Pi 2 pulsations and the substorm current wedge: Low‐latitude polarization
Pi 2 pulsations and the substorm current wedge: Low‐latitude polarization
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Pi 2 脉动和亚暴流楔：低纬度极化
DOI：
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发表时间：
1989
期刊：
影响因子：
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通讯作者：
W. Hughes
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文献类型：
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作者：
M. Lester;H. Singer;D. Smits;W. Hughes
亚暴相关的Pi 2波的中纬度观测已经建立了极化椭圆长轴相对于亚暴电流楔方向的模式。本文的目的是将中纬度观测与低纬度观测联系起来。在位于40°N磁纬的美国空军地球物理实验室（AFGL）磁强计网络的两个南部台站测量了Pi 2波偏振参数（椭圆率、偏振方向和水平波椭圆的长轴方向或方位角）。对于相同的事件，位于55°N的AFGL网络的五个北方站的H和D分量海湾被用来确定亚暴流楔的位置。然后，椭圆率和方位角的波进行了检查相对于当前的楔。我们发现，在电流楔内，低纬（40°N）台站的偏振方位角的纵向图象与中纬（55°N）观测的方位角图象一致。而在楔形区以外，靠近场向流的边缘处，方位角在低纬不像在55°N那样发生变化。中低纬观测值之间的差异可以部分地由低纬站的正H分量海湾的额外观测来解释，这表明当前楔的地基签名在纵向范围上随着纬度的降低而增加。与这些观测结果相一致的是，模式计算表明，低纬H分量正海湾的区域在低纬比在中纬更宽。至于偏振方向，在楔的内部和东部，偏振方向主要是逆时针的，就像在中纬度一样。然而，与中纬度观测相反，楔形以西的偏振主要是顺时针的，这意味着在55°N和40°N之间的偏振