Middle atmospheric water vapor vertical profiles obtained during the YOPP SOP in early 2018 at Thule Air Base, Greenland, by means of a ground-based microwave spectrometer (VESPA-22)

In the frame of the OASIS-YOPP project, measurements of stratospheric water vapor profiles have been carried out at the Thule High Arctic Atmospheric Observatory (THAAO, thuleatmos-it.it/) during the winter Arctic Special Observing Period of the YOPP. The THAAO is located on South Mountain, at 220 m a.m.s.l., in the proximities of the Thule Air Base (76.5 °N, 68.8° W). Water vapor stratospheric vertical profiles are obtained by means of a ground-based microwave spectrometer (VESPA-22) which observes the 22.235 GHz water vapor emission line with a 400 MHz bandwidth and a frequency resolution of 30 kHz.

From the spectral measurements vertical profiles are estimated using an Optimal Estimation algorithm which relies on the pressure broadening characteristics of spectral lines at these frequencies. Vertical profiles are considered reliable for scientific purposes from approximately 26 to 75 km altitude. Spectra have a 20-minute time resolution but are integrated over a 24-hour cycle before being inverted to obtain vertical profiles.