ProfessorIver Cairns

Project Opportunities

Title: Explaining Correlations between Whistler Waves and Auroral Kilometric Radiation

Summary of opportunity:

Intense radio emissions are often correlated with whistler waves when observed on the ground, despite being produced by different processes in space. We will use numerical simulations to study the linear conversion at density gradients of radio emissions into several types of plasma waves, and then apply this fundamental theory to multiple regions of space.

Opportunity synopsis:

Radio antennas in the arctic regions and on Antarctica observe multiple types of radio emission and waves associated with solar activity and related space weather events in Earth’s magnetosphere. Auroral kilometric radiation (AKR), z-mode waves, and whistler waves are generated by energetic electrons in Earth’s auroral regions and observed on the ground and in space. Interestingly z-mode and whistler waves often occur in association with the AKR and have very similar timings and fine structures. The project will use an existing simulation code to study the linear mode conversion of z-mode waves into whistler waves and then radio emission in order to explain how the emissions reach the ground and why they are correlated. The conversion of z-mode waves into whistlers and of whistlers into radio emissions does not appear to have been studied before and should be widely applicable to other space contexts.

Project Opportunities

Title: Radio Emissions from the Edge of our Solar System

Summary of opportunity:

The two Voyager spacecraft have observed strong radio waves generated when shocks produced by solar activity cross into the local interstellar medium. This project will develop a detailed quantitative theoretical model for the generation and propagation of the radio emission from its source to the Voyager spacecraft for all the radio outbursts to date. The theory will be compared with observations from the Voyager and New Horizons spacecraft.

Opportunity synopsis:

NASA’s two Voyager spacecraft have observed strong levels of radio waves in the range 2 – 4 kHz that are stimulated when shocks produced by solar activity cross into the local interstellar medium. This region, where interstellar magnetic field lines are hung up on the helipause boundary that separates the solar and interstellar plasma, is called the plasma depletion layer (PDL). Special conditions should exist in the PDL. This project is to produce a detailed quantitative model for the generation and propagation of the radio emission between its source and the Voyager spacecraft for all the radio outbursts to date (whether inside or outside the solar system), to predict the properties inside the source region and of the PDL, and to compare the predictions with observations from the Voyager and New Horizons spacecraft. This involves (1) modernizing an existing analytic theory for the radio emissions, by Cairns (the proposed supervisor), Mitchell, and Zank, (2) combining the theory with state-of-the-art global simulations of the solar system’s interactions with the local interstellar medium with and without travelling shock, and (3) developing and using a ray-tracing code to predict the propagation of the radio emission from the source regions in the PDL to observers. The global simulations will be provided by colleagues Zank and Pogorelov at the University of Alabama at Huntsville in the USA, so the project will involve extensive Australia-USA collaboration, some travel, and be directly relevant to the long-awaited new NASA projects IMAP and Interstellar Probe.