磁云边界层与间断的观测研究

利用WIND飞船的磁场和等离子体观测数据,分析了1995年2月至2003年8月之间82个磁云中的边界层事件.我们认为(1)磁云边界层中方向间断DD(Directional Discontinuity)类型中RD(Rotational Discontinuity),TD(Tangential Discontinuity),ED(Either Discontinuity),ND(NeitherDiscontinuity)的分布为37:18:44:1(%),与背景太阳风中的分布51:12:35:2(%)不同;主要区别在于RD与TD的比例变化. (2)磁云边界层的内外边界切向间断的比例很高,占总数的20%,而且两侧的密度和温度平均相对变化分别为|△N/N|=0.24和|△T/T|=0.19,大于边界层内部的平均值,显示了更多的切向间断特征;此外,磁云边界层中方向间断的出现频次约为太阳风中的1.87倍. (3)磁云边界层中方向间断的法向分布在θ-φ平面中不是随机分布,而是以θ=-24.90°,φ=217.49°为几何中心,主要是指向远离太阳的方向,而不是简单的各向同性分布.初步结果表明,间断是磁云边界层中的重要结构,它有着不同于背景太阳风间断类型比,为诊断磁云边界层的形成机理提供了依据.

WIND Observation of Magnetic Cloud Boundary Layer and Discontinuity

82 boundary layer events in magnetic cloud between 1995.2---2003.8 were analyzed, using the data measured by WIND instruments. It is suggested from the results that: (1) Among the types of the directional discontinuity (DD), the distribution of RD (Rotational Discontinuity), TD (Tangential Discontinuity), ED (Either Discontinuity), ND (Neither Discontinuity) is 37:18:44:1. It is different from 51:12:35:2 in solar wind. (2) The ratio of TD at boundary of Magnetic Cloud Boundary Layers (MCBL) is high, that is 20 percents of all the DD. And the relative variety of temperature and density at either side of discontinuity is |ΔN/N| = 0.24 and |ΔT/T|= 0.19, that is higher than the average inside the MCBL. It has much more TD' characters. The number of DD in MCBL per day is 1.87 times than that in solar wind; (3) The distribution of DD' normal direction in θ-φ plane is likely a sinusoid structure, the center of which is θ = - 24.90 o, φ =217.49 o that points to opposite direction to the sun. It is rather than a simple isotropy distribution. The preliminary results suggest that discontinuities are the important structures in MCBL which has different distribution of DD' type. This paper could provide some evidences for analyzing the formation of MCBL.