To minimize these biases, it is possible to simulate higher temporal resolution of the storm tracks by linear interpolation applied to the original tracks. This introduces error into estimates of cyclone frequency, with cyclone counts systematically underestimated. Uncertainties in the mapping result from an incomplete catchment of cyclones by the grid cells: the coarse temporal resolution of data causes fast-moving storms to skip grid boxes. Tracking is performed using an automated procedure, based on computer animation of the sea level pressure fields. The uncertainties associated with the mapping of cyclone numbers and frequencies are analyzed using the 42-yr winter climatology of cyclone tracks derived from 6-hourly NCEP-NCAR reanalysis. Mean duration of southern cyclones has decreased in summer. Minimum air pressure of the deepest southern cyclones has decreased during the 63 years thus, they have become more intense. Southern cyclones had lower air pressure, and they last longer in average than all cyclones, which have formed in same regions over Southern Europe. They have had lower air pressure than the cyclones, which have moved towards the western part of Northern Europe. Most of these low-pressure systems headed to the eastern part of Northern Europe. The largest number of the southern cyclones has formed over Northern Italy and its surrounding areas. Long-term changes in these characteristics were detected. The low-pressure systems were analyzed in terms of their frequency, duration and sea-level pressure. All these cyclones obtained from the database of cyclones were considered to affect weather conditions in Northern Europe. In this study, southern cyclones were defined as lows formed south of 50° N, east of the 0° meridian and west of 60° E, which crossed 55° N on their trajectory. Correlation analysis revealed statistically significant relationships between the frequency of thunder days related to southern cyclones and the frequency of southern cyclones, also between the frequency of thunder days related to southern cyclones and days of other thunder events.Īn analysis of spatio-temporal characteristics of southern cyclones in Northern Europe during the period 1948–2010 is presented. The results of our study demonstrate that the intensity of thunderstorms related to southern cyclones is higher than that of other thunderstorms. The number of cloud-to-ground lightning strikes related to southern cyclones was larger than that of any other thunder events. The number of thunder days was largest when the centres of southern cyclones passed a measuring station at a distance less than 500 km. In the thunder season, however, this percentage was much higher, reaching up to 80% in summer months. At the same time, 29.2% of all southern cyclones were accompanied by thunderstorms. A total of 545 southern cyclones and 2106 thunderstorm days were detected, whereas 11.3% of the observed thunder days were associated with southern cyclones. The relationships between the frequency and duration of thunderstorms, lightning and southern cyclones over Estonia are presented for the period 1950-2010. The frequency of incoming cyclones showed an increase in the Bering Strait, Alaskan, Baffin Sea, and East The mean annual SLP of deep cyclones decreased significantly, particularly for deepĪrctic cyclones. The most significant changes in the seasonal parameters associated While the frequency of shallow Arctic cyclones decreased. Of deep cyclones that entered the Arctic basin, as well as the frequency of cyclones that formed within it, clearly increased, those that entered the Arctic basin, increased significantlyĭuring the period 1948–2002, but that the frequency of Arctic cyclones formed within the Arctic basin did not. The analysisĭescribed herein shows that the frequency of incoming cyclones, i.e. Were grouped into sectors by using the point on latitude 68° N at which the cyclone entered the Arctic region. Changes in the variables in the first, last, deepest and northernmost points of cyclones were studied. Deep cyclones with a mean sea level pressure (SLP) of below 1,000hPa, were analysed separately from shallowĬyclones. The Arctic basin is defined as the area north of Changes in the frequency and air pressure of cyclones that enter or are formed within the Arctic basin are herein examinedīy applying the database of cyclones created using NCEP/NCAR re-analysis.