Evolution of the Geomagnetic Daily Variation at Tatuoca, Brazil, From 1957 to 2019: A Transition From Sq to EEJ
Evolution of the Geomagnetic Daily Variation at Tatuoca, Brazil, From 1957 to 2019: A Transition From Sq to EEJ
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DOI：
10.1029/2020ja028109
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发表时间：
2020-08
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影响因子：
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通讯作者：
G. Soares;Y. Yamazaki;I. Cnossen;J. Matzka;K. Pinheiro;A. Morschhauser;P. Alken;C. Stolle
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作者：
G. Soares;Y. Yamazaki;I. Cnossen;J. Matzka;K. Pinheiro;A. Morschhauser;P. Alken;C. Stolle
自1957年以来，巴西地区的磁赤道向北移动了1，100多公里，大约在2013年经过巴西北方的Tatuoca地磁观测站。我们恢复并处理了1957年至2019年地磁场水平（H）分量的TTB小时平均值，从而可以调查由于长期变化，太阳活动，季节和月相的影响而导致的日变化的长期变化。还研究了H的日间变异性和TTB时的反向电射流发生率。直到20世纪90年代，电离层太阳安静电流主导了TTB的安静时间日变化。2000年后，由于赤道电急流（EEJ）的贡献，日变化的幅度变得明显更大。随着磁赤道的接近，H的季节性和逐日变化性增加，但它们的振幅归一化为平均日变化保持在相似的水平。与此同时，以同样方式归一化的月球变化幅度从5%增加到12%。在EEJ区域内，上午逆电射流（MCEJ）的发生率随着磁赤道的接近而增加，而下午逆电射流（ACEJ）则没有。来自CHAMP和Swarm卫星数据的EEJ电流显示，在EEJ区域内，MCEJ速率随磁纬度而变化，而ACEJ速率基本恒定。利用热层-电离层-电动力学环流模式（Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model）对不同地磁主场位形的模拟表明，TTB地磁日变的长期变化可以归因于主场的长期变化。
The magnetic equator in the Brazilian region has moved over 1,100 km northward since 1957, passing the geomagnetic observatory Tatuoca (TTB), in northern Brazil, around 2013. We recovered and processed TTB hourly mean values of the geomagnetic field horizontal (H) component from 1957 until 2019, allowing the investigation of long‐term changes in the daily variation due to the influence of secular variation, solar activity, season, and lunar phase. The H day‐to‐day variability and the occurrence of the counter electrojet at TTB were also investigated. Until the 1990s, ionospheric solar quiet currents dominated the quiet‐time daily variation at TTB. After 2000, the magnitude of the daily variation became appreciably greater due to the equatorial electrojet (EEJ) contribution. The H seasonal and day‐to‐day variability increased as the magnetic equator approached, but their amplitudes normalized to the average daily variation remained at similar levels. Meanwhile, the amplitude of the lunar variation, normalized in the same way, increased from 5% to 12%. Within the EEJ region, the occurrence rate of the morning counter electrojet (MCEJ) increased with proximity to the magnetic equator, while the afternoon counter electrojet (ACEJ) did not. EEJ currents derived from CHAMP and Swarm satellite data revealed that the MCEJ rate varies with magnetic latitude within the EEJ region while the ACEJ rate is largely constant. Simulations with the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model based on different geomagnetic main field configurations suggest that long‐term changes in the geomagnetic daily variation at TTB can be attributed to the main field secular variation.