Climatology of cyclones with a southern origin, and their influence on air temperature and precipitation in Estonia

Cyclones with a southern origin that passed over Estonia between 1948 and2004 were analysed in terms of their frequency, duration, and sea-level pressure.Long-term changes in these characteristics, and the influence of these cyclones on surface air temperature and precipitation, were analysed.For the purposes of this study, "southern cyclones" were defined to be the ones that formed south of 47N and east of the 0 meridian, and entered a circle of 1000-km radius centred in Estonia.These events, which were obtained from a database of cyclones, were considered to have had an effect on weather conditions in Estonia.Although few trends were statistically significant, southern cyclones were in general found to weaken over the period studied.The number and duration of southern cyclones decreased over the period, and sea-level pressure increased.Southern cyclones induced an increase in temperature if they pass over Estonia from the west, and a decrease in temperature if they pass over Estonia from the east.On average 10% of annual precipitation in Estonia was related to cyclones with a southern origin.