A multi-instrument exploration of the cusp ionosphere

当地时间接近中午时分，在北纬80度和南纬80度附近的北极高地，起源于地球导电核心的磁场向上延伸，并与日侧磁层顶磁连接。这个亚太阳磁层顶是地球磁场第一次接触高超音速太阳风气流的点，以及嵌入其中的源于太阳的行星际磁场。这就产生了磁层尖点，这是太阳风产生的能量进入由地球磁场控制的空间区域和它们下面的大气区域的主要入口点。这种能量转移是通过一种称为磁重联的过程进行的。因此，近地空间的这一关键区域对于理解整个地球磁层、电离层和高层大气中的能量、质量和动量流动，以及我们对“空间天气”的理解至关重要。磁层尖点是长期的研究兴趣领域，但它们在空间和时间上的高度可变性质使其成为一个极具挑战性的区域，难以完全理解。在这里，我们描述了一个基于NASA令人兴奋的新空间任务Tracers的多仪器研究计划，该任务将于2022年底发射，PI提案是该计划的指定合作者。示踪剂方案有赖于与地面仪器的协调。对示踪器特别感兴趣的是斯瓦尔巴特地区，这是北极高地的一个地区，拥有独特的良好仪器，例如许多光学仪器和由NERC资助的EISCAT斯瓦尔巴雷达。北半球冬至前后，斯瓦尔巴群岛中午处于黑暗之中，月亮在地平线以下长达10天。这种条件为涉及尖点极光光学观测的多仪器尖点实验提供了一个独特的机会。我们的多仪器研究方案需要建造和部署一个新的最先进的数字成像雷达系统--汉卡萨米极光成像雷达系统(HIRS)。毛发将从芬兰的Hankasalmi向北望去，视野集中在斯瓦尔巴地区，揭示出在约100万平方公里的电离层区域内高空间和高时间分辨率的电离层尖区电动力学。在这个方案中，由双追踪器航天器拍摄的从尖点区域析出的高能离子的低地球轨道测量将提供尖点重新连接过程的时间和空间结构的测量结果。从毛发和相关的地面仪器对重新连接线的足迹进行磁性共轭测量，将测量重新连接线的长度和位置。HAIRS将提供边界运动和边界附近探测到的对流速度的分析，从而能够计算映射到电离层的重联率。这种仪器组合将为了解尖点重联的时间和空间行为及其在控制地面空间天气方面的作用提供一个前所未有的机会。在这里描述的科学计划之外，HIRS将提供重要的补充数据集，以支持即将在斯堪的纳维亚半岛较低纬度由NERC资助的EISCAT 3D雷达系统，该系统将于2021年投产，该系统也将位于HIRS的视野中。HIRS还将直接补充太阳风磁层电离层链接探测器(SMILE)，该探测器将于2023年发射，这是欧洲航天局(ESA)和中国科学院(CAS)的联合任务。由英国航天局和其他欧洲机构提供的创新的SMILE广域软X射线成像仪将获得太阳风影响磁层的区域的独特测量，这些区域与本方案研究的区域直接磁连接。

At near-noon local times, at locations in the high arctic near 80 degrees North and South, the magnetic fields which originate in the conducting core of our planet extend upwards and are magnetically connected to the dayside magnetopause. This subsolar magnetopause is the point where the magnetic field of the Earth first touches the highly supersonic solar wind flow, and the interplanetary magnetic field of solar origin which is embedded in it. This creates the magnetospheric cusps, which are the primary entry points for energy of solar wind origin into the regions of space controlled by the terrestrial magnetic field, and the atmospheric regions which underlie them. This energy transfer occurs through a process called magnetic reconnection. As such, this crucial region of near-Earth space is fundamental to understanding the flow of energy, mass and momentum throughout the Earth's magnetosphere, ionosphere and upper atmosphere, and hence in our understanding of "space weather". The magnetospheric cusps are longstanding areas of research interest, but their highly variable nature, in both space and time, makes them a highly challenging region to fully understand. Here we describe a multi-instrument research programme based around an exciting new NASA space mission, TRACERS, due for launch in late 2022, on which the proposal PI is a named collaborator. The TRACERS programme relies on coordination with ground-based instrumentation. Of particular interest for TRACERS is the Svalbard region, an area of the high arctic uniquely well instrumented with, for example, numerous optical instruments and the NERC-funded EISCAT Svalbard radar. Around northern winter solstice Svalbard is in darkness at noon, and for ~10 days the moon is below the horizon. Such conditions offer a unique opportunity for multi-instrument cusp experiments involving cusp auroral optical observations. Our multi-instrument research programme requires the construction and deployment of a new state-of-the art digital imaging radar system, the Hankasalmi auroral imaging radar system (HAIRS). HAIRS will look northwards from Hankasalmi in Finland, having a field of view centred over the Svalbard region, revealing the ionospheric cusp region electrodynamics at high spatial and temporal resolution over a ~1 million square kilometre region of the ionosphere.In this programme, low earth orbit measurements of energetic ions precipitating from the cusp region taken by the twin TRACERS spacecraft will provide measurements of the temporal and spatial structuring of the cusp reconnection processes. Magnetically conjugate measurements of the footprint of the reconnection line from HAIRS and associated ground-based instrumentation, will measure the length and the location of the reconnection line. HAIRS will provide an analysis of the boundary motion, and of the convection velocities detected near the boundary, allowing a calculation of the reconnection rate mapped down to the ionosphere. Such a combination of instrumentation will provide an unprecedented opportunity to understand the temporal and spatial behaviour of cusp reconnection and its role in controlling terrestrial space weather. Outside of the science programme described here, HAIRS will offer vital complementary datasets to support the upcoming NERC-funded EISCAT 3D radar system at lower latitudes in Scandinavia, coming on stream in 2021 which will also lie in the HAIRS field of view. HAIRS will also directly complement the Solar wind Magnetosphere Ionosphere Link Explorer (SMILE), launching in 2023, a joint mission between the European Space Agency (ESA) and the Chinese Academy of Sciences (CAS). The innovative SMILE wide-field Soft X-ray Imager (SXI), provided by the UK Space Agency and other European institutions, will obtain unique measurements of the regions where the solar wind impacts the magnetosphere, regions which are directly magnetically connected to the area under study in this programme.