6,3,1,2- 1University of Bern, Institute of Applied Physics, Bern, Switzerland
- 2University of Bern, Oeschger Center for Climate Change Research, Bern, Switzerland
- 3ETH Zurich, Institute for Atmospheric and Climate Science, Zurich, Switzerland
- 4ETH Zurich, Geological Institute, Zurich, Switzerland
- 5mylab elektronik GmbH, Bubikon, Switzerland
- 6Empa, Laboratory for Air Pollution/Environmental Technology, Dübendorf, Switzerland
- 7Federal Office of Meteorology and Climatology MeteoSwiss, Payerne, Switzerland
We present seasonal post Hunga-Tonga measurements (2023-2025) of upper tropospheric and lower stratospheric water vapor over the Alpine region, obtained from deployments of balloon-borne frost point hygrometers within the Swiss H2O Hub, a consortium dedicated to water vapor measurements from ground to space. The chilled mirror hygrometers consist of the CFH (Cryogenic Frostpoint Hygrometer) instrument with classical cryogen, as well as two low global warming potential instruments: CFH-DIA (CFH using a mixture of dry ice and alcohol) and PCFH (Peltier Cooled Frostpoint Hygrometer).
The CFH measurements compare well to collocated space-borne Aura/MLS H2O retrievals, confirming the increased water vapor content in the lower stratosphere after the Hunga-Tonga eruption, with MLS being on average drier than the CFH reference by about 0.1-0.3 ppmv at around 20 km altitude over Switzerland. Starting May 2024, the temporal availability of MLS H2O observations decreased to around one week per month, due to the duty-cycling of the MLS 190 GHz receiver, in order to extend its lifespan.
We find that, despite a reduced cooling power (which is governed by the sublimation of CO2), CFH-DIA can be used as alternative reference to CFH for the Swiss H2O Hub, with a residual risk of losing frost control in certain atmospheric situations (e.g., when the 2nd cleaning cycle of CFH-DIA occurs above the tropopause).
The PCFH instrument uses thermoelectric cooling with custom-made heat sinks. It has undergone important design revisions through 2023-2025, improving heat dissipation, the quality of the optical signal, and controller operation. We find that the redesigned instrument is able to provide atmospheric dew or frost point measurements from the ground up to at least 23 km, with little preparation efforts due to a fully-electric design.
These new developments in chilled mirror hygrometry pave the way for environmentally friendly, high accuracy, and high vertical resolution observations of water vapor in the UTLS.
How to cite: Poltera, Y., Wienhold, F. G., Artho, V., Brossi, S., Brossi, T., Brunamonti, S., Romanens, G., Brun, A., Luo, B., Peter, T., and Stober, G.: Observations of post Hunga-Tonga UTLS water vapor over the Alpine region with balloon-borne low-GWP frost point hygrometers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14905, https://doi.org/10.5194/egusphere-egu26-14905, 2026.
