On the effect of the initial magnetic polarity and of the background wind on the evolution of CME shocks

Abstract

Abstract. The shocks and magnetic clouds caused by Coronal Mass Ejections (CMEs) in the solar corona and interplanetary (IP) space play an important role in the study of space weather. In the present paper, numerical simulations of some simple CME models were performed by means of a finite volume, explicit solver to advance the equations of ideal magnetohydrodynamics. The aim is to quantify here both the effect of the background wind model and of the initial polarity on the evolution of the IP CMEs and the corresponding shocks. To simulate the CMEs, a high density-pressure plasma blob is superposed on different steady state solar wind models. The evolution of an initially non-magnetized plasma blob is compared with that of two magnetized ones (with both normal and inverse polarity) and the differences are analysed and quantified. Depending on the launch angle of the CME and the polarity of the initial flux rope, the velocity of the shock front and magnetic cloud is decreased or increased. Also the spread angle of the CME and the evolution path of the CME in the background solar wind is substantially different for the different CME models and the different wind models. A quantitative comparison of these simulations shows that these effects can be quite substantial and can clearly affect the geo-effectiveness and the arrival time of the events.

Propagation of an Earth-directed coronal mass ejection in three dimensions

“…Other models show that the internal confi guration of the erupting fl ux rope can have an important eff ect on its propagation through the corona. Th e orientation of the fl ux rope, either normal or inverse polarity, will determine where magnetic reconnection is more likely to occur, and therefore change the magnetic confi guration of the system to guide the CME either equator-or poleward 10 . Alternatively, modelling the fi lament as a toroidal fl ux rope located above a midlatitude polarity inversion line results in non-radial motion and acceleration of the fi lament, because of the guiding action of the coronal magnetic fi eld on the current motion 11 .…”

“…Th e non-radial motion we quantify here may be evidence of the drawn-out magnetic dipole fi eld of the Sun, an eff ect predicted at solar minimum because of the infl uence of solar wind pressure 40,41 . Other possible infl uences include changes to the internal current of the magnetic fl ux rope 11 , or the orientation of the magnetic fl ux rope with respect to the background fi eld 10 , whereby magnetic pressure can function asymmetrically to defl ect the fl ux rope poleward or equatorward depending on the fi eld confi gurations. CME angular width expansion .…”

“…Travelling at speeds of up to 2,500 km s − 1 and with masses of up to 10 16 g, they are recognized as drivers of geomagnetic disturbances and adverse space weather on Earth and on other planets in the solar system 1,2 . Aff ecting our magnetosphere with average magnetic fi eld strengths of 13 nT and energies of ~ 10 25 J, they can cause telecommunication and Global Positioning System (GPS) errors, power grid failures and increased radiation risks to astronauts 3 .…”

“…In the low solar atmosphere, it is postulated that high-latitude CMEs undergo defl ection as they are oft en observed at diff erent position angles than their associated source region locations 8 . It has been suggested that fi eld lines from polar coronal holes may guide high-latitude CMEs towards the equator 9 , or that the initial magnetic polarity of a fl ux rope relative to the background magnetic fi eld infl uences its trajectory 10,11 . During this early phase, CMEs are observed to expand outwards from their launch site, although plane-of-sky measurements of their increasing sizes and angular widths are ambiguous in this regard 12 .…”

Solar signatures and eruption mechanism of the August 14, 2010 coronal mass ejection (CME)

“…While we can measure the velocities of CMEs fairly easily with various spacecraft, we currently have no adequate way to estimate the orientation of the CME magnetic field at the time it arrives at Earth. We can make an estimate of the magnetic field structure when the CME is launched based on photospheric observations, but geometrical changes of the CME -such as deflection and rotation -as it moves through interplanetary space may directly influence its geomagnetic effectiveness (Chané et al 2005;Zuccarello et al 2012;Isavnin et al 2014;Kay et al 2016).…”