A statistical study of the local time asymmetry of Pc 5 ULF wave characteristics observed at midlatitudes by SAMNET
A statistical study of the local time asymmetry of Pc 5 ULF wave characteristics observed at midlatitudes by SAMNET
复制标题
SAMNET中纬度地区Pc 5 ULF波特征局时不对称性统计研究
DOI：
--
复制
发表时间：
1997
期刊：
影响因子：
--
通讯作者：
D. Orr
中科院分区：
文献类型：
--
作者：
G. Chisham;D. Orr
在联合王国亚极光磁力仪网络（SAMNET）一年多的中纬度磁力仪数据中，共确定了129个Pc 5事件。估计了与这些事件有关的水平极化波数和方位波数，并研究了它们随磁地方时的变化。一个显着的本地时间不对称性是明显的Pc 5波的特性与明显不同的偏振和方位波的特性发生在中午的两侧。主要是顺时针偏振和向西相位传播的早晨部门的意见表明，大多数早晨部门Pc 5波是中纬度签名的太阳风驱动的场线共振发生在高纬度地区。有人建议，这些波的最有可能的能源是开尔文-亥姆霍兹不稳定性在磁层顶边界或腔/波导模式，促使脉冲变化的太阳风。在早晨观测到的极化方位角（椭圆方向）变化很大，这被解释为黎明前后出现的电离层电导率梯度很大，这改变了阿尔芬波的电离层旋转90°。认为下午扇形Pc 5波是磁层中压缩波的地面特征，主要是空腔/波导模式。在下午部分几乎没有磁力线共振的证据。腔/波导模式在磁层中的可能的主导作用，提高了在上午和下午部门的优惠频率的观察。
A total of 129 Pc 5 events were identified in more than a year of mid-latitude magnetometer data from the United Kingdom Sub-Auroral Magnetometer Network (SAMNET). The horizontal polarization and azimuthal wavenumbers associated with these events were estimated, and their variations with magnetic local time were studied. A marked local time asymmetry was apparent in the Pc 5 wave characteristics with distinctly different polarization and azimuthal wave characteristics occurring on either side of noon. The morning sector observations of predominantly clockwise polarization and westward phase propagation suggest that the majority of the morning sector Pc 5 waves are the midlatitude signature of solar wind driven field line resonances occurring at higher latitudes. It is suggested that the most likely energy sources for these waves are the Kelvin-Helmholtz instability at the magnetopause boundary or cavity/waveguide modes prompted by impulsive variations in the solar wind. The large variation in the polarization azimuths (ellipse orientations) observed in the morning sector was interpreted as a result of the large ionospheric conductivity gradients that occur around and after dawn, which alter the ionospheric rotation of Alfven waves from 90°. It is suggested that the afternoon sector Pc 5 waves are the ground signature of compressional waves in the magnetosphere, mainly cavity/waveguide modes. There is little evidence of field line resonances in the afternoon sector. The possibly dominant role of cavity/waveguide modes in the magnetosphere is heightened by the observation of preferential frequencies in both the morning and afternoon sectors.