| The occurrence regularity of great-storm Coronal Mass Ejection(CME)and its influence on the earth space environment are important issues to be studied in space weather.The auroras observed at low and middle latitudes in geographic coordinates are caused by drastic changes in the solar wind and the geomagnetic field.Solar eruptions are the main driving sources of geomagnetic activities,which have stronger southward component of magnetic field,faster proton velocity and higher proton density.Empirical formulae from DMSP satellite observations indicate that the equatorward boundary of auroral oval and the magnetic latitude of the equatorward boundary of auroral observations are positively related with the intensity of geomagnetic activity and geomagnetic field.Based on the millennia scale auroras recorded at low and middle geographic latitudes,this work uses the paleomagnetic field model of the corresponding time to deduce the correlation between latitude and geomagnetic disturbance,and to infer the existence of great CMEs and their correlation with solar activity.The aurora records used in this paper are from the General Collection of Astronomical Records in Ancient China,and the time range of the records is from 193 B.C.to 1911 A.D.,309 auroras had been recorded.In this work,a dipole magnetic field model CALS10 k.1b,which has been proposed by archeological magnetism for nearly ten thousand years,is adopted.The geomagnetic latitudes of the auroras observed in the year of recording are calculated based on the North Geomagnetic Pole(NGP)long-term variation model.According to the empirical relationship among the geomagnetic latitude of equatorward boundary of auroral oval,Dst index and magnetic field intensity of auroral oval,the auroras caused by the corotation interaction region(CIR)and medium and low intensity CMEs were excluded,and the auroras caused by great CMEs were identified.The results show that the geomagnetic latitude of China decreased rapidly after the shift of the NGP in 1500 A.D.This shift provides a good opportunity to study the existence of historical great magnetic storms.In this study,60 auroras caused by storms which have Dst index less than-350 n T were identified from 1518 A.D.to 1911 A.D.By comparing the observed time distribution of low latitude auroras caused by these great magnetic storms with the reconstructed sunspot number from 1610 A.D.to 1910 A.D.,it was found that these great CMEs occurred during the maximum and minimum periods of solar activity.These results support the distinct mechanism of super CME eruption during solar grand minimum..Based on the sunspot records in the "Chinese Ancient Astronomical Records General Collection",this paper analyzes the age without sunspots and auroral records.The four non-aurora and nonsunspot periods are highly consistent with the three solar minima reported in the study of cosmic ray isotopes.In addition,four new possible solar minima have been found.In this thesis,the Space Weather Model Framework(SWMF)is also used to calculate the position and area of the cusp and the settling ions flux through the cusp when the geomagnetic field and solar wind change significantly.For the current interplanetary magnetic field and the colatitude of the magnetic axis less than 15 degrees,a stronger geomagnetic field will produce a larger area of the cusp and a higher downward ion flux.When the absolute value of the residual latitude of the magnetic axis is larger than 15 degrees,different geomagnetic field intensity has different effects on the polar tip region in daytime and night.During the Maunder Minimum,the downward ion flux in the cusp is also lower than it is at present,but the cusp area was close to the present one.It suggests that during the Maunder Minimum,the range of auroral oval may have been closer to the present,but the brightness of the auroras and the frequency of auroras observed at low and middle latitudes may have been lower than current levels. |
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