Erdfernerkundung - Numerische Physik: Modellierung

5.5. CAWSES 269
Abbildung 5.37: Ionization rates of electrons and protons combined for a gradual solar energetic
particle event (left) and an impulsive one (right) [217]
MeV are obtained from the CPME (Charged Particle Measurement Experiment) on board
IMP (Interplanetary Monitoring Platform). Comparison with the higher energy electron instrument
on IMP shows that in both events the electron spectrum can be extended down to
5 MeV. For the June event, proton spectra in the range 0.29 MeV to 440 MeV are obtained
from the same instrument; for the October event proton spectra in the range 0.8 MeV to 500
MeV were taken from GOES (Geostationary Operations Environmental Satellite) because
IMP measurements are less reliable due to failure of the anticoincidence scintillator.
§ 893 The left hand side of Fig. 5.37 shows the modeled ion pair production rates for protons
(dotted), electrons (dashed) and the sum of both (solid line) in the 4 October event for 6 hours
containing the high energy maximum; at later times the instrument is saturated. Ionization
of the electrons can amount to up to about 1/3 of that of protons in the height range 50 to
70 km, at lower altitudes electron contribution is insignificant – which is partly due to our
abrupt cut off of the electron spectrum at 5 MeV.
§ 894 The ion pair production rates for the main phase (1 day) of the impulsive June event
are shown on the right hand side of Fig. 5.37. Again the contribution of electrons is visible
only above 50 km, however, around 70 km the ion pair production by electrons even exceeds
that of the protons.
Conclusions
§ 895 The main results of the Monte Carlo simulation are:
R1 for 1 MeV to 500 MeV protons ionization rates are essentially the same in the Monte
Carlo simulation and in a continuous energy loss model.
R2 for 1 MeV to 50 MeV electrons the consideration of bremsstrahlung shifts the ionization
well beyond the Bragg peak to lower altitudes.
R3 electrons in SEP events contribute to ion pair production rates in the height range 50
to 70 km; the amount depends on whether the particle event originated in an impulsive or a
gradual flare.
§ 896 As a consequence of R1, the consideration of secondaries in the Monte Carlo simulation
cannot explain the difference between the observed and modeled electron densities
in the October 1989 event as suggested by Verronen et al. [245]. Instead, R3 suggests that
the inclusion of electrons in the analysis of SEP events might explain such differences. It
should be noted that implications of R3 depend on the focus of research: in the very large
events electron contributions are more or less a 10% effect and thus might be neglected as
c○ M.-B. Kallenrode 2. Juli 2008