The Influence of the Climatic Peculiarities on the Electromagnetic Waves Attenuation in the Baltic Sea Region

Abstract

The peculiarities of the climatic conditions in the Baltic Sea Region are reviewed. According to the values of rain rates measured in the Lithuanian Weather Stations with the 10- minute's integration time, a relation between the rain rate and the annual precipitation has been derived. The model for one-minute rain rate calculation on the months starting from May up to September in Lithuania has been presented. The values of the electromagnetic waves attenuation due to the rain have been determined. The cloud attenuation has been computed by using the meteorological data measured at the ground level. The semi empirical method has been used. The values of the speciflc attenuation under conditions of cloud cover have been determined. Knowledge of the electromagnetic waves attenuation due to rain and clouds is desirable while planning the communication systems, especially at frequencies of 10GHz and above. Most of the methodologies for the prediction of rain attenuation on radio waves paths require the knowledge of the rain rate R-value. Rain rate data is presented in units of length per unit time (in millimeters per hour), but in practice it is measured over intervals of typically one minute, flve minutes, hour or yearlong. In (1), it was mentioned that the integration time ¢t (time between the readings of the values of rainfall amount) is important parameter and it can change the R-value. Most of the rain attenuation prediction methods require one-minute rain rate value. One-minute rain rate (mm/h) is the rainfall for one minute (mm/min) multiplied by 60. Rainfall rate is highly variable. Therefore, the rain rate and rain attenuation are analyzed for concrete climatic conditions. However, the electromagnetic waves attenuation due to rain under the Baltic Sea Region climatic conditions has been analyzed not enough (2,3). The electromagnetic waves attenuation due the clouds, as far as we know, has been not analyzed under Lithuanian climatic conditions. The main goals of this paper were to determine the one-minute value of rain rate by using ten-minutes rainfall amount data measured in the Lithuanian Weather Stations and to estimate the values of the electromagnetic waves attenuation due to the rain and the clouds. 2. THE PECULIARITIES OF THE CLIMATIC CONDITIONS IN THE BALTIC SEA REGION The climate of Baltic Sea Region (BSR) is speciflc. BSR, being in the transition geography zone from Baltic Sea climate to Atlantic and continentals East Europe climate, may be distinguished for its variable climate. The average amount of precipitation in the BSR is 679mm. The average nebulosity in the region is 50%. The minimal nebulosity (46%) occurs in spring (4). The increase of nebulosity is going from north to south. In this paper we analyze Lithuanian climate more particularly. The climate of Lithuania is deflnable as middling cold, with the snowy winters. There are 20{30 thaw days even in mid-winter. In Lithuania, humid weathers predominate all over the year. The annual precipitation in rainy wet year is almost twice higher than in dry year. The values of annual rainfall measured in the localities of Lithuania are presented in Table 1. The showers are observed in the warm period of the year. Such climate is typical climate of the middle part of the East Europe. The climate of the west part of Lithuania (for example, of Klaipeda) is specifled as the moderate warm climate. The average temperature of the coldest month is more than i3 - C. Such type of the climate is dominating in the West Europe. Vilnius is one of the cloudiest localities of Lithuania. There are about 100 overcast days in the year.