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Akasofu, S.-I.

Publications and source records attributed to Akasofu, S.-I..

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Auroral displays near the 'foot' of the field line of the ATS-5 satellite

Summary of an extensive correlative study of ATS-5 particle and magnetic field data with all-sky photographs from Great Whale River which is near the 'foot' of the field lines passing through the ATS-5 satellite. In particular, an effort is made to identify specific particle features with specific auroral displays during substorms, such as a westward traveling surge, poleward expansive motion, and drifting patches. It is found that, in early evening hours, the first encounter of ATS-5 with hot plasma is associated with the equatorward shift of the diffuse aurora, but not necessarily with westward traveling surges (even when the satellite is embedded in the plasma sheet). In the midnight sector, an injection corresponds very well to the initial brightening of an auroral arc. Specific features of morning sector auroras are difficult to correlate with specific particle features.

Akasofu, S.-I.↗
NASA NTRS1973

Equatorward shift of the cleft during magnetospheric substorms as observed by Isis 1

Isis 1 satellite observations of the cleft position during magnetospheric substorms show that the cleft shifts equatorward as the interplanetary B sub z component turns southward and substorm activity increases and that it shifts back toward higher latitudes as substorm activity subsides and B sub z returns northward. Also, unusually low latitudes for the cleft (less than 70 deg invariant latitude) were found during geomagnetic storms with significant Dst values and large negative B sub z values. Significant shifts occur in the cleft location with no accompanying effect seen in the AE index; however, B sub z is observed to be southward during these periods.

Yasuhara, F.↗
NASA NTRS1973

Variations of three-dimensional anisotropy of cosmic rays during Forbush decreases.

Variations of three-dimensional anisotropy of cosmic rays during Forbush decreases are examined by a spherical harmonic method and by constructing successive isointensity contour maps in the solar ecliptic coordinate system. The east-west and north-south anisotropies are studied statistically and for several individual events; the data are based on cosmic ray records from about 24 stations for the 3-year period from 1966 to 1968. For the individual events, the high anisotropies of about 4% are examined in terms of the convective, diffusive and density gradient components of the differential streaming as well as the interplanetary magnetic field and solar wind. In each case, vector gradients are derived that lead to the observed anisotropies, and the magnitude of these gradients is typically 10-20 times that of the quiet time interplanetary gradient.

Yoshida, S.↗
NASA NTRS1973

Simultaneous observations of auroras from the South Pole Station and of precipitating electrons by Isis 1.

On the basis of the simultaneous observations of auroras from the South Pole and of precipitating electrons by the Isis 1 satellite it is shown that (1) a midday auroral arc (photographed on black and white film) occurs within the cleft (cusp) region projected to the appropriate auroral height along the geomagnetic field; (2) in the evening sector an aurora, observed by Isis 1 and the South Pole all-sky camera, extended for at least 5 hours of local geomagnetic time in the expected position of the auroral oval; and (3) during a period of extreme magnetic quiet, cleftlike electrons were observed just poleward of a narrow region of intense precipitation in the midnight sector. An earth-sun oriented arc was seen at the projected location of the intense electron flux.

Winningham, J. D.↗
NASA NTRS1973

Electric field observations by incoherent scatter radar in the auroral zone.

Analysis of ion drift velocity measurements, made for a 24-hour period in February 1972 by the incoherent scatter radar at Chatanika, Alaska (L = 5.7), provides a detailed view of electric fields and currents in the auroral zone. Large northward electric fields were seen in the evening sector, and an abrupt change to southward occurred at the start of a midnight sector substorm. The westward electric field was generally much smaller than the north-south electric field but showed a rapid increase at the time of a westward auroral surge. Study of global magnetograms and all-sky camera photographs has led to the identification of five substorms during the 24-hour observation period. These substorms were sufficiently separated in time to allow identification of the electric field and current variations in late afternoon, evening, and morning local time sectors.

Banks, P. M.↗
NASA NTRS1973

A possible current system associated with the Sqp variation.

It is suggested that the quiet day daily magnetic variation in the polar cap region, Sqp, results partly from the short-circuit effect of the magnetotail current by the polar ionosphere. This implies that there is an inward field-aligned current from the dawnside magnetopause to the forenoon sector of the auroral oval (positively charged) and an outward field-aligned current to the duskside magnetopause from the afternoon sector of the oval (negatively charged), together with the ionospheric (Pedersen and Hall) currents. The distribution of the magnetic field vectors of both combined current systems agrees with the observed Sqp vector distribution. The space charges provide an electric field distribution which is similar to that which has been observed by polar orbiting satellites.

Kawasaki, K.↗
NASA NTRS1973

Cross-correlation analysis of the AE index and the interplanetary magnetic field Bz component.

A cross-correlation study between magnetospheric activity (the AE index) and the southward-directed component of the interplanetary magnetic field (IMF) is made for a total of 792 hours (33 days) with a time resolution of about 5.5 min. The peak correlation tends to occur when the interplanetary data are shifted approximately 40 min later with respect to the AE index data. Cross-correlation analysis is conducted on some idealized wave forms to illustrate that this delay between southward turning of the IMF and the AE index should not be interpreted as being the duration of the growth phase.

Meng, C.-I.↗
NASA NTRS1972

Photographs of the front of the expanding auroral bulge during an auroral substorm.

Selected photographs from a 1968 NASA airborne expedition of the spectacular and theoretically intriguing poleward expansive phase of auroral substorms are presented. They illustrate many of the common features of the front of the expanding auroral bulges, such as violent curl motions, the formation of new arcs at the front, and north-south aligned arcs just inside the bulge. A simultaneous magnetic record is also presented and briefly discussed.

Akasofu, S.-I.↗
NASA NTRS1972

Magnetospheric substorms - A model.

An attempt is made to integrate and interpret various polar and magnetospheric substorm phenomena as consequences of the acceleration process of auroral particles which could result from the diversion of a part of the magnetotail current to the night side of the auroral oval. Thus, this paper is not intended to be a literature survey, but to present a way along which magnetospheric substorms might be studied in the future.

Akasofu, S.-I.↗
NASA NTRS1972

Solar-terrestrial physics.

The work is concerned with solar influences on the earth's upper atmosphere and electromagnetic environment partly through solar ultraviolet and X rays, but particularly through corpuscular radiations. The sun and interplanetary space, the internal structure and magnetic field of the earth, the terrestrial atmosphere and photochemistry, and the dynamics of the upper atmosphere and dynamo action are considered. The formation of the magnetosphere, energetic particles, plasma, and electromagnetic waves in the magnetosphere, solar storms and their extension into interplanetary space, and magnetospheric storms are treated.

Akasofu, S.-I.↗