Space and Atmospheric Physics

The ionosphere is a component of the upper layer of the Earth's atmosphere, ionised by solar UV and X-rays, and cosmic radiation to give free electrons at 50-1000 km altitude. It is the boundary of the atmosphere and space environments, shielding the Earth’s surface from x-rays which arise from solar flares, the radiation belts and, with the geomagnetic field, from particles in the solar wind.

We undertake research involving the monitoring and modelling of the Ionosphere to increase understanding of both long and very short term variations which can have significant effects on:

• Long-range communication and remote sensing at high frequency radio waves.
• Accuracy of GPS derived positions.
• Orbits of low-earth orbiting satellites due to atmospheric drag.
• Electrical components on satellites due to electrostatic charging.

The ionosphere is also the environment where visual phenomena occur such as aurora, meteors, noctilucent clouds, sprites and elves.

We focus on the development and exploitation of new radar, optical and GPS techniques for remote sensing of the atmosphere.

Ground-based radar and optical studies, explore the dynamics and structure of the atmosphere over a wide range of time scales. There is particular interest in the development of new hardware and data analysis techniques, as well as on data acquisition and interpretation.

Many of the techniques developed by the group have become widely adopted on a world-wide basis as the standard methods in the field.

We study winds, waves and turbulence in the lower atmosphere up to 15-20 km and obtained the first such measurements using a VHF wind profiler in the southern hemisphere. These radar systems are designed to be as versatile as possible, so that a wide range of experiments can be carried out. The large height range which can be covered enables the coupling of energy and momentum between different atmospheric regions to be investigated.

Other radar measurements of winds in the 60-100 km height range are made using MF (Medium Frequency) radars at a range of sites. Observations made using such systems at widely separated locations gives a global perspective to our investigation of atmospheric dynamics.

At any given moment, there is a steady stream of small and occasionally large debris colliding with Earth.

Heated by the hypervelocity impact with the atmosphere, meteors leave trails of evaporated material that are valuable tracers in the otherwise difficult to study upper atmosphere around 70-110 km above the surface.

The plasma produced during atmospheric entry by meteors is an excellent reflector of radio waves from radars. We take advantage of this by operating a number of radars across the world to study both the atmosphere and meteors themselves. This includes:

Atmospheric research

Radar detection of meteor trails enables the study of winds, temperature, and changes in density in the upper atmosphere. This helps us to understand small and large-scale variations in an otherwise inaccessible region of the atmosphere, improving our knowledge of changes in Earth’s climate, the impact of space weather events, and developing novel measurements to support spaceflight activities.

Astronomy

Meteors come from a variety of sources in the solar system, organised in both diffuse clouds responsible for a steady background and narrow filaments that produce occasional bursts of intense meteor shower activity. Radars meteor detections during day and night in any weather enable us to determine the original orbits of meteoroids, helping us understand the distribution and evolution of material in the solar system.

Numerical modelling

Computer simulations are an important tool in understanding the physical processes of meteors and the atmosphere. Constructing a model of a physical system enables researchers to test assumptions by comparing calculated predictions with observed data. Numerical modelling is used to assist in the development of better radar antenna arrays and signal processing, characterise the accuracy of wind measurements, predict the motion of solar system debris on astronomical time scales, explore the complex interaction of meteoric plasma with Earth’s atmosphere and magnetic field, among many other fields of research.

Ionospheric radars

The Space and Atmospheric Physics Group operates a 64kW Medium Frequency (VHF) radar at the Buckland Park field site. This radar obtains wind measurement from the lower ionosphere from 50 to 100 kilometres.

Ionospheric radars

The Space and Atmospheric Physics Group operates a 64kW Medium Frequency (VHF) radar at the Buckland Park field site. This radar obtains wind measurement from the lower ionosphere from 50 to 100 kilometres.

Boundary layer radars

The Space and Atmospheric Physics Group in collaboration with Atrad and Bureau of Meteorology operates a 20 kW, Boundary Layer - Tropospheric Radar (BLT), operating at 55 MHz, at the Buckland Park field site. This radar obtains wind measurements from 300 m up to 10 km (depending on atmospheric conditions).

Meteor radars

Meteor radars can be used to measure winds in the 70-110km height region; estimating the diffusion rate of ions - which is related to air temperature and pressure; and astronomical surveys of where meteors come from both within and outside the solar system.

