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北京白家疃台的ＵＬＦ磁感应仪投入运行以来，经常观测到一种频率比较低的ＵＬＦ磁场扰动信号，其幅度和周期均随时间变化．由于不同于各种人为电磁源引起的干扰，所以，常常把它作为一种ＵＬＦ地震电磁发射前兆．然而和磁照图的对比分析表明，这种磁扰信号都出现在磁暴发生期间，而且没有发现观测到这类信号没有磁暴的情形．因而，在目前的认识水平上尚不能把它作为一种ＵＬＦ地震电磁发射前兆来看待．这种信号的主要特征是：在磁暴期间间断性地出现，每段信号出现的持续时间、信号段出现的频次和扰动幅度与磁暴的类型和磁暴的大小有关系．扰动的波形特征也与磁暴的类型有关．ＳＣ型磁暴与ＧＣ型磁暴相比，ＵＬＦ磁扰的幅度较大，持续时间较长；Ｋ指数较大的磁暴期间出现的ＵＬＦ磁扰比Ｋ指数较小的磁暴期间的幅度大、频次高、持续时间长，并且扰动信号的频率多变．ＵＬＦ磁感应仪上的这种暴间磁扰的起始时间及最强信号出现的时段与磁照图上的磁暴的起始时间和最强信号出现的时段相比，不一致的居多数，相同的只有４４％左右．扰动信号的周期从几秒到几百秒不等，强度一般介于０．０４～８ｎＴ之间．根据对上述信号的功率谱分析，ＵＬＦ暴间磁扰的优势频率约为０．０６Ｈｚ，而且谐波上也有相当的能量?
Since the ULF magnetic induction instrument of Beijing Baijiatuan has been put into operation, it has often observed a kind of low frequency ULF magnetic disturbance signal whose amplitude and period change with time. Because it is different from the interference caused by various man-made electromagnetic sources, it is often used as a kind of ULF seismic electromagnetic launch precursor. However, a comparative analysis with a magnetic map shows that these magnetic disturbances occur during the occurrence of a magnetic storm, and no such situation is observed. Therefore, it can not yet be regarded as a kind of precursor to the ULF seismic electromagnetic launch at the current level of understanding. The main features of this signal are intermittent appearance during the storm, the duration of each segment of the signal, the frequency of occurrence of the segment, and the magnitude of the disturbance as a function of the type of storm and the magnitude of the storm. Disturbed waveform features are also related to the type of magnetic storm. Compared with the GC type magnetic storm, SC magnetic flux has a larger magnitude and longer duration of magnetic interference than the GC type magnetic storm. The magnetic susceptibility of the ULF magnetic perturbation during the larger K index is higher than that of the K-type magnetic storm, The duration is long and the frequency of the disturbance signal varies. The onset time of the violent magnetic disturbance and the appearance of the strongest signal on the ULF magnetic induction instrument are different from the onset of the magnetic storm on the magnetic stripe and the period when the strongest signal occurs. The same Only about 44%. Disturbance signal cycle from a few seconds to hundreds of seconds, the intensity is generally between 0.04 ~ 8nT. According to the power spectrum analysis of the above signal, the dominant frequency of ULF violent interference is about 0.06Hz, and there is considerable energy on the harmonics.