Magnetic connection from the Earth to the solar corona, flare positions and solar energetic particle observations

Dipartimento di Fisica, Università della Calabria, Ponte P. Bucci, cubo 31C, 87036 Arcavacata di Rende, Cosenza, Italy e-mail: pommois@fis.unical.it

Received: 27 January 2005
Accepted: 3 March 2005

Abstract

Solar energetic particle (SEP) events are often associated with solar flares. Such particles propagate through the interplanetary medium, where significant levels of magnetic turbulence are found. We study the magnetic connection from the Earth to the solar corona in three dimensional magnetic turbulence. In the numerical simulation, different turbulence levels and solar wind velocities can be used. Input to the simulation is from web-based data sets, and comparison is made with the solar flare observations contained in the Goes catalogue for the years 1996, 1997, 1998, following solar minimum. For this data set, we find that SEPs can reach the Earth when the difference in the heliographic longitudes of the flare and of the magnetic foot point of the Earth is 25°–30° at most. On the other hand the longitudinal angular semi-width of the magnetic field line random walk in the solar wind, when mapped to the solar corona, is found to be typically –10°. The discrepancy between the two values can be explained either by the presence of a flare – associated coronal mass ejection shock, with a longitudinal semi-size of ~, or by particle propagation, which could be enhanced over the field line random walk by, e.g., gyroresonant effects, or by the presence of magnetic shear between the fast and the slow streams which enhances the longitudinal spread of field lines.