Electromagnetic Drivers in the Upper Atmosphere: Observations and Modeling
Electromagnetic Drivers in the Upper Atmosphere: Observations and Modeling
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高层大气中的电磁驱动因素：观测和建模
DOI：
10.1007/978-94-007-2914-8_4
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
Zolotov
中科院分区：
文献类型：
--
作者：
Namgaladze;Förster;Prokhorov;Zolotov
本章介绍并讨论了“Cluster”上的电子漂移仪器（EDI）、低地球轨道卫星CHAMP上的加速度计以及GPS卫星舰队收集的总电子含量（TEC）的全球地图所获得的一些最新测量结果。它旨在利用高层大气模式（UAM）的第一性原理数值模拟，更好地了解地球高层大气中全球相互关联的复杂等离子体物理和电动力学过程。研究结果显示了由磁层和发震源产生的电离层电场，并揭示了它们对热层动力学和TEC模式的影响。在2003年10月28日，也就是上一个太阳活动周期中著名的万圣节超级风暴的前一天，我们将UAM模拟的高纬度热层中性风与CHAMP观测的不同行星际磁场（IMF）条件进行了比较。模拟结果表明，高层大气对国际货币基金组织在强度和方向上的变化具有直接的响应和高度的敏感性。对“岩石圈-大气-电离层”耦合问题的调查允许统计地描述被视为地震前兆的gps测量的TEC变化：(1)相对于即将到来的地震事件之前的平静条件，异常强烈（30-90%或更多）的TEC正或负偏差，按震级不小于5级，与震中附近地区有关。(2)典型异常最大表现区在纬度1500 km以上，经度3500 ~ 4000 km。(3)异常生存时间为地震释放时刻前数小时或数天至数周。(4)在磁共轭区也经常报道类似的效应。(5)在低纬强地震中，存在与电离层f2区赤道异常改变有关的影响。从最近几次强烈地震事件（2010年1月12日，海地；2011年1月1日和2日，阿根廷和智利；2011年3月11日，日本）之前的TEC偏差分析来看，这些震前TEC特征扩展了终止和“禁止”时间效应。我们强烈认为，这些TEC异常出现的主要原因是在地震成因的纬向电场的影响下，f2区电离层等离子体的垂直漂移。地震准备期间大气放射性水平的增加导致近地大气电离和电导率的增大。另一种（可能更有效的）电离机制是所谓的正空穴。下层大气电阻的变化导致在地球和电离层之间产生外部电流，并引起电离层电场和TEC的相应扰动。用UAM模拟了这些扰动，并与GPS TEC观测结果进行了比较。比较表明，模型与观测值吻合得很好。给出了电离层地震前兆探测的方法建议。
This chapter presents and discusses some of the most recent measurements obtained by the Electron Drift Instrument (EDI) on “Cluster,” the accelerometer on board the low-Earth-orbiting satellite CHAMP, and global maps of total electron content (TEC) gathered by the fleet of GPS satellites. It aims at a better understanding of the globally interconnected complex plasma physical and electrodynamic processes of the Earth’s upper atmosphere by means of first-principle numerical modeling using the Upper Atmosphere Model (UAM). The study results show ionospheric electric fields, generated by magnetospheric and seismogenic sources, and reveal their influence on the thermospheric dynamics and the TEC pattern. UAM simulations of the thermospheric neutral wind at high latitudes are compared with CHAMP observations for varying interplanetary magnetic field (IMF) conditions on 28 October 2003, the day before the famous Halloween superstorm of the previous solar cycle. The simulations show the immediate response of the upper atmosphere and its high sensitivity to IMF changes in strength and orientation. Investigation of the ‘lithosphere–atmosphere–ionosphere’ coupling problem allowed statistically describing GPS-measured TEC variations treated as precursors to earthquakes as (1) anomalous strong (30–90% and more) TEC-positive or -negative deviations relative to the quiet conditions before the forthcoming seismic event, not less than M5 by magnitude, linked to the near-epicenter area. (2) The typical zone of the anomaly maximum manifestation extends more than 1,500 km in latitude and 3,500–4,000 km in longitude. (3) Anomaly living time is from several hours or days to couple of weeks before the earthquake release moment. (4) Analogous effects at the magnetically conjugated area are often reported. (5) In the case of strong low-latitudinal earthquakes, there are effects related to the modification of the ionospheric F2-region equatorial anomaly. From the analysis of the TEC deviations before a few strong recent seismic events (12 January 2010, Haiti; 1 and 2 January 2011, Argentina and Chile; 11 March 2011, Japan), these pre-earthquake TEC signatures are extended with terminator and ‘ban’-time effects. We strongly believe that the main reason for the appearance of these TEC anomalies is the vertical drift of F2-region ionospheric plasma under the influence of a zonal electric field of seismic origin. Increase of the atmospheric radioactivity level during earthquake preparation leads to enlargement of the ionization and electric conductivity of the near-ground atmosphere. Another (and possibly more effective) ionization mechanism proposed is the so-called positive holes. Changes of resistance of the underlying atmosphere lead to the generation of an external electric current flowing between the Earth and the ionosphere and to the corresponding disturbances of the ionospheric electric field and TEC. These disturbances were modeled by UAM and compared with the GPS TEC observations. Comparison shows satisfactory agreement between the model and observations. Methodical recommendations for detection of ionospheric earthquake precursors are given.
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