A New Three-Dimensional Asymmetric Bow Shock Model With Dipole Tilt Effects

The solar wind-magnetosphere coupling is an important part of solar-terrestrial environment,and it is also one of the parts that have been widely concerned.This process is very complicated,and the solar activity can directly affect the earth's space environment through this process.The Earth's bow shock is create by the interaction of the supersonic solar wind with the magnetospheric obstacle.The bow shock is a very important interface,when the satellites through the bow shock,its environment will change significantly.In catastrophic space weather conditions,it will cause great damage to the satellites.Therefore,investigating the shape of the bow shock is of great significance on space weather forecast and the satellite environment monitoring.Using the bow shock crossing events from four spacecrafts: IMP8,Geotail,Magion-4,and Cluster 1 a new three dimensional asymmetric bow shock model is constructed.The model is parameterized by the solar wind dynamic pressure,the interplanetary magnetic field,magnetosonic Mach number,solar wind ?,and dipole tilt angle.It is shown that the shape and size of bow shock are both affected by the dipole tilt angle.The dipole tilt angle causes asymmetries in the meridional plane.This paper compares Peredo et al.[1995] model,Merka et al.[2005] model,Chao et al.[2002] model and the new model established in this paper under extreme solar wind conditions,large dipole tilt angle and calm solar wind conditions.The main results of this paper are as following:(1)The bow shock subsolar standoff distance an the north-south asymmetry increase with the dipole tilt angle;(2)As the dipole tilt angle positively increases,in the equatorial plane the shock flaring angle is slightly reduced;while in the meridional plane the flaring angle obviously decreases in south hemisphere and keeps almost unchanged in north hemisphere;The flaring angle in the north hemisphere is larger than in south hemisphere.The effects of negative dipole tilt angle on shock flaring are just the opposite of those for positive tilt and the effects of dipole tilt angle on the shape of the bow shock is north-south symmetric.The model results are also validated by comparing with one previous empirical model,and it is demonstrated that the new model can better describe the rotational asymmetry and north-south asymmetry of the Earth's bow shock.(3)During the extreme solar wind conditions,the prediction results of Peredo et al.[1995] model and Merka et al.[2005] model are not accurate;however,the prediction results of Chao et al.[2002] model are good.The new model can describe the three-dimensional bowshock,and can provide a reference for the prediction of bow shock under extreme solar wind conditions.For the bow shock crossings with larger dipole tilt angles,our new model shows more better performance with a smaller standard deviation than other models.Peredo et al.[1995] model and Merka et al.[2005] model have large standard deviation.For the calm solar wind conditions,the new model and Chao et al.[2002] model can predict the bow shock better,however,Peredo et al.[1995] model have large standard deviation.