Modelling asymmetric current sheets in Earth’s magnetosphere

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

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?

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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Propagation of information within coronal mass ejections

[This originally appeared as a UKSP science nugget] Coronal mass ejections (CMEs) are huge, episodic eruptions of solar plasma and magnetic field which travel through the solar corona and out into the heliosphere. At Earth, they drive the most severe geomagnetic storms and thus are the primary focus of space-weather forecasting. Using white-light imagers, individual CMEs can be tracked continuously from the low corona, through the solar wind, all the way to Earth [1] and beyond. Such observations show CMEs apparently bouncing off each other [2] and deflecting off other coronal and solar wind structures [3]. Thus it is tempting to think of a CME as a coherent structure; a single – perhaps even quasi-solid — body, playing out a game of solar billiards. Such structural coherence has two physical requirements. Firstly, coherence requires a restoring force which can (at least partially) resist deformation by external factors. E.g., A bubble is a coherent body as surface tension communicates external forces across the entirety...
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