Auroras at the South Pole

2 8 I.

6 1

510

iS

2144 9173

SHOCK NORMAL INCLINATION

Figure 1. Graphical representation of the statistical correlation between the direction of north-south anisotropy and the inclination of the shock normal with respect to the ecliptic for 15 epochs. The shock parameters for the circled points are regarded as relatively more reliable.

Figure 2. A phase inversion event, in which the sense of the north-south asymmetry changes abruptly. The associated storm-sudden commencements denoting the arrival at earth of interplanetary shock waves are indicated.

MARCH-APRIL, 1970

waves with respect to the ecliptic plane. For each cosmic ray storm that coincided with interplanetary shocks for which the parameters had been well defined, the north-south anisotropy was evaluated using an analytical procedure that we have developed for this purpose. The results are summarized in figure 1, where the sense of north-south anisotropy (that is, the direction from which the larger cosmic ray flux arrives) is plotted as a function of the inclination of the associated shock wave (Chao and Lepping, 1974). It is clear that, in most cases, a north-directed anisotropy is associated with a shock arriving from south of the ecliptic, and vice versa. Further, a similar analysis of the same events has established that the north-south anisotropy is unrelated to the heliolatitude of the associated September/October 1975

solar flare, in accordance with our earlier conclusion (Duggal and Pomerantz, 1970). In light of this new result, we are attempting to understand the highly complex and interesting events during which the sense of the north-south anisotropy changes its direction abruptly (Pomerantz and Duggal, 1972). Figure 2 shows an example of such a phase inversion event. In this storm of March 1970, the axial anisotropy produces lower intensity at the arctic station Thule than at McMurdo during the onset phase, and the reverse effect during the recovery phase. It is striking that the change in direction is associated with a geomagnetic sudden storm commencement. This suggests that the reversal of the phase in the cosmic ray anisotropy perpendicular to the plane of the ecliptic is probably attributable to the effects of the arrival of the additional interplanetary shock wave. This research was supported by National Science Foundation grant uv-40904. References Chao, J . K., and R. P. 1.cpping. 1974. A correlative study of SSC's, interplanetary shocks, and solar activity. Journal of Geophysical Research, 79: 1799. Duggal, S. P., and M. A. Pomerantz. 1970. Transient northsouth asymmetries of cosmic radiation. Ada Physica Hungaricae (supplement 2), 29: 351. Duggal, S. P., and M. A. Pomerantz. 1971. Cosmic ray anisotropies perpendicular to the equatorial plane. 12th International Conference on Cosmic Rays. Proceedings, 2: 723. Duggal, S. P., and M. A. Pomerantz. In press. Interplanetary shock waves and the north-south anisotropy in cosmic rays. 14th International Conference on Cosmic Rays. Proceedings, MG 7-10. Nagashima, K., S. P. Duggal, and M. A. Pomerantz. 1968. Cosmic ray anisotropy in three-dimensional space. Planetary and Space Science, 16: 29. Pomerantz, M. A., and S. P. Duggal. 1972. North-south anis()tr()pies in the cosmic radiation. Journal of Geophysical Research, 77: 263.

Auroras at the South Pole S.-I. AKASOFU

Geophysical Institute University of Alaska College, Alaska 99701 An important subject in magnetospheric physics during the last several years has been the role of 225

3 JUL

r

Ill 191

1712 UT

Four DMSP-1 satellite photographs that show different sizes of the auroral oval (in the afternoonevening sector). These were taken from above the South Pole region.

the north-south component B of the interplanetary magnetic field in magnetospheric processes. We have already shown, based on all-sky photographs taken from the Alaska meridian chain of stations, that the size of the auroral oval is partially controlled by the B component (Akasofu et al., 1973). A better way of studying this relationship is to continuously monitor the auroral oval with a television camera aboard a satellite orbiting high above the polar region. We are far from having such an ideal situation, although we do have DMSP-1 satellite photographs taken at about 100-minute intervals. This is less than ideal because DMSP photographs cannot cover the entire oval. A fortunate combination of the inclinations of the geomagnetic axis and of the DMsP-1 satellite with respect to earth's rotation axis makes it possible to observe the afternoon-evening half of the oval around 1600 to 1700 universal time (UT). This period coincides with the period when the South Pole is located in the midday sector. We also hope to be able to work with Soviet scientists who operate an all-sky camera at Mirnyy, which is located in the midnight sector around 1600 to 1700 UT. By combining all-sky photographs from the South Pole and Mirnyy stations, as well as from the DMs p -1 satellite, it therefore will be possible to continuously monitor changes in oval size for a few hours each day. The figure illustrates how much the size of the oval (the afternoon-evening half) varies on different days. In each photograph the top of the oval is the midday part and the bottom is the midnight part. The South Pole is located in the midday vicinity of the oval and Mirnyy is located in the midnight sector. 226

Since the auroral oval approximates the boundary of the polar cap from which the open magnetic flux originates, it is possible to derive the total magnetic flux in the magnetotail and to observe its changes (Akasofu, 1975; Akasofu, in press). This research was supported by National Science Foundation grant O pp 71-04051. References Akasofu, S.-!., P. D. Perreault, F. Yasuhara, and CA. Meng. 1973. Auroral substorms and the interplanetary magnetic held. Journal of Geoph.sical Research, 78: 7490. Akasofu, SA. 1975. North-south Component (if the interplanetary magnetic field and large-scale aurora! dynamics. Nature, 256: 191. Akasofu, S.-!. In press. The roles of the north-south component of the interplanetary magnetic field on large-scale auroral dynamics observed by the DMSP satellite. Planetaiy and Space Science.

Atmospheric processes and energy transfers at the South Pole J . J . CARROLL and K. L. COULSON Department of Land, Air, and Water Resources University of California, Davis Davis, California 95616

This project's principal objective is to determine all of the components that are important in the ANTARCTIC JOURNAL