Abstract:

In order to predict the effects of space weather on Earth, it is important to know the properties of the interplanetary magnetic  field (IMF). Of special interest is the southward component Bz of the IMF, which is the main driver for geomagnetic storms. Focusing on coronal mass ejections (CMEs), we try to predict the southward magnetic component Bz, the arrival time and speed at Earth and the resulting disturbance storm time index (Dst index). The Dst index is an important indicator for space weather activity and several methods exist for its prediction from in-situ data. Using data from Venus Express (VEX) and the model provided by Burton et al. 1975 in comparison to the O'Brien and  McPherron 2000 model, we attempt to forecast the Dst index. In order to do so, CME speed, solar wind background speed and the magnetic field strength of the IMF are  required. We used a drag based model to obtain the speed of the CME between the Sun and 1 AU. For the background solar wind speed, the ENLIL model (a numerical solar wind model) is utilized. The decay of the magnetic  field with increasing distance from the Sun is calculated based on a power law, known from observations. Our investigation of a CME, that was hitting Earth on 16th of June 2012, shows a predicted arrival time at Earth, ~6 hours late compared to the true arrival, lying well within the general uncertainty of such predictions. Both models for Dst prediction show a lower than true Dst value, while the Burton et al. model provides promising results. The advantage of this method is a lead time in Dst prediction of ~14 hours (and even more for a spacecraft closer to the sun), compared to a prediction lead time of only ~40 minutes, using a L1 located spacecraft. Furthermore the prediction method be applied to data from any in-situ spacecraft located between Sun and Earth (given the correct alignment), like Helios, Solar Orbiter or Solar Probe Plus.