DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

Energetic Particle Population in the Heliosphere
energetic storm particles
Popu- temporal spatial energy acceleration
lation scales scales range mechanism
GCR continuous global GeV to > TeV diffusive shock
AGCR continuous global 10 – 100 MeV shock?
SEP ? ? keV – 100 MeV reconnection, stochastic
selective heating, shock
ESP days extended keV – 10 MeV diffusive shock,
shock-drift, stochastic
RII 27 days extended keV – 10 MeV diffusive shock
PBSP continuous local keV – MeV diffusive shock, shock drift
with the solar cycle. The anomalous component
stems from originally neutral particles which became
ionized as they traveled through interplanetary
space towards the sun. The now charged
particles are then convected outwards with the
solar wind and are accelerated at the termination
shock, the outer boundary of the heliosphere.
3. Solar energetic particles (SEP) are accelerated
in solar flares, their injection therefore is
point-like in space and time. Energies extend
up to about 100 MeV, occasionally even into the
GeV range. In this case, particles can also be observed
from the ground (see ground level event).
Properties of solar energetic particles differ, depending
on whether the parent flare was gradual
or impulsive. See gradual flare, impulsive flare.
4. Energetic storm particles (ESP) are accelerated
at interplanetary shocks. Originally, ESPs
were thought to be particle enhancements related
to the passage of an interplanetary shock.
The name was chosen to reflect their association
with the magnetic storm observed as the
shock hits the Earth’s magnetosphere. Today,
we understand the particle acceleration at the
shock, their escape and the subsequent propagation
through interplanetary space as a continuous
process lasting for days to weeks until the
shock finally stops accelerating particles. See
energetic storm particles.
5. Recurrent intensity increases (RII) are due to
particles accelerated at the shocks around corotating
interaction regions (CIRs). The energetic
particles can even be observed remote from
these co-rotating shocks at distances where the
shocks have not yet been formed or at higher
solar latitudes when a spacecraft is well above
the streamer belt where the CIR form. See corotating
interaction region.
© 2001 by CRC Press LLC
6. Planetary bow shock particles (PBSP) Particles
accelerated at a planetary bow shock are a
local particle component with energies extending
up to some 10 keV. An exception is the
Jovian magnetosphere where electrons are accelerated
up to about 10 MeV. With a suitable
magnetic connection between Earth and Jupiter,
these Jovian electrons can be observed even at
Earth’s orbit.
energetic storm particles Particles accelerated
at an interplanetary shock. The name stems
from the first observations of shock-accelerated
particles: around the time of shock passage
at the Earth when the interaction between the
shock and the magnetosphere caused a geomagnetic
storm, an increase in particle intensities
could be observed, which was termed energetic
storm particles.
Originally, the term referred to a bump in the
intensity on the decaying flank of a solar energetic
particle event. In protons up to energies
of a few hundred keV, such a bump lasted for
some hours around the time of shock passage.
Energetic storm particles are observed only at
quasi-parallel shocks, where they are accelerated
by diffusive shock acceleration. At quasiperpendicular
shocks, on the other hand, short
shock-spikes, lasting only for some 10 min, are
observed at the time of shock passage. Thus,
the appearance of the shock accelerated particles
strongly depends on the local angle θ Bn between
the magnetic field direction and the shock normal
and the dominant acceleration mechanism
related to this local geometry.
Today, the term energetic storm particles is
often is used in a broader context and basically
refers to the fact that part or all of the observed
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