Photospheric Magnetic Field Evolution And Initial Process Of Coronal Mass Ejection

The Sun is the closest star to us.Solar eruptions,such as coronal mass ejections(CMEs)and flares,have an important impact on space weather and the Earth's climate The magnetic field on the Sun plays an important role in solar activities.At present,we can use observation data and models to simulate the long-term changes of the global magnetic field,and we can also reproduce the dynamic evolution process of the local magnetic field in a short time.A solar magnetic flux transport model has the ability to demonstrate the magnetic evolution of the Sun,thus providing a foundation for space weather forecasting.To predict the Sun's magnetic environment more precisely,many versions of magnetic flux models have been developed.We utilized two models that were created by Yeates et al.(2007)(hereinafter referred to as the Y model)and Worden and Harvey(2000)(hereinafter referred to as the WH model)to predict the short-term changes of 10.7 cm radio flux(F10.7)during 2003-2014.Both models performed very well in estimating F10.7 values.The statistical results of analyzing the correlation coefficient,mean absolute error,mean square error,relative error,frequency distribution,etc.show that the Y model is superior to the WH model.The meridional flow and diffusion process used in the WH model do not agree with the observations.Such discrepancies may influence estimates of the global flux.CMEs are large eruptions of plasma and magnetic field from the Sun and propagate into interplanetary space.Understanding the evolution of the CME is important for us to evaluate its impact on space weather.With the help of numerical simulation,we can reproduce the occurrence and development process of the CME.Many studies about simulating CMEs are based on artificial flux ropes.However,the three dimensional vector magnetograms can be observed by the Helioseismic and Magnetic Imager(HMI)on board Solar Dynamic Observatory(SDO),and the three dimensional vector velocity field can be tracked by the differential affine velocity estimator for vector magnetograms(DAVE4VM).We use these information as the boundary condition to investigate the physical mechanisms for the flux rope formation and the cause of the CME eruption near the real background.We present a three dimensional numerical MHD data-driven model for the simulation of the CME that occurred on 2015 June 22 in the active region NOAA 12371.We solve a full set of magnetohydrodynamic(MHD)equations by using the conservation element and solution element(CESE)numerical method.The bottom boundary is driven by the vector magnetograms obtained from SDO/HMI and vector velocity maps derived from DAVE4VM method.The numerical results show two elbow-shaped loops formed above the polarity inversion line(PIL),which is similar to the tether-cutting picture proposed by Moore et al.(2012,2018).The temporal evolutions of magnetic flux show that the sunspots underwent cancellation and flux emergence.The signature of velocity field derived from the tracked magnetograms indicated the persistent shear and converging motions along the PIL.The simulation shows that two elbow-shaped loops were reconnected and formed an inverse S-shaped sigmoid,suggesting the occurrence of the tether-cutting reconnection,which was supported by observations of the Atmospheric Imaging Assembly(AIA)telescope.Then,the analysis of the decline rate of the magnetic field indicated that the flux rope reached a region where torus instability was triggered.We conclude that the eruption of this CME was caused by multiple factors,such as photosphere motions,reconnection,and torus instability.Moreover,our simulation successfully reproduced the three-component structures of typical CMEs.