Multipoint measurements of magnetospheric substorms: onset timing and tail reconnection rates

磁层亚暴的多点测量：爆发时间和尾部重联率

• 批准号: PP/E001947/1
• 负责人: James Wild
• 金额: $ 36.53万
• 依托单位: Lancaster University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=PP%2FE001947%2F1
• 关键词: Multipoint; measurements; magnetospheric; substorms; onset

The Earth possesses a magnetic field which is approximately dipolar in shape - very similar to the magnetic field produced a simple bar magnet. Magnetic field lines emerge from the planet at one magnetic pole and extend out of the atmosphere and many thousands of kilometres into space, before returning to the magnetic pole in the opposite hemisphere. Rather than being a vacuum, the region of space that these field lines pass through is filled with plasma - an electrically conducting gas made up charged particles. Most of these particles originate in the Earth's atmosphere having been produced by ultraviolet sunlight which ionises gases in the high altitude atmosphere. The Sun also possesses a strong magnetic field. As nuclear processes generate energy in the solar interior, the outer layer of the solar atmosphere expands outwards through the solar system (forming the solar wind), and carries with it remnants of the Sun's magnetic field (the interplanetary magnetic field). When the solar wind and interplanetary magnetic field arrive at the Earth, they collide with the Earth's magnetic field and are diverted around the planet. The cavity carved out of the solar wind by the Earth's magnetic field is called the magnetosphere. Inside the magnetosphere the plasma and magnetic field originate mainly from the Earth. Outside of the magnetosphere, they originate from the Sun. At the boundary between the interplanetary and terrestrial magnetic fields on the dayside of the Earth, the field lines sometimes orient themselves in opposite directions. When this happens, the field lines can merge or 'reconnect' across the boundary. In other words, closed magnetic field lines that start and finish at the Earth's surface in opposite hemispheres can be opened so that one end stays fixed to the Earth while the other extends outwards into the solar wind. Since the solar wind is constantly streaming away from the Sun, the newly-opened magnetic field line is dragged and stretched away from the Earth. Therefore, because of the process of magnetic reconnection at the dayside boundary, the Earth's dipolar magnetic field is stretched out on the planet's nightside to form a long magnetic tail that points away from the Sun. If the Earth's magnetic field was continuously being peeled away and dragged into the tail, eventually there would be no field left on the dayside of the planet. However, a process in the tail periodically acts to reduce the amount open magnetic field in the tail and return closed field to the dayside - this process is magnetic reconnection. By reconnecting two open magnetic field lines a closed magnetic field is produced (like typing together the two loose ends of a piece of elastic). However, the resulting closed field is highly stretched and, just like a stretched elastic band, it contracts back towards the Earth, catapulting some of the magnetospheric plasma Earthward. The reconnection process in the tail is not steady. Generally magnetic field builds up in the tail until some critical point is reached. Somehow, reconnection is triggered and stretched magnetic field is removed from the tail and returned to the Earth. The period when tail field is building is known as the substorm growth phase, while the explosive release of energy in the tail associated with reconnection and the closure of open field lines is known as the substorm expansion phase. However, the processes that cause the triggering of the expansion phase (i.e. that mechanisms that trigger the catapult) remain unclear - it is one of the biggest uncertainties in solar-terrestrial physics. This investigation will use measurements from instruments on spacecraft located in the tail and observations made from the Earth in order to determine the triggering mechanism of magnetospheric substorms.

地球拥有一个近似偶极形状的磁场-非常类似于一个简单的条形磁铁产生的磁场。磁力线从地球的一个磁极出现，延伸出大气层，进入数千公里的太空，然后返回到另一个半球的磁极。这些场线穿过的空间区域不是真空，而是充满了等离子体--一种由带电粒子组成的导电气体。这些粒子中的大多数起源于地球大气层，是由紫外线阳光电离高空大气层中的气体产生的。太阳也有很强的磁场。当核反应在太阳内部产生能量时，太阳大气层的外层向外膨胀穿过太阳系（形成太阳风），并携带着太阳磁场的残余（行星际磁场）。当太阳风和行星际磁场到达地球时，它们与地球的磁场发生碰撞，并围绕地球转向。由地球磁场从太阳风中切割出来的空腔被称为磁层。在磁层内部，等离子体和磁场主要来自地球。在磁层之外，它们来自太阳。在地球昼面的行星际磁场和地球磁场之间的边界处，磁力线有时会朝向相反的方向。当这种情况发生时，场线可以合并或“重新连接”越过边界。换句话说，在地球表面开始和结束的相对半球的闭合磁场线可以打开，以便一端保持固定在地球上，而另一端向外延伸到太阳风中。由于太阳风不断地远离太阳，新打开的磁场线被拖离地球。因此，由于昼侧边界的磁场重联过程，地球的偶极磁场在地球的夜侧被拉伸，形成一条远离太阳的长磁尾。如果地球的磁场不断地被剥离并被拖入尾部，最终地球的向阳面将没有磁场。然而，在尾部的一个过程周期性地减少了尾部的开放磁场，并将闭合磁场返回到昼侧-这个过程是磁重联。通过重新连接两个开放的磁场线，产生了一个封闭的磁场（就像将一块橡皮筋的两个松散端打字一样）。然而，由此产生的闭合场是高度拉伸的，就像一个拉伸的弹性带，它向地球收缩，将一些磁层等离子体向地球反射。尾部的重联过程是不稳定的。一般来说，磁场会在尾部积聚，直到达到某个临界点。不知何故，重新连接被触发，拉伸的磁场被从尾巴上移除并返回地球。尾场建立的时期被称为亚暴增长阶段，而与重联和开放场线关闭相关的尾部能量爆炸性释放被称为亚暴扩张阶段。然而，导致膨胀阶段触发的过程（即触发弹射器的机制）仍然不清楚-这是日地物理学中最大的不确定性之一。这项调查将利用位于尾部的航天器上的仪器的测量结果和从地球上进行的观测，以确定磁层亚暴的触发机制。

项目成果

The influence of magnetospheric substorms on SuperDARN radar backscatter

• DOI: 10.1029/2007ja012910
• 发表时间: 2008-04
• 期刊: Journal of Geophysical Research
• 作者: J. Wild;A. Grocott

Combining incoherent scatter radar data and IRI-2007 to monitor the open-closed field line boundary during substorms

结合非相干散射雷达数据和IRI-2007监测亚暴期间的开闭场线边界

• DOI: 10.1029/2010ja015751
• 发表时间: 2010
• 期刊: Space Physics
• 作者: Woodfield E

Midnight sector observations of auroral omega bands MIDNIGHT SECTOR AURORAL OMEGA BANDS

午夜扇区极光欧米茄带观测 午夜扇区极光欧米茄带

• DOI: 10.1029/2010ja015874
• 发表时间: 2011
• 期刊: Space Physics
• 作者: Wild J

Simultaneous THEMIS in situ and auroral observations of a small substorm

• DOI: 10.1029/2008gl033794
• 发表时间: 2008-08-12
• 期刊: GEOPHYSICAL RESEARCH LETTERS
• 影响因子: 5.2
• 作者: Donovan, E.;Liu, W.;Rae, I. J.
• 通讯作者: Rae, I. J.

Superposed epoch analysis of the ionospheric convection evolution during substorms : onset latitude dependence

亚暴期间电离层对流演化的叠加历元分析：爆发纬度依赖性

• 发表时间: 2008
• 作者: A. Grocott;J. Wild;S. Milan;T. Yeoman
• 通讯作者: T. Yeoman