Impact of weather pattern on initiation of hot and cold weather conditions in Ukraine

Abstract

The topicality of the study is stipulated by the need to diagnose, monitor and predict the weather conditions causing temperature anomalies in Ukraine in order to prevent their adverse impact on the country's economy. On the climate change background, extreme weather events become more frequent and intense. The forecast for anomalous events can be significantly improved if the main types of atmospheric circulation related to those events will be identified. This paper aims to identify the main circulation processes causing the initiation of hot and cold weather conditions in Ukraine. These conditions are the so-called indices of extremes: summer days (SU), tropical nights (TR), ice days (ID), and frosty days (FD), calculated using the daily minimum and maximum air temperature at the regular grid points covering the territory of Ukraine with a spatial resolution of 0.75×0.75 degrees. The GWL circulation types were obtained from the Hess-Brezovsky objective classification for the atmospheric processes, which is widely used for synoptic analysis in Europe. The GWL circulation types differ by the location of ridges (anticyclones) and troughs (cyclones) on the 500 hPa isobaric surface. The difference from most other atmospheric circulation classifications is that each GWL remains for at least 3 days. If the transition to another GWL lasts more than 1 day, such days are considered as the previous or next GWL, whichever is most similar.
 The frequencies for ten types of weather patterns by the Hess-Brezovsky classification for the period from 1971 to 2001 were analyzed for Ukraine, and the circulation types, which are the most common for summer days, tropical nights, frosty days and frosty nights, were detected. It was shown that the extreme hot or frost weather conditions are in most cases initiated by the same circulation type. Also, the initiation of hot and frost weather is almost completely unaffected by the weather pattern caused by the third, fifth and ninth types of the GWL classification.