New Directions for Radiation Belt Research
New Directions for Radiation Belt Research
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辐射带研究的新方向
DOI：
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
G. Reeves
中科院分区：
文献类型：
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作者：
A. Chan;C. Rodger;G. Reeves
50多年来，地球的辐射带一直困扰着科学家们。科学家们知道能量极高的电子和质子被困在地磁场中，但它们是如何变得如此强大的呢？测量表明，辐射带的强度可以变化好几个数量级，但是什么使它们变化如此之大？太阳活动和行星际扰动影响了辐射带的结构和特征，但是将因果联系起来的过程是什么呢？研究人员还没有找到这些基本问题的答案。然而，最近的观测和理论工作已经导致对辐射带研究新方向的日益共识，这将是回答这些问题的关键。这些问题不仅对科学很重要——辐射带动态也有重要的经济和社会后果。辐射带内的质子和电子具有能量，可以穿透航天器和太空仪器的主体，潜在地影响这些结构内的材料、电路和探测器。来自这些粒子的穿透辐射对航天器系统有各种各样的不利影响，包括总剂量、物质激活、位移损伤、内部充放电和单事件扰动/闭锁。这些穿透辐射效应会导致卫星故障、在轨性能下降，在极端情况下，还会造成昂贵的（和破坏性的）卫星故障。由于卫星材料与辐射带电子和质子相互作用产生的二次辐射，对科学和操作仪器中的探测器的影响可能更为复杂。二次辐射产品包括电子、中子、X射线和伽马射线。了解带电粒子加速到极端能量的过程对于预测和减轻它们的空间天气影响以及理解高能粒子加速的基本性质至关重要，高能粒子加速也存在于不易接近的太阳、行星和天体物理系统中。在过去的十年中，关于地球辐射带的新观测、理论和模型的发表速度急剧增加。在如此快节奏的变化时期，反思新的发展如何相互联系以及在哪些领域开始形成共识和争议是有益的。最近在库克群岛拉罗汤加举行的辐射带物理学国际讲习班提供了这样一个机会。这次研讨会是自1994年以来一系列会议中最新的一次，这些会议将科学家聚集在一起，就辐射带物理学和相关的磁层和日球层过程进行非正式但深入的讨论。科学讨论经常强调对特定假设的意见或证据的差异，产生创造性的摩擦，从而导致进一步的调查（参见Shprits等人[2008a， 2008b]，了解辐射带主题的最新概述）。不太常见的是揭示新的共识的讨论。然而，这样的共识间隔也很重要——它们使科学活动重新聚焦于重大的开放性问题。拉罗汤加辐射带研讨会在辐射带研究的几个关键议题上取得了显著的一致意见：局部加速在电子辐射带动力学中的重要性，电磁“合唱”波（一种特定类别的电磁波）作为加速源的作用，合唱波在消耗辐射带中发挥的竞争作用，加速和损失的其他候选过程，以及可用于定量测试理解的新理论工具和数值模型。
The Earth’s radiation belts have fascinated and puzzled scientists for more than 50 years. Scientists know that extremely energetic electrons and protons are trapped in the geomagnetic field, but how did they get so energetic? Measurements show that the radiation belts can change in intensity by many orders of magnitude, but what makes them change so dramatically? Solar activity and interplanetary disturbances affect the belts’ structure and characteristics, but what are the processes that connect cause to effect? Researchers do not yet have answers to these fundamental questions. However, recent observational and theoretical work has led to a growing consensus on the new directions in radiation belt research that will be the key to answering these questions. These questions are not important just to science— radiation belt dynamics also have important economic and societal consequences. Protons and electrons within the radiation belts have energies that can penetrate the bodies of spacecraft and space instruments, potentially affecting the materials, circuits, and detectors inside those structures. The penetrating radiation from these particles has a variety of adverse effects on spacecraft systems including total dose, material activation, displacement damage, internal charging/ discharge, and single-event upsets/latch-up. These penetrating radiation effects are responsible for satellite malfunctions, degradation of on-orbit performance, and in extreme cases, expensive (and disruptive) satellite failures. The effect on detectors in scientific and operational instruments can be even more complex because of secondary radiation, produced by the interaction of satellite materials with radiation belt electrons and protons. Secondary radiation products include electrons, neutrons, X rays, and gamma rays. Understanding the processes that accelerate charged particles to extreme energies is critical for predicting and mitigating their space weather effects as well as for understanding the fundamental nature of energetic particle acceleration, which is also present in less accessible solar, planetary, and astrophysical systems. Over the past decade, the rate of publication of new observations, theories, and models of the Earth’s radiation belts has increased dramatically. During times of such fast paced change, it is useful to reflect on how new developments interrelate and where areas of consensus and controversy are beginning to crystallize. Such an opportunity was offered recently at an international workshop on radiation belt physics held on Rarotonga, in the Cook Islands. This workshop was the latest in a series of meetings dating back to 1994 that have brought scientists together to hold informal yet in-depth discussions of radiation belt physics and related magnetospheric and heliospheric processes. Scientific discussions often highlight differences in opinion or evidence for a particular hypothesis, producing creative friction that leads to further investigations (see Shprits et al. [2008a, 2008b] for recent overviews of radiation belt topics). Less common are discussions that reveal new common understandings. Yet such intervals of consensus are also important—they refocus scientific activity on major open questions. The Rarotonga radiation belt workshop resulted in remarkable agreement on several key topics in radiation belt studies: the importance of local acceleration in electron radiation belt dynamics, the role of electromagnetic “chorus” waves (a specific class of electromagnetic waves) as the source of that acceleration, the competing role that chorus waves play in depleting the radiation belts, other candidate processes for acceleration and losses, and the new theoretical tools and numerical models that can be used to quantitatively test understanding.