Influence of Temperature Inversions on Zenith Attenuation of Microwave Radiation in the Atmosphere

Abstract

We show that atmospheric zenith attenuation measured by a water vapor radiometer at 20.7 GHz at the Russian Metrological Institute of Technical Physics and Radio Engineering (VNIIFTRI, Mendeleyevo, Moscow Oblast) can significantly exceed (by up to 0.15 dB) values calculated from the Liebe model with temperature profiles smoothly and monotonically decreasing with altitude. These events of excess attenuation are related to elevated inversions in the observed temperature profiles obtained by averaging radiosonde data from the city of Dolgoprudny (22 km from VNIIFTRI). Greater attenuation differences corresponded to more intense inversions. On days and nights when the difference between measured and calculated attenuations at a frequency of 20.7 GHz was small, the average radiosonde temperature profiles monotonically decreased starting from ground level and differed little from the model profiles. Correcting the model temperature profile by adding temperatures measured by radiosondes at altitudes of 0.5–4.0 km eliminated most of the excess in measured attenuation over calculated values. The significant difference in attenuation values at a frequency of 20.7 GHz arose primarily in the cold months with an average occurrence rate of about 20% during both daytime and nighttime. This is consistent with long-term observations of temperature inversions in Dolgoprudny.