ИСТИНА

Thermal stratification of the Atmospheric Boundary Layer (ABL) significantly influences on dispersion of atmospheric pollutants, heat loss in tall buildings, propagation of radio-waves, etc. In Moscow region it is measured by radiosondes in Dolgoprudny (close suburbs of Moscow), sensors at different levels both at high (310 m) mast in Obninsk (small town on 100 km southward from Moscow) and at 540 m TV Tower in Ostankino (close to the city centre), and vertical “ECHO-1” SODAR by GDR production which operates at Moscow University (southwestern periphery of the city) since 1988. Its operation frequency is 1666.7 Hz; vertical range is from 25 to 800 m; spatial resolution is 12.5 m. Three sources of data represent direct (in situ) measurements of temperature profiles whereas the SODAR data about the stratification are indirect. They are available from analysis of SODAR echograms. All results have been analyzed for the last quarter a century (since the beginning of 1990s till recent years). According to the SODAR data in summer time, both probability of surface inversions at night and their durability reduced for the period from 1990 to 2016, so now they appear in the evening as a rule later and brake down in the morning earlier than 25 years ago. This result is confirmed by the data of TV Tower sensors in the city centre. However other data sources demonstrate different results. In suburbs (according to radiosondes) the probability of surface inversions, on the contrary, became a bit larger, whereas at far rural zone it remains nearly the same by the data of mast sensors. As for thickness and intensity of surface inversions, both parameters reduced in close suburbs and do not demonstrate clear changes at far rural zone. A fall of both thickness and intensity by radiosonde data is statistically significant according to Student’s t-test. This effect may be explained by gradual intensification of the Moscow urban ‘heat island’. It is not a surprise as well that in the city centre (TV Tower) an intensity of surface inversions is significantly lower than in other locations. Unlike urban conditions, far rural zone (Obninsk) demonstrates a stability of the ABL thermal stratification in time. Long-term dynamics of the air temperature vertical gradients have been studied as well. Thus, some of results allow detecting influence of big city on the thermal stratification. This work was supported by the Russian Science Foundation (project 16–17–10275).