Science, Technology and Engineering

The project will investigate large-scale electric currents of millions of amperes that flow in the auroral ionosphere (auroral electrojet, shown on the left). The aims of this project are (1) to study the relationship between the electric currents and electric fields driving them and (2) to model the propagation conditions for radio waves passing through the region of intense currents/fields. The project involves analysis of the data from the stereoscopic over-the-horizon radars (OTHR) including two radars operated by La Trobe University in Tasmania and in New Zealand that measure electric fields in conjunction with the data from the ground-based magnetometers that detect the ionospheric electric currents. The modeling part of the project involves implementation of the radio ray-tracing simulations with the aim of determining the exact location of the ionospheric radar echoes relative to the electrojet current. This research will potentially lead to improvements in the OTHR radars’ ability to pinpoint echoes which is important in navigation and defense applications.

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Studies of plasma structures naturally occurring in the auroral ionosphere (click on the picture on the left) 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. Frequency agility of the SuperDARN radars also implies that the scale/wavelength dependence can be studied. The aim of this project is to investigate scale dependence of the ionospheric echo power and velocity utilising (1) historical data collected by several radars in the SuperDARN network and supporting instrumentation and (2) data collected in special experiments to be designed and implemented using Australian component of the SuperDARN, TIGER which currently consists of two radars in Tasmania and New Zealand operated by La Trobe University. The experimental results obtained are to be compared with theoretical predictions and previous studies with VHF and UHF radars. The candidate is expected to attain strong data-processing skills and solid understanding of the plasma physics involved.

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The coherent backscatter from magnetic-field-aligned auroral irregularities (radar aurora) in the decameter range (~12-m wavelength) is routinely detected by the HF radars such as TIGER radars (shown on the left) operated by La Trobe University. At the typical altitudes of coherent HF echo detection, the two-stream or Farley-Buneman (F-B) and gradient-drift (G-D) plasma instabilities are considered to be the two primary mechanisms of plasma structuring. The role that the plasma density gradients play in the irregularity generation, however, depends strongly on the altitude range in question. The aim of this project is to develop a general theory of the F-B and G-D instabilities that would be applicable to any altitude range within the ionosphere. As a first step a general dispersion equation is to be derived using plasma density and momentum conservation fluid equations. A dispersion equation is to be analyzed using analytical and numerical methods with the view of determining conditions under which the irregularity velocity would differ the most from that of the background plasma. Experimental evidence in support of the theoretical predictions is to be sought using the data collected by the TIGER radars.

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Coherent High Frequency (HF) radars such as SuperDARN are oblique-sounding radars with the typical angles of echo arrival of 10º-30º above the horizon and typical ranges along the radar beam (slant ranges r) probed of 180-3000 km. The SuperDARN radars are thus capable of detecting the echoes from a range of ionospheric altitudes h. Typically, the short-range echoes (r = 225-765 km) originate from the E region (h = 95-120 km), and the longer-range echoes (r = 765-3000 km) come from the F region (h = 180-400 km). These two bands of echoes are evident on the diagram on the left. This simplified picture however needs to be refined as the slant ranges of echoes of different origin often overlap and the boundaries strongly depend on geometry of observations (mainly location and orientation of the radar) as well as upon the geophysical conditions at the time of observations. The aim of this project is to identify the typical features and characteristics of the short-range E-region echoes as seen by the HF radars in view of applying this knowledge to development of algorithm for unambiguous identification of the E region echoes in the SuperDARN data. The Australian component of the SuperDARN network, TIGER, consisting of two closely located HF radars in Tasmania and New Zealand often observes echoes appearing and disappearing almost simultaneously within the near fields-of-view (r < 765 km) of both radars, which provides an excellent opportunity for this investigation. Additional insights can be obtained from the analysis of the data from other radars in the SuperDARN network, both in the Southern and Northern hemispheres. The project involves data analysis from the radars and supporting instrumentation (magnetometers, riometers, ionosondes, low-orbit and geostationary satellites). The candidate is expected to develop a solid understanding of the plasma physics of irregularity formation and to become proficient with the space physics data products and analysis techniques.

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Aurora borealis (northern light) and aurora australis (southern lights, shown on the left) are spectacular high-latitude phenomena originating from the atmospheric particles that, when being bombarded by the energetic particles from the solar wind, emit light at characteristic frequencies/wavelengths. The solar wind particles also ionize the neutral atmosphere creating pairs of ions and electrons. The enhanced ionization or electron concentration associated with the energetic particle precipitation can be detected by various instruments including riometers that measure the radio wave (cosmic noise) absorption (CNA) by electrons. During magnetospheric substorms the solar energy energy and particles stored in the magnetotail are quickly released creating vast auroral displays (left). This project aims at the investigation of the response time of auroral absorption to the substorm onset. This project involves the data analysis from the imaging riometers in Northern Scandinavia and at Australian Antarctic station, Davis. The candidate is expected to attain strong data processing skills and solid understanding of the ionospheric and magnetospheric physics involved.

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