Empirical high‐latitude electric field models
Empirical high‐latitude electric field models
复制标题
DOI：
10.1029/ja092ia05p04467
复制
发表时间：
1987-05
影响因子：
--
通讯作者：
J. Heppner;N. Maynard
中科院分区：
文献类型：
--
作者：
J. Heppner;N. Maynard
对动力学探索者2号卫星的电场测量数据进行了分析，以扩展以前从黎明-黄昏OGO 6测量数据发展起来的经验模型（J. P. Heppner, 1977）。该分析包含了从极地交叉进入和离开所有磁本地时区的高纬度地区的大量数据。与之前的分析类似，该模型基于明显不同的极帽和日侧对流模式，这些模式是作为行星际磁场Y分量符号的函数而发生的。通过推导出北半球+Y行星际磁场（IMF）和南半球- Y行星际磁场的一种模式（模式BC），以及北半球- Y行星际磁场和南半球+Y行星际磁场的两种模式（模式a和DE），我们的目标是用最少数量的特征模式来表示对流电场的典型分布。OGO 6模式最显著的大尺度修正是：(1)在白天，早晚对流单体的纬向重叠与IMF Y分量的符号相反；(2)在夜晚，在BC模式条件下出现了从Harang不连续向极地向西的气流区；(3)对流单体焦点位置的磁局地时偏移。在上述建模之后，对IMF Z分量明显为正（向北）的情况进行了详细检查。忽略不规则性模糊模式识别的季节性依赖情况，观测结果从与新的BC和DE模型的合理一致，到不同特征主要出现在白天高纬度地区的情况。对强+Bz条件下的这些差异进行分析，使用不同MLT区域的通道，发现BC和DE模型的偏差都可以通过将夜间小单体的焦点向正午方向和正午以外的方向扩展来模拟，其变形大致类似于延长的夜间小单体的旋转扭曲。早晨单体对模式BC形变的适应在日侧75°不变纬度附近形成一条狭窄的东对流舌。模式DE形变将清晨单体向夜间压缩，使清晨单体向太阳的对流在0400 ~ 0700 MLT扇区转向极纬。在这两种情况下，双单元格模式的变形导致昼侧极区向太阳方向对流，同时保持了夜侧对流模式的完整性。因此，为解释极地地区+Bz条件下的向阳对流而设计的三单元和四单元模式所面临的夜侧困境就不会出现。
Electric field measurements from the Dynamics Explorer 2 satellite have been analyzed to extend the empirical models previously developed from dawn-dusk OGO 6 measurements (J. P. Heppner, 1977). The analysis embraces large quantities of data from polar crossings entering and exiting the high latitudes in all magnetic local time zones. Paralleling the previous analysis, the modeling is based on the distinctly different polar cap and dayside convective patterns that occur as a function of the sign of the Y component of the interplanetary magnetic field. The objective, which is to represent the typical distributions of convective electric fields with a minimum number of characteristic patterns, is met by deriving one pattern (model BC) for the northern hemisphere with a +Y interplanetary magnetic field (IMF) and southern hemisphere with a −Y IMF and two patterns (models A and DE) for the northern hemisphere with a − Y IMF and southern hemisphere with a +Y IMF. The most significant large-scale revisions of the OGO 6 models are (1) on the dayside where the latitudinal overlap of morning and evening convection cells reverses with the sign of the IMF Y component, (2) on the nightside where a westward flow region poleward from the Harang discontinuity appears under model BC conditions, and (3) magnetic local time shifts in the positions of the convection cell foci. The modeling above was followed by a detailed examination of cases where the IMF Z component was clearly positive (northward). Neglecting the seasonally dependent cases where irregularities obscure pattern recognition, the observations range from reasonable agreement with the new BC and DE models, to cases where different characteristics appeared primarily at dayside high latitudes. The analysis of these differences for strong +Bz conditions, using passes through different MLT zones, led to finding that the deviations from both the BC and DE models could be modeled by extending the evening cell foci toward, and beyond, noon with a deformation that roughly resembles a rotational twist of the extended evening cell. The morning cell accommodation to the model BC deformation produces a narrow tongue of eastward convection near 75° invariant latitude on the dayside. The model DE deformation compresses the morning cell toward the night hours such that the sunward convection in the morning cell is diverted to polar latitudes in the 0400 to 0700 MLT sector. In both cases, the deformations of the two-cell patterns lead to sunward convection in dayside polar regions while maintaining the integrity of the nightside convection pattern. Thus the nightside dilemmas that plague three- and four-cell models designed to explain sunward convection in polar regions under +Bz conditions do not appear.