Abstract
In comparison to the global average, the climate in the Baltic Sea region, including in Estonia, has warmed up particularly fast. From synoptic climatology's point of view, a question can be posed: is this warming caused by changes in the frequency of particular circulation types or warmer weather started accompanying these types? The main aim of present study is to analyze the relationship between increase of air temperature and changes in atmospheric circulation during the period of 1966-2015. Changes in the frequency of circulation types belonging to 12 classifications from COST733 data set and changes in accompanying air temperature were analyzed. The circulation types were divided into 'warm' and 'cold' for a given season according to daily temperature anomalies in three Estonian meteorological stations. On the basis of the similar air flow direction circulation types from different classifications were selected for intercomparison. Linear trend analysis showed that there were only a few statistically significant (p<0.05) changes in the frequency of circulation types. The major changes occurred in spring – the frequency of eastern and northeastern flow types has decreased, and the frequency of types related to northwestern flow has increased. However, the positive temperature anomalies have increased for practically all circulation types. A particularly great warming has taken place in winter 'cold' types. In conclusion, the increase of Estonian air temperature during the analyzed period is more likely associated with the changes of temperature within circulation types than of their frequency.
Highlights
IntroductionEspecially global warming is one of the major challenges of our time
Climate change, especially global warming is one of the major challenges of our time
Here we demonstrate only the results of Türi station as it represents the majority of air temperature variations on the Estonian mainland
Summary
Especially global warming is one of the major challenges of our time. The average global air temperature of the last decades is already about 0.8◦C above the 20th century average of 13.9◦C (IPCC, 2014; NOAA, 2018). The air temperature in the Baltic Sea basin is warming even more rapidly. In the Northern part of the Baltic Sea basin (north of 60◦N) the annual mean temperature anomalies from 1871 to 2011 were 0.11◦C per decade and in the Southern part (south of 60◦N) 0.08◦C per decade (BACC Author Team, 2015). Studies on Estonia have shown that the air temperature in Estonia has risen about 2◦C during the last half century (Jaagus, 2006; Jaagus et al, 2014).
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