Direct penetration of anisotropic solar proton flux through the postnoon magnetopause: evidence of magnetosphere anomaly?
Abstract
Count rates of two closely located neutron monitors (NMs) at Oulu and Apatitysometimes depicted an unusually different behavior during an anisotropic onsetphase of a number of ground level enhancements (GLEs) caused by relativisticsolar cosmic rays. Of 24 years of observations ( 27 GLE) there were revealed 4 suchcases. In all of them the NM with a higher count rate (Oulu on 2 May 1998 and 15April 2001, Apatity on 23 September, 1978 and 14 July 2000) was located in the so-called 14 MLT region (14-16 hours of Magnetic Local Time) known as location ofintense field aligned currents, dayside auroras etc. At the same time the calculatedasymptotic cones of Apatity and Oulu stations were "looking" under the large angleto an IMF direction and in any way could not accept an anisotropic solar proton fluxpropagating along the IMF. Nevertheless one of the station pair which was locatedinside the 14-16 MLT sector showed an excess in count rate due to anisotropicfraction of solar proton flux. Together with the Apatity and Oulu NMs data ouranalysis comprised also the data on the worldwide NM network as well ascomputation of their asymptotic cones These were done by means of trajectorycalculations in the up -to date magneto pheric models of Tsyganenko 1989 and 1996.sOn the basis of observed data we can assume, that the cause of marked unusualdifference between Apatity and Oulu GLE effect can be the not discounted anomalyin the afternoon magnetosphere. .It can be connected, for example to the structure ofnagnetospheric cleft. The noted here effect specifies necessity of additional study ofmagnetosphere structure in the afternoon sector that may be a subject to occurringhere intensive geophysical processes.
- Publication:
-
34th COSPAR Scientific Assembly
- Pub Date:
- 2002
- Bibcode:
- 2002cosp...34E2095V