Physics
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008espm...12.3.30l&link_type=abstract
"12th European Solar Physics Meeting, Freiburg, Germany, held September, 8-12, 2008. Online at http://espm.kis.uni-freiburg.de/,
Physics
Scientific paper
The explanation of many astrophysical, solar ans space weather processes face the same conundrum: explaining how reconnection can be an active agent for energy exchanges in macroscopic systems. The ?rst problem is that the detailed study of reconnection leads to the conclusion that reconnection is a very localized process developing in tiny regions (called diffusion regions) within the overall system. However effective such a localized process may be, still how can it affect large fractions of the system energy? There is a need to explain how a vast area of magnetic ?eld and energy can undergo such a process when it takes place on very small scales. A suggestion has been made that reconnection might take place in large areas in the form of a cluster of many diffusion regions filling a significant area of the domain. This proposal is very attractive, but evidence for such a process is still lacking, either as direct observational evidence or as simulation demonstration.
A second dif?culty is to achieve the required rate of reconnection. Reconnection requires dissipative processes usually not present in a simple description of the plasma as a resistive ?uid: the level of resistivity present in the system is vastly insuf?cient to explain the observed rates. Reconnection can be fast on the microscopic scales or when the process of reconnection is driven by ?ows (spontaneously generated in the system or created externally).
We report here a possible mechanism capable of inducing a turbulent (meant here simply to imply a chaotic process) reconnection region encompassing a large scale portion of a macroscopic system and where reconnection aliments itself requiring no external ?ows to keep a fast rate of reconnection.
Within a MHD approach we ?nd magnetic reconnection to progress in two entirely different ways. The ?rst is well known: the laminar Sweet-Parker process. But a second, completely different and chaotic reconnection process is possible. This regime has properties of immediate practical relevance: (i) it is much faster, developing on scales of the order of the Alfven time, and (ii) the areas of reconnection become distributed chaotically over a macroscopic region. The onset of the faster process is the formation of closed-circulation patterns where the jets going out of the reconnection regions turn around and force their way back in, carrying along copious amounts of magnetic ?ux.
Reference:
G. Lapenta, Physical Review Letters, 100, June, 2008.
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