V_r:A new index to represent the variation rate of geomagnetic activity

By calculating the hourly standard deviation of the first-order differences of the horizontal geomagnetic com- ponent minute data, a new index Vr to represent the variation rate of the geomagnetic field was introduced. Vr-indices show similar trends in the temporal change at different observatories and have simultaneous peak values at the observatories cov- ering a large span geographically, which reveals that the source of geomagnetic disturbances represented by Vr is in the mag- netosphere. Based on the comparison among Vr, Kp and ap, it is found that generally Vr changes linearly with Kp and ap, which means that the rapid changes of magnetic field usually exist together with magnetic disturbances. But there are excep- tions. As Vr can be easily produced by individual observatory in quasi real time and is more sensitive to the variation rate of geomagnetic field rather than the field itself, it can be expected to serve for monitoring or predicting the geomagnetic-induced event in a quick and intuitive way.

Study of marine geomagnetic diurnal variation correction based on Wavelet Transform

Based on the existing geomagnetic diurnal variation theory and correction method,this paper makes a comprehensive analysis of the international geomagnetic quiet diurnal variation by Fourier Transform and one-dimensional Continuous Wavelet Transform.The frequency band greater than 0.2 Hz is the embodiment of the geomagnetic disturbance field in the frequency domain.Discrete Wavelet Transform is used to separate the variation,thus improving accuracy of the existing geomagnetic diurnal variation correction method.According to the characteristics of variation and Discrete Wavelet Decomposition,Sym8 wavelet is selected as the basic wavelet to decompose the data at 7 layers.The long-term and short-term variation of geomagnetic diurnal variation are effectively separated from the geomagnetic disturbance part under the condition of ensuring the fidelity.Compared with the results of Fourier Series decomposition and low-pass filter,the processing effect of Discrete Wavelet Transform is better.The effective separation and correction of short-term,long-term variation and geomagnetic disturbances can improve the quality of diurnal variation correction in marine geomagnetic measurement,reduce the error accumulation in the process of marine geomagnetic data processing,and improve the scientificity and accuracy of the current diurnal variation correction methods.

Electromagnetic response function for the semi-annual variations estimated by the single-station method using the night-time values of the geomagnetic fields

The geomagnetic night-time values were used to estimate the electromagnetic response function Q1 for half-year period. If the spatial structure of the source field can be described by the approximation, one can estimate the Q1 value using the single-station Z/H method. This technique enables us to carry out regional deep gcomagnetic sounding by the method. The data used for analyses are geomagnetic night-time values for about, typically, 26 years from 5 good-quality stations and for several years from 34 stations distributed over the globe. The results indicate that the night-time values yield more reliable response estimates for half-year period compared to the usual estimates obtained from daily means. It implies that the approximation for the night-time fields holds good for the half-year period, but the daily means are not suitable for estimating the response function of the semi-annual variations by using the single-station method. Source field analyses for daily means data and night-time means data have also been carried out in this paper.

Geomagnetic solar flare effect on February 4 and 6，1986 at the china Antarctic Great wall Station

Taking the sampled every minute values of the horizontal, declination and vertical components H, D, Z and theintensity of total field F calculated from H and Z on the magnetograms at ten geomagnetic observatories in Chinain the same periods, and at the china Antarctic Great wan station (CAGWS), the authors conducted the maximum entropy analysis and band-pass filtration of these data and obtained the following results: (1) At the PeriodT=10-90 min geomagnetic solar flare effect (sfe) is evident on the sunlit hemisphere. It is more pronounced atperiods 15, 20, 25 and 30 min, and most prominent at 30-35 min. The solar X-ray spectra at the same timeshowed their peaks at 10 and 15 min ; (2) The period T=10-70 min of sfe at the CAGWS in the westernHemisphere was also recognizable after spectral analysis and filtration, but the corresponding period of the maximum amplitude was different from that in the sunlit hemisphere. The results further proved that the geomagnetic effect of solar flares could also be observed in the dark hemisphere I (3) The subsolar POints of two solar flareswere found around Lanzhou, and the associated current density in the ionosphere was about 24 A/km. Thetransitional zone from positive to negative sfe was found around the geographic latitude p￣ 22'-- 24'N, wherethe sfe in H-crochet was almost illegible.