Computer Science
Scientific paper
Jun 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011phdt........10r&link_type=abstract
Ph.D. Thesis, Universitat de Barcelona, 2011
Computer Science
Space Weather, Solar Energetic Particle Events, Shocks, Mhd Simulations, Coronal Mass Ejections
Scientific paper
Gradual SEP events is one of the greatest hazards in space environment, particularly for the launch and operation of spacecraft and for manned exploration. Predictions of their occurrence and intensity are essential to ensure the proper operation of technical and scientific instruments. However, nowadays there is a large gap between observations and models these events that can lead to predictions. This work focuses on the modelling of SEP events, particularly, on the influence of the observer's relative position and of the shock strength, on the simulated SEP flux profiles.
Part I of the thesis, deals with 3D MHD simulations of interplanetary shocks. We have studied the potential relevance of the latitude of the observer on the evolution of the strength of the shock and its influence on the injection rate of shock-accelerated particles; thus, on the resulting flux profiles. It is the first time that such dependence on the latitude is quantified from the modelling of SEP events, because most of the codes used so far to simulate interplanetary shocks are not 3D codes or they have been applied to near-ecliptic events.
To study the influence of the latitude of the observer and the strength of the shock in the SEP flux profiles, we have simulated the propagation of two shocks (slow and fast) up to several observers placed at different positions with respect to the nose of the shock. We have calculated the evolution of the plasma and magnetic field variables at the cobpoint, and we have derived the injection rate of shock-accelerated particles and the resulting proton flux profiles to be measured by each observer. We have discussed how observers located at different positions in space measure different SEP profiles, showing that variations on the latitude may result in intensity changes of up to one order of magnitude.
In Part II, we have used a new shock-and-particle model to simulate the 1 March 1979 SEP event that was observed by three different spacecraft. These spacecraft were positioned at similar radial distances but at significantly different angular positions, with respect to the associated solar source location. This particular scenario allows us to test the capability of the model to study the relevance of longitudinal variations in the shape of the intensity flux profiles, and to derive the injection rate of shock-accelerated particles. Despite the interest of multi-spacecraft events and due to the restrictions that they impose, this is just the second multi-spacecraft scenario for which their shock-particle characteristics have been modelled.
For the first time, a simulation of a propagation of an interplanetary shock has simultaneously reproduced the time shock arrival and the relevant plasma jumps across the shock at three spacecraft. We have fitted the proton intensities at the three spacecraft for different energy channels, and we have derived the particle transport conditions in space. We have quantified the efficiency of the shock at injecting particles in its way toward each observer, and we have discussed the influence of the observer's relative position on the injection rate of shock-accelerated particles. We have concluded that in this specific event the evolution of the injection rate can not be completely explained in terms of the normalized velocity jump.
The work performed during this thesis shows that the injection rate of shock-accelerated particles and their resulting flux profiles depend both on the latitude and on the longitude of the observer. This implies that more SEP events have to be modelled in order to quantify this conclusion on firm ground.
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