Daily records of the dynamics, ionization and structure of the Antarctic mesosphere from Scott Base

An investigation into the ionospheric D-region of the atmosphere was initiated in 1982 with the installation of radar equipment (Polarimeter and HF radar) at Scott Base. The radar operated by remote sensing of winds at altitudes of 60-120km. The radar is part of an international global scale radar network for the measurement of prevailing winds, atmospheric waves and atmospheric tides. The purpose of the project was to gain insight into, and an understanding of, the mechanisms which influence the behaviour of the polar mesosphere. The investigation is primarily concerned with the ionisation of the earth’s atmosphere in the height interval from 40km to 120km. This particular portion of the atmosphere includes the normally neutral stratosphere, the weakly ionized mesosphere and the E-region of the ionosphere. The investigation utilises a 2.9MHz backscatter radar system for which the high power pulse transmitter is located at Scott Base and the receiving instrumentation is installed at Arrival Heights. The reason for conducting this experimental programme in Antarctica is the fact that the earth’s magnetic field is almost perpendicular to the earth’s surface in the polar regions. Consequently, highly energetic charged particles from the sun or other extra-terrestrial sources are permitted to penetrate deep into the earth’s atmosphere where they release their energy and cause ionization of the atmosphere that is electrically neutral at temperate latitudes. Therefore, the main objectives of the programme are to obtain data from which the ionisation profile in the specified height interval of the atmosphere can be computed and to interpret these data in terms of the physical processes which govern the Antarctic mesosphere including: (1) Determination of the normal (undisturbed) photo ionization characteristics of the polar mesosphere on a diurnal basis during perpetual daylight conditions, (2) determination of the residual ionization during perpetual darkness, and its variation with solar or magnetic time, (3) determination of the scattering characteristics of mesospheric irregularities, (4) investigation of ionization (magnitude and height) during disturbed ionospheric conditions associated with auroral or polar-cap absorption and magnetic storms and the investigations of precursors to these events, (5) the investigation of phenomena which appear to be unique to the Antarctic mesosphere, such as the occurrence of a low altitude ionization layer, and its dependence on season of the year and local magnetic time and K-index, (6) the collection of data which pertain to ‘once only’ and unanticipated events, such as a massive solar flare, a severe magnetic disturbance, or a stratospheric warming event and (7) study of ionospheric winds and the effects of wave motion in the D-region. In order to achieve these goals, data are collected for twelve minutes every hour of the day and for every day of the year. Continuous records have been maintained and are ongoing. The same records are recorded from Birdlings Flat, Canterbury, New Zealand and are used for comparisons.