A. Anttila et T. Sahla, ERNE observations of energetic particles associated with Earth-directed coronal mass ejections in April and May, 1997, ANN GEOPH, 18(11), 2000, pp. 1373-1381
Citations number
22
Categorie Soggetti
Space Sciences
Journal title
ANNALES GEOPHYSICAE-ATMOSPHERES HYDROSPHERES AND SPACE SCIENCES
Two Earth-directed coronal mass ejections (CMEs), which were most effective
in energetic (similar to1-50 MeV) particle acceleration during the first 1
8 months since the Solar and Heliospheric Observatory (SOHO) launch, occurr
ed on April 7 and May 12, 1997. In the analysis of these events we have dec
onvoluted the injection spectrum of energetic protons by using the method d
escribed by Anttila et al. In order to apply the method developed earlier f
or data of a rotating satellite (Geostationary Operational Environmental Sa
tellites, GOES), we first had to develop a method to calculate the omnidire
ctional energetic particle intensities from the observations of Energetic a
nd Relativistic Nuclei and Electrons (ERNE), which is an energetic particle
detector onboard the three-axis stabilized SOHO spacecraft. The omnidirect
ional intensities are calculated by fitting an exponential pitch angle dist
ribution from directional information of energetic protons observed by ERNE
. The results of the analysis show that, compared to a much faster and more
intensive CMEs observed during the previous solar maximum! the acceleratio
n efficiency decreases fast when the shock propagates outward from the Sun.
The particles injected at distances < 0.5 AU from the Sun dominate the par
ticle flux during the whole period, when the shock propagates to the site o
f the spacecraft. The main portion of particles injected by the shock durin
g its propagation further outward from the Sun are trapped around the shock
, and are seen as an intensity increase at the time of the shock passage.