A comparison of the features of windstorms Kyrill and Emma based on seismological and meteorological observations

Abstract

In mid-January 2007 and at the turn of February and March 2008, two extremely strong windstorms, i.e. Kyrill and Emma, hit most of the central European countries. These windstorm hurricane-force winds caused serious damage to structures, to a large number of properties, cars, trees and, moreover, some fatalities were documented, as well. During the period mentioned, secondary and/or ocean-generated microseisms (T = 4-8 s) recorded by broad-band seismographs at the seismic station Ostrava-Krasne Pole (OKC) (Czech Republic) were analysed. These microseisms were caused by ocean surface oscillations related to the propagation of depression lows over the North Atlantic Ocean. While the peak-to-peak displacement amplitudes observed during windstorm Kyrill reached values of up to 2 μm, during the passage of Emma, the amplitudes were about 1.5 μm. Predominating periods of oscillations were observed within the interval T ≈ 5.4-5.7 s for both windstorms, while the FFT analysis documented two distinct peaks in calculated spectra, namely at f ≈ 0.16-0.18 Hz and/or T ≈ 5.5-6.2 s and at f ≈ 0.06-0.08 Hz and/or T ≈ 12.5-16.5 s, corresponding with secondary and primary microseisms, respectively. The second part of the input data represent some results of regular meteorological observations, i.e. wind speed, wind gusts and wind direction, which were completed with the description of the origin and development of both studied low-pressure systems. During the passage of Kyrill the maximum velocity of the wind gusts in northern Bohemia (at the top of Mt. Sněžka in the Giant /Krkonose/ Mts.) was estimated to be 60 m/s (218 km/h), while during Emma it reached 54 m/s (194 km/h) at the same observation site. In principle, it was found that the velocity of the windstorm Emma spreading was lower as compared with windstorm Kyrill. Moreover, a description of the origin and development of both low-pressure systems is attached. Their features were compared using all the data from the seismological observatory and meteorological stations related to both windstorms being available. The resulting values of the selected parameters, chosen for comparison, are given in Table 2.