Yearly variations in the low-latitude topside ionosphere
Yearly variations in the low-latitude topside ionosphere
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DOI：
10.1007/s00585-000-0789-0
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发表时间：
2000-07
影响因子：
1.9
通讯作者：
G. J. Bailey;Y. Su;K. Oyama
中科院分区：
文献类型：
--
作者：
G. J. Bailey;Y. Su;K. Oyama
对Hinotori卫星的观测进行了分析，以确定低纬度顶部电离层电子密度和电子温度的年度变化。观测结果表明，在低纬度地区存在着赤道不对称的顶面电子密度，即密度在一个春分点高于另一个春分点。这种不对称性是半球相关的，在北方半球的3月春分和南半球的9月春分时电子密度较高。这种不对称性随着两半球纬度的增加而增强。不对称的行为没有明显的纵向和磁活动变化。本文用热层电离层等离子体耦合模型（CTIP）研究了分点不对称性的一种机制。模拟结果再现了所观察到的春分不对称性，并表明这种不对称性是由于全球热层环流的影响导致热层响应缓慢，从而导致春分时热层和电离层的南北不平衡造成的。观测还表明，电子密度与电子温度的关系在白天和夜间是不同的。白天电子温度的年变化与电子密度呈负相关，但磁纬低于10°的地区除外。在夜间，相关性为正。关键词：电离层（赤道电离层;电离层-大气相互作用;等离子体温度和密度）
Observations made by the Hinotori satellite have been analysed to determine the yearly variations of the electron density and electron temperature in the low-latitude topside ionosphere. The observations reveal the existence of an equinoctial asymmetry in the topside electron density at low latitudes, i.e. the density is higher at one equinox than at the other. The asymmetry is hemisphere-dependent with the higher electron density occurring at the March equinox in the Northern Hemisphere and at the September equinox in the Southern Hemisphere. The asymmetry becomes stronger with increasing latitude in both hemispheres. The behaviour of the asymmetry has no significant longitudinal and magnetic activity variations. A mechanism for the equinoctial asymmetry has been investigated using CTIP (coupled thermosphere ionosphere plasmasphere model). The model results reproduce the observed equinoctial asymmetry and suggest that the asymmetry is caused by the north-south imbalance of the thermosphere and ionosphere at the equinoxes due to the slow response of the thermosphere arising from the effects of the global thermospheric circulation. The observations also show that the relationship between the electron density and electron temperature is different for daytime and nighttime. During daytime the yearly variation of the electron temperature has negative correlation with the electron density, except at magnetic latitudes lower than 10°. At night, the correlation is positive.Key words:Ionosphere (equatorial ionosphere; ionosphere-atmosphere interactions; plasma temperature and density)