Other
Scientific paper
Dec 1957
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1957phrv..108.1563l&link_type=abstract
Physical Review, vol. 108, Issue 6, pp. 1563-1576
Other
14
Scientific paper
The propagation of solar cosmic rays produced in the February 23, 1956 flare has been studied from the time they leave the flare region to the time when the terrestrial cosmic-ray intensity reaches a maximum value. Within this interval there are observed not only strong anisotropies in the incident radiation, but also relatively large differences in time (<=9 minutes) between the commencements of the intensity increases in different parts of the world. This distribution of time delays is superposed upon the transit-time delay which all particles experience between production and detection. From these experimental results, and the calculations of orbits onnecting the sun and earth at the time of the flare, it is shown that there are broad impact zones on the earth within the first ten minutes of the cosmic-ray intensity increases. Using the recently deduced flare-particle spectrum, cosmic-ray intensities at the top of the atmosphere have been determined for the different impact zones. For this flare event the "2000 hour" impact zone becomes as important as the "0900" and "0300" hour impact zones. These results demonstrate that the first flare particles arriving at the earth were not of low energy, and that the low-energy particles arrived later-the delay being an inverse function of energy. This energy-dependent spread of first arriving particles is called the dispersion effect arising from the mode of particle propagation from the flare source to the earth. These conclusions show that back scattering from disordered magnetic fields beyond the orbit of the earth does not account for the time delays. Various alternatives are considered for production of this distribution of onset times. The most likely process appears to be propagation through magnetic fields by diffusion. Since the impact-zone data for all geomagnetic latitudes, including both polar regions, predict a distant source in the direction of the sun but of order one radian solid angle in the sky, and since sufficient diffusion around the earth to produce the required time delays would destroy the observed impact-zone effects, it is suggested that there may exist a diffusing envelope around the sun which accounts for both the apparent source size and the dispersion effect. Small irregularities in the general solar dipole field are invoked to produce the diffusion. Calculations show that the predicted dispersion effect agrees with the observations, and that other details following from diffusion are satisfied. There is evidence of a dispersion effect for the flare particles of November 19, 1949. The implications of these results for possible uniform magnetic-field distributions between the sun and earth are reviewed, and it is shown from the orbit calculations and the dispersion effect that the predictions are not in agreement with observations. There is a transition period between the time when impact zones are dominant and the time when isotropy sets in. The subsequent storage of the solar cosmic-ray particles is not further considered in this paper, except for the bearing of these observations at early times upon the character of the interplanetary storage magnetic fields.
Lüst Reimar
Simpson André J.
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