Tuesday, 11 February 2003
Performance of the Meteolabor "Snow White" chilled-mirror hygrometer in the tropical troposphere: Comparisons with the Vaisala RS80 A/H-Humicap sensors
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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