Layer of Northwest Bohemia

Abstract

The influence of the direction of wind in 850 mb level upon the difference between the temperature of air measured 2 m over ground on the meteorological station Újezd u Jirkova (287 m above sea level) and the temperature of air in 850 mb was studied. Wind direction and air temperature in 850 mb level were derived (interpolated) from the maps of absolute topography. All data about wind direction in 850 mb level and about vertical difference of temperature between the height of 2 m above ground and the hight of 850 mb level (approximately 1,5 km above sea level) for one a. m. and one p. m. of local time from the period of 41 month were processed. Both the previous studies from air pollution climatology and the practical experience from synoptic meteorology have shoved that the difference betwen air temperatures near ground and in 850 mb level is the good indicator of temperature stratification which may be valid for the solution of some problems of the dispersion of airborne matters. Author analysed relations between the direction of upper wind and the deviations of the differencies between the near ground temperature and the temperature in 850 mb level from the mean values of these differencies for one a. m. and one p. m. in every month. For the months of winter half-year both at one a. m. and at one p. m., expressive tendency to the occurence of more than in average stable temperature stratification was ascertained when upper wind blows from S, SE or SW. In the same months and hours temperature stratification tends markedly to be less stable than normally during this time when upper wind blows from NW, N or NE. Under W stream in 850 mb level, temperature stratification on the whole is less stable than under E stream. But different results were obtained for one p. m. during months of summer half-year. In this case, the relationships between the stability and upper wind direction are much less significant than during winter half-year at one a. m. and one p. m. or than during summer half-year at one a. m. Weak dependence of stability on the direction of upper wind during summer half-year at one p. m. (during the time when the radiational balance of the earth surface reaches its highest values) is apparently the consequence of the fact that at this time the influence of circulation conditions upon vertical profile of temperature is partly compensated by the influence of radiational factors.