The role of dynamic brightenings in coronal heating

C. E. Parnell*

*Corresponding author for this work

Research output: Contribution to specialist publicationArticle

6 Citations (Scopus)


Back in the 70s, Levine, and then, in the 80's, Parker, suggested that multiple small-scale events may be the source of the corona's background heat. These events, named nanoflares and microflares due to their energy content with respect to a large flare, can, to a certain extent, now be detected. The key question is, are there enough nanoflares/microflares to heat the corona? Nanoflares, microflares and large flares are all assumed to follow a power-law distribution. Therefore the focus has been to try and find the index of this power law and, hence, determine the probability distribution function of (nano/micro)flares. Many authors have attempted to answer this question, but all have failed to come up with the definitive answer. Here, the reasons why this question has caused so many problems are given including an explanation of what the real sources of errors are in the estimates of the power-law index. Furthermore, the alternative method of indirect detection of nanoflares is discussed. It is found that for a single data set the power-law index can be estimated, by making reasonable assumptions, to lie anywhere between 1.5 and 2.6! With the current data and our current understanding of the physical parameters of the corona it is not possible to rule out any of the above values for alpha and, therefore, the technique of determining the importance of nanoflares using direct detection to find the slope of the power-law distribution is not feasible. This, however, does not mean that nanoflares and microflares are not important for coronal heating. In deed, it has recently been discovered that the quiet-sun coronal magnetic field breaks and reconnects all its connections in a time of just 1.4 hours. Clearly, this mass of field connectivity changes is continuously injecting energy into the corona and is likely to be the source of numerous weak events that cover the entire quiet sun.

Original languageEnglish
Number of pages8
Specialist publicationEuropean Space Agency, (Special Publication) ESA SP
Publication statusPublished - 1 Dec 2004


  • Sun: Corona Heating


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