A STUDY OF MAGNETIC STORMS AND AURORAS. Scientific Report NO. 7

Technical Report · Wed Mar 01 00:00:00 EST 1961

OSTI ID:4748671

Akasofu, S; Chapman, S

; > s for magnetic disturbance fields are proposed, based on the theoretical consideration of the electric current systems by which they are produced. A typical magnetic storm begins suddenly when the onrush of the front of the solar gas is halted by the earth's magnetic field. This effect (DCF field) is most markedly observed as a sudden increase of the horizontal component of the earth's field (the storm sudden commencement, abbreviated to ssc) like a step function. In many cases, however, the change of the field during the ssc is more complicated, and different at different places. Such a complexity superposed on the simple increase (DCF) is ascribed to a complicated current system generated in the polar ionosphere (DP current). It is found that the changes of electromagnetic conditions in the polar regions are communicated, without delay, to lower latitudes, even down to the equatorial regions. It is inferred that the equatorial jet is affected by such a change and produces the abnormal enhancement of ssc along the magnetic dip equator. From the extensive analysis of several magnetic storms that occurred during the IGY and IGC, it is suggested that the capture of the solar particIes in the outer geomagnetic fleld occurs when irregularities, containing tangled magnetic fields and high energy protons embedded in the solar stream, impinge on the earth. Thus the development of a magnetic storm depends on the distribution of such irregularities in the stream. The motions and resulting currents and magnetic fields of such trapped solar particles are studied in detail for a special model. It is inferred that a large decrease (DR field) must follow the initial increase; it is ascribed to the ring current produced by such motion of solar protons of energy of order 500 Kev. It is proposed that during the storm there appears a transient storm-time belt well outside the outer radiation belt. It is predicted that the earth's magnetic field is reversed in limited regions when the ring current is appreciably enhanced. This involves the formation of neutral lines there. These may be of two kinds, called X lines or 0 lines according as they are crossed or encircled by magnetic lines of force. These may be entirely separated or may be joined to form a loop, called an OX loop. It is shown that one of them, the X line, which is connected with the auroral ionosphere by the lines of force, could be the proximate source of the particles that produce the aurora polaris. By postulating the existence of such X-type neutral lines at about 6 earth radii, an explanation is obtained of the detailed morphology of the aurora. This includes the auroral zones and their changes, the nighttime peak occurrence of auro ras, their thin ribbon-like structure and their multiplicity, their diffuse and active forms and the transition between them (break-up), the required electron and proton flux, and the ray and wavy structures. Among the most important phenomena associated with the sudden change of the aurora from the diffuse to the active form are the simultaneous appearance of the auroral electrojet and the resulting polar magnetic disturbances (DP sub-storms). Several typical DP sub-storms are studied in detail. It is concluded that a westward auroral jet is produced by a southward electric field. It is shown that an instability of the sheet-beam issuing from along the X-type neutral line can produce a southward electric field of the required intensity. The southward electric field produces an eastward motion of the electrons in the ionosphere. This may be identified with the eastward motion of an active aurora and with the westward auroral electrojet. Besides such large changes of the field, there often appear various quasi- sinusoidal changes of the fieId, much less intense. They are supposed to be hydromagnetic waves, some of which are generated in the outer atmosphere and propagated through the ionosphere, where a certain amount of their energy is dis

• Research Organization: Alaska. Univ., College. Geophysical Inst.; High Altitude Observatory, Climax, Colo.; Michigan. Univ., Ann Arbor. Inst. of Science and Tech.
• NSA Number: NSA-16-033278
• OSTI ID: 4748671
• Report Number(s): UAG-R-112
• Resource Relation: Other Information: Orig. Receipt Date: 31-DEC-62
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

GEOLOGY, MINERALOGY, AND METEOROLOGY
AURORAE
BEAMS
COSMIC RADIATION
CURRENTS
DISTRIBUTION
EARTH
ELECTRIC FIELDS
ELECTROMAGNETIC FIELDS
ELECTRONS
ENERGY
GEOPHYSICS
HEATING
HYDROMAGNETIC WAVES
IONOSPHERE
MAGNETIC FIELDS
MAGNETIC STORMS
MAGNETOHYDRODYNAMICS
MOTION
PROTONS
RADIATION BELTS
SUN
TRANSIENTS
TURBULENCE
VARIATIONS