Random Walks of Magnetic Bright Points and Coronal Loop Heating

Details Random Walks of Magnetic Bright Points and Coronal Loop Heating Random Walks of Magnetic Bright Points and Coronal Loop Heating

May 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000aas...196.4903l&link_type=abstract

American Astronomical Society, 196th AAS Meeting, #49.03; Bulletin of the American Astronomical Society, Vol. 32, p.750

Statistics

Scientific paper

The random walks of small-scale ( ~ 0.2 arcsec) magnetic bright points (MBPs) in the lanes between photospheric granules are anomalous. The temporal growth of the q-th moment of the displacement r(t) is a power law with exponent q γ (q)/2. For normal, Gaussian walks γ (q)= 1 for all q. However, for the MBP walks on time scales < 45 minutes we find that γ (2)<1 and that γ (q) is a decreasing function of q. Many viable models for the heating of coronal loops are based on the additon of energy via twisting and braiding of magnetic flux lines by the random motions of their footpoints. If the MBPs are associated with such footpoints, then the statistics of their motions are directly relevant to coronal heating. For example, a number of models derive heating rates based on moments of the displacements and include the standard assumption that γ = 1. However, this assumption is wrong for MBPs, and the actual value of γ depends on exactly which moment enters the expression. All such models are therefore subject to modification. The result γ (2)<1 is a result of pauses in the MBP walks on all time scales (''fractal time'') up to ~ 45 min. This implies that the motions of an individual footpoint are not statistically stationary. This in turn means that the injection of energy into a given loop will be strongly variable and intermittent. This can be related to observations of the details of variability in coronal loop emissions, giving information on the locations of energy deposition and on time scales of energy release. We thus hope to further constrain acceptable heating models. This work was supported in part by NSF Grant ATM-9628882.

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