Analysis On The Temporal-spatial Distribution Characteristics Of Geomagnetic Activity Index Vr And Primarily Study On Their Mechanism

The aspect of monitoring and prediction of geomagnetic disturbances is one of the fundamental works in geomagnetic observation and study. In daily work, we often use geomagnetic index to describe the overall intensity of geomagnetic disturbance in every period or grade the intensity of a certain magnetic disturbance. There are no fewer than 50 geomagnetic indices nowadays, and Kp index is the most widely used index. However, In the process of data analyzing, we found that even in quiet time there are still a few magnetic disturbances existed when the Kp indices are very small. In addition, these disturbances can be easily identified from the minute values of the geomagnetic element but there is no index to describe it. Therefore, we put forward a new magnetic activity index so called Vr, (Variation, the standard deviation of the first differences of magnetic field), which is used to describe the high frequency magnetic disturbances.Based on the analysis of Vr index of H and D(VrH and VrD) from data of 41 geomagnetic observatories in China and 4 geomagnetic observatories abroad in 2008～2010, both temporal and spatial variation characteristics of VrH and VrD were observed. For temporal variations, the VrH and VrD showed 27 solar-cycle recurrences, and the VrD showed significant seasonal variation while the VrH did not, VrH was related to solar wind speed (SWS), and their correlation coefficients were 0.97,0.70 and 0.88. VrD with seasonal variation removed was also related to SWS, and their correlation coefficients were 0.96,0.77and 0.5(The low relative coefficient in 2010 was affected by unexplained anomaly change of Vr in March). For spatial variations, within mainland China, VrH and VrD also increased with latitude. Meanwhile both local-time dependences and an obvious dusk-dawn asymmetry existed, which might be related to the asymmetric ring current, the partial ring current and the field-aligned current. The studies suggested that Vr index be used for illustrating fast variation of geomagnetic field, and revealed impact of SWS, partial ring current and field-aligned current on geomagnetic field.