The solar chromosphere is the region between the Sun's surface and its hot, million-degree corona. Within this complex interface zone, only a few thousand kilometers deep, the density of the gas drops by a factor of about one million and the temperature increases from about five thousand to one million kelvin. Almost all of the mechanical energy that drives solar activity is converted into heat and radiation within this interface. Many physical processes shape the intricate system of solar magnetic fields, energetic particles, and radiation that power the corona. The solar wind itself has long been suspected of originating in this region, perhaps in the cooler "coronal holes," but identifying the precise origin sites required high spatial resolution observations.
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