Coronal heating

Abstract

The energy flux required to maintain the radiation emitted by the quiet corona in closed field regions is about the same as that needed to drive the fast solar wind on open field lines (10 6 ergs/ cm −2 sec). At deeper levels, where the temperature is less than 2 10 5 K, there is no great difference in the morphology between the supergranules and network in closed and open field regions. It is therefore reasonable to presume that the heating process for the quiet closed corona is the same as in the high speed wind emanating from coronal holes. It is our view that the heating process is a consequence of small-scale flare activity in or near network boundaries and is mainly the result of fresh magnetic flux being pushed into the network from its sides by the large-scale convection associated with supergranules. The consequences of small-scale flare activity are that there should be a continual production of waves, energetic particles and hot rapidly moving plasma. In particular the wave spectrum may contain a large amount of power at (relatively) high frequencies which can be converted into heat by ion-cyclotron absorption. We show that it is possible to obtain a reasonable picture of the temperature structure of the quiet corona in closed field regions and the fast solar wind using these ideas.