IAFE   05512
INSTITUTO DE ASTRONOMIA Y FISICA DEL ESPACIO
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
The inteplanetary magnetic field associated to the propagation of solar relativistic particles
Autor/es:
MASSON, S.; DASSO S.; DEMOULIN, P.; KARL-LUDWIG K.
Reunión:
Conferencia; EGU General Assembly; 2010
Resumen:
The origin and the propagation of high energetic solar particles (450
MeV- few GeV) in the interplanetary medium remains a complex topic.
These relativistic solar particles, detected at the Earth by neutron
monitors (called Ground level enhancement, GLE), have been previously
accelerated close to the Sun. In order to be detected at the Earth,
these relativistic particles have to travel along an interplanetary
magnetic field (IMF) connecting the acceleration site and the Earth.
Generally, the nominal Parker spiral (SP), is considered for ensuring
the magnetic connection to the Earth. However, in most of GLEs the IMF
is highly disturbed, and the active regions (ARs) associated to the GLEs
are not always located close to the footprint of the nominal Parker
spiral. If the AR is not connected to the Earth by the nominal Parker
spiral, which is the IMF connecting the acceleration site and the Earth
during the GLEs? A possible explanation of relativistic particles
propagation under these circumstances are transient magnetic structures,
travelling in the IMF as Interplanetary coronal mass ejections (ICMEs).
In order to check this interpretation, we studied in detail the magnetic
connection for 10 GLEs of the last solar cycle. Using the magnetic
field and the plasma parameter measurements (ACE/MAG and ACE/SWEPAM),
we find that relativistic particles associated to ARs located close to
the footprint of the nominal Parker spiral tend to propagate along this
nominal Parker spiral (2 clear cases) or in a solar wind disturbed by a
previous magnetic perturbation (3 cases). Instead, the GLEs associated
to ARs which is clearly not-well connected tend to propagate in an
interplanetary coronal mass ejection or in the back of a previous ICME.
More specifically on the 3 not-well connected cases, two propagate in
the back of an ICME and one of them propagates in the ICME. Depending
in which IMF particles propagate, the path length can display
significant differences. Using the velocity dispersion method applied to
energetic protons measured by SoHO/ERNE and the relativistic particles
measured by the neutron monitor network, we determined the path length
travelled by particles. These lengths are consistent with the IMF
determined previously. Thus, when particles travel, e.g. in an ICME, the
length approaches 2 AU, whereas the length associated to particles
propagating along the nominal Parker spiral is of the order of 1-1.2 AU.
This consistency in the results leads us know the interplanetary
medium in which these relativistic particles propagate for these 10
GLEs, which can be relevant if we want to study deeply each event.