Longitudinal dependence of the daily geomagnetic variation during quiet time
Longitudinal dependence of the daily geomagnetic variation during quiet time
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DOI：
10.1029/2002ja009287
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发表时间：
2002-11
影响因子：
--
通讯作者：
P. Sager;Tian-Sen Huang
中科院分区：
文献类型：
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作者：
P. Sager;Tian-Sen Huang
[1]在春分静时，地磁场的日变化具有纵向依赖性，这是在倾角/经度框架中观察到的。考虑了两种解释：(1)恒定倾角下地磁纬度的纵向变化；(2)主磁场的纵向变化，它调节电离层发电机电动势，决定和约束电离层半球之间的场向电流（FAC），以保持电流的连续性。Prairie View电离层发电机模型利用磁坐标模拟了国际地磁基准场（IGRF）内的半球间耦合，并用于该研究。在非洲和美洲中纬度地区观测到的两种不同类型的磁变化可以用地磁纬度的差异来解释。IGRF的纵向效应也很明显。它们解释了一个独特的特征（高原上4lt左右赤纬的大正偏移）。在非洲中纬度地区，它们提高了水平分量振幅和赤纬的早晨减小，IGRF比偶极主场更能再现这些变化。FAC对模拟这三种情况至关重要，因为FAC在中午前后产生的地磁场变化高达水平电流贡献的40%。
[1] The daily variation of the geomagnetic field during quiet time at equinox features a longitudinal dependence, which is observed in the dip-latitude/longitude frame. Two explanations are considered: (1) the longitudinal changes of the geomagnetic latitude at constant dip-latitude and (2) the longitudinal variations of the main field, which modulates the ionospheric dynamo e.m.f. and determines and constrains the field-aligned currents (FAC) that flow between ionospheric hemispheres to maintain the current continuity. The Prairie View ionospheric dynamo model simulates this inter-hemispheric coupling within the International Geomagnetic Reference Field (IGRF) by using magnetic coordinates, and is used for this investigation. Two distinct types of magnetic variation observed at midlatitudes in African and American sectors are explained by the differences in geomagnetic latitude. IGRF longitudinal effects are also in evidence. They account for one singular feature (a large positive excursion of the declination around 4 LT at Plateau). At African midlatitudes, they improve the horizontal component amplitude and the morning decrease of the declination, which are better reproduced with IGRF than with a dipolar main field. FAC, which generate a variation of the geomagnetic field of up to 40% of the horizontal current contribution around midday, are essential to simulate these three cases.