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A Universal Planetary Substorm Model

通用行星亚暴模型

基本信息

批准号：
ST/P004016/1
负责人：
Robert Burston
金额：
$ 64.27万
依托单位：
University of Bath
依托单位国家：
英国
项目类别：
Fellowship
财政年份：
2017
资助国家：
英国
起止时间：
2017 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=ST%2FP004016%2F1
关键词：
Universal Planetary Substorm Model

项目摘要

The sun continuously emits a stream of electrically charged particles, known as the solar wind, into space. This wind, travelling at 100s to 1000s km/s, propagates throughout the solar system and all the planets move through it as they orbit the sun. Planets like the Earth are protected from the dangers of the solar wind since the charged particles that it consists of are hindered from striking the surface by a strong internally generated magnetic field. Without this field, the solar wind would strip away the atmosphere and cause enormous damage to living cells, making macroscopic life as we understand it impossible. Although the surface is protected, the solar wind does have important effects, the largest of which is the distortion of Earth's magnetic field, which becomes compressed on the up-stream side of the solar wind and stretched into a long "magnetotail" on the down-stream side. This magnetotail extends beyond the orbit of the moon to a distance over 1,000 times the radius of Earth itself. Events in the magnetotail known as "substorms" accelerate particles from space into Earth's upper atmosphere where they have numerous impacts, the most spectacular of which is the triggering of the Aurora Borealis and Aurora Australis. There are also numerous technological impacts, including electrical charging and increased drag on spacecraft in Low Earth Orbit, which can lead to reduced operational lifetime of the satellites. Substorms can be described as a simple electrical circuit with a generator in the magnetotail and a resistor in the upper atmosphere linked by "wires" following lines of magnetic force, however the effects of this circuit are not easily predictable because the generator is not creating a steady current. Instead the current varies depending on the "weather conditions" of the solar wind, which provides the energy source for the circuit.Mercury, Saturn and Jupiter have magnetotails similar in form to that of Earth and also experience substorms. At Mercury the substorm circuit generator is driven by the solar wind, as it is at Earth but at Saturn and Jupiter there is another source of energy for the generator - the planets' own rapid rotation. Jupiter's substorm circuit generator is dominated by this rotational energy source but is still influenced by the solar wind. At Saturn the substorm generator's energy is supplied in significant amounts by both rotational and solar wind inputs.The aim of this project is to model the substorm electrical circuit for any planet with a magnetotail similar to that of Earth or Jupiter with the intent of understanding the circumstances when substorms are present, when they occur in a predictable, periodic fashion and when they exhibit chaotic, unpredictable behaviour in terms of the energy input from the solar wind and rotational sources. This will allow limits to be placed on the timescale that forecasting of the effects of the substorm circuit is possible for, in the same way that limits can be calculated for the useful timescale of a weather forecast.Because the model will not be limited to any one set of planetary characteristics (particularly rotational speed, magnetic field strength and orbital distance) or specific set of solar wind conditions, it will not be limited to just one planet but instead can be used for any planet with a magnetotail like Earth's. This means it can be used to make predictions about planets outside the solar system which in turn can be used to help understand the habitability of these planets of from the perspective of protection of the surface from stellar wind particles.

太阳不断地向太空发射带电粒子流，称为太阳风。这种风以每秒100到1000公里的速度传播到整个太阳系，所有的行星在绕太阳运行时都会穿过它。像地球这样的行星受到保护，免受太阳风的危险，因为它所组成的带电粒子受到内部产生的强大磁场的阻碍，无法撞击表面。如果没有这个场，太阳风会剥离大气层，对活细胞造成巨大损害，使我们所理解的宏观生命成为不可能。虽然表面受到保护，但太阳风确实有重要的影响，其中最大的影响是地球磁场的扭曲，它在太阳风的上游一侧被压缩，并在下游一侧被拉伸成一个长长的“磁尾”。这条磁尾延伸到月球轨道之外，距离超过地球半径的1,000倍。磁尾中被称为“亚暴”的事件加速粒子从空间进入地球的高层大气，在那里它们产生了许多影响，其中最壮观的是触发北极光和南极光。还有许多技术影响，包括充电和增加低地球轨道航天器的阻力，这可能导致卫星运行寿命缩短。亚暴可以被描述为一个简单的电路，在磁尾有一个发电机，在高层大气中有一个电阻器，通过磁力线连接起来，但是这个电路的效果不容易预测，因为发电机没有产生稳定的电流。相反，电流的变化取决于太阳风的“天气条件”，太阳风为电路提供能量。水星、土星和木星的磁尾在形式上与地球相似，也会经历亚暴。在水星，亚暴电路发电机是由太阳风驱动的，就像在地球一样，但在土星和木星，发电机还有另一种能源-行星本身的快速旋转。木星的亚暴回路发电机主要由这种旋转能源控制，但仍受到太阳风的影响。在土星，亚暴发生器的能量主要由旋转风和太阳风输入提供。该项目的目的是模拟任何具有类似地球或木星磁尾的行星的亚暴电路，目的是了解亚暴存在时的情况，当它们以可预测的周期性方式发生时，当它们表现出混乱时，在太阳风和旋转源的能量输入方面的不可预测的行为。这将允许对预测亚暴环流影响的时间尺度设置限制，就像可以计算天气预报有用时间尺度的限制一样。（特别是转速、磁场强度和轨道距离）或特定的太阳风条件，它将不仅限于一个行星，而是可以用于任何像地球一样具有磁尾的行星。这意味着它可以用来预测太阳系外的行星，反过来又可以用来帮助从保护表面免受恒星风粒子影响的角度来理解这些行星的可居住性。