PLANETARY WAVE ACTIVITY IN THE LOWER IONOSPHERE DURING THE DYANA CAMPAIGN

On the basis of MEM spectrum analyses, the main fluctuations formed in the lower ionosphere in the period range 3-35 days during the DYANA campaign are studied. The wave response of the lower ionosphere to changes in the thermal and dynamical regime is investigated separately for several altitudinal regions and because of the occurrence of a pronounced minor stratospheric warming during and mid-February, also separately for the first (1 January-14 February) and the second (15 February-31 March) part of DYANA. According to different patterns of planetary wave activity in various ionospheric data, the lower ionosphere can be divided into altitudinal regions: the lowest D-region, the lower D-region, the upper D-region and the bottom part of the E-region. An attempt to identify the wave number of the best pronounced fluctuations, existing in most time series, with a mean period of about 12 days, indicates the zonal wave number K = 1. In general, the ionospheric data do not provide a well-consistent pattern of the planetary wave activity in the lower ionosphere during the DYANA campaign. Nevertheless, it seems to be sure that (1) the patterns of planetary wave activity in the first and the second half of DYANA are very different, and (2) changes in planetary wave activity over Europe appear to be arranged according to altitude, not latitude or longitude.