Jet stream patterns over Europe in the period 1950–2001 – classification and basic statistical properties

Abstract

Primary goal of presented study is to classify the most frequent patterns of the upper tropospheric jet stream over Europe. Wind fields were grouped into separated classes with the help of the correlation-based Lund’s technique. The treatment of vector fields with Lund’s method was achieved by replacement linear Pearson coefficient with vector correlation coefficient. The outstanding features of the upper-level circulation and ground-based weather associated with each jet type were analysed. Finally, basic statistics of jet stream patterns (frequency, duration time, day-to-day changes of jet structure) as well as their trends were estimated. The analysis was conducted on the basis of mean daily wind components at 200 hPa level, air temperature at 850 hPa, sea-level pressure, vertical velocity and geopotential at 500 hPa level. Data set was extracted from the NCEP/NCAR Reanalysis. The warm half-year in the period 1950–2001 was taken into consideration. The first 15 most frequent jet types, including 60.8% of the sample, were selected. Three jet stream types (C, E and I) are associated with distinct temperature changes in western Europe. Another three types (B, F and O) cause significant thermal advection in eastern and central Europe. Seasonal differences in frequency and duration time of jet stream patterns are also observed. Meridional types (A, C and D) dominate in spring, while in summer, patterns with intensified zonal flow prevail (B, E and J). At last, it is worth noticing that the majority of selected jet types pronounce an increase in day-to-day changes of wind field, which may indicate slight enhancement of circulation dynamics in the upper troposphere.