科研之友
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摘要
In order to obtain information about ionospheric scintillation caused by small-scale irregularities in the sporadic E (E-S) layer, the data from GPS-CHAMP radio occultation measurements with 50 Hz resolution were treated and analyzed in this paper. The main purpose of this study is to investigate the longitudinal variations which are represented by the occurrence rates of the scintillation caused by irregularities in the E-S layer. Also, the statistical analysis of the relationship between the occurrence rate of irregularities in the E-S layer and season, dip latitude and solar activity is carried out. @@@ For our purpose to get the longitudinal variation of irregularities, the data from GPS-CHAMP radio occultation was binned for every 10 degrees in longitude into 36 geographical longitude bins. The bins are all 30 degrees wide in zonal and 5 degrees wide in meridional. To get the dip latitudinal variation, the data was binned for every 1 degrees in dip latitude into 171 dip latitude bins (85 degrees S to 85 degrees N) which are all 10 degrees wide in meridional. Then we calculated the occurrence rates of E-S layer irregularities in each bin which were defined as the ratio of the number of occultation events occurring scintillation to the total number of all occultation events in the same bin. The method of Fourier analysis was applied to decompose them to extract the different order harmonic waves especially the WN-4. To examine the seasonal dependence of the longitudinal variations, each year was divided into four seasons. The periods during one and half month before and after the vernal equinox, the summer solstice, the autumn equinox and the winter solstice are defined as spring, summer, autumn and winter, respectively. @@@ By using the data from GPS-CHAMP radio occultation and the Fourier series decomposition technology, we quantitatively investigated the feature of the wavelike fluctuation in longitudinal structure of occurrence rates of irregularities in the E-S layer and their dependence on the season, dip latitude and solar activity. The main results can be drawn as follows: (1) Longitudinal structures of irregularities in the E-S layer mainly contain the WN-1 to WN-5 components in addition to the WN-0 component (longitudinal average value), indicating that the longitudinal variations of irregularities in the E-S layer has the feature of multiple wave-numbers. (2) Wave components in different latitude and different season exhibit notable difference, WN-4 components are most obvious in the EIA peak region and occur most frequently in summer and autumn. (3) Occurrence rates of irregularities in the E-S layer vary with the dip latitude. In dip equator region and mid-latitude region, the rates are lower than those in the EIA peak region and the aurora region. (4) Occurrence rates of irregularities in the E-S layer show a strong seasonal dependence. The rates are the highest in summer, then in autumn, and the lowest in winter and spring. (5) Occurrence rates also exhibit inter-annual variation, which reduces with the decrease of solar activity. @@@ Fourier series decomposition analysis was used to investigate the longitudinal structure which provides new understanding of the longitudinal variations of irregularities causing scintillation in the E-S layer. It is found that there exists the structure with seasonal dependent multiple wave numbers in the longitudinal variations of the occurrence rates of the E-S layer irregularities causing scintillation. The amplitude of WN-4 component is most intense in the EIA peak region. The results can provide insights into the understanding of the generation mechanism of longitudinal structure of the E-S layer irregularities and the coupling process between the lower atmosphere and the ionosphere.
- 出版日期2016-8
- 单位武汉大学
