Nanoflares and coronal activity Nanoflares

typical flaring coronal loops observed trace in euv rays

telescopic observations suggest solar magnetic field, theoretically frozen gas of plasma in photosphere, expands semicircular structures in corona. these coronal loops, can seen in euv , x-ray images (see figure on left), confine hot plasmas, emissions characteristic of temperature of 1 few million degrees.

many flux tubes relatively stable seen in soft x-ray images, emitting @ steady rate. flickerings, brightenings, small explosions, bright points, flares , mass eruptions observed frequently, in active regions. these macroscopic signs of solar activity considered astrophysicists phenomenology related events of relaxation of stressed magnetic fields, during part of energy have stored released particle kinetic energy (heating); via current dissipation, joule effect, or of several non-thermal plasma effects.

theoretical work appeals concept of magnetic reconnection explain these outbursts. rather single large-scale episode of such process, though, modern thinking suggests multitude of small-scale versions reconnection, cascading together, might better description. theory of nanoflares supposes these events of magnetic reconnection, occurring @ same time on small length-scales wherever in corona, numerous, each providing imperceptibly small fraction of total energy required in macroscopic event. these nanoflares might resemble tiny flares, close 1 each other, both in time , in space, heating corona , underlying many of phenomena of solar magnetic activity.

episodic heating observed in active regions, including major events such flares , coronal mass ejections provoked cascade effects, similar described mathematical theories of catastrophes. in hypothesis solar corona in state of self-organized criticality, stressing of magnetic field should enhanced until small perturbation switches on many small instabilities, happening occurs in avalanches.

one of experimental results cited in supporting nanoflare theory fact distribution of number of flares observed in hard x-rays function of energy, following power law negative spectral index. sufficiently large power-law index allow smallest events dominate total energy. in energy range of normal flares, index has value of approximately -1.8 . actually, though, negative spectral index larger 2 required in order maintain solar corona via nanoflare hypothesis

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