地球等离子体片中爆震流的理论研究

地球等离子体片中持续时间很短的快速流动事件最近受到很多关注，这些事件被Angelopoulos等称为爆震流，简要回顾了爆震流的理论研究。当前理论认为，爆震流是磁泡（含较少等离子体的磁流通管）在交换不稳定性的作用下在等离子体片中的流动，磁泡图像很自然地解释了等离子体片中观测到的爆震流。理论预期的快速流在横穿磁尾方向的尺度，它的速度伴随着磁场松驰，压力和密度的降低以及电离层和地面特征都已被观测证实。

THEORETICAL STUDY OF THE BURSTY BULK FLOWS IN EARTH''''S PLASMA SHEET

The short duration, fast moving events in the Earth’s plasma sheet have received quite a lot of attentions recently. Such events were termed bursty bulk flows after the paper by Angelopoulos et al. These flow pulses usually last for 10 minutes and have flow speed above 400 km/s. The present paper gives a brief review of the study on the bursty bulk flows. Current theory suggested that the bursty bulk flows are the flows of bubble (underpopulated magnetic flux tube) in the plasma sheet. Under the action of interchange instability, bubble is propelled earthward. Birkeland currents flow at the boundary between the bubble and the background medium, downward the ionosphere from the dawn side boundary and upward from the dusk side boundary. The cross section of a bubble at the equatorial plane would have an elongated streamline shape with the cross tail size of the order of 2 Earth radius. Bubble picture naturally explains characteristics of the bursty bulk flows observed in the plasma sheet. Some numerical simulations have reproduced the observed high-speed flow and the shape of the line of associated magnetic field. Observations have confirmed the expected bubble property, which includes its cross tail size, speed, more dipolar magnetic field, decrease in pressure and density, ionospheric and ground signatures. Both theoretic calculation and observation have demonstrated that the bursty bulk flows are the main mechanism for the magnetic flux and plasma particles transport in the Earth's plasma sheet.