HR: 1340h
AN: A13E-1599    [Abstracts]
TI: Statistics of the Arctic cyclone activity and tracks
AU: * Sepp, M
EM: mait.sepp@ut.ee
AU: Jaagus, J
EM: jjaagus@ut.ee
AB: The objective of this study is to analyse changes in frequency and parameters of the development of the cyclones formed within the Arctic Circle and outside the Arctic but moving into it during the period 1948-2002. The database of cyclones described by Gulev et al. (2001) was used in this study. The database consists of cyclone tracking output of the 6-hourly NCEP/NCAR reanalysis SLP fields using the software worked out by Grigoriev et al. (2000). Cyclones are presented by the geographical coordinates of their centres and SLP at these points. The Arctic basin is defined here as an area located north from 68°N. Arctic cyclones are defined as cyclones that have formed north from 68°N while entering cyclones have formed south from that borderline and have entered into the Arctic Circle north from 68°C. Also, deep cyclones with minimum sea-level pressure below 1000 hPa and shallow cyclones were selected. The following variables are determined and studied: total number of cyclones, duration of cyclones expressed in the number of tracking points with 6-hours interval, mean sea-level pressure of cyclones, sea-level pressure at the first, last, deepest and the northernmost points of cyclones. A longitude of the point on the parallel 68°N is calculated where the cyclone has entered the Arctic region. According to these points, the entering cyclones are grouped into sectors. The sectors are chosen by 40-degree longitude while the number of cyclones in the middle of the sectors is usually higher than near to the borders. All together eight 40-degree sectors were defined for the analysis and two 20-degree sectors were selected – in the south-eastern part of Greenland and in the Canadian Arctic Archipelago between 100–80°W. Time series of annual and seasonal mean values are formed. Seasons were defined by grouping three months – winter (DJF), spring (MAM), summer (JJA) and autumn (SON). Linear regression analysis is applied for detecting long-term changes. A linear trend is calculated for every time series and their significance level is found using the Student's t-test. Trends are considered statistically significant on P<0.05 level. The main conclusions concerning long-term changes in cyclone activity are the following: 1) The total number of the entering into the Arctic Circle cyclones has significantly increased during 1948-2002, but not of the Arctic cyclones formed within the Arctic Circle (north from 68°N). 2) Percentage of deep and shallow entering cyclones has not changed. The number of deep cyclones (mean SLP below 1000 hPa), deep entering as well as deep Arctic cyclones, has clearly increased while the number of shallow Arctic cyclones has decreased. The biggest changes in seasonal values revealed in winter. 3) Duration of the cyclones almost has not changed. 4) Mean SLP of deep cyclones has decreased significantly. This change is more substantial in case of deep Arctic cyclones. This trend exists during all seasons with the exception of autumn. The change is the highest in winter. 5) Generally, the frequencies of tracking points with deep pressure have increased and mean pressure has decreased in the first, last, deepest and northernmost tracking points. Increase in total number of entering into the Arctic basin cyclones in winter is much higher than during the rest of the three seasons all together. 6) An increase in the number of entering cyclones has taken place in the sectors of the Bering Strait, Alaska, Baffin Sea and East Siberia. References Grigoriev, S., Gulev, S. K., Zolina, O. (2000). Innovative software facilitates cyclone tracking and analysis. EOS 81. Gulev, S. K., Zolina, O., Grigoriev, S., (2001). Extratropical cyclone variability in the Northern Hemisphere winter from the NCEP/NCAR reanalysis data. Climate Dynamics 17, 795–809
DE: 1620 Climate dynamics (0429, 3309)
DE: 1635 Oceans (1616, 3305, 4215, 4513)
DE: 1704 Atmospheric sciences
DE: 1833 Hydroclimatology
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting