Why is there more ionosphere in January than in July? The annual asymmetry in the F2-layer
Why is there more ionosphere in January than in July? The annual asymmetry in the F2-layer
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DOI：
10.5194/angeo-24-3293-2006
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发表时间：
2006-12
影响因子：
1.9
通讯作者：
H. Rishbeth;I. Müller-Wodarg
中科院分区：
文献类型：
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作者：
H. Rishbeth;I. Müller-Wodarg
抽象的。把两个站的北半球和南半球的值加在一起，12-1月份的联合峰值电子密度NmF2大于6-7月份。这同样适用于总高度积分电子含量。这种南北极之间的“F2层年不对称性”通常为30%，因此大大超过了由于日地距离的年变化而导致的离子产生的7%的不对称性。尽管在近70年前的电离层数据中就注意到了这一点，但这种不对称性仍然无法解释。利用电离层探空仪数据和从国际参考电离层得到的值，我们表明，从赤道到亚极光的所有纬度在中午和午夜都存在这种不对称性，并且在太阳最低点比太阳最高点有更大的不对称性。我们在热层的MSIS模型中发现了类似的中性成分的不对称性。用热层-电离层-等离子体层(CTIP)耦合模式进行的数值计算给出了电子密度和中性成分的年不对称性比观测到的要小得多。在模式中考虑中间层潮汐的影响不大。在考虑了不能解释这种不对称性的可能的解释之后，我们得到的结论是，不包括在我们的计算中的低层大气(低于30公里)的动力影响最有可能是造成不对称性的原因。
Abstract. Adding together the northern and southern hemisphere values for pairs of stations, the combined peak electron density NmF2 is greater in December-January than in June–July. The same applies to the total height-integrated electron content. This "F2-layer annual asymmetry" between northern and southern solstices is typically 30%, and thus greatly exceeds the 7% asymmetry in ion production due to the annual variation of Sun-Earth distance. Though it was noticed in ionospheric data almost seventy years ago, the asymmetry is still unexplained. Using ionosonde data and also values derived from the International Reference Ionosphere, we show that the asymmetry exists at noon and at midnight, at all latitudes from equatorial to sub-auroral, and tends to be greater at solar minimum than solar maximum. We find a similar asymmetry in neutral composition in the MSIS model of the thermosphere. Numerical computations with the Coupled Thermosphere-Ionosphere-Plasmasphere (CTIP) model give a much smaller annual asymmetry in electron density and neutral composition than is observed. Including mesospheric tides in the model makes little difference. After considering possible explanations, which do not account for the asymmetry, we are left with the conclusion that dynamical influences of the lower atmosphere (below about 30 km), not included in our computations, are the most likely cause of the asymmetry.