Lecturer: Hans Nilsson (IRF) Date: 2014-01-30 10:30 Place: Aniara
Oxygen ion heating and transport in the Earth's magnetotail
The Earth's atmosphere is a source for oxygen ions in the near-Earth space. The richest source is that of the polar cusps, located at the dayside edge of the polar caps. These ions flow along magnetic field lines and we have previously shown that a large fraction of these ions are transported into the magnetosheath and lost from the magnetosphere of Earth. However a significant fraction of these ions, as well as other oxygen ions flowing up from the nightside auroral zone, are transported into the magnetotail of Earth. The large scale flow of the magnetotail brings the ions down into the region around the central tail current sheet, known as the plasma sheet. There the ions are transported back towards Earth. For protons, which constitute the majority of the ions in the magnetotail for most circumstances, the Earthward transport is frequently in the form of short-lived high speed flows, so called bursty bulk flows (BBF). Upon looking at a few case studies we discovered that when the protons are accelerated to very high velocity (more than 200 km/s), usually the oxygen ions did not follow. We have followed up this discovery with a statistical comparative study of proton and oxygen transport in the plasma sheet of the Earth's magnetotail. We discuss the significant difference in the dynamics of the two ion species and attempt to explain the differences in terms of finite gyro radius effects. The gyro radius of oxygen ions is much larger than that of protons, and the oxygen ions are therefore less "frozen in" to the magnetic field as compared tot he protons.
Created 2013-10-03 10:47:42 by Uwe Raffalski Last changed 2014-01-23 13:21:23 by Mats HolmstrÃ¶m