Plasma Diffusive Flows in the Topside Ionosphere From Radio Occultation Measurements by COSMIC
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摘要: 从等离子体运动方程出发, 利用COSMIC星座的掩星数据, 借助相关经验模式, 计算了太阳活动低年顶部电离层O+场向扩散速度和扩散通量, 并分析了其全球分布和日变化特征. 结果表明, 白天等离子体扩散速度的方向随高度增加由向下(极向)逐步变为向上(赤道向), 方向转变的高度一般在hmF2+80 km以下. 在白天较高高度, 南北磁纬10º ~20 º存在着向上方向的最大扩散速度和扩散通量; 而在夜间, 南北磁纬30º~40 º存在向下方向的最大扩散速度和扩散通量. 在分点, 南北半球的扩散通量和扩散速度大致对称; 而在至点, 扩散通量存在着明显的南北半球不对称现象. 另外, 不同纬度的扩散速度有着不同的日变化特征.Abstract: O+ field-aligned diffusive velocities and fluxes in the topside ionosphere have been calculated from electron density profiles retrieved from COSMIC radio occultation measurements. The diffusive velocities and fluxes from October 2006 to October 2007 at low-latitude and mid-latitude have been statistically analyzed. The results show that daytime diffusive fluxes changed gradually from downward to upward as altitude increased. The transition height is below hmF2+80 km. The largest values of the upward diffusive fluxes and velocities during the daytime occur at geomagnetic latitudes from 10º to 20º above hmF2+80 km, whereas during the nighttime the maximum downward fluxes occur at geomagnetic latitudes from 30º to 40º. Diffusive fluxes are roughly symmetric around the magnetic equator during equinoxes. But they are asymmetric during solstices, the winter hemisphere has smaller fluxes than the summer hemisphere does. In addition, the diurnal variations have latitudinal dependences.
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Key words:
- Topside ionosphere /
- Diffusive velocity /
- Diffusive flux /
- Radio occultation
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