Wavelet Analyses of Geomagnetic Data regarding Major Geomagnetic Disturbances

The purpose of this study was to analyze the associated spectrum of geomagnetic field,frequencies intensity and the time of occurrence.We calculated the variation of the correlation coefficients,with mobile windows of various sizes,for the recorded magnetic components at different latitudes and latitudes.The observatories we included in our study are USA(Surlari),HON(Honolulu),SBA(Scott Base),KAK(Kakioka),THY(Tihany),UPS(Uppsala),WNG(Wingst)and Yellowknife(YKC).We used the data of these observatories from International Real-time Magnetic Observatory Network(INTERMAGNET)for the geomagnetic storm from October 28-31,2003.We have used for this purpose a series of filtering algorithms,spectral analysis and wavelet with different mother functions at different levels.In the paper,we show the Fourier and wavelet analysis of geomagnetic data recorded at different observatories regarding geomagnetic storms.Fourier analysis hightlights predominant frequencies of magnetic field components.Wavelet analysis provides information about the frequency ranges of magnetic fields,which contain long time intervals for medium frequency information and short time intervals for highlight frequencies,details of the analyzed signals.Also,the wavelet analysis allows us to decompose geomagnetic signals in different waves.The analyses presented are significant for the studies of the geomagnetic storm.The data for the next days after the storm showed a mitigation of the perturbations and a transition to quiet days of the geomagnetic field.

CHARACTERISTICS OF Sq VARIATION OF GEOMAGNETIC FIELD AT THE GREAT WALL STATION, ANTARCTICA IN WINTER

In this paper the characteristics of Sq variation of geomagnetic field in the region of the Chinese Great Wall Station (CGWS), Antarctica, in winter are analyzed from geomagnetic data obtained at the Geomagnetic Observatory of CGWS. The result enables us to reveal the following aspects: (1) The pattern of Sq variation at CGWS in early (Apr.) and Late winter (Sep.) is similar to that at Beijing Geomagnetic Observatory (BJO) at the middle latitude in the Northern Hemisphere. It may be controlled by the midlatitudinal ionospheric dynamo current. Amplitude of Sq variation is very small, and the harmonics in 8 hours or shorter periods in midwinter (June and July) is predominant because of the decreased effect of solar ultraviolet radiation and the dominant geomagnetic disturbance at high latitudes. (2) The vectors of Sq-equivalent current in the daytime are about five times more than that in the night. The direction of the vectors is clockwise in the daytime (08-15h) and counterclockwise in the night in early and late winter. Both of the vectors are very small because of the effect of the current density in the ionosphere is relatively weak in midwinter. The direction of vectors of Sq-equivalent current at CGWS in early and late winter is different from that in midwinter. It may be affected by the ionospheric current and field-aligned current in the polar region.

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.

Variations of Thermosphere Density Based on Joint Analysis of In-Situ Measurement Data From Shenzhou Spacecrafts

Based on the measurements made by Atmospheric Density Detectors(ADDs) onboard Chinese spacecraft Shenzhou 2-4,the variations of thermosphere density are revealed.During the quiet period,the density at spacecraft altitude of 330~410 km exhibited a dominant diurnal variation,with high value on dayside and low value on nightside.The ratio of the diurnal maximum density to the minimum ranged from 1.7 to 2.0.The ratio shows a positive correlation with the level of solar activity and a negative correlation with the level of geomagnetic activity.When a geomagnetic disturbance comes,the atmospheric density at the altitude of 330～410 km displayed a global enhancement.For a strong geomagnetic disturbance,the atmospheric density increased by about 56%,and reached its maximum about 6～7 hours after the geomagnetic disturbance peak. The density asymmetry was also observed both in the southern and northern hemisphere during the geomagnetic disturbance peak.

The state-of-the-art of the China Seismo-Electromagnetic Satellite mission

The China Seismo-Electromagnetic Satellite(CSES) mission was proposed in 2003 and approved in 2013 after ten years' scientific and engineering demonstrations. To meet the requirement of scientific objectives, the satellite is designed to be in a sunsynchronous orbit with an altitude of 507 km and descending node time of 14:00 LT. The CSES satellite carries 8 instruments,including search-coil magnetometer(SCM), electric field detector(EFD), high precision magnetometer(HPM), GNSS occultation receiver(GOR), plasma analyzer package(PAP), langmuir probe(LAP), high energetic particle package(HEPP) and detector(HEPD), and tri-band beacon(TBB), among which HEPD is provided by Italian Space Agency. The CSES satellite was launched successfully on February 2, 2018, and is planned to operate for 5 years. The CSES mission is the first satellite in China to measure geophysical fields, which will have a lot of application prospects in the study of seismology, geophysics, space sciences, and so on.