Science, Technology and Engineering

Studies of plasma structures naturally occurring in the auroral ionosphere have traditionally attracted a lot of interest in such areas as communications, navigation, plasma physics. Modulations in the free electron concentration are caused by various plasma instability processes driven by the large-scale plasma density gradients, electric fields, neutral atmosphere motions. These modulations or waves are routinely detected by the over-the-horizon radars such as SuperDARN, which provides an excellent opportunity for studying ionospheric waves under a wide range of conditions. Coherent radars detect backscatter from magnetic-field-aligned irregularities or waves that also act as tracers of the plasma flows in the ionosphere and magnetosphere. Studies of auroral irregularities involve data analysis from variety of sources such as coherent radars, plasma drift-meters, magnetometers, etc. Satellite communication and positioning systems such as GPS are adversely affected by scintillations, random fluctuations in radio signal amplitude and phase caused by the ionospheric irregularities. A detailed knowledge of the irregularity production mechanisms is required in order to predict scintillation occurrence.

The convection studies with ground-based instruments such as SuperDARN radars have several advantages such as global coverage and relatively good spatial and temporal resolution. The combined SuperDARN viewing area at present covers most of the auroral zone in both the Northern and Southern hemispheres. The Australian component of the SuperDARN, TIGER, which consists of the two radars in Tasmania and New Zealand (left), is operated by La Trobe University and capable of making observations in the subauroral region of the Earth's ionosphere. This capability is especially important since the subauroral phenomena such as subauroral flow channels, are relatively poorly understood. An example of the longitudinally extended channel-like subauroral regions of enhanced electric fields/plasma convection observed by the TIGER radars is shown on the left. The subauroral plasma flow channels are believed to originate from the magnetospheric-ring-current-induced electric fields during disturbed conditions that map onto the ionospheric low conductivity zone (trough) equatorward of the auroral high conductivity zone (auroral oval) with positive feedback reinforcing the ionospheric part of the current. It is thus important to understand the subauroral flow channels as they are one of the most dramatic manifestations of magnetosphere-ionosphere coupling.

Besides propagation conditions, the HF scatter is affected in a significant way by the radio wave absorption. The bulk of auroral absorption is due to energetic (>20 keV) electrons ionising the neutral gas at D/E-region heights. In the polar cap, solar flares produce greatly enhanced absorption causing blackouts in the radio communication. There is just one problem that needs to be investigated in the context of the space weather. During the substorms, the precipitating particles from the magnetotail cause similar, although less dramatic, effects in the upper atmosphere. My work is also focused on the investigation of various processes associated with the energetic particle precipitation in the high-latitude ionosphere. It involves data analysis from the imaging riometers (the IRIS system in Finland is shown on the left), magnetometers, and radars, as well as particle detectors and analysers. In order to distinguish between different precipitation mechanisms the principal approach is to combine the data from ground- and satellite-based instruments.