Ground-based measurements of middle atmospheric water vapor at 183 GHz during very dry tropospheric conditions

Microwave studies of the stratospheric and mesospheric H₂ O profile have been so far carried out mostly by means of observations of its weak resonance line at 22.2351 GHz. Some measurements have also been obtained from airborne observations of 3_1,3→2_2,0 H₂O line at 183.3101 GH _z. This line is strong enough to be generally opaque in the troposphere. The authors report on the first ground-based observation of stratospheric/mesospheric water at 183 GHz, obtained in January 1991 at the IRAM 30-m radiotelescope in Sierra Nevada, Spain (alt. 2850 m) during exceptionally dry conditions (0.2 precipitable mm water). Upper stratospheric and mesospheric water vapor profiles were obtained using the same inversion methods currently employed for the microwave lines of O₃ and other minor atmospheric gases. Results are consistent with most measurements at 22 GHz