Results of Year-Round Remotely Sensed Integrated Water Vapor by Ground-Based Microwave Radiometry

Based on two years of measurements with a time resolution of 1 min, some climatological findings on precipitable water vapor (PWV) and cloud liquid water (CLW) in central Europe are given. A weak diurnal cycle is apparent. The mean overall diurnal variation was about 0.15 cm in summer and 0.05 cm in winter, equivalent to 8% and 5%, respectively. The PWV increase starts in summer at about 0800 local time and has a maximum of about 0.02 cm h−1 between 1000 and 1500 local time, equivalent to about 1% PWV h−1. There was, on average, no PWV variation during the night in winter. PWV decreased in winter during the morning with a maximum of 0.01 cm h−1 and increased in the afternoon with a maximum of 0.01 cm h−1. Thus, the accuracy of the monthly means of PWV based on monitoring systems with low-time resolution (satellites, radiosondes) is only slightly affected by the diurnal course of PWV in central Europe. On average an increase in PWV and CLW was found in the 30-min interval before precipitation in summer. The PWV increase was, however, only about 0.1 cm or 5% of PWV within the last 2 h before rain. The corresponding CLW increase was 0.1 mm, which is considerable as precipitation was observed when CLW reached 0.3–0.4 mm.