Our modern society is becoming increasingly dependent on the constant stream of information sent out by satellites orbiting Earth. However, highly energetic rays traversing the near-Earth space environment pose a constant threat to the electronics on board these satellites. In addition, humankind’s renewed interest in manned missions to the Moon and Mars requires the protection of the spacecraft crew members against the high radiation doses that they will encounter during their interplanetary voyage. A profound understanding of the ever changing radiation conditions in our solar system is thus crucial, in order to efficiently protect our space-based assets and to succeed in our future ventures in space.
A major part of the high intensity radiation in interplanetary space has a solar origin, and consists of electrons, protons, and heavier ions that have undergone significant acceleration during solar eruptive events such as flares and coronal mass ejections (CMEs). These particles are referred to as solar energetic particles (SEPs), and are typically much more energetic than solar wind particles. The solar wind is a turbulent stream of charged particles originating from the Sun and filling up the entire heliosphere. This highly conductive plasma drags the magnetic field of the Sun out into space, giving rise to the interplanetary magnetic field (IMF). This IMF can be very complex and affects how SEPs propagate through our solar system.
In a recent study1 published in Astronomy and Astrophysics, we combined a model of the solar wind with a model of SEPs, to study how the solar eruption of 12 July 2012 produced a large SEP event. In this study we combined the solar wind and CME model named EUHFORIA1 (European Heliospheric Forecasting Information Asset) with the SEP acceleration and transport model named PARADISE2
(Particle Radiation Asset Directed at Interplanetary Space Exploration). EUHFORIA is a data-driven model that solves the magntohydrodynamic equations to simulate the propagation of CMEs through complex solar wind configurations. In a next step, PARADISE evolves energetic particle distributions through the EUHFORIA solar wind, hereby considering how the turbulent IMF affects the transport of SEPs.
Figure 1: The SEP intensities in gray shades, propagating through a solar wind with a non-uniform speed (bright colors). The highest SEP intensities are attained at the CME shock wave, which is characterized by a high solar wind speed (reddish colors).
Figure 1 shows an example snapshot of the simulations of the July 2012 event, depicting the modeled SEP intensities in gray shades and the solar wind speed in the background. The highest SEP intensities are found at the shock wave driven by the CME, which is acting as a powerful particle accelerator. In Figure 2, we show a comparison between the modeled and the observed SEP intensities near Earth for different energies. The good agreement between the simulations and observations at low energies shows that these SEPs were likely accelerated at the CME shock on its voyage through interplanetary space. At higher energies, the agreement between the observations and simulation is less good, indicating that those SEPs may have been already accelerated in the solar atmosphere, i.e., the solar corona. In the future, we will upgrade our models so that they include the corona and see if this allows us to also explain the most energetic SEPs.
Figure 2: Simulated (solid lines) and observed (dots) SEP intensities measured near Earth. The dots in the background is data measured by the Advanced Composition Explorer (ACE) spacecraft. The dashed vertical lines indicate the arrival times of the shock (left) and the CME’s magnetic cloud (right).
1 Pomoell, J. and Poedts, S., “EUHFORIA: European heliospheric forecasting information asset”, Journal of Space Weather and Space Climate, vol. 8, 2018. doi:10.1051/swsc/2018020.
2 Wijsen, N., “PARADISE: a model for energetic particle transport in the solar wind”, PhDT, 2020. KU Leuven and University of Barcelona.
See the full journal publication at Wijsen, N. et al., “Observation-based modelling of the energetic storm particle event of 14 July 2012”, Astronomy and Astrophysics, vol. 659, 2022. doi:10.1051/0004-6361/202142698.
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