stratospheric Water Vapour

in the Arctic (AWIPEV Research Base in Ny-Ålesund, Spitsbergen)

Weather phenomena -with high humidity, cloud formation and precipitation- occur in the lowermost ~10 km of the atmosphere, the so-called troposphere. The stratosphere above is very dry, with only about 4 to 10 water molecules among 1 million air particles. Thus, the required measurements accuracy for stratospheric water vapor is in the order "ppmv" (parts per million by volume). As the daily launched radiosondes do not provide such an accuracy, they provide reliable humidity data only in the troposphere.

Yet, the amount of stratospheric water vapor is relevant for climate, since water vapor is a greenhouse gas and thereby radiatively affects stratospheric temperature. Furthermore, the water vapor concentration plays a role in microphysical cloud formation processes, and in the stratosphere as an effect on the formation and characteristics of polar stratospheric clouds that affect stratospheric ozone depletion

Frostpoint Hygrometer Measurements

For the detection of stratospheric water vapor vertical profiles, a cryogenic frostpoint hygrometer (CFH) sonde is launched by balloon at the AWIPEV research base every two months. During the flight, the reflectivity of a small mirror in the ambient air is detected. Cooling and heating controls a frost layer on the mirror surface while temperature is registered precisely. With the measured ambient temperature it is then possible to retrieve the frostpoint temperature and thus the water vapor content.