Research On The Statistical Characteristics Of Solar Filament Long-term Activity

The Sun is the nearest star to our earth, the only one high-resolution imag-ing observed and studied in the universe. It is the only source of light and heatindispensable for all life on the earth, maintaining a proper environment requiredfor human existence and all life activities on the earth. Therefore, the study onsolar activity and its varying pattern is very important for the research and ser-vice on the Sun-Earth relations, the research and prevention of some naturaldisasters. Filaments, one of the most basic activities phenomena in the solaratmosphere, can be used as makers of solar activity characterization in the chro-mosphere. Firstly, the filament background knowledge and the research status offilament long-term activity patterns are introduced briefly. Then the statisticalcharacteristic analysis of filament long-term activity is presented in detail. Themain results are as follows:1. In order to better understand the behavior of “rush to the poles”, we usedthe cross-correlation analysis and the wavelet transform methods to investigatethe periodic characteristics and the phase relationship of two groups of solar fila-ments at high latitudes observed from March1919to December1989. The lengthof the solar cycle derived from the continuous wavelet transform is a function oflatitude, but still shows a significant11-year cycle. The most significant periodsof the solar filaments, respectively at higher latitudes than50and60, are10.77and10.62years by using the wavelet transform method. The solar filaments athigher latitudes than50have a time lead of six months with respect to the onesat higher latitudes than60from the cross-correlation analysis. Diferent solarcycles exhibited diferent phase relationship between two parts of solar filaments.The analysis of the cross-wavelet transform also indicates that the solar filamentsat higher latitudes than50lead the ones at higher latitudes than60in the en-tire time interval. The relationship between the phase diference of two groups ofsolar filaments and the intensity of solar activity is also discussed. What’s more,the poleward shifting speeds are estimated. 2. Cross-correlation analysis and wavelet transform methods are used toinvestigate whether high-latitude solar activity leads low-latitude solar activity intime phase or not, using the data of the Carte Synoptique solar filaments archivefrom Carrington solar rotations (CRs)876to1823. From the cross-correlationanalysis, high-latitude solar filaments have a time lead of12CRs with respectto low-latitude ones. Both the cross-wavelet transform and wavelet coherenceindicate that high-latitude solar filaments lead low-latitude ones in time phase.Furthermore, low-latitude solar activity is better correlated with high-latitudesolar activity of the previous cycle than with that of the following cycle, which isstatistically significant. Thus, the results confirm that high-latitude solar activityin the polar regions is indeed better correlated with low-latitude solar activity ofthe following cycle than with that of the previous cycle, namely, leading in timephase.3. In the present study, we investigate the north-south asymmetry of solarfilaments at low (<50) and high (>60) latitudes, respectively, using dailyfilament numbers from January1998to November2008(solar cycle23). Wefound that the northern hemisphere is dominant at low latitudes for cycle23.However, a similar asymmetry does not occur for solar filaments at high latitudes.Thus, the hemispheric asymmetry of solar filaments at high latitudes in a cycleappears to have little connection with that at low latitudes. The results supportthat the observed magnetic fields at high latitudes includes two components: onecomes from the emergence of the magnetic fields from the solar interior and theother comes from the drift of the weak magnetic activity at low latitudes.4. We present a case study of two successive filament eruptions at thesoutheast limb of the Sun observed by Solar Dynamics Observatory (SDO) on2012April19. At the initial stage of the first filament (F1) eruption, one leg ofthe F1moved toward the second filament (F2) and swept the F2. The interactionbetween two filaments occurred. A CME was observed by SOHO/LASCO afterthe F1eruption. One of the bright flare ribbons and the dimming regions formedafter the F1eruption were found to move toward the F2. When the F1erupted,the large-scale overlying coronal loops of the F1were pushed out toward thesoutheast of the Sun by its expanding. During the eruption, the large-scale overlying coronal loops of the F2began to open toward the southeast. Followingthe opening of the large-scale overlying coronal loops, the F2became instable andbegan to erupt. A two-ribbon flare and a weak CME were formed after the F2eruption. These observations evidenced that the interaction of two filaments andthe opening of the large-scale overlying coronal loops caused by the F1eruptionare the most important reason that led to the F2eruption.