Introduction to magnetospheric physics

A magnetosphere is formed when the magnetized solar wind interacts with magnetized planets such as Mercury, Earth, Jupiter, Saturn, Uranus and Neptune. The solar wind transports energy, momentum and mass throughout the entire solar system, and processes at the magnetopause (boundary between the solar wind and magnetosphere) determine how much of these physical quantities is captured by the magnetosphere of any particular planet. Of course, the magnetosphere is not able to store an infinite amount of energy; a particularly beautiful end result of this energy unloading can be sometimes seen as aurora at high latitudes in the northern and southern hemispheres.

A magnetosphere can be considered as a big machine consisting of many parts, each of them having its own special function. The physical laws, of course, are the same everywhere; accordingly, the action of each part of this big machine is determined by the local magnetic field topology and plasma dynamics. In Earth's magnetophere the main plasma sources are the solar wind and the ionosphere; but the main plasma source in Jupiter's magnetosphere is the volcanic moon Io. So the plasma environments around different planets can be very different.

In addition to ground-based observations (radars, magnetometers), there are several spacecraft making plasma and electromagnetic field measurements throughout the solar system , so we have lots of data regarding different parts of this "machine". Analytical theory and computer simulations are tools through which we can analyze this data and thereby understand the physical mechanisms behind the observed phenomena. On the other hand, observations and comparisons between different magnetospheres provide us a laboratory to test our models and improve them.

The basic behaviour of plasma can be understood with help of magnetohydrodynamics (MHD), which describes plasma as a one-fluid medium, where macroscopic quantities such as plasma density, pressure and velocity are defined as averages over all particle species. These quantities are coupled together by Maxwell's equations, macroscopic continuity equations and generalized Ohm's law. MHD is like Navier-Stoke equations for ordinary fluid plus the electromagnetic terms.

Each student in our group is working with different part of this "magnetospheric machine" by using and developing MHD simulations. MHD is not always applicable: if, for instance, we would like to model processes developing small scale filamentary field and current structures, additional terms in the generalized Ohm's law must be included.

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