Influence of clouds on attenuation of electromagnetic waves

Abstract

The semi-empirical method for determination of the cloud attenuation was used. The cloud attenuation was determined by using the meteorological data measured at the ground level. It was assumed that the clouds would form at some height above the ground level when the conditions for vapour condensation would be present and the liquid water content in the air would be above zero at that height. The values of height have been determined by using the values of temperature at the ground level, the dew point temperature, and the temperature gradient. The calculation results show that known relation between the temperature and the cloud base height is not always suitable for Lithuanian climate conditions. According to the meteorological data measured in the weather stations, relation between the height and temperature within the cloud, recommended by International Telecommunication Union, was chosen. Only summer profile was suitable to use under conditions investigated here. The values of relative humidity and temperature at the ground level were used in calculations of liquid water content within the clouds. The values of specific attenuation under conditions of cloud cover were computed by using the obtained liquid water content values at frequencies starting from 10 GHz and up to 70 GHz.

Atmospheric Attenuation due to Humidity

“…The analysis of the cloud cover over the localities of Lithuania data shows that the relationship (11) can be used only in the cases when the middle or high clouds are formed over those localities. (Tamošiūnaitė et al, 2008).…”

“…This factor must be considered when analyzing rain attenuation and cloud attenuation. Our first attempt to determine the specific cloud attenuation under the Lithuanian climatic conditions is presented in (Tamošiūnaitė et al, 2008;Zilinskas et al, 2008). The humid weather predominates over the year in Lithuania.…”