GRID-SITES: Gridded Solar Iterative Temperature Emission Solver for Fast
  DEM Inversion

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Abstract

The increasing size of solar datasets demands highly efficient and robust analysis methods. This paper presents an approach that can increase the computational efficiency of differential emission measure (DEM) inversions by an order of magnitude or higher, with the efficiency factor increasing with the size of the input dataset. The method, named the Gridded Solar Iterative Temperature Emission Solver (Grid-SITES) is based on grouping pixels according to the similarity of their intensities in multiple channels, and solving for one DEM per group. This is shown to be a valid approach, given a sufficiently high number of grid bins for each channel. The increase in uncertainty arising from the quantisation of the input data is small compared to the general measurement and calibration uncertainties. In this paper, we use the Solar Iterative Temperature Emission Solver (SITES) as the core method for the DEM inversion, although Grid-SITES provides a general framework which may be used with any DEM inversion method, or indeed any large multi-dimensional data inversion problem. The method is particularly efficient for processing larger images, offering a factor of 30 increase in speed for a 10 megapixel image. For a time series of observations, the gridded results can be passed sequentially to each new image, with new populated bins added as required. This process leads to increasing efficiency with each new image, with potential for a \(\approx\)100 increase in efficiency dependent on the size of the images.

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Energy release in the solar corona from spatially resolved magnetic braids.

J. Cirtain, L Golub, A Winebarger … (2013)

It is now apparent that there are at least two heating mechanisms in the Sun's outer atmosphere, or corona. Wave heating may be the prevalent mechanism in quiet solar periods and may contribute to heating the corona to 1,500,000 K (refs 1-3). The active corona needs additional heating to reach 2,000,000-4,000,000 K; this heat has been theoretically proposed to come from the reconnection and unravelling of magnetic 'braids'. Evidence favouring that process has been inferred, but has not been generally accepted because observations are sparse and, in general, the braided magnetic strands that are thought to have an angular width of about 0.2 arc seconds have not been resolved. Fine-scale braiding has been seen in the chromosphere but not, until now, in the corona. Here we report observations, at a resolution of 0.2 arc seconds, of magnetic braids in a coronal active region that are reconnecting, relaxing and dissipating sufficient energy to heat the structures to about 4,000,000 K. Although our 5-minute observations cannot unambiguously identify the field reconnection and subsequent relaxation as the dominant heating mechanism throughout active regions, the energy available from the observed field relaxation in our example is ample for the observed heating.