Detailed studies of meteor radar detection are also leading to new insights into the density of the upper atmosphere and the composition of meteoric material that is deposited in the atmosphere.

Meteors are narrow trails of plasma that form behind bodies entering the atmosphere. Many objects are entering Earth’s atmosphere at any given moment, most of them about the same size or smaller than a grain of sand. These objects, called meteoroids, travel at speeds in excess of 10 km/s and are heated by collisions with air molecules to temperatures hot enough for evaporation to occur.

The evaporated molecules and atoms are travelling fast enough that further collisions with air molecules can knock electrons off. The mixture of free electrons and ions, called plasma, in a narrow trail behind the meteoroid reflects radio waves.  Using the right radio frequency, meteor trails are excellent targets for study with radar.

Most meteor radars used today are comprised of a single transmitting antenna and a receive array of five antennas. The receive antennas are arranged to form two perpendicular interferometer baselines. The angle to returning radio waves from meteor radar echoes is determined by comparing the phase of the radio waves on the different antennas.

Our radars operate in 33-55 MHz VHF portion of the electromagnetic spectrum and can detect as many as 35,000 meteors per day.

We operate radars at Buckland Park near Adelaide, and Davis Station in Antarctica, as well as with partner institutions at locations across the globe.

Photometers

A three-field photometer observes the atmospheric nightglow from the 557.7 nm atomic oxygen (O(1S)) and 730 nm hydroxyl (OH (8-3) Meinel) bands, at 97 and 87 km in altitude respectively.

The instrument was initially designed to study the characteristics of internal gravity waves in the mesosphere with periods of up to several hours. It has evolved to allow the determination of some much longer-term and more fundamental atmospheric parameters on the global scale, as well as providing a useful means of comparison with the other co-located instruments studying the same region.

Atmospheric airglow and its origin

At any location, and even on the clearest and calmest of nights, the Earth's sky isn't completely dark. Many would instinctively think that a phenomenon like the Auorora Australis or Borealis may be responsible for this; this is true, but such a thing is only observed in the regions of higher latitudes.

As a matter of fact, the Earth has its own natural light source ubiquitous in the upper atmosphere - a result of various chemical processes dependent on the atmosphere's temperature and dynamics. In the mesosphere-lower-thermosphere (MLT) region (altitude ~ 100 km), where the air pressure is roughly one millionth of that at the Earth's surface, the incoming solar radiation has sufficient energy to dissociate (ionise) the molecules constituting the atmosphere, resulting in this region being composed mainly of free electrons and ions.

Depending on the background temperature and pressure, these free electrons and ions may recombine to create neutral molecules. Given the large oscillations in temperature and pressure propagating through the atmosphere on a global scale at all altitudes (including those in the MLT) and the varying solar radiation intensity throughout a given 24-hour period, the composition of this region ends up being very dynamic.

The Radio Acoustic Sound System (RASS) system can be used in conjunction with their VHF radars to obtain temperature measurements from near ground to over 5 km. Actual coverage is very dependent on speaker placement and background winds.

• Emeritus Professor Iain Reid
• Emeritus Professor Bob Vincent
• Associate Professor Andrew MacKinnon
• Associate Professor Murray Hamilton
• Dr Joel Younger
• Professor Bruce Ward - Adjunct
• Associate Professor David Holdsworth - Adjunct: DST Group
• Associate Professor Trevor Harris - Adjunct: DST Group
• Associate Professor Manuel Cervera - Adjunct: DST Group
• Professor Stuart Anderson - Adjunct
• Associate Professor Andrew Klekociuk - Adjunct: AAD

• Dr Bronwyn Dolman - Visiting Research Fellow: ATRAD
• Dr Peter May - Adjunct Associate Lecturer: BoM
• Dr David Neudegg - BoM
• Dr Sujata Kovalam
• Dr Michael Hatch

• Simon Curtis - Lidar
• Andrew Spargo - Meteor and MF radar, spectrometer, photometer, satellite
• Andrew Heitmann - Ionospheric propagation and disturbance
• Tom Chambers
• Baden Gilbert
• Daniel Field
• Lenard Pederick

• Low: low mode
• High: high mode (low mode with extended acquisition range)
• SA: Spaced Antenna
• DBS: Doppler beam steering

• FCA: Full Correlation Analysis
• DAE: Differential Absorption Experiment

Aerospace airglow imagers

• Adelaide
• Alice Springs

CCD spectrometer

• Buckland Park