A NEW GROUND-BASED, CRYOGENICALLY COOLED RADIOMETER FOR MIDDLE ATMOSPHERIC WATER VAPOR MEASUREMENTS

A. Filinis^1,2, A. Bell^1,2, A. Murk^1,2, G. Stober^1,2

¹University of Bern, Institute of Applied Physics (IAP), ²University of Bern, Oeschger Centre for Climate Change Research (OCCR)

Continuous monitoring of atmospheric trace gases in the middle atmosphere presents significant challenges. Remote sensing instruments are essential for understanding and characterizing changes in atmospheric chemical composition. Although water vapor is present in low concentrations in the middle atmosphere, it plays a critical role as one of the most significant greenhouse gases, profoundly influencing climate change. Water vapor is a key climate variable, important for radiative balance, and is involved in various chemical reactions, including ozone depletion through the formation of polar stratospheric clouds.

With the ongoing decommissioning of the AURA-MLS instrument, which has long pro-vided valuable measurements of the 183 GHz water vapor line, there is a growing need to ensure continuity in middle atmosphere water vapor observations. To support this effort, the Institute of Applied Physics (IAP) has developed a new state-of-the-art radiometer, CRYOWARA (Cryogenic Water Vapor Radiometer), designed to measure radiation emitted from the 22 GHz water vapor line. CRYOWARA will succeed the existing MI-AWARA (Microwave Atmospheric Water Vapor Radiometer), continuing the long-term time series of water vapor profiles at the Zimmerwald observatory in Switzerland with enhanced sensitivity and technological advancements.

The primary distinction of CRYOWARA is its partially cryogenically cooled front end, which significantly reduces instrumental noise. This enhancement will enable more ac-curate water vapor retrievals at higher altitudes, further advancing the study of middle atmospheric dynamics. At the MicroRad 2026 conference, we will present the instrument’s architecture and calibration techniques along with the first water vapor retrievals of the finalized instrument.