Abstract
Forecasting the geomagnetic effects of solar storms, known as coronal mass ejections (CMEs), is currently severely limited by our inability to predict the magnetic field configuration in the CME magnetic core and by observational effects of a single spacecraft trajectory through its 3‐D structure. CME magnetic flux ropes can lead to continuous forcing of the energy input to the Earth's magnetosphere by strong and steady southward‐pointing magnetic fields. Here we demonstrate in a proof‐of‐concept way a new approach to predict the southward field B z in a CME flux rope. It combines a novel semiempirical model of CME flux rope magnetic fields (Three‐Dimensional Coronal ROpe Ejection) with solar observations and in situ magnetic field data from along the Sun‐Earth line. These are provided here by the MESSENGER spacecraft for a CME event on 9–13 July 2013. Three‐Dimensional Coronal ROpe Ejection is the first such model that contains the interplanetary propagation and evolution of a 3‐D flux rope magnetic field, the observation by a synthetic spacecraft, and the prediction of an index of geomagnetic activity. A counterclockwise rotation of the left‐handed erupting CME flux rope in the corona of 30° and a deflection angle of 20° is evident from comparison of solar and coronal observations. The calculated Dst matches reasonably the observed Dst minimum and its time evolution, but the results are highly sensitive to the CME axis orientation. We discuss assumptions and limitations of the method prototype and its potential for real time space weather forecasting and heliospheric data interpretation.
Highlights
We have recently seen the emergence of novel techniques to describe the evolution of coronal mass ejections (CMEs) from the Sun to the Earth by combining CME parameters derived from observations with geometrical and physics-based approaches; they are appropriately called “semiempirical” models
The magnetic flux rope (MFR) moves according to the drag-based model (DBM) (Vršnak et al, 2013), and we set the background solar wind speed to 400 km sÀ1, which is the solar wind speed at L1 around the CME launch time
For adding a variability to the background solar wind, the speed values outside of the synthetic MFR are randomly taken from a normal distribution centered around 400 km sÀ1 with a standard deviation of 10 km sÀ1, and the magnetic field at MESSENGER is set to 25 nT, with a random variation of about 1 nT in the total field
Summary
We have recently seen the emergence of novel techniques to describe the evolution of coronal mass ejections (CMEs) from the Sun to the Earth by combining CME parameters derived from observations with geometrical and physics-based approaches; they are appropriately called “semiempirical” models They either model the full propagation of the CME magnetic flux rope (MFR) and its deformation in the solar wind (Isavnin, 2016) or use solar observations to set the type of MFR (e.g., Bothmer & Schwenn, 1998; Marubashi et al, 2015; Mulligan et al, 1998; Palmerio et al, 2017) and subsequently simulate the Earth’s trajectory through the structure (Kay et al, 2017; Savani et al, 2015, 2017). We just need to figure out how to use this key
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