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Introduction

Atmospheric circulation of different scales, as well as the distribution of some trace gases (ozone) is believed to be influenced by solar and geomagnetic activity (van Loon and Labitzke, 1993; Kodera, 1991; Bucha, 1993; Bochnícek et al., 1993). Many more or less probable explanations of the observed correlations were also given by Tinsley and Dean (1991), Hood (1995) and Hood et al. (1995). These extra-terrestrial factors are often correlated with the parameters describing the oscillations of global atmospheric system such as QBO and ENSO with very impressive results (Baldwin and Dunkerton, 1997, Salby,1995, Labitzke and van Loon, 1988, van Loon and Labitzke, 1993).

As many attempts were made in dealing with connections between the changes in circulation of different scales and interannual factors, such as solar and geomagnetic activity parameters, internal oscillations of the atmospheric system (QBO, ENSO, North Atlantic Oscillations - NAO or others), as many approaches were introduced in these attempts. The standard approach in describing stratospheric fields is the use of the amplitude of the principal zonal wave numbers and their variability, mainly during winter and spring (Naujokat and Labitzke,1993). These parameters are able to reflect polar vortex distorsion or breakdown, and allow us to inspect changes in large-scale stratospheric circulation quickly. But this approach does not include processes of synoptic and sub-synoptic scales whose origins are at lower latitudes. In our previous studies (e.g., Halenka and Mlch, 1996) we analysed the connections between the ozone profile structure and circulation patterns characterized in terms of the standard classification of synoptic types (Gerstengarbe et al.,1993). Even though this approach (based on a subjective classification of tropospheric circulation) does not seem to be convenient for such purposes concerning mainly lower stratosphere circulation, it is capable of providing new insights into this problem through the very close connection between the winter upper troposphere and the lower stratosphere (Petzoldt et al., 1994; Holton and Tan, 1980, 1982). Interesting results concerning changes in synoptic variability have also been presented by Goeber and Hense (1995). Therefore, the need for parameters which are able to encompass a wide range of scales leads to the application of complex decomposition of stratospheric fields by spectral method as shown in Halenka and Mlch (1998). This technique is more complicated in the sense of interpretation, however, it provides a very comprehensive survey of circulation characteristics. Being quite smooth and regular without larger small-scale disturbances, stratospheric fields could be spectrally represented in terms of only a very few significant wave components of low wave numbers. Simple characteristics of the circumpolar vortex might thus become available, which would provide us good possibility of further analysis.