MIST

Magnetosphere, Ionosphere and Solar-Terrestrial

Latest news

MIST recognised in 2018 RAS awards

MIST Council would like to congratulate those who have been recognised for contributions to the field by the Royal Astronomical Society recently, but particularly we would like to congratulate those members of the MIST community who are to be honoured at the next National Astronomy Meeting.

Emma Bunce has won the Chapman Medal for outstanding contributions to the understanding of the magnetospheres of gas giants, Matt Taylor has won the Service Award for his exceptional work in co-ordinating and contributing to ESA's Rosetta mission, and Jim Wild has been awarded the James Dungey lectureship for his excellent and highly relevant work on substorms and reconnection in the magnetotail. We would also like to congratulate Kerri Donaldson Hanna for winning the Winton Award for planetary science.

MIST Council applauds each of the winners, alongside the other academics who will be recognised in Liverpool this spring!

More details are available at the RAS website.

New MIST councillors in 2017

Congratulations to Jasmine Sandhu and Jonny Rae, both at MSSL, who have been elected (and, in Jonny’s case, re-elected) to MIST Council. They join Ian McCrea (Chair - RAL), Sarah Badman (Lancaster), Luke Barnard (Reading) and John Coxon (Southampton), all of whom continue in their posts.

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Rishbeth Prizes 2017

Congratulations to Jade Reidy (University of Southampton) and Mervyn Freeman (British Antarctic Survey) for winning this year's Rishbeth prizes for their presentations at the National Astronomy Meeting at the University of Hull this July.

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Nigel Wade

Nigel Wade
Nigel Wade - University of Leicester

It is with deep sadness that we have to inform the MIST community of the untimely death after a short illness of Nigel Wade who worked in the Radio and Space Plasma Physics (RSPP) group at Leicester for over 30 years.

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New Members of MIST Council

After a hard-fought campaign by the five candidates, the results of the MIST Council elections are now in!

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The Broadband Excitation of 3-D Alfvén Resonances (FLRs) in a MHD Waveguide

By Tom Elsden, Department of Mathematics and Statistics, University of St. Andrews, St. Andrews, UK

Field line resonance (FLR) has been the theoretical mechanism used to explain a myriad of ground and spaced based observations of ultra low frequency (ULF) waves in Earth’s magnetosphere. FLR is a plasma physics process whereby energy from a global oscillation (fast mode) can be transferred to local oscillations along magnetic field lines (Alfvén mode), where the fast mode frequency matches the local Alfvén frequency. This process was first studied analytically where the plasma was only inhomogeneous in the radial direction (mathematically 1D) [Southwood, 1974, Chen and Hasegawa, 1974] and has since been extended both analytically and numerically to more complicated systems [e.g. Lee and Lysak, 1989, Chen and Cowley, 1989, Wright and Thompson, 1994, Russell and Wright, 2010].

A feature of FLRs in complicated geometries, such as a dipole, is that the poloidal (radial) and toroidal (azimuthal) Alfvén frequencies are different [e.g. Radoski, 1967]. This infers that the location where the FLR will occur is dependent on the polarisation of the Alfvén wave. This property has recently been explored theoretically in 3D [Wright and Elsden, 2016] and forms the basis of this current work. The magnetosphere is asymmetric and therefore requires an understanding of FLR in 3D. We look at wave coupling in an excessively asymmetric waveguide in order to study the physics clearly.

The figure below taken from Elsden and Wright [2018], displays cuts in the equatorial plane from a 3D MHD waveguide simulation using a 2D dipole magnetic field geometry. In each panel, the x-axis is the radial direction (α) and the y-axis the azimuthal direction (β), and the density varies with azimuth. The left panel shows the energy density (dimensionless units) integrated along a field line, showing an accumulation of energy along curved resonance paths, where the FLR polarisation is between poloidal and toroidal. The middle and right panels show the square root of the kinetic energy in the equatorial plane, revealing ridges which develop by phase mixing in 3D. We find that with a broadband driver it is the natural fast waveguide modes which drive FLRs. Such modes are fairly insensitive to the form of the driver, and hence the resonances are seen at the same locations for many different driving stimuli. This means that the resonances are a property of the medium, and can hence be used as a seismological tool to infer properties of the equilibrium. Finally, the key point is that traditionally FLRs are regarded as having a strictly toroidal polarisation. However, here we have shown in 3D that they can have other polarisations.

Elsden, T. and A. N. Wright (2018), The Broadband Excitation of 3D Alfvén Resonances in a MHD Waveguide, J. Geophys. Res. Space Physics, 123, doi:10.1002/2017JA025018

Figure: Left: Energy density integrated along a field line. Black dashed line represents a theoretical prediction of the main FLR location. Middle: Square root of the the kinetic energy in the equatorial plane. Right: Same as middle but annotated for use in other plots in the paper.