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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Forecast uncertainty in the near-Earth solar wind conditions

By Luke Barnard Comment Closed
Long lead-time space-weather forecasts require accurate prediction of the solar wind conditions in near-Earth space. The current state-of-the-art involves coupled numerical models initialised using photospheric magnetic field observations. This deterministic approach means there is no estimate of forecast uncertainty. Large ensembles with perturbed boundary conditions aren’t really feasible due to computational expense.  We have developed a method for producing a large ensemble of near-Earth solar wind conditions using the numerical model output with a simple 1-dimensional solar wind model (http://onlinelibrary.wiley.com/doi/10.1002/2017SW001679/full). This approach produces a probabilistic solar wind forecast which accurately captures the forecast uncertainty. ...
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How much magnetic flux does the heliosphere contain?

By Luke Barnard Comment Closed
There is no direct means to measure the amount of magnetic flux dragged out from the corona by the solar wind to form the “open” solar flux (OSF) component which forms the heliosphere.  If we start at the photosphere and work upwards, the estimate of OSF is strongly technique dependent. If we start with in situ spacecraft data, there are ambiguities about the amount of twisting up of magnetic flux, which means that the resulting OSF estimate varies with the time resolution of the data used. In a new study published in JGR (http://onlinelibrary.wiley.com/doi/10.1002/2017JA024631/full), we show how suprathermal electron observations can be used to unambiguously determine the open flux from in situ observations.  There was an approximately factor 2 variation in the flux content of the heliosphere from the solar maximum of cycle 23 to the subsequent solar minimum. ...
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