In recent years the main focus of my research has been on radar backscatter from the auroral E-region ionosphere, what is often called radio or Radar Aurora.

What is it?
The visual Aurora, or Northern Lights, is produced when energetic electrons (and sometimes protons) spiral downwards along the earth's magnetic field and strike the atoms and molecules of the atmosphere; this causes them to glow at heights of 100 to 200 km (and sometimes higher) above the surface of the earth. These downward beams of particles are usually accompanied by strong electric currents flowing horizontally in the ionosphere at heights of about 100 - 120 km. If these currents become sufficiently intense they become unstable, and wave-like density fluctuations develop in the ionosphere having wavelengths in the range from tens of metres to a few centimetres.

Diagram of radar reflection from aurora
Such plasma instabilities are capable of strongly reflecting radio waves having comparable wavelengths (for direct backscatter, the plasma wavelength causing the reflection is exactly half the radar wavelength), so it is possible to study these instabilities by pointing a radar towards the ionosphere in locations where aurora occur. The first observations of radar aurora were made in the 1940's, shortly after the invention of radar. Radars operating at frequencies between 50 MHz (plasma wavelength 3 m) and about 400 MHz (plasma wavelength 38 cm) are commonly used to study the radar aurora, but echoes have also been detected at higher and lower frequencies.

My particular interest - large magnetic aspect angle observations

Large aspect angle scattering
The simplest theory of these plasma instabilities predicts that they should be detected when the radar is pointed almost exactly perpendicular to the direction of the earth's magnetic field. As soon as the radar beam makes an angle of more than 2 or 3 with the plane perpendicular to the earth's magnetic field, that simple theory predicts that no radar echoes should be detected. However, for many years radars in Canada have commonly obtained auroral echoes at magnetic aspect angles (as this angle is called) which can be as large as 10 or 20. Recently my research has concentrated particularly on these large-aspect angle radar auroral observations. This is an interesting area of study, because the phenomenon is inherently non-linear, and theories which relate to these observations are just being developed.