Cusp-latitude Pc3 spectra: band-limited and power-law components
Cusp-latitude Pc3 spectra: band-limited and power-law components
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尖点纬度 Pc3 谱：带限和幂律分量
DOI：
10.5194/angeo-20-1539-2002
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发表时间：
2002
影响因子：
1.9
通讯作者：
R. Morris
中科院分区：
文献类型：
--
作者：
P. Ponomarenko;B. J. Fraser;F. Menk;S. Ables;R. Morris
本文的工作试图填补上游产生的Pc 3 -4波与尖纬度观测到的宽带ULF噪声的比较研究的空白。我们对三年尖纬度地面磁力仪数据的光谱特性进行了统计分析，发现平均白天Pc 3 -4光谱的特征在于两个主成分：上游相关的带限增强（“信号”）和幂律背景（“噪声”），S（f）/ f 4。基于这些信息，我们开发了一种算法，可以在谱域中对这两个分量进行反卷积。信号增强的频率随IMF幅值线性增加，f（mHz）= 4.4| BIMF|（nT），并且其功率在IMF锥角xB ' 20和160附近以及在10：30-11：00 MLT处最大。这两个光谱分量表现出类似的半年变化与分点极大值。背景噪声功率随Bz向南增大而增大，Bz向北基本保持不变.其日变化与Pc 5磁力线共振功率相似，最大值出现在MLT 09：00附近。带限信号和宽带噪声分量分别与太阳风速度/ V 5.71 sw和/ V 4.12 sw呈幂律增长。因此，有效信噪比随着Vsw的增大而增大。观测结果表明，噪声的产生与重联过程有关。
This work attempts to fill a gap in compara- tive studies of upstream-generated Pc3-4 waves and broad band ULF noise observed at cusp latitudes. We performed a statistical analysis of the spectral properties of three years of cusp-latitude ground magnetometer data, finding that the average daytime Pc3-4 spectra are characterized by two principal components: an upstream-related band-limited en- hancement ('signal') and a power-law background ('noise') with S(f) / f 4 . Based on this information we devel- oped an algorithm allowing for the deconvolution of these two components in the spectral domain. The frequency of the signal enhancement increases linearly with IMF mag- nitude as f (mHz) ' 4.4|BIMF|(nT), and its power maxi- mizes around IMF cone angles xB ' 20 and 160 and at 10:30-11:00 MLT. Both spectral components exhibit similar semiannual variations with equinoctial maxima. The back- groundnoise power grows with increasing southwardBz and remains nearly constant for northward Bz. Its diurnal varia- tion resembles that of Pc5 field-line resonance power, with a maximum near 09:00 MLT. Both the band-limited signal and broad band noise components show power-law growth with solar wind velocity / V 5.71 sw and / V 4.12 sw , respectively. Thus, the effective signal-to-noise ratio increases with in- creasing Vsw. The observations suggest that the noise gen- eration is associated with reconnection processes.