The MINIS Balloon Campaign: Duskside Relativistic Electron Precipitation.

摘要

The Earth's radiation belts are a dynamic population of highly-energetic (> MeV) electrons and ions trapped in the dipole geometry of the Earth's magnetic field . These particles can strongly influence atmospheric chemistry, satellite operations, human explorers, long distance communications and even the electrical grid. The belts are also the most accessible laboratory for study of the particle acceleration that we see taking place throughout the universe. This dissertation presents the results from the MINIS balloon campaign, a January 2005 effort to observe the loss of relativistic electrons from the belts through relativistic electron precipitation (REP). MINIS launched 6 balloon payloads equipped with X-ray spectrometers into high-altitude, high-latitude, long-duration flights. These flights took place during a dramatic series of solar activity that set off a -99 Dst geomagnetic storm. During the storm sudden commencement phase, three payloads measured bremsstrahlung X-rays from electrons hitting the top of the atmosphere, making MINIS the first multi-point measurement of relativistic electron precipitation. The observations took place at dusk local times, consistent with other high energy precipitation observations from single point balloons. Measuring the scale size and motions of the precipitation region as well as its energy and intensity allow improved measurement of the average loss rate as well as more tightly constraining the instantaneous loss rate from the belts. Scale sizes and motions can also be better tied to the physical structures in the belts which lead to these particle losses. During the MINIS observed precipitation, the scale size was at least 0.6 L (a unit of Earth radii when mapped to the magnetic equator) by 1 hour of magnetic local time, and expansion rates of the precipitation were well faster than the drift rate for ∼MeV electrons. The MINIS balloons also served as a proof of concept for a much larger balloon campaign that began in January 2013 and will continue at least until February 2014. That campaign, BARREL, and estimates of what it will observe as well as a possible satellite mission to observe REP are also detailed here.