| Abstract | 基于WIND飞船1995-2014年观测到的13042例非激波太阳风动压脉冲结构(Dynamic Pressure Pulse, DPP)事件列表,统计分析DPP事件法向分布特征,讨论其种类分布.研究发现:DPP事件上下游磁场矢量之间的夹角分布统计上呈双幂律谱分布;60.46%的非激波DPP事件法向矢量的倾斜角-方向角(thetan-phin)主要集中分布在-50° ≤thetan≤ 50°,160° ≤phin≤ 250°的区域内;thetan-phin分布图的中心位置大概为(-22.83°, 186.59°);根据DPP的上下游磁场变化特征,可将DPP分为切向间断(TD)、旋转间断(RD)、混合间断(ED)及其他间断(ND)结构,四者所占比例分别为46.42%,19.53%, 27.47%, 6.58%.统计结果表明DPP事件TD占优.此外,TD/RD数量的比值在太阳活动低年时明显偏大.研究结果可为下一步准确预报DPP到磁层的传播时间以及探究DPP的形成机理等提供观测依据. |
| Other Abstract | Based on the Solar Wind Dynamic Pressure Pulse (DPP) events observed by the WIND spacecraft from 1995 to 2014, the distribution of the orientation and the type of DPPs is statistically analyzed. Firstly, the distribution of the angle ∆theta between the magnetic field vector in the preceding region and that in the succeeding region is well fitted by a piecewise function with double power-law distribution. Secondly, the Minimum Variance Analysis (MVA) method is used to determine the normal of DPP. In order to obtain a reliable normal of DPP, the MVA eigenvalue ratio lambda_2/lambda_3≥ 2 and ∆theta ≥ 30° are taken into constraints. The directions of the investigated DPPs mainly concentrate in a certain region of-50° ≤ thetan≤ 50°, 160° ≤ 250°, and the center of the investigated DPP is at the point of theta = -22.83°, phi = 186.59°. Thirdly, DPP can be classified into four types of discontinuities such as Tangential Discontinuity (TD), Rotational Discontinuity (RD), Either Discontinuity (ED), and Neither Discontinuity (ND). The proportion of these four types of DPP is 46.37%, 19.57%, 27.49% and 6.57%, respectively. The results show that most DPP belong to TD, and the proportion of TD and RD are much larger than ED and ND during the solar minimum. The results would help to improve the accuracy of forecasting of the transit time between the WIND observation and the magnetosphere response and to study the formation mechanism of DPP. |
