Climatology of the equatorial thermospheric mass density anomaly
Climatology of the equatorial thermospheric mass density anomaly
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DOI：
10.1029/2006ja012199
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发表时间：
2007-05
影响因子：
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通讯作者：
Huixin Liu;H. Lühr;S. Watanabe
中科院分区：
文献类型：
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作者：
Huixin Liu;H. Lühr;S. Watanabe
[1] 赤道异常是热带地区地球热层-电离层耦合的一个有趣且重要的特征。它是在大气的电离和电离部分中发现的异常纬度分布。其春分点配置由倾角赤道附近的最小值和两侧的两个最大值组成。这种异常的电离层一侧通常被称为赤道电离异常 (EIA)，自 20 世纪 30 年代以来早已被人们认识到。然而，它的热层对应物直到 20 世纪 70 年代才被 Dynamic Explorer 2 卫星看到。 2005 年，CHAMP 卫星最近揭示了它的全球图景。在本文中，我们利用 4 年的 CHAMP 测量结果调查热层中赤道质量异常 (EMA) 的气候学，对之前的研究进行了补充。我们的分析揭示了 EMA 随季节和太阳通量水平的强烈变化。 EMA 结构在春分点附近最为突出，当 F10.7 = 150 时，峰谷比约为 1.05。在至日附近，它关于倾角赤道不对称。夏季半球的密度峰值比冬季半球提前 1-2 小时达到最大值，并且达到更高的值。 EMA 区域的密度每半年变化一次，在春分点附近达到最大值。 EMA 波峰的纬度位置经历季节性变化，明显跟随日下点的移动。还发现 EMA 结构在太阳通量水平较高时变得更加明显。 EMA 波峰的位置和强度都与相应季节和太阳通量水平的 EIA 波峰的位置和强度密切相关，因此表现出强烈的等离子体中性相互作用。此外，全球平均密度明显存在两个季节不对称性，3月/12月的密度比9月/6月高约15-20%。
[1] The equatorial anomaly is an interesting and important feature of the Earth's thermosphere-ionosphere coupling in tropical regions. It is an anomalous latitudinal distribution found in both the ionized and unionized part of the atmosphere. Its equinox configuration consists of a minimum near the dip equator flanked by two maxima on both sides. The ionospheric side of this anomaly, often referred to as the equatorial ionization anomaly (EIA), has long been recognized since the 1930s. However, its thermospheric counterpart was only to be glimpsed by the Dynamic Explorer 2 satellite in the 1970s. A global picture of it has been rather recently revealed by the CHAMP satellite in 2005. In this paper we complement previous studies by investigating the climatology of the equatorial mass anomaly (EMA) in the thermosphere using 4 years of CHAMP measurements. Our analysis has revealed strong variation of the EMA with season and solar flux level. The EMA structure is most prominent around equinox, with a crest-to-trough ratio about 1.05 for F10.7 = 150. Near solstices, it is asymmetric about the dip equator. The density crest attains maximum 1–2 hours earlier and reaches higher values in the summer hemisphere than in the winter hemisphere. The density in EMA regions varies semiannually, with maxima near equinoxes. The latitudinal locations of the EMA crests undergo a seasonal variation, obviously following the movement of the subsolar point. The EMA structure has also been found to become more pronounced at higher solar flux levels. Both the location and magnitude of the EMA crests closely follow those of the EIA in corresponding seasons and solar flux levels, hence demonstrating strong plasma-neutral interaction. Furthermore, two seasonal asymmetries clearly present in the globally averaged density, with the density in March/December being ∼15–20% higher than that in September/June.