Physics of auroral phenomena : proceedings of the 34th Annual seminar, Apatity, 01 - 04 March, 2011 / [ed.: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 231 с. : ил.

L.N. Sidorova, S.F. Filippov 70 VERNAL ш 50 40 30 20 10 0 70 60 50 40 30 20 10 0 WINTER Ш I 0- <2 S LONGITUDE, deg. LONGITUDE, deg. Let’s consider another fact. It is easy to notice that bifurcation of the main EFI probability maximum only slightly pronounced in statistics of Su et al. (2006) is clearly visible in the statistics o f McClure et al. (1998). He* DENSITY DEPLETIONS Fig. 1. Longitudinal distributions of PHc+ (histograms and smoothing curves) calculated for VERNAL and WINTER from the ISS-b data within ±20-50° INVLAT in the Northern (a, d) and Southern (c, f) Hemispheres. Longitudinal distributions o f P^o. 5 %. Р<ы).з%! Prsf> Pb 650 obtained within the equatorial region (±20° DIPLAT) (b, e). Po>o. 5 % (McClure et al., 1998) is shown by thin black line. PB 65 u (Watanabe and Oya, 1986) is shown by thick light grey line. PRSF (Maryama, Matuura, 1980) is shown by thin grey line. Po><u% (Su et al., 2006) (dotted line) is presented by right scale. Po>o. 5 i% (Basu et al., 1976) is shown for WINTER (e) by thick dark grey line. According to Maryama and Matuura (1980) the bifurcated maximum is already very well pronounced structure which is distinctly reflected in the PHe+plots of the both hemispheres. Comparison with the longitudinal statistics of the plasma bubbles (Рвб 5 о) shows no so good similarity. Nevertheless, the main tendency takes place as before. According to the theory the major cause for the longitudinal irregularity occurrence is an alignment of the sunset terminator with the magnetic meridian (Abdu et al., 1981; Tsunoda, 1985). Maximum uplift of irregularities is expected in so called “node seasons” (equinox seasons), when the sunset terminator and magnetic meridian are nearly parallel. It seems this conclusion is also fair for He+ density depletion occurrence, if we suppose that EFIs and He+density depletions are of the same equatorial origin. That is why the PH(~ plots of the different hemispheres are of almost the same intensity and practically equally developed. What about some discrepancy in the shape of the PHe+ curves in the different hemispheres? Apparently, it can be explained by superposition of some factors. First of all, the light differences in the shape of variations are caused by features of the magnetic field of the different hemispheres or so-called “magnetic declination effect”. Winter conditions. The most dramatic insolation differences take place for the different hemispheres during winter solctice. Apparently, it should expect the significant differences of PHe+in the different hemispheres. Let’s consider the plot in the Northern Hemisphere (NH). It is easy to notice good enough similarity between the PHe+ curve and the most part of the equatorial plots. It is possible to see the clear tendency of the distortion of the main maximum of the equatorial plots, which finally “develops” in the PHc+plot. So, the main maximum appeared as widened peak in P<j>o. 5 i%(Basu et al., 1976) is seen with slightly outlined bifurcation in PrsF (Maryama and Matuura, 1980) and with twin peaks in Pa>0. 5 %(McClure et al., 1998). At last this bifurcated maximum turn into the PHe+maximum with two separate crests and deep internal valley. The main Po>0.5i%maximum covers the longitudes o f 240°-30°. The main bifurcated PHe+maximum appears almost at the same longitudes however with light shifting in respect to other main equatorial peaks. Worthy note that the “thin” details of the EFI statistical plots are also “developed” in the PHe+ curve. The minor local Pa>0.5%and Prsf maxima near 60° longitude also appear in the NH as minor local maximum of PHe+- Local PHe+ maximum near 150°-180° longitude needs in special comments. It is possible to doubt about a reliability of this second PHe+ peak. However, any doubt disappears when we see the similar second maximum in the P ^ . 51 %pattern (Basu et al., 1976) and the small but clear amplitude growth o f Pa>0 s% (McClure et al., 1998). Another part of the equatorial plots (Рс>0.з%(Su et al., 2006), PB65o (Watanabe and Oya, 1986)) has surprisingly good similarity with the PHe+ curve in the Southern Hemisphere (SH) (Fig. 1). The main maxima of the Ро>0з%, 140