Heliospheric evolution of CMEs and their space weather impact
Coronal mass ejections (CMEs) are huge clouds of magnetized plasma that are expelled from the Sun's outermost layer with speeds of some hundred up to 3000 kilometers per second. The fastest CMEs can reach Earth in less than one day after being expelled from the Sun, and may cause severe geomagnetic storms when impacting on the Earth's magnetosphere. We are working on a better understanding of the expansion and propagation of CMEs through the space between the planets in the inner heliosphere, in order to achieve a better forecasting of CME arrival and their impact on the Earth's atmosphere. Such knowledge is of crucial importance since strong CMEs are the major cause of severe disturbances of our Earth's space weather, thus endangering our modern technological infrastructure, in particular satellites in Earth orbit and power grids on the ground.
We apply and develop new techniques to study in detail the evolution of CMEs from Sun to Earth and beyond. For this we use multi-point image and in-situ data provided by a wealth of instruments currently available for solar physics purposes. In this respect most important are the NASA missions SDO and STEREO. STEREO consists of two identical satellites, STEREO-A and -B, that view the Sun from different locations in an orbit close to 1 AU (note that STEREO-B is currently not operational). Combining results derived from remote sensing observations and 3D reconstruction methods, we evaluate the in-situ measurements of the CME plasma and magnetic field data to determine their physical characteristics.
Multiple CMEs are able to collide which results in complex magnetic structures that are affecting near Earth space more strongly compared to single isolated CME events. In this respect, particular attention in our scientific investigations is drawn on CME-CME interaction events, as well as the influence on CME propagation by the ambient solar wind and preconditioning of interplanetary space.
The resulting outcome of these studies is basis for the developments of tools and applications as currently under action for the ESA Space Saftey Programme (swe.ssa.esa.int) as Expert Service Center for Heliospheric Weather (swe.uni-graz.at).