12th Conference on Middle Atmosphere

Tuesday, 5 November 2002
Performance of the Meteolabor "Snow White" chilled-mirror hygrometer in the tropical troposphere: Comparisons with the Vaisala RS80 A/H-Humicap sensors
Masatomo Fujiwara, Kyoto Univ., Uji, Japan; and M. Shiotani, F. Hasebe, H. Voemel, S. Oltmans, P. W. Ruppert, T. Horinouchi, and T. Tsuda
The "Snow White" hygrometer is a low-cost, chilled-mirror hygrometer for radiosonde applications provided by a Swiss company, Meteolabor AG. We conducted a total of 54 Snow White soundings at five tropical stations in different seasons in 2000-2001. All soundings were made with Vaisala RS80 radiosondes equipped either with the A-Humicap (22 soundings) or H-Humicap (32) relative humidity (RH) sensor. Comparisons of the RH with respect to liquid water between the Snow White and the different RS80 Humicap sensors are made. The Snow White measurements show reasonable agreement with the H-Humicap measurements from the surface up to about 12 km (above -50C air temperature), the region where the H-Humicap sensor can be considered reliable. The comparison between the Snow White and A-Humicap sensors shows the known A-Humicap dry bias error at low temperatures and second dry bias error in the wet lower troposphere. The latter error ((A-Humicap RH) nearly equals to 0.9 x (Snow White RH) above 50% RH) may be a common problem for the recent A-Humicap sensors. These intercomparisons confirm the validity of the Snow White measurements at least up to the tropical upper troposphere and above 3-6% RH.

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