The Role of Gurevich Ion Acceleration in Heating the Solar Corona

Abstract:

Our adherence to the notion of radial, thermal continuity from the photosphere to interplanetary space, and to the principle that all coronal heating is impulsive, helps to explain the sustained failure to explain the two major conundrums in our understanding of the Sun's atmosphere, namely the high temperature at its outer margins and its illogical thermal gradient. An alternative conspectus is that the atmosphere is structured in response to a sequence of three distinct heating regimes separated by thermal triggers, although this scheme does not rule out some degree of synchronisation between the various temperature signals (as with pericircadian biological rhythms) without necessarily impugning their fundamental independence. The first two units are the chromosphere, defined by ohmic heating, and the Transition Region, characterised by the Joule-Thomson effect. The present paper focuses on the third unit, the corona, which is dominated by plasma expansion in the near-vacuum of space, and suggests that the high temperature of its outer reaches is attained by heating driven by the acceleration of ions above their thermal energy rather than by waves, nanoflares or magnetic reconnection. The plasma expansion process, provisionally named here after its early proponent A.V. Gurevich, is activated by the sharp decline in radiative cooling that defines the upper limit of the Transition Region, and can be traced by way of the slow solar wind well into interplanetary space. It has been investigated in the wake of artificial satellites and of the Moon but remains beyond the reach of direct laboratory analysis though evidently not to computer modelling, and it may be investigated by analysis of the solar wind and of the GCR flux. The isotopic record, particularly that of ¹⁰Be, adds millennial depth to the narrative and reinforces the contrasting image of sunspots as mere symptoms of a deeper truth, just as elemental abundances and streamer rays confirm the dynamic kinship beween the corona and the slow solar wind.