My primary research interests lie in the Solar Energetic Particles (SEPs). SEPs are fast electrons and charged ions that we observe during solar eruptions. Their origin is, after several decades of research, still being debated. The SEPs are also a part of Space Weather research, which concentrates on the phenomena in space that can have an effect on us humans. The fast charged particles can penetrate human tissue and electronic instruments, and thus constitute a serious risk to the space endeavours of the human kind.
My primary contribution to the SEP research here at UCLan currently consists of trying to unravel the propagation of the SEPs in the interplanetary space. As charged particles, the SEPs are affected by electromagnetic forces, and thus, in the turbulent plasmas of the interplanetary space, they do not propagate along a direct path from the Sun. The follow the large-scale spiral structure, the "Parker Spiral", of the heliospheric magnetic field, and scatter off the magnetic field irregularities. This propagation is often described as a combination of diffusion and convection of the particles.
Because of the scattering, we must understand the SEP propagation in the interplanetary space in order to be able to understand how the SEP acceleration and release at the Sun is related to other phenomena during a Solar eruption. Unfortunately, our understanding on how to model the spread of particles into the heliosphere is still far from complete. In particular, the spread of particles across the mean Parker Spiral magnetic field is not properly understood. This is crucial for both understanding the SEP acceleration mechanisms, and for the forecasting of SEP intensities at Earth, as currently we cannot reliably determine whether the width of an SEP event is due to the width of the acceleration region close to the Sun, or due to the spreading of the particles in the interplanetary space.
Our contribution to understanding of the cross-field propagation goes beyond the diffusion description of the particles, as we follow the complete orbit of the particle in the turbulent magnetic fields. The turbulent fields are described as superposition of waves, and the crucial question is: how to make the modelling of turbulence as realistic as possible. We have studied in particular the effect of structuredness of the turbulence using envelopes to "break" the turbulence into non-coherent packets, as the turbulence is a nonlinear phenomenon. Our models can be used to study the rate the particles spread in space, and how the spreading compares to other, more simple models
In addition to working on understanding SEP propagation in interplanetary space, I am also working on modelling the SEP acceleration processes. Here, I have been working with Rami Vainio (University of Helsinki, Finland) and Markus Battarbee (University of Turku, Finland) on modelling SEP acceleration in the shock waves in the solar corona.
The shock waves in the corona are related to the coronal mass ejections (CMEs), the vast magnetic structures ejected from the Sun during the solar eruptions. These CMEs are hurled from the Sun at velocities faster than the magnetosonic speed, and thus drive a shock ahead of them, as a supersonic jet does.
Such shocks are considered as the primary contributor to SEPs in large events (although this is still debated). The particles are accelerated by first-order Fermi mechanism, as the particles scatter in the upstream and downstream of the shock, gaining energy at each crossing of the shock front.
As the acceleration mechanism requires scattering, it requires turbulent magnetic field. We are studying the effect of the accelerated particle streams generating this turbulence themselves. In this manner, the acceleration process can be bootstrapped: the accelerated particles amplify the turbulence, making subsequent acceleration even faster and more efficient.
The acceleration process is, however, highly dynamic, and we have shown that the intensity of the injected particles is an important factor for the attainable SEP energies and intensities. In addition, the acceleration of minor ions depends on the evolution of the proton acceleration in a considerable way, and the geometry of the coronal field lines determines the attainable energies of the particles.