磁层顶附近流场剪切度的确定

磁层顶附近的流场剪切度与磁层顶附近能量转换的程度有关.很多磁层顶数值模拟用到流场剪切度这个输入参数,但一直是假设的.本文利用Cluster多卫星同时观测数据及独特的时空分辨功能,采用线性插值和重心坐标的方法确定了磁层顶附近流场的剪切度.通过对晨侧和昏侧磁层顶及附近磁层磁鞘流场剪切度的真实空间分布的研究结果表明,在平静的太阳风条件和地磁条件下磁层顶附近流场剪切度有时也很大,可达每百公里330 km/s的相对速度差.但在很多情况下流场是弱剪切的,在上千公里的距离上只有每秒几十公里的相对速度差.本文确定流场剪切度的方法可以推广用来确定任一位置的流场剪切度.

Shear Rate Determination of Flow Near Magnetopause

Shear rate of flow near magnetopause is related to the degree of energy transfer near magnetopause.Many numerical simulations near magnetopause have to use shear rate of flow as an important input parameter.However,up to now it is still hypothetical and not realistic.By simultaneous multipoint observations of Cluster,using methods of linear interpolation and barycen- tric coordinates,we have determined shear rate of flow near magnetopause,an observational spatial parameter that can not be obtained until Cluster.Observational spatial distribution of shear rate of flow at dawn side and dusk side of magnetopause,magnetosphere and magnetosheath nearby has been analysed,Data analysis demonstrates that shear rate of flow as large as velocity difference of 330 km/s over the distance of 100 km can exist near magnetopause sometimes even under quiet solar wind and geomagnetic conditions.Under many circumstances shear rate of flow near magnetopause is small,with the spatial velocity difference of dozens of km/s over the distance of 1000 km.The method we have adopted here can be used widely to determine shear rate of flow at any location.