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《Chinese Journal of Space Science》 2004-04
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MA Ruiping XU Jiyao Center for Space Science and Applied Research, The Chinese Academy of Sciences, Beijing 100080  
Using the geomagnetic data of daily variation of Z component observed from 1972 to 1993 at Guangzhou station, the low frequency components that include the annual average, the annual variation and the semiannual variation, and the short period component with periods less than 60-day are analyzed year after year. The daily averages of the F_(10.7) also are analyzed. The daily variations of Z at Guangzhou station can approximately reflect the magnitude of the equatorial electro jet. The results show that, the annual averages of daily variations of Z are favorably linearly correlative with the annual averages of the F_(10.7); the annual variation with the amplitude of about 5 nT and summer maxima is existent in every year, it is not virsually correlative with the solar activity and it is a seasonal effect; the semiannual variation with equinoctial maxima is existent, the amplitude of the semiannual variation is obviously greater at solar maximum than at solar minimum, for example, the amplitude of the semiannual variation is about 10 nT at 1981 that is the year of solar activity maximum, but the amplitude is about 2 nT at 1976 that is the year of solar activity minimum; the oscillation with period about 27 day which relate to solar rotation and the oscillations with periods close to 16, 10, 5, 2 d which relate to the planetary wave are obviously existent. The spectral characteristics of the geomagnetic daily ranges of Z at Guangzhou station prompts further investigation into the physical mechanism of that the ionosphere is affected by the middle and lower atmosphere.