ABSTRACT
Antarctica is a region of great importance for studies of geomagnetism and allied fields. The present-day geometry of the Earth's main magnetic field causes the high-latitude region of the atmosphere to be directly affected by the increase in magnetospheric energy during geomagnetic storms and substorms. Intense energy input from the magnetosphere can result in visually spectacular aurora and changes in the ionosphere that affect HF (high frequency) communication. Increases in the convective electric field and auroral particle precipitation produce intense currents in the ionosphere, which are monitored through magnetic field measurements. Changes in the ionosphere are also monitored using a riometer, which measures the strength of the 30-MHz galactic radio waves that impinge on the Earth's atmosphere and thereby gives information on the changes in absorption of this signal due to changes in the ionospheric electron density. Apart from the dramatic short-term changes in the geomagnetic field recorded at Antarctica, which may be attributed to external causes, it has emerged that the Earth's complex main magnetic field, which has its origin in the fluid outer core of the Earth at a depth of about 2900 km below the surface of the Earth, is also undergoing a systematic rapid decline in the Antarctic region. The Indian Institute of Geomagnetism (IIG) started geomagnetic field measurements in Antarctica during the first Indian Antarctic Expedition in 1981–1982. With the setting up of a permanent base at Dakshin Gangotri (DG) in 1983–1984, observations were taken on a regular basis with a proton precession magnetometer (PPM), fluxgate magnetometer, and riometer. The observations were shifted to Maitri in 1990 after the DG station was abandoned, and some additional instruments were deployed at Maitri. The observations have indicated the importance of the location of Maitri, being a subauroral location during magnetically quiet periods. Thus, attributes sometimes change, however, during magnetically disturbed times when magnetospheric effects expand spatially from their quiet time locations. A large decrease in the main magnetic field observed at Maitri is now emerging as important for monitoring the evolution of reverse magnetic flux patches due to physical processes occurring in the molten iron outer core of the Earth. The present review of studies in geomagnetism and allied aspects during the past 23 Indian Antarctic expeditions summarizes the observations made during such studies and their importance.
