Aura Characteristics Of Geomagnetic Storm Intensity Of Galactic Cosmic Rays

More and more researches have shown that most of the intense geomagnetic storms are caused by fast coronal mass ejections in interplanetary space (ICMEs). Though the ACE satellite can provide solar wind data in almost real time for prediction of geomagnetic storms, the time interval is too short (shorter than 30-min) for effective predictions of major geomagnetic storms. This situation can't meet the needs in practical use. So it is worthwhile to find ICMEs much earlier.When structures of CMEs are traveling in the interplanetary space and towards to the earth, some galactic cosmic ray (OCR) may penetrate through the structures or be refracted by them before reaching the earth's surface. Because OCRs' speed is very high, so they reach the earth's surface much earlier than the CMEs. It is the very reason that many scientists try to make the prediction of geomagnetic storms by analyzing GCRs variation properties before the commencement of a geomagnetic storm.Many scientists have made efforts to study the relationships between the events of CMEs and GCRs' intensity variation. There are mainly two kinds of GCRs properties used to predict geomagnetic storms. One of them is GCRs' anisotropy and the other is GCRs' spectrum. Though many results have been obtained so far, it is still in the research stage and far from being used in practical predictions.This paper analyzed the data obtained at McMurdo and Thule neutron monitor (NM) stations and at Guangzhou muon monitor station during the CME event in March 1991. The results show that in this event when the CME structure passed the earth, it was shifted to the earth's southern hemisphere and the strongest magnetic structure associated with the CME passing the earth at about 2000UT, March 24.1991. We also made a statistical study on precursors appeared in GCRs before major and large geomagnetic storms only by using the two cusp stations' NM data obtained at McMurdo and Thule. The statistical results show that there are about 66.7% geomagnetic storms with precursors in GCRs. We can roughly judge the CMEs' direction when passing through the earth by using the two NM station data. In addition, the study shows that the CMEs' traveling direction is also an important factor, which influence the intensity of the geomagnetic storms.We also analyzed GCRs data from Beijing super-neutron-monitor (SNM) by using FFT and power spectrum method. The data were collected before the occurrence of several geomagnetic storms. The results show that there are really obvious scintillation in GCRs intensity at the periods of 10-60 minutes as expected by many scientists, such as Dorman, et al.Then we analyzed the data observed at Beijing SNM between two solar cycles' transitional phases by using wavelet method. The wavelet function is Morlet wavelet. The results can show when the 24-hour period of the GCRs disappeared and when they emerged again. We also analyzed the 27-day periodicity of the GCRs' intensity. We still analyzed the time-frequency variation properties of the data before several selected geomagnetic storms. The result shows that the GCRs' intensity with period of 16-32hours increased remarkably for those events that OCRs intensity increased before the geomagnetic storms. The OCRs intensity with the periods of 32-64 hours increased remarkably for those events that OCRs intensity decreased before the geomagnetic storms, while the intensity of OCRs with the periods shorter than 24-hour are not obvious.Because catastrophic space weather events occur in general very suddenly, such as geomagnetic storms with sudden commencements. Forbush decrease (Fds) in OCRs intensity is also a kind of sudden event. The properties of these sudden events' are very evident. The CMEs traveling in the interplanetary space may also affect the OCRs intensity suddenly, such as the CME in Jan. 1997. Comparison with the Fds, the OCRs sudden variation degree is less remarkable and often is very weak, so it is usually not easy to find such kind of variation. By using wavelet method, for the firs...