Planet. Spasx Sci. 1968. Vol. 16. pp. 129 to 133. PerSamon Pms.
Printed in Northern bland
OVAL IN THE IGY AND IQSY PERIOD AND A RING CURRENT
IN THE MAGNETOSPHERE (Received 4 Jufy 1967)
Investigation of auroral pattern from the IGY data showed that the atmosphere luminescence is observed most often along the aurora1 oval, displaced on to the night side in relation to the geomagnetic pole. Various forms of aurorae are located along the oval depending on local time (Feldstein, 1960,1964,1966; Khorosheva, 1962,1963; Akasofu, 1964; Akasofu and Kimball, 1965). The oval sixes change with the degree of geomagnetic activity (Feldstein and Starkov, 1967; Akasofu, 1966). Figure 1 gives two examples of comparison of the aurora1 belt with the aurora1 oval, its edges being obtained statistically (Feldstein and Starkov, 1967). The map basically shows the position of the lower edge of the aurora1 region. The whole region has been shaded black when there are aurorae close to one another. It represents the more or less approximate location of the aurora1 region, since it was hard to determine the position of the lower boundary with diffuse aurorae or aurorae on the horizon. On the daytime side of the belt from 3 hours to 16 hours local geomagnetic time the altitude of the aurora was taken as 150 km. The altitude distribution of the bottom edge of the arcs and bands according to the results of simultaneous photographic observations at the Piramida and Murchison Bay stations (p, N 76”) (see Starkov 1967) is given in Fig. 2. The lower border of aurorae is seen to be most often located at the height of 150 km. A typical peculiarity of this ~tribu~on is a comparatively slow decrease towards great altitudes. As a comparison the dotted line in the same figure shows the altitude distribution of the aurorae obtained at Tiksi Bav (cp w 65”) with a maximum at altitudes of 100-120 km Urulrienko. . 1965). - The altitude of the lower edge’was therefore taken as 110 km for the rest of the time. . 05 hr 00 mm UT, December 19, 1957 corresponds to a commencement of a bay-like disturbance, Qindex on the night side is -1. Figure la gives the location of a luminescence region within an oval but the aurorae above Godhavn station. A restriction of the latitude area with the overhead aurora, observations at the stations Arctica-2, Farewell and Saskatoon where no aurorae were observed clearly, indicates the Iikely coincidence of instantaneous aurora1 pattern and oval location, defined statistically. Breaks in the belt in Fig. la are explained by the absence of observations at the corresponding longitudes. Some stations used 16-mm films and the ascafilms in WDCB2 are not always of good quality, therefore on the Hms sometimes it was difficult to identify aurora1 forms. Generally, distribution of aurora1 displays corresponds to the scheme suggested in an earlier paper (Feldstein, 1966). On the day side weak-rayed aurorae are located. At the station Piiamida a thin arc is observed in the zenith and weak rays in the north. At the station Wiese weak rays occupv al1 the northern part of the sky. Aurora1 brightness is not areat. Long, probably homo~neou~ arcs, &ing through all the frame, are-located ~fpre~midnight and-after midnight (stations Aklavik. Julianehaab). At Churchill station the aurora is much briehter. At the zenith a rayed arc is observed, and in the south a weaker extensive uniform arc with a ray st&ture at the eastern edge. For 16 hr 30 min on December 8, 1958 (Fig. lb) an ionospheric current pattern, responsible for the observed magnetic disturbance, is drawn on the map together with an aurora1 pattern shown by thin lines. Between the current lines flows a current of 15,000 A, the total current when induction in the Earth is allowed for being 60,000 A. For positive disturbances only a line of the electrojet maximum is given, the current direction is given by arrows. At near midnight hours the stations in Alaska observed rather intensive aurorae, filling up almost all the oval. At the station Piramida (the day side) rayed arcs of somewhat mean intensity are located in the zenith, and at Arctica 2 a weak arc, which should be referred to as the aurorae of a polar cap type (Feldstein et al., 1967). The main mass of aurorae is located within the oval edges, along which a westward current runs. Thus, an instantaneous amoral pattern during the IGY period corresponds well to an aurora1 oval location obtained statistically (Feldstein and Starkov, 1967). In this connection it is
interesting to see whether the regularities of oval edge variations for the ICY period remain the same in the years with low so&r activity. Oval edge variation was considered at 4 hr around midnight by the all-sky camera data of the USSR cameras C-180 for 1963-1965, The methods of ascafhm procession are analogous for the XGY and IQSY periods and given by Starkov and Feldstein (1967). The edge location for the IGY period from Smrkov and Feldstein (1967) and IQSY fs given in Fig. 3. The comparisan shows that the character of edge location variations and the oval width during the years of the minimum and maximum of solar activity on the whole remains the same. In both cases the southern edge invariably moves towards the equator as the geomagnetic activity increases. The northern edge at Q = 0 is located more to the north as at Q = 1, and onIy during mean and strong polar disturbances does it begin to move towards the pole. The main peculiarity of the auroral oval location during the IQSY com-
dashed line shows the amoral oval with the corresponding index Q. (Feldstein and Starkov, 1967). The field of view of the all-sky cameras without aurorae is limited by a circle (R = 50 km). The black circle on the edge of the map is the direction of the Sun. The
pared with the XGY is that with the same intensity of polar geomagnetic disturbance it is displaced towards higher latitudes. On average this displacement is 1”. These results agree well with the variation of aurora1 oval zone location on the night side of the Earth from IGY to IQSY according to Feldstein et al. (1966). In the years of the solar activity minimum the centre line of the oval at Q > 2 is situated at ~1”N 69”, and as a contrast to the years of the maximum even at Q = 7 its displacement to the south is not observed. During the IQSY at Q = 1 a displacement of the northern edge to the south only begins, while in the IGY period it achieves 2”. In #heyears of low soIar activity an increase of the rate of displacement of the southern edge to the south is not observed at Q > 6. The width of the oval in both cases increases linearly with increasing geomagnetic activity. Beginning from Q = 2 the oval width during the IQSY period is always somewhat smaller than in the IGY period, the relation of the widths changing little and constituting 1.051.1. One of the possible reasons for aurora1 oval displacement towards the equator in the years of maximum may be an effect of the ring current DR, the intensity of which is, on average, smaller in the years of the
Fm. 2. AIXITUDEDISTRIBUTION OR THE LOWER BORDER OF AURORAE AT DlPFEENT LATrmDEs. Full lines for p’ - 76” (Starkov, 19671, dashed lines for r# - 65” (Andrienko, 1965). A relative number of arcs in the i&ma1 of 5 km is along the axis of abscissa.
FIG. ?. THE DEPENDENCXZ OF THE LOCATION OF THE AURORAL OVAL EDGESON THE INDEX Q DURINi3 THE ICY AND IQSY PERIODS. The
region of the overhead aurorae is hatched. The dashed line represents the centre line of the auroral oval.
solar activity minimum than in the IGY period. Therefore, we considered a variation of the oval location in around midnight hours dependiig on the value &-variation with the same value of the polar magnetic disturbance DP, which was estimated by Q-index. The data on It,fvariation according to Sugiura (1965) were used. The location of the nearpolar and equatorial oval edges at Q = 3 and 5 (weakly and meanly disturbed magnetic field) was considered. Figure 4 gives a location of the oval edges depending on the value of D,+uiation. The mean square deviation is equal to about 1” of the latitude. A peculiarity of the equatorial edge location is its more southern location with positive D,# than with small negative ones. The currents on the magnetosphere surface, increased before the beginning of magnetic storms and stipulated by the envelope of the magnetosphere by corpuscular strema (Mead, 1964) may influence an oval location on the night side. An increase of Da, results in an equatorward shift of both edges of the oval, that is, all the oval displaces to the south. Here is a difference of the effect of DR from DP on the oval location, when we observe an oval expansion with the increase of intensity of polar geomagnetic disturbances the southern edge displaces to the equator, and the northern one to the pole. The displacement of the nearpolar edge to the south in the DR-increase is slower than the equatorial one, therefore we observe some expansion of the oval but rather negligible. These data agree with the location of quiet aurora1 arcs on USA territory during the period of a developed ring current (Akasofu and Chapman, 1963). Figure 3 shows that with the ova1 expansion with Q-index increase the centre line is practically constant and equal to ‘p’ - 675” for the IGY period and 9’ - 69” for the IQSY period. With &-increase the central line of the oval shifts southwards. The graph of this dependence is given in Fig. 5. For Q = 5 and Q = 3 the oval centre lines with the same value of DR coincide and linearly displace equatorwards with the D,,-variation increase. Thus, the character of variation in the oval location with DR increase is the same as during the transition from the years of the minimum to the years of the maximum of solar activity cycle. In both cases there is a displacement of the northern and southern edges towards the equator with a negligible expansion. If the mean value of &-variation during the IQSY period (at Q > 2) decreased by 30 y, then such a variation is quite enough to explain the observed difference between the years of the maximum and minimum of the solar activity cycle. As when there is no DP, the intensity of a ring current is usually very sma11, the conditions at Q =i O-l during the periods of the IGY and IQSY should be the same. As Fig. 3 shows the location of aurora1 belt during the years of minimum and maximum approximately coincides when there are no magnetic disturbances. The World Data Centre B2 Ismiran Moscow, U.S.S.R.
Y. I. F~LDSTEM
The Polar Geophysical Institute Academy of Sciences Murmansk, U.S.S.R.
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