A method for pre-processing ULF electric field disturbances observed by DEMETER and its case application analysis
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摘要: 基于法国DEMETER卫星观测的超低频(ULF)电场波形， 本文提出了更简单易实施的ULF电场扰动预处理方法. 利用该方法， 对文献中已报道的2010年2月27日智利MS8.8地震前的ULF电场扰动进行了更全面的分析. 结果表明： 已报道的20°S—40°S地磁纬度带内的ULF电场扰动并非仅出现在最靠近震中的半轨道， 而是出现在较大的经度范围内. 大范围ULF电场扰动的区域正好位于南大西洋异常区， 很可能受到该区域异常磁场的影响. 南大西洋异常中心区域的ULF电场扰动表现出共轭特征， 即在南北地磁纬度20°—40°范围内ULF电场均出现约5 mV/m的扰动， 北纬地区的ULF电场扰动幅度相比南纬地区更小. 而在南大西洋异常中心区域外的ULF电场扰动则仅在20°S—40°S地磁纬度带内出现， 在其共轭区并未观测到ULF电场扰动. 这可能是由于南大西洋异常中心区域外的ULF电场扰动幅度比中心区域更小所致， 在电离层中由于碰撞效应更易被衰减， 因此ULF电场扰动无法传播至其共轭区. 本文的方法和结果可为后续更全面地分析卫星在电离层高度记录的ULF电场扰动提供参考.
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关键词:
- DEMETER卫星 /
- 超低频(ULF)电场扰动 /
- 南大西洋异常区
Abstract: This paper presents a method for pre-processing ULF electric field disturbances based on ULF waveforms observed by French DEMETER satellite. This method is simpler and easier to carry out. We analyze comprehensively ULF disturbances before the Chile MS8.8 earthquake on 27 February 2010， which have been reported in the literature， by using our method. The results show that reported ULF disturbances in 20°S—40°S geomagnetic latitude bands do not just appear on the half-orbit that is the closest to the epicenter， but ULF disturbances are observed in a wider longitude range. The large range with ULF disturbances is located in the region of South Atlantic anomaly (SAA)， and ULF disturbances may be affected by the geomagnetic field anomaly in this region. ULF disturbances in the center of SAA region show a conjugate distribution， i.e.， electric field fluctuates with the amplitude of 5 mV/m at 20°—40° north and south geomagnetic latitudes. The amplitude of ULF disturbances at northern latitudes is weaker than those at southern latitudes. However， ULF disturbances outside the center of SAA region are only observed at 20°S—40°S geomagnetic latitudes， and there are no ULF fluctuations in the conjugate region. As ULF fluctuations outside the center of SAA region with the weaker amplitude are easier to be attenuated because of collision effects in the ionosphere， ULF disturbance cannot propagate to the conjugate region. The method and results in this paper can provide references for subsequently thorough analyses on ULF fluctuations recorded by satellites in the ionosphere. -
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图 1 DEMETER卫星DC/ULF频段Ex， Ey和Ez分量波形示例(2010年2月17日301241半轨)
(a) 卫星观测的Ex， Ey和Ez原始波形； (b)滑动平均得到的Ex， Ey和Ez趋势波形； (c) 图(a)减去图(b)所得到的去除趋势后的Ex， Ey和Ez扰动波形
Figure 1. An example of Ex， Ey and Ez components of waveform data in the DC/ULF frequency band observed by DEMETER (half-orbit number 301241 on February 17， 2010)
(a) Original waveforms of Ex， Ey and Ez components in DC/ULF frequency band observed by DEMETER; (b) The trends of waveforms of Ex， Ey and Ez components by moving average； (c) De-trending waveforms of Ex， Ey and Ez components through corresponding waveforms of plot (a) minus that of plot (b)
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图 2 2010年2月17日(智利地震前10天)全球的上行半轨道
半轨道号标示于各半轨的右侧， 星形为智利地震的震中位置
Figure 2. Up-going half-orbits all over the globe on February 17， 2010 (10 days before the Chile earthquake)
Half-orbit numbers are marked on the right side of each half-orbit. The star represents the epicenter of Chile earthquake
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图 3 2010年2月17日(智利地震前10天)夜间301271半轨DC/ULF频段Ex， Ey和Ez分量的原始波形(a)和去除趋势后的电场扰动波形(b)
Figure 3. Original waveforms (a) and de-trending waveforms (b) of Ex， Ey and Ez components in the DC/ULF frequency band of half-orbit number 301271 on the night side on February 17， 2010 (ten days before the Chile earthquake)
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