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Catastrophic cooling of impulsively heated coronal loops View all abstracts by submitter

Cesar A. Mendoza-Briceno   Submitted: 2004-11-01 03:57

The physical mechanisms that cause the heating of the solar corona are still far from being completely understood. However, recent highly-resolved observations with the current solar missions have thrown clear evidence for frequent and very localized heating events near the chromosphere, which may be responsible for the observable high temperatures of the coronal plasma. In this paper, we perform one-dimensional hydrodynamic simulations of the evolution of a hypothetical loop model undergoing impulsive heating through the release of localized Gaussian energy pulses near the loop's footpoints.We find that when a discrete number of randomly spaced pulses is released, the loop heats up and stays at coronal temperatures for the whole duration of the impulsive heating stage provided that the elapsing time between successive heat injections is lesssim 215 s. For elapsing times longer than this critical value, coronal temperatures can no longer be maintained at the loop apex in spite of continued impulsive heating. As a result, the loop apex cools down catastrophically well below the initial state, reaching chromospheric temperatures (sim 104 K) and leading to the typical hot-cool temperature profile characteristic of a cool condensation. For a large number of pulses (up to sim 1000) having a fully random spatio-temporal distribution, the variation of the temperature along the loop is highly sensitive to the spatial distribution of the heating. As long as the heating concentrates more and more at the loop's footpoints, the temperature variation is seen to make a transition from that of a uniformly heated loop to a flat, isothermal profile along the loop length. Concentration of the heating at the footpoints also results in the more frequent appearance of rapid and significant depressions of the apex temperature during the loop evolution, most of them ranging from sim 1.5 imes 106 to sim 104 K and lasting from about 3 to 10 minutes. This behavior bears a tight relation with the strong variability of coronal loops inferred from {it SOHO} observations in active regions of the solar atmosphere.

Authors: Cesar A. Mendoza-Briceno, Leonardo Di G. Sigalotti & Robert Erdelyi
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Publication Status: ApJ, 2005, 624, 1080-1092 (in press)
Last Modified: 2005-05-09 03:18
Go to main E-Print page  Quasi-Periodicity in global solar radio flux at metric wavelengths during Noise Storms  Catastrophic cooling of impulsively heated coronal loops  Edit Entry  Download Preprint  Delete Entry 

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