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Filamentary structure in the upper atmosphere

高层大气中的丝状结构

基本信息

批准号：
NE/H024433/1
负责人：
Betty Lanchester
金额：
$ 49.7万
依托单位：
University of Southampton
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2010
资助国家：
英国
起止时间：
2010 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FH024433%2F1
关键词：
Filamentary structure upper atmosphere

项目摘要

The subject of our study is the aurora borealis, or northern lights, which is an amazing natural lightshow in the sky, seen regularly at high latitudes such as northern Scandinavia, but rarely at the latitudes of the UK. We use the aurora as a diagnostic to find out many things about the environment around the Earth, mainly in the region of upper atmosphere called the ionosphere. That environment is made up of 'plasma' (ionised gas) often called the fourth state of matter, which makes up over 95% of the directly observable material in the cosmos. Yet it is strangely difficult to maintain and study within Earth's biosphere. The upper atmosphere provides an ideal natural laboratory for its study since there is no need to consider collisions of the plasma with container walls. The story of the aurora begins at the Sun, which is a continuous but very variable energy source, in the form of a plasma stream (the 'solar wind') which impacts on the Earth. We are interested in understanding the smallest scale auroral structures, and how the energy changes within them influence the large scale environment. To study the aurora, we use a special instrument which has three cameras looking at different 'colours' simultaneously. The proposed research is for studies of very dynamic and structured aurora at the highest possible resolution. The instrument is named ASK for Auroral Structure and Kinetics. It was designed to measure a small circle of 3 degrees in the 'magnetic zenith' i.e. straight up along the Earth's magnetic field. Particles from the Sun spiral along these imaginary magnetic field lines, and lose energy when they collide with atmospheric oxygen and nitrogen. The exact colour (or wavelength of the light) depends on how much energy the incoming particle started with, and what molecule or atom it hits. The ASK cameras help to unravel this complicated process by making very precise measurements in space and time of three emissions which have different physical origins. We will combine these optical measurements with measurements from special radar experiments, which are designed to use a technique known as interferometry to measure structures smaller than the beam width, and with accuracy of position and height better than has been possible to date. The radar imaging technology is new in the field of incoherent scattering radar and will be one of the cornerstones of a future project that is called EISCAT_3D. The technology employed is Aperture Synthesis Imaging Radar (ASIR). It is very similar to the technology used by radio astronomers (VLBI, Very Long Baseline Interferometry) to image stellar objects, and also has some similarity with the SAR (Synthetic Aperture Radar) technique used onboard airplanes and satellites to map the Earth's surface and other planetary surfaces. In the radio astronomy case the source itself spontaneously emits radiation that is collected by a number of passive antennas. In ASIR, the radar transmitter acts like a camera flash to illuminate the target (the ionosphere or atmosphere) and a number of antennas collect the scattered radiation exactly as in the radio astronomy case (or like the lens of a camera). From this point on, the two cases are essentially identical. To construct the image of the target, the cross-correlation between the signals is calculated from all different pairs of receivers. By using the radar imaging technique we will become the pioneers of this new technique in Europe.

我们研究的主题是北极光，或称北方光，这是天空中令人惊叹的自然光秀，经常在斯堪的纳维亚半岛北方等高纬度地区看到，但在英国的高纬度地区很少看到。我们使用极光作为诊断来了解地球周围环境的许多事情，主要是在被称为电离层的高层大气区域。这种环境是由“等离子体”（电离气体）组成的，通常被称为物质的第四状态，它构成了宇宙中95%以上的直接可观察物质。然而，在地球的生物圈内进行维护和研究是非常困难的。高层大气提供了一个理想的自然实验室进行研究，因为没有必要考虑碰撞的等离子体与容器壁。极光的故事始于太阳，太阳是一个连续但非常可变的能量源，以等离子流（“太阳风”）的形式影响地球。我们有兴趣了解最小尺度的极光结构，以及它们内部的能量变化如何影响大尺度环境。为了研究极光，我们使用了一种特殊的仪器，它有三个相机同时观察不同的“颜色”。拟议的研究是为了以尽可能高的分辨率研究非常动态和结构化的极光。这台仪器被命名为ASK for Auroral Structure and Kinetics。它的设计是为了测量一个3度的小圆圈在“磁天顶”，即直上沿着地球的磁场。来自太阳的粒子沿着这些假想的磁场线螺旋运动，当它们与大气中的氧气和氮气碰撞时会失去能量。光的确切颜色（或波长）取决于入射粒子的初始能量，以及它撞击的分子或原子。ASK相机通过在空间和时间上对三种不同物理来源的辐射进行非常精确的测量，有助于解开这一复杂的过程。我们将联合收割机将这些光学测量与特殊雷达实验的测量相结合，这些实验旨在使用称为干涉测量的技术来测量小于波束宽度的结构，并且具有比迄今为止更好的位置和高度精度。雷达成像技术是非相干散射雷达领域的新技术，将成为未来EISCAT_3D项目的基石之一。所采用的技术是孔径合成成像雷达（ASIR）。它非常类似于射电天文学家使用的技术（VLBI，甚长基线干涉测量）来成像恒星物体，也与机载飞机和卫星上使用的SAR（合成孔径雷达）技术有一些相似之处，以绘制地球表面和其他行星表面。在射电天文学的情况下，源本身自发地发射辐射，这些辐射被许多无源天线收集。在ASIR中，雷达发射机就像照相机闪光灯一样照亮目标（电离层或大气层），许多天线收集散射辐射，就像射电天文学中的情况一样（或像照相机的透镜）。从这一点上看，这两个案件基本上是相同的。为了构建目标的图像，从所有不同的接收器对计算信号之间的互相关。通过使用雷达成像技术，我们将成为欧洲这项新技术的先驱。