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Solar Protons and Magnetic Storms in July 1961

G. F. PieperA. J. ZmudaC. O. BostromBrian J. O'Brien

出版	American Geophysical Union, 1962
URL	http://books.google.com.hk/books?id=LGzmsgEACAAJ&hl=&source=gbs_api

註釋The State University of Iowa's satellite Injun 1 (1961o2) was launched at 0422 UT on June 29, 1961, and is in an orbit of 67° inclination with apogee 998 km and perigee 881 km. Among the Injun instruments are silicon p-n junction detectors sensitive to protons with energy between 1 and 15 Mev, and a Geiger counter sensitive to protons of energy above 40 Mev. These units detected solar protons during the period of considerable solar activity extending from July 11 to 28, an epoch containing twelve flares of class 2 or 3 and six major magnetic storms that can be divided into four distinct solar proton events. In this period the proton intensity varied widely, with a maximum unidirectional flux of 33,000 particles/cm2 sec ster for 1- to 15-Mev protons occurring during the storm of 1115 UT, July 13, and a maximum omnidirectional flux of 900 particles/cm2 sec for protons of energy above 40 Mev in the storm of 1121 UT July 18. In general, the energy spectrum varied from storm to storm and within a single storm. The temporal and spatial characteristics of the solar proton flux are correlated with details of geomagnetic storms and other solar-terrestrial phenomena such as polar-cap absorption. Some 1- to 15-Mev protons leak out of the main solar stream and enter the geomagnetic field many hours before the onset of a magnetic storm. These particles are observed only on magnetic shells of L with values between 4.8 and 6.1 earth radii, the range corresponding to the undisturbed geomagnetic cutoffs. A large influx of 1- to 15-Mev protons occurs during the last part of the initial phase of the storm and during the early part of the main phase, indicating their previous containment in the storm-producing plasma. A marked equatorial shift of the cutoff latitude occurs during the main phase of the storm. A sharp decrease in the flux in the main phase is followed by a slower exponential decay with a relaxation time of about one day for the 1- to 15-Mev particles. This decay begins after the peak of the main phase and extends through the recovery period of the storm, during which the geomagnetic cutoff gradually returns to its prestorm value. The possibility that the 1- to 15-Mev particles are geomagnetically trapped during the exponential decay is discussed. Considerable fluxes of protons with energy above 40 Mev were observed during only one of the four solar proton events reported. The storm-time cutoffs of these protons occurred at L values lower than the corresponding cutoffs observed with the 1- to 15-Mev protons. These observations and those reported for similar events by other workers are compared in detail. An over-all picture for such events is proposed.