Inter-comparision and Application of Atmospheric Humidity Profiles Measured by CFH and Vaisala RS80 Radisondes

Vertical profiles of atmospheric humidity simultaneously measured by balloon-borne Cryogenic Frostpoint Hygrometer (CFH) and Vaisala RS80 radiosonde in Tengchong, Yunnan in August 2010 are analyzed. Currently, CFH is the reference instrument in the measurement of atmosphere water vapor profile. RS80 radiosonde is ever extensively used in the world before the middle of 1990s. The humidity data measured by CFH is used to assess the quality of RS80 radiosonde humidity data. The difference of RS80 radiosonde humidity data in day and night time respectively compared to CFH data is also given in individual inter-comparison. The results have revealed there is a large dry bias produced by the RS80 humidity sensor with average of (23.7±18.5)%, and the daytime dry bias is (13.5±14.8)% larger than that in the nighttime owing to solar radiation heating on the humidity sensor. In addition, RS80 radiosonde is almost incapable of measuring the valuable humidity data in the transition region from upper troposphere to lower stratosphere. For the integrated precipitable water (PW) amounts from the profiles of GTS1, RS80, CFH and their comparisons with GPS measurements, CFH integrated PW is (4.3±2.0) mm (number of samples is 11) higher than that of GPS because that CFH tends to be saturation at moist condition, especially when passes through cloud in lower troposphere, while the PW differences of RS80, GTS1 from the GPS measurements are (0.2±1.4) mm (number of samples is 12) and (-0.2±2.2) mm (number of samples is 43) respectively. The value of GPS PW is not sensitive to the humidity variations in the altitudes above upper troposphere. CFH is demonstrated as an effective instrument measuring water vapor concentration in the circumstance with lower temperature as well as lower humidity, such as in the upper troposphere and lower stratosphere. Owing to dry bias, RS80 radiosonde detects less middle or high clouds than CFH does, especially in the detection of high clouds above 6000 m where the low humidity value from RS80 radiosonde almost cannot indicate the occurrence of cloud. Therefore, the occurrence frequency and altitude of high cloud would be much underestimated if RS80 radiosonde water profiles are used.