Space weather and high-energy phenomena

Living in the neighborhood of the Sun means that the planets in the solar system are subjected to the consequences of its long-term and short-term activity. The large variety of heliospheric phenomena that are driven by the variability of the sun over periods of minutes, hours and even years, also coined "space weather", can affect numerous facets of everyday life on and around Earth. In the present talk, we will focus on the solar activity occurring on small to medium timescales.

On small timescales, we will look at how solar flares, the most energetic events in our solar system, are responsible for the intense brightenings in the UV and X-ray domains, as well as injecting solar energetic particles and coronal mass ejections (CMEs) into the interplanetary medium. The wealth of data from space and ground missions in the whole electromagnetic spectrum, associated with developments of numerical models, have provided a deeper knowledge on the behaviour of regions responsible of solar flares. We will briefly discuss how both observations and modelling help bring together a generic picture of the mechanisms taking place during solar flares, and how there is still a gap needed to understand the link between the high-energy domain affected by flares and the behaviour of magnetic fields at the Sun.

On medium timescales, we will investigate the variability of the solar wind, especially the propagation of solar wind structures such as CMEs and CIRs/SIRs, and their interaction with planets in the solar system. Such studies are made possible due to the existence of a large heliospheric fleet of observatories, from planetary probes and rovers to dedicated heliospheric missions. These interplanetary detections of CMEs and CIRs/SIRs offer some constraints on the link with their sources at the Sun, as well as on their propagation mechanisms. They also provide a better understanding on their effects on planetary environments, as can be seen with phenomena such as the Forbush decrease. Finally, we will also look at the modeling efforts developed in the past few years, and how recent and upcoming space missions will help us to bridge the gap between the Sun's activity and the variability seen in the heliosphere.