Instruments

• Introduction
• Riometers
• Magnetometers
• Searchcoil Magnetometer
• Fluxgate Magnetometer
• Optical Instruments

Magnetometers

Both the sun and the earth have magnetic fields, generated by electrical currents flowing inside the respective bodies. In addition to electromagnetic radiation (e.g., light, radiowaves, x-rays), the sun emits an electrically-charged gas (solar wind plasma) which carries the 'frozen-in' solar magnetic field along with it as it streams away from the sun. The plasma is composed almost entirely of electrons and protons. Perturbations in the plasma density/magnetic field propagate as Alfven waves. At 1-AU (astronomical unit - the mean distance of the earth from the sun) the solar wind plasma density is about ten particles per cubic centimeter, the solar wind speed is about 400 km/s, and the magnitude of the interplanetary magnetic field (IMF) is about 10 nT.

If there were no solar wind, the earth's magnetic field would be dipolar, but the pressure of the solar wind causes the simultaneous distortion of the earth's magnetic field, and deflection of the solar wind around the earth. Not surprisingly, the steady-state configuration resembles the 'bow shock' around the prow of a moving boat, so that designation has been used in the identification of the magnetospheric analog. The complicated steady-state configuration contains several distinct regions, as shown in the figure. This picture represents merely an 'average' view of the conditions that prevail in globally-defined regions during quiet conditions. The steady-state environment represents an equilibrium balance between the energy input from the solar wind, and processes which transfer energy within the magnetosphere, including energy deposition into the atmosphere. Because of the tilt of the earth's magnetic dipole axis (about 11.5 degrees), the magnetic pole performs a diurnal rotation around the geographic pole. This causes distortions in the steady-state magnetosphere, and these effects are accentuated by the seasonal tilt of the rotational axis with respect to the solar ecliptic plane (about 23 degrees). The picture during disturbed times is extremely dynamic, and the physical processes involved in the transfer of energy under these conditions are not well understood.

The investigation of solar/magnetic storm-time phenomena is the single principal purpose of much of the upper atmosphere research at South Pole Station. Magnetic substorms are responsible for the creation of various dynamic processes in the magnetosphere, including flux transfer events associated with magnetic merging regions in the boundary layer between the solar wind and the inner magnetosphere; precipitation of solar wind/boundary layer plasma directly into the atmosphere through the polar cusp/cleft; plasmoids in the magnetospheric tail which are associated with the energization and precipitation of energetic electrons into the nightside atmosphere, creating westward travelling surges, among other effects; pulsating auroras in the morningside auroral oval, caused by large-scale precipitation modulations with periods on the order of several minutes; expansion of the auroral oval to lower magnetic latitudes; mid-afternoon poleward surges of auroral structures into the polar cap from the auroral oval, etc. All of these phenomena are accompanied by perturbations in the terrestrial magnetic field; the surface magnetic field strength at auroral latitudes is about 60,000 nT, and perturbations of about 1000 nT are common during disturbed times, sometimes lasting for several days, but usually with time scales of only minutes or hours.