Balloon Observations of MeV Electron Precipitation

拟议的项目是一系列气球有效载荷的准备和飞行，以研究从地球辐射带外区沉淀到大气层中的高能电子，以及随后的数据分析。所考虑的电子是相对论的(动能大于电子静止质量511keV)。这些电子可能会对地球同步轨道上的卫星造成损害。它们被困在赤道大约4到6个地球半径之间的地球磁层中，这意味着它们下来时会撞到北极圈和南极圈附近的地球。引发降水的原因有很多，有些与磁暴有关，有些在任何情况下都可能发生。气球研究的不是电子本身，而是韧致辐射过程在撞击大气层时发出的X射线。因此，气球可以观测到发生在其位置100公里或更远范围内的所有降水，并可以跟踪排放随时间的变化。大多数卫星只在自己的位置上观测电子，而且移动得太快，无法观察降水事件的演变。直到20世纪70年代，气球一直被广泛用于研究非相对论电子(大约20-200keV)的沉淀。当相对论电子撞击大气层时，它们可以产生足够的电离，从而产生化学上重要的“奇数氮”(例如，NO2和其他化合物)。根据情况的不同，这些化合物可以破坏平流层的臭氧，也可以结合并使氯原子失活，从而更有效地破坏臭氧，从而可能部分保护臭氧层。尽管人们普遍认为，与人类活动引起的氯的增加和减少相比，它们在这两种情况下的作用都很小，但这种作用还没有得到很好的研究，可能是对主要化学物质的重要扰动。拟于2004年12月/2005年1月举行的宣传活动将涉及各种相对论电子沉淀过程的物理学、它们在空间和时间上的出现模式以及沉淀电子的能量和数量。最后一点与辐射带中相对论电子的总体平衡以及它们对大气化学的影响有关。

The proposed project is the preparation and flight of a series of balloon payloads to study energetic electrons precipitated from the outer zone of the Earth's radiation belts into the atmosphere, and the subsequent data analysis. The electrons under consideration are relativistic (kinetic energy greater than the electron rest mass of 511 keV). These electrons can be responsible for damage to satellites in geosynchronous orbit. They are trapped in the Earth's magnetosphere between roughly 4 and 6 Earth radii at the equator, which means they hit the Earth near the Arctic and Antarctic circles when they come down. The precipitation can be triggered by a number of causes, some associ-ated with magnetic storms and some which can occur under all conditions. The balloons study not the electrons themselves, but rather x-rays emitted by the bremsstrahlung process when they hit the atmosphere. A balloon can therefore watch all the precipitation, taking place within a hundred kilometers of its location or more, and can track the variability of the emission with time. Most satellites only observe electrons at their own position, and move too quickly through the precipitation zone to observe the evolution of the precipitation events. Balloons were used ex-tensively until the 1970s to study precipitation of non-relativistic electrons (roughly 20-200 keV). When relativistic electrons hit the atmosphere, they can produce enough ionization to create chemically important amounts of "odd nitrogen" (e.g. NO2 and other compounds). Depending on the circumstances, these compounds can either destroy stratospheric ozone or else bind up and deactivate chlorine atoms which destroy ozone even more efficiently, and thus perhaps partially protect the ozone layer. Although their role in either case is widely understood to be small compared to that of increases and decreases in chlorine introduced by human activity, that role is not well studied and may represent an important perturbation on the main chemistry. The campaign proposed for December 2004/January 2005will address the physics of the various relativistic electron precipitation processes, their patterns of occurrence in space and time, and the energy and number of electrons precipitated. The last point is relevant to the overall balance of relativistic electrons in the radiation belts and also to their impact on atmospheric chemistry.