月球表面及空间环境对太阳风与地球风的响应

月球空间作为日-地-月空间的重要组成部分,是研究基础空间物理以及等离子体与类月天体(无大气且无全球磁场)相互作用的天然实验室,也是影响月球探测任务实施的重要环境因素。面向月球科研站等月球探测任务的国家重大战略需求,亟需聚焦月球空间环境对太阳风与地球风的响应,其中不仅包括常规监测月球空间天气(包括监测太阳风、地球风、能量带电粒子和中子辐射及波动环境、月尘和外逸层等)以保障人类探月登月的空间环境安全,也包括研究各种空间粒子与月表物质和电磁场的相互作用。可利用多卫星观测、遥感监测、月表就地探测、数据分析、数值模拟等手段发现新的物理现象或揭示新的物理机制,探寻太阳系中不同天体空间物质循环过程与辐射环境的差异及其产生原因,从而拓展我们对地球和行星宜居性的认识,并为月球科研站等月球后续任务的实施提供参考。

The effect of non-storm time substorms on the ring current dynamics

During geomagnetically active times such as geomagnetic storms,large amounts of energy can be released into the Earth’s magnetosphere and change the ring current intensity.Previous studies showed that significant enhancement of the ring current was related to geomagnetic storms,while few studies have examined substorm effects on ring current dynamics.In this study,we examine the ring current variation during non-storm time(SYM-H>−50 nT)substorms,especially during super-substorms(AE>1000 nT).We perform a statistical analysis of ring current plasma pressure and number flux of various ion species under different substorm conditions,based on Van Allen Probe observations.The plasma pressure and ion fluxes of the ring current increased dramatically during supersubstorms,while little change was observed for substorms with AE<1000 nT.The results shown in this study indicate that a non-storm time super-substorm may also have a significant contribution to the ring current.

太阳立体探测任务设想

太阳空间探测在太阳物理前沿科学问题研究和空间天气预报应用研究方面具有重要的意义.人类在60余年的太阳空间探测活动中,取得了一系列重要成果,但仍存在诸多根本性重大问题有待解决.太阳立体探测可以克服单视角观测的局限,获取全方位、多要素的物理数据,促进解决太阳物理中的重大科学问题.本文介绍了太阳内部结构和磁场起源、太阳活动机理研究、太阳活动的全日球空间天气效应和空间天气预报模式研究4个科学目标,太阳立体探测任务空间布局、系统组成和探测器总体设计,以及太阳立体探测任务的有效载荷配置和主要技术指标.

太阳系边际探测研究

本文在综述太阳系边际探测的发展历程和现状基础上,基于太阳系边际探测的发展趋势,阐释了太阳系边际探测的4类科学目标,提出了我国太阳系边际探测的总体目标、阶段目标及近期探测任务设想,给出了应重点研究和突破的6类关键技术,为我国太阳系边际探测的论证与实施提供参考.

THEMIS observation of a magnetotail current sheet flapping wave

A flapping wave was observed by THEMIS-B(P1)and THEMIS-C(P2)probes on the dawn side of the magnetotail,while the solar wind was generally stable.The magnetic activity was quite weak,suggesting that this flapping wave was generated by an internal instability,which normally occurs during magnetic quiet times.Our analysis shows that the flapping wave was propagating downward with a tail-aligned scale of at least 3.7 R E and did not show much change in shape during its propagation from P1 to P2.Correlation analysis employed to estimate the time lag between the corresponding half waveforms of P1 and P2 shows that the propagating velocities along the current sheet normal directions were close to each other in the beginning,but increased linearly later on.The average wavelength of the flapping wave is approximately 4 R E.Theoretical analysis suggests that the ballooning type wave model may not be the mechanism for the observed flapping wave,but that the magnetic double-gradient instability model is a more plausible candidate.

Braking of high-speed flows in the magnetotail:THEMIS joint observations

The motion and deceleration processes of plasma sheet high-speed flows have great significance to magnetospheric particle acceleration,magnetic field perturbation,magnetic flux transport,triggering of substorm,and the current system formation in the magnetotail.From February to April 2009,two satellites of the Time History of Events and Macroscale Interactions during Substorms mission,THA and THE,were often separated largely in Z direction,but had small X and Y separations.Such special configuration allows simultaneous observations of highspeed flows at the center and boundary of the plasma sheet.Based on selected case study and statistical analysis,it is found that for about 89%of the events we selected,the probe further away from the neutral sheet observed the high-speed flow earlier than the one close to the center,and the flow is mainly field aligned.And for about 95%events the probe further away from the neutral sheet observed higher X component of the plasma flow.With the hypothesis that parallel flow keeps the same speed during its earthward propagation while central plasma sheet stream uniformly or suddenly brakes on its way to the earth,we deduced the position where the deceleration begins to be between 13 Re and 17 Re downtail,where thenear-earth reconnection is supposed to occur.In addition,our statistical results show that dipolarization fronts observed in the central plasma sheet are more prominent than those observed in the plasma sheet boundary layer ahead of the high-speed flow.

Observations of the step-like accelerating processes of cold ions in the reconnection layer at the dayside magnetopause

Cold ions of plasmaspheric origin have been observed to abundantly appear in the magnetospheric side of the Earth's magnetopause. These cold ions could affect the magnetic reconnection processes at the magnetopause by changing the Alfvén velocity and the reconnection rate, while they could also be heated in the reconnection layer during the ongoing reconnections. We report in situ observations from a partially crossing of a reconnection layer near the subsolar magnetopause. During this crossing, step-like accelerating processes of the cold ions were clearly observed, suggesting that the inflow cold ions may be separately accelerated by the rotation discontinuity and slow shock inside the reconnection layer.

Pressure gradient evolution in the near-Earth magnetotail at the arrival of BBFs

Using in situ observations from THEMIS A, D and E during the 2008–2011 tail season, we present a statistical study of the evolution of pressure gradients in the near-Earth tail during bursty bulk flow(BBF) convection.We identified 138 substorm BBFs and 2,197 non-substorm BBFs for this study. We found that both the pressure and the BZcomponent of the magnetic field were enhanced at the arrival of BBFs at the spacecraft locations. We suggest that the increase of BZduring non-substorm BBFs is associated with flux pile-up. However, the much stronger enhancement of BZduring substorm BBFs implies the occurrence of magnetic field dipolarization which is caused by both the flux pile-up process and near-Earth current disruption. Furthermore, a bow-wave-like high pressure appears to be formed at the arrival of substorm BBFs,which is responsible for the formation of region-1-sense FACs. The azimuthal pressure gradient associated with the arrival of substorm BBFs lasts for about 5 min. The enhanced pressure gradient associated with the bow waveis caused by the braking and diversion of the Earthward flow in the inner plasma sheet. The results from this statistical study suggest that the braking and azimuthal diversion of BBFs may commonly create azimuthal pressure gradients, which are related to the formation of the FAC of the substorm current wedge.