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Solar energetic particles

Modelling of gradual SEP events: an example

The movie below shows the modelling of the evolution of the interplanetary shock and the cobpoint, and the fitting to the proton intensity-time profiles measured at 1.0 AU during the gradual proton event on 13 December 2006.

The right panel shows:

  1. The first snapshot shows the radial velocity contours of the background solar wind, simulated from 1.03 solar radii to 1.02 AU (from dark blue to light blue, as shown in the colour bar at the right). Note that the solar wind reaches its stationary speed at ~40 solar radii.
  2. Succeeding snapshots: The evolution of the MHD simulated interplanetary shock, propagating on top of this solar wind, from 4 solar radii to ~1.0 AU (L1 point, black dot). The maximum shock velocity occurs at the nose of the shock, in the negative X-axis direction (colour coded from dark red to light green).
  3. The location of the cobpoint at the front of the shock (red point). The first cobpoint occurs about half an hour after the launch of the driven shock, at ~5 solar radii, then it slides clockwise along the shock front as the shock expands out warding the Sun.
  4. The interplanetary magnetic field line (white trace) that at each time step connects the observer at L1 with the front of the shock. This field line is extracted from the MHD simulation: it results in a Parker spiral form upstream of the shock and it bends in the post shock sheath.
The left panel shows:
  1. Three measured proton intensity-time profiles (coloured dots) at L1, the lower energy channel is from the SOHO/ERNE instrument and the other two from the STEREO-A/HET telescope.
  2. The vertical green line marks the shock passage at L1.
  3. The white lines represent the synthetic flux profiles obtained from the fitting using the shock-and-particle model. This model assumes that the shock-accelerated particles are injected onto the interplanetary magnetic field line connecting with the observer at the cobpoint.

In this event, high-energy particles are observed shortly after the first cobpoint is established, thus the first injection of shock accelerated particles occurs when the shock is still close to the Sun. The lower energy profiles start increasing later than that because of the presence of a background population of particles, but mainly due to their smaller velocity and due to particle propagation effects along the interplanetary magnetic field.

Note that the high energy proton flux peaks a few hours after the onset of the event, while the low-energy intensity peaks at the shock arrival. Thus, indicating that the shock is efficient at accelerating high energy protons when it is close to the Sun, but as it propagates away, it becomes only efficient at accelerating low-energy particles.

If you use this movie, please refer to:
Aran A., N. Agueda, C. Jacobs et al. 2011, American Geophysical Union, Fall Meeting 2011, abstract #SH33B-2051A.

The research leading to the modelling performing this movie received funds from the European Space Agency under the Solar Energetic Particle Environment Modelling (A href="http://sepem.aeronomie.be/">SEPEM) Project (ESA-ESTEC/Contract No 20162/06/NL/JD). The work at the University of Barcelona was partly funded by the project AYA2010-17286 of the Spanish Ministerio de Ciencia e Innovación and at KU Leuven, this research was partly funded by the KU Leuven project GOA/2009-009, FWO project G.0729.11 and 06260 and PRODEX project C90205.

Angels Aran and Blai Sanahuja, 2012.
Contact: aaran@am.ub.es


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Last update: 24 April 2013

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