Do The Solar Flares Originating From An Individual Active Region Follow A Random Process Or A Memory-dependent Correlation?

Solar flares,with energies ranging from 10²⁸erg to 10³²erg,are the sudden mag-netic energy release in the solar atmosphere.The forecast of solar flares is one key issue of space weather and has been studied for decades.However,there is still some debates about whether deterministic forecasting is possible if the flare occurs randomly,as ex-pected by the self-organized criticality?SOC?system.It is therefore necessary to know whether the occurrence of a flare is related to a previous event or is a stochastic process.From a statistical point of view,the waiting time distributions?WTDs?provide a useful tool to understand the correlation of sequential eruptions.We investigate the waiting time statistics of solar flares both in a flare-productive active region?AR?of the solar cycle 24 and in a 3D magnetohydrodynamic?MHD?simulated active region.The statistical models of a discrete random process and a con-tinuous memory-dependent process are applied to interpret the flare waiting time dis-tributions.Our results indicate that the flare occurrence in an individual active region maintains a certain amount of memory,probably arises from the MHD turbulence rather than from the intermittent avalanches in a self-organized criticality system.It differs from the occurrence of‘super flares'when treating the star/Sun as a single nonlinear system.The thesis is organized as follows:We first present a brief background of solar and stellar flares in Chapter 1.In Chapter 2,we introduce the basic concepts of the SOC,and its applications performed by numerical cellular automaton and frequency distributions of flares.In Chapter 3,we show the evolution of the AR 12673 and a simulated active region,and investigate the statistics of flare occurrence.In Chapter 4,we further analyze the flare WTDs,which are then fitted with statistic models of both a discrete random process and a continuous memory-dependent process,respectively.The Kolmogorov-Smirnov?K-S?test is applied to examining the reliability of the Poisson hypothesis.Chapter 5 is dedicated to the summary and perspectives.