High accuracy humidity measurements using the standardized frequency method with a research upper-air sounding system

Abstract

Water vapour is the most important greenhouse gas in the atmosphere. The knowledge of water vapour distribution is of great importance for both operational purposes and climatological investigations. Several years ago the method of standardized frequencies was developed at Lindenberg Observatory of Deutscher Wetterdienst for the calculation of relative humidity (hereinafter RH) profiles measured with a H-Humicap research sonde type based on Vaisala's RS90 operational radiosonde. Firstly, this paper presents the further improvement of that method and gives a description of the method and of the calibration technique. RH profiles in the troposphere can be determined using the method of standardized frequencies with an absolute accuracy of 1% RH. The resolution of those humidity measurements is 0.01% RH. Results of about 70 radiosonde ascents are presented and as an example one ascent is compared to Lidar RH measurements. Secondly, a correction function for humidity profiles measured with RS80 A-Humicap (world-wide used operational radiosonde) is presented in this paper. It can also be applied to historical RS80 data sets. The third aim of this paper is to give some prospects/possibilities for relative humidity measurements in the stratosphere. Further investigations are necessary to improve our calibration model for humidity measurements in the upper stratosphere, especially at pressure levels lower than 200 hPa.