The Test MIST Special Meeting, Southampton, March 26-28th, 2018


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In its own words MIST is “the community of Magnetosphere, Ionosphere and Solar-Terrestrial researchers working in the United Kingdom. We represent the interests of MIST scientists and hold meetings to showcase MIST science twice a year”.

It is a group which focuses on Space Science, both theoretically and empirically, covering everything from Solar physics [see Shannon’s work] to Planetary Atmospheres, incorporating data from many space-missions, ground-based measurements (for Earth) and models which underpin our current understanding.

MIST holds two meetings a year: Autumn MIST, a one-day meeting; and Spring MIST, a longer 2.5 day meeting (unfortunately these names lead to a lot of pictures of dewy mornings when using Google…).

Each Spring MIST meeting is given a name based on a local geographical feature, this year we were at Southampton University near the River Test. The “Special” is to honour MIST’s 50th anniversary. Less obvious to me was why people kept laughing when the name was mentioned. The only clue was “Any similarity to low frequency emissions on 198 kHz is purely coincidental”. If you like cricket, this may be obvious… but for the rest of us, it’s a reference to the cricket ‘Test Match Special’ radio broadcast. Good thing we’re scientists and not comedians.

This year, it’s safe to say that the Reading delegation took over the meeting. With 9 of us attending (6 presenting!) the Reading Space group was definitely very well represented. Mike Lockwood gave an excellent speech at the conference dinner on the importance of MIST to the community and how he has seen it evolve over the years. See below to read about what everyone presented.

The bi-annual meetings are excellent for keeping up with the current state of the UK’s space-science research as well as maintaining a more informal atmosphere due to the small nature of the community (there were around 60 people at Spring MIST ’18). I find that this all comes together to form a very inviting platform for those of us just starting out in research.

This year’s spring MIST group photo

Shannon Jones presented a poster, “Solar Stormwatch: Using citizen science to investigate CME distortions”.

Coronal mass ejections (CMEs) are the main drivers of hazardous space weather. We are using a novel dataset, created with the help of many citizen scientists through the Solar Stormwatch project, to investigate the effect of the solar wind on these storms. Participants track the shape of CMEs in images from the heliospheric imagers on board the twin STEREO spacecraft, providing an unprecedented level of detail (Barnard et al., 2017). We intend to use this data to extend the work of Savani et al. (2010), looking at how CMEs are distorted under varying solar wind conditions. 

Sarah Bentley gave a talk, “A solar wind-parameterised, probabilistic model of ground-measured ULF waves in Earth’s magnetosphere”.

Large scale ultra-low frequency (1-15 mHz) plasma waves in the magnetosphere are involved in the energisation and transport of radiation belt electrons, a hazardous environment for the satellites underpinning our everyday life. We can construct a statistical model predicting when and where we see these waves in the magnetosphere solely using causally correlated solar wind properties [Bentley et al., 2018]. Unlike existing models, this can be used probabilistically, so that instead of outputting a single value for the power in these waves at each location we can use a probability distribution. Sampling from these distributions turns out to be the best way of predicting total power over a longer event while using the mean values is the best way of predicting the power in the oncoming hour. Using these predicted power values we will eventually be able to predict the effect of these waves on radiation belt particles more precisely over a larger range of the magnetosphere.

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Oliver Allanson gave a talk, “Particle-in-cell models of diffusion due to whistler mode waves: comparing quasi-monochromatic to broadband waves”.

The momentum space diffusion of electrons due to whistler mode waves is a cornerstone of our current theoretical framework of acceleration (and loss) in Earth’s outer radiation belt. The quasilinear theory of wave-particle interactions provides us with a tractable method to estimate the amount of momentum space diffusion that occurs for a range of wave and ambient plasma conditions. Underlying quasilinear theory is the assumption that waves are broadband, incoherent, and of small amplitude. The right-handed whistler mode manifests in different ways throughout the outer belt: structured chorus, incoherent hiss, near monochromatic transmitter waves, lightning generated whistlers, and large amplitude nonlinear wave packets. It is possible that incoherent hiss is the only example that satisfies all of the formal requirements of quasilinear theory. We use particle-in-cell simulations (the EPOCH code) to model different cases, i.e. from near monochromatic to unstructured broadband, and from small amplitude to large. Through the use of various diagnostics, we explore whether the quasilinear diffusion description is a reasonable description of each case.

Clare Watt gave a talk, “The origin of the whistler-mode spectral “gap” at half electron gyro-frequency in the magnetosphere”.

Near-Earth space contains high-energy electrons, high-energy protons, and a host of different electromagnetic waves that exist over a wide-range of frequencies. Because of the Earth’s magnetic field, and the presence of the high-energy charged particles, the electromagnetic waves do not behave exactly like light in a vacuum, rather they are guided along and across the magnetic field, and interact with the electrons and protons to transport energy and momentum throughout the system. One type of waves are known as whistler-mode waves. They have frequencies of roughly 100-1000Hz and interact with the high-energy electrons in the outer radiation belt. These interactions are thought to be responsible for the energisation of the outer radiation belt. But the waves themselves have many fascinating and mysterious features. Decades of in-situ observations of the waves reveal a persistent frequency gap. Many theories have been put forward to explain the gap, but most rely upon special circumstances that are not guaranteed throughout space. Our recent physics-based simulations reveal a ubiquitous process that can explain the frequency gap, and what’s more, we have identified an independent observational test for the process. Our simulations revealed this new process because advances in computing and simulations allow us to use higher resolution than before – previous work had missed the important fine details of the interaction. At MIST, we reported not only on our simulation results, but also on the recently-published evidence from NASA Van Allen Probes and NASA Magnetosphere Multi-Scale that confirms our independent observational test.

Mike Lockwood gave a talk, “A homogenous aa index”.

Originally complied for 1868-1968 by Mayaud, and extended to the present day by ISGI (International Service for Geomagnetic Indices), the aa geomagnetic index has been a vital resource for studying space climate change over the past 150 years. However, there have been debates about the intercalibration of data from the different measuring stations. In addition, the effect of drift in geomagnetic latitude of the stations, caused by the secular change in the Earth’s field, has not been allowed for. As a result, the components of the aa index for the southern and northern hemispheres have drifted apart. We have corrected for these effects and also for the time-of-day and time-of-year sensitivity of the stations. The resulting indices for the northern and southern hemisphere now agree very closely and the aa index for all years shows a time-of-day and time-of-year “equinoctial” response pattern, as seen in the am index which has been compiled by ISGI from a much larger network of stations since 1959.

Chris Scott gave a talk, “The ionospheric response to intense bombing during World War II”.

There is an increasing number of case studies that demonstrate that the ionosphere can be perturbed from below. The explosion of the chemical plant at Flixborough in 1974 was sufficiently energetic that its effects were detected in the ionosphere (Jones and Spracklen, 1974), lightning has been shown to enhance ionospheric sporadic-E layer electron concentrations (Davis and Johnson, 2005) and there is much interest in the impact of earthquakes on the ionosphere (e.g. Astafyeva et al, 2013). The influence of the troposphere was also cited as the source of unknown variability in modelling work by Rishbeth and Muller-Wodarg (2006). Throughout the second-world war, routine measurements of the Earth’s ionosphere were made at Slough, UK. In this study we will use these data to investigate the impact on theionosphere of various bombing campaigns in order to determine the threshold above which such explosions can be detected in the upper atmosphere.

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