GPS-CHAMP掩星探测的E_S层不规则结构经度变化规律(2001—2008)

本文利用GPS-CHAMP高分辨率的掩星探测数据,考察了E_S层不规则结构随地理经度和随季节、倾角磁纬与太阳活动的变化特征.研究发现,E_S层不规则结构的经度变化以波数1~5分量为主,呈现出多重波数特征.在低纬度带存在显著的波数4分量,其幅度存在季节依赖,在夏季和秋季明显高于春季和冬季.E_S层不规则结构出现率随倾角磁纬的变化表现为赤道区和中纬度区较低,低纬区和极区较高.E_S层不规则结构出现率的季节变化和年均值的逐年变化表现为夏季出现最频繁,秋季次之,冬春季最弱,随太阳活动水平的减弱而降低.

Longitudinal variations of ES layers irregularities based on GPS-CHAMP occultation measurements (2001-2008)

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.#br#For our purpose to get the longitudinal variation of irregularities, the data from GPS-CHAMP radio occultation was binned for every 10° in longitude into 36 geographical longitude bins. The bins are all 30° wide in zonal and 5° wide in meridional. To get the dip latitudinal variation, the data was binned for every 1° in dip latitude into 171 dip latitude bins (85°S to 85°N) which are all 10° 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.#br#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.#br#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.