Statistical analysis of the total magnetic flux decay rate in solar active regions

We used line-of-sight magnetograms acquired by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory to derive the decay rate of total unsigned magnetic flux for 910 ephemeral and active regions (ARs) observed between 2010 and 2017. We found that: i) most of the ARs obey the power law dependence between the peak magnetic flux and the magnetic flux decay rate, $DR$, so that $DR\sim \Phi^{0.70}$; ii) larger ARs lose smaller fraction of their magnetic flux per unit of time than the smaller ARs; iii) there exists a cluster of ARs exhibiting significantly lower decay rate than it would follow from the power law and all of them are unipolar sunspots with total fluxes in the narrow range of $(2 - 8) \times 10^{21}$ Mx; iv) a comparison with our previous results shows that the emergence rate is always higher than the decay rate. The emergence rate follows a power law with a shallower slope than the slope of the decay-rate power law. The results allowed us to suggest that not only the maximum total magnetic flux determines the character of the decaying regime of the AR, some of the ARs end up as a slowly decaying unipolar sunspot; there should be certain physical mechanisms to stabilize such a sunspot

Order out of Randomness : Self-Organization Processes in Astrophysics

Self-organization is a property of dissipative nonlinear processes that are governed by an internal driver and a positive feedback mechanism, which creates regular geometric and/or temporal patterns and decreases the entropy, in contrast to random processes. Here we investigate for the first time a comprehensive number of 16 self-organization processes that operate in planetary physics, solar physics, stellar physics, galactic physics, and cosmology. Self-organizing systems create spontaneous {\sl order out of chaos}, during the evolution from an initially disordered system to an ordered stationary system, via quasi-periodic limit-cycle dynamics, harmonic mechanical resonances, or gyromagnetic resonances. The internal driver can be gravity, rotation, thermal pressure, or acceleration of nonthermal particles, while the positive feedback mechanism is often an instability, such as the magneto-rotational instability, the Rayleigh-B\'enard convection instability, turbulence, vortex attraction, magnetic reconnection, plasma condensation, or loss-cone instability. Physical models of astrophysical self-organization processes involve hydrodynamic, MHD, and N-body formulations of Lotka-Volterra equation systems.Comment: 61 pages, 38 Figure