No abstract

No abstract

Cyclonic and anticyclonic activity over western Siberia for 1976-2004 is considered. Trajectories of motion of baric formations of various genesis and their frequency are analyzed.

No abstract

No abstract

In the process of warming, the atmosphere of Western Siberia gets warmer and wetter due to local sources of moisture. This is accompanied with amplification of convection processes in the warm seasons and increasing frequency of extreme weather phenomena. Trends in atmospheric instability and their causes on a territory located in the Ob-Irtysh interfluve and limited by 50–64 °N, 60–95 °E, including the Vasyugan Swamp, are analyzed. The swamp boundaries distinctly marked on temperature maps in the last decade indicate changes in the thermal radiation of the swamp surface. These changes in heterogeneity of heating and heat exchange are reflected in changes in atmospheric instability as well. The greatest changes in the atmospheric temperature mode have been observed in the Great Vasyugan Swamp.

The following radar characteristics of squall clouds in southeastern western Siberia are studied: the frequency of the maximum height of cumulonimbus clouds in squalls, the height of the 0ºC isotherm, radar reflectivity at three levels, maximum reflectivity, and a complex criterion of thunderstorm likelihood. The radar characteristics are determined for squalls in different synoptic situations. The results of this study can significantly improve the existing methods of squall forecasting. Squalls (wind increases of more than 25 m/s) cause cummulative losses comparable to droughts, spring floods, and forest fires [2], because squalls, like tornadoes, are difficult to predict. Satellite and meteorological radar data are used to improve the forecast skill of hazardous hydrometeorological events. It should be noted that radar characteristics of thunderstorm clouds, unlike those of squalls, are well studied [3,5,6,10,15,16] and are successfully used in practice. Radar characteristics of convective formations generating squalls have been rarely investigated in recent years [7,9], and such studies have not been carried out for western Siberia until present.The goal of the present work is to study radar characteristics of Cb clouds associated with squalls and to choose the most informative ones for squall forecasting near the airport of Tomsk.Since 1987, a synoptic-radar method has been used at the Tomsk aerological station for squall forecasting. The method is based on the data of the incoherent meteorological radar MRL-5 with a range of 55 dB. In [4,14], a method for squall diagnosis is proposed for Cb clouds with tops no less than 10 km.This study is based on radar characteristics derived from operational radar measurements at the Tomsk airport radar station during the summers from 1991 to 2004. According to [11,13], the wind speed in the squall exceeds 10 m/s, and the squall duration is a minute or more. The squall is considered as a severe weather event if the wind speed (including wind gusts) is equal to or greater than 25 m/s [12]. We took as a squall case each radar echo located in the near field (30´30 km) that detected the event, and the instantaneous maximum wind speed was considered. In all cases, the times of radar and visual observations coincided or differed by ±20 min. A total of 58 squall cases were observed, of which 26% were detected in May, 21% in June, and 27% in July. The following characteristics were studied: forecast weather events; the maximum height or the upper boundary of the radar echo (H max ); the 0ºC isotherm height (H 0 ); the -22ºC isotherm height (H -22 ); the logarithm of radar reflectivity at the level of precipitation (logZ 1 ), at the level corresponding to the crystallization initiation (logZ 2 ), and at the level of mass crystallization (logZ 3 ); the height of the third level (H Z log 3 ); maximum radar reflectivity (logZ max ); and a complex criterion of thunderstorm likelihood (Y cr ) determined according to [14] as a product of the logZ 3 minimum in a thunderstorm and H -22 ....

No abstract