A diagnosis of the plasma waves responsible for the explosive energy release of substorm onset

By Teo Bloch Comment Closed
During geomagnetic substorms, stored magnetic and plasma thermal energies are explosively converted into plasma kinetic energy. This rapid reconfiguration of Earth’s nightside magnetosphere is manifest in the ionosphere as an auroral display that fills the sky. Progress in understanding of how substorms are initiated is hindered by a lack of quantitative analysis of the single consistent feature of onset; the rapid brightening and structuring of the most equatorward arc in the ionosphere. Here, we exploit state-of-the-art auroral measurements to construct an observational dispersion relation of waves during substorm onset. Further, we use kinetic theory of high-beta plasma to demonstrate that the shear Alfven wave dispersion relation bears remarkable similarity to the auroral dispersion relation. In contrast to prevailing theories of substorm initiation, we demonstrate that auroral beads seen during the majority of substorm onsets are likely the signature of kinetic Alfven waves driven unstable in the high-beta magnetotail.   Paper: A diagnosis of the plasma waves responsible for the explosive energy release of...
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Nudging solar wind forecasts back towards reality

By Teo Bloch Comment Closed
In order to forecast space weather, it is necessary to accurately model the solar wind, the continually expanding solar atmosphere which fills the solar system. At present, telescopic observations of the Sun's surface are used to provide the starting conditions for computer simulations of the solar wind, which then propagate conditions all the way from the Sun to Earth. But spacecraft also make direct measurements of the solar wind, which provide useful additional information that is not presently used. In this study we use a simple solar wind model to develop a method to routinely "assimilate" spacecraft observations into the model and thus improve space‐weather forecasts. This data assimilation (DA) approach closely follows that of terrestrial weather prediction, where DA has led to increasingly accurate forecasts. We use artificial and real spacecraft observations to test the new solar wind DA method and show that the error in predicting the near‐Earth solar wind can be reduced by around a fifth using...
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Modelling asymmetric current sheets in Earth’s magnetosphere

By Luke Barnard Comment Closed
During a magnetic reconnection event, stored energy that had been bound up in stressed electromagnetic fields is released in the form of heat and the kinetic energy of particles. The NASA MMS mission is currently making diffusion-region measurements of these phenomena in the Earth’s Magnetosphere, with unprecedented levels of accuracy and resolution. Our work presents a theoretical model of a structure in space known as an asymmetric current sheet, such as the MMS mission may encounter in the magnetopause. The model can be implemented into particle-in-cell simulations of reconnection, with which to compare to the results from MMS satellite data. This will help us understand the fundamental physics of asymmetric magnetic reconnection. Exact Vlasov-Maxwell equilibria for asymmetric current sheets O. Allanson, F. Wilson, T. Neukirch, Y.-H. Liu and J.D.B. Hodgson, Geophysical Research Letters, 44, 17, 8685-8695 (2017) DOI: 10.1002/2017GL074168...
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