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SDO image at 193 A.Coronal mass ejections (CMEs) are large amounts of plasma and magnetic flux expelled from the Sun into the interplanetary medium (heliosphere). CMEs play the main role in creating disturbed space weather conditions by driving geomagnetic storms that may disrupt satellite operations, navigation systems, and radio communications. Studies of CMEs, in particular of their initiation and propagation, are therefore a key topic in solar physics and space weather research.

A CME is geoeffective if it arrives at the Earth and its magnetic field has a suitable configuration: the north-south component Bz of the interplanetary magnetic field should be oriented southward, strong and long-lasting. In recent years, there has been a significant progress in improving the accuracy of the CME arrival predictions, but predicting the Bz configuration is still difficult. The problem of Bz prediction is very complex as the magnetic configuration of a CME close to the Sun is poorly known, and its evolution on the way from the Sun to the Earth depends on a number of factors, including the interaction of the CME with the background solar wind (e.g. deceleration/acceleration, deformation, erosion, shock wave formation). The resulting configuration at 1 AU may include the ICME (interplanetary CME), the shock driven by the ICME, and the sheath region between them. The simplest ICME configuration is that of a magnetic flux rope. The geoeffective southward Bz may be contained both inside the ICME and inside the sheath. In the latter case, the strength of the Bz component crucially depends on the related shock parameters, which, in turn, depend on the ICME interaction with the background solar wind. Another degree of complexity is added by the intrinsically three-dimensional structure of CMEs and ICMEs.

Our current knowledge on the CME-ICME structure is poorly constrained by observations. The remote-sensing instruments allow tracking the propagation of CMEs in white light (from the corona up to more than 1 AU), but these observations do not provide information on their magnetic field. From the white light observations, it is often even difficult to distinguish between the CME and the CME-driven shock wave. The in situ instruments provide one or several one-dimensional cuts though the CME volume, which is insufficient to derive its full three-dimensional structure. Therefore, one has to rely on models, which are presently not realistic enough to predict the magnetic field configuration of ICMEs. In addition, presently the routinely available in-situ measurements are only at 1 AU (L1 if discounting STEREO), which therefore does not allow forecast with a sufficient lead time (for satellite operators etc).


EUHFORIA - EUropean Heliospheric FORecasting Information Asset
Three-dimensional view of a snapshot from a EUHFORIA_0 model run for the June 23, 2015 event that caused a significant geomagnetic storm. The color indicates the radial speed in the ecliptic plane as well as a meridional plane containing Earth. The CME is visible as the red area, while green and blue show fast and slow solar wind streams, respectively. Grey curves visualize the structure of the complex magnetic field.



CME3D Reconstruction of CMEs
3D reconstruction of the CME in the STEREO/SECCHI COR1 field of view on March 5, 2012. The CME reconstruction was done using forward modelling technique by Thernisien et al. 2006, 2009.The reconstructed flux rope is denoted with the green grid croissant.



RadioRadio Triangulation of the Shock Signatures
WIND WAVES dynamic spectrum (time/frequency diagram, with color-coded emission intensity) shows two types of solar radio bursts, type III bursts (radio signature of electrons accelerated along the open field lines) and type II burst (radio signature of electrons accelerated at the shock front). Type II radio bursts are observed in dynamic spectrum as slowly drifting emission, usually showing fundamental and harmonic bands, both often split in two parallel lanes of similar frequency drifts and intensity behaviour (Nelson & Melrose 1985; Vršnak et al. 2001).