Interhemispheric asymmetry of the equatorial ionization anomaly in solstices observed by COSMIC during 2007–2012
Interhemispheric asymmetry of the equatorial ionization anomaly in solstices observed by COSMIC during 2007–2012
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DOI：
10.1002/2014ja020820
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发表时间：
2015-04
期刊：
影响因子：
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通讯作者：
X. Luan;Pan Wang;X. Dou;Y. Liu
中科院分区：
文献类型：
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作者：
X. Luan;Pan Wang;X. Dou;Y. Liu
利用2007-2012年COSMIC卫星的电离层掩星观测资料，分析了冬至季节赤道电离距平（EIA）的半球不对称性变化。引入半球不对称指数（Ah）来定量表征EIA峰的相对半球间不对称性或南北差异。季节，太阳活动，和纵向的半球不对称性的依赖关系进行了研究，在这些低到中高太阳活动水平。结果表明：（1）冬季到夏季半球的强峰转换一般发生在中午到下午（约11：00-14：00 LT），而EIA半球的不对称型向强峰转换实际上早于2-3 h。(2)在六月至日和十二月至日之间的EIA半球不对称性中观察到了显着的差异。在六月至日，从较强的冬季波峰到夏季波峰的转换发生较晚，因此，较强的冬季波峰持续时间较长的上午期间。(3)在午后，EIA峰的相对半球间不对称性大小与太阳活动有明显的负相关，而在早晨，EIA峰的相对半球间不对称性大小与太阳活动的相关性较弱。(4)脑嵴的半球间不对称性及其过渡时间随脑嵴的不同而不同。此外，还发现Ah变化率的纵向和季节变化与离子产生率的半球不对称性的相应变化基本一致。我们的研究结果表明，光化学过程也可能发挥作用的EIA半球的不对称性，除了从跨赤道中性风和赤道喷泉效应的重要贡献。
The ionospheric radio occultation measurements from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites during 2007–2012 are utilized to analyze variations of the hemispheric asymmetry in the equatorial ionization anomaly (EIA) in solstice seasons. A hemispheric asymmetry index (Ah) is introduced to quantitatively characterize the relative interhemispheric asymmetry or north‐south differences of the EIA crests. The seasonal, solar activity, and longitudinal dependences of the hemispheric asymmetry are investigated during these low to moderately high solar activity levels. Our main findings are as follows: (1) The transition of stronger crest from the winter to summer hemispheres generally took place during noon to afternoon hours (~11:00–14:00 LT), whereas the change of the EIA hemispheric asymmetry pattern toward a stronger summer crest actually started 2–3 h earlier. (2) Remarkable differences were observed in the EIA hemispheric asymmetry between June and December solstices. In June solstice, the transition from stronger winter to summer crests occurred later, and consequently, the duration with stronger winter crest lasted longer during the morning period. (3) In the afternoon hours, the magnitudes of relative interhemispheric asymmetry of EIA crests were obviously anticorrelated with the solar activity, while in the morning hours their solar activity dependence was weak. (4) Interhemispheric asymmetry of the crests and its transition time varied with longitudes. It is also found that the longitudinal and seasonal variations of the change rate of Ah was generally consistent with the corresponding variations of hemispheric asymmetry in ion production rate. Our results indicate that the photochemical process may also play a role in the EIA hemispheric asymmetry, in addition to the important contribution from the transequatorial neutral wind and equatorial fountain effects.