My main research since 1985 has been theoretical/computational modeling of the Earth's Magnetosphere - the cavity the Earth's magnetic field carves out of the solar wind. The magnetosphere extends from about 1000 km above the Earth to about 10 RE (1 RE = 1 Earth Radius = 6378 km) in the Sunward direction and to at least 300 RE in the anti-Sunward direction. It is a complex region of low density charged particles (i.e. a plasma, with densities from less than 1 particle/cc to over 1000 particles/cc) interacting with each other, electric and magnetic fields, and a plethora of plasma waves.

I study the motion of these charged particles and its relation to various interesting observable phenomena. One observable effect of magnetospheric particle dynamics is the Aurora, or Northern (and Southern) lights. Caused by particles accelerated from the magnetosphere into the ionosphere and upper atmosphere, where they collide with neutral atoms causing the beautiful glow. Here is an image taken by NASA's Dynamics Explorer satellite of the auroral oval during a magnetospheric substorm:



Substorms are caused by a disturbance in the solar wind interacting with the magnetosphere, but the physics of how such a disturbance affects the magnetospheric system to ultimatley produce the observed aurora and its complex temporal evolution is not well understood. Observational evidence indicates that the magnetotail region plays an important role in storing and releasing energy in the form of ions and electrons streaming toward the auroral region.
One working model predicts a plasma instability in the tail region which should result in a magnetic structure called a magnetic neutral line. The problem is that no neutral lines have ever been observed directly by a spacecraft, so remote sensing techniques are required. In a series of papers since 1988 I and my collaborator Ted Speiser have studied particle motion in magnetic structures such as neutral lines and predicted several possible signatures of these structures.
Our neutral line signature is a "ridge" in the ion distribution function. The distribution function, which tells how likely it is to observe an ion with a given velocity, can be measured on board satellites. An example of a ridge is shown below. The horizontal axis is the ion velocity parallel to the magnetic field and the vertical axis is the velocity perpendicular to it. The colors run from blue (low probability) to red (high probability), and the ridge, running diagonally toward the lower right, can be clearly seen:
Modeled Ion Distribution Function in the Geomagnetic Tail:

We've taken data from the ISEE-1 and AMPTE/IRM satellites and found evidence that neutral line ridges have been observed. Does this mean that neutral lines have been observed? Not quite. There is no guarantee that the ridge signature couldn't be caused by some other phenomenon. Nonetheless, looking at other measurements on board the spacecraft, we show that the neutral line hypothesis is consistent with the measurements.

more to come...

** still under Construction (obviously) **