IWV time series is at present too short to determine the trend for all-weather conditions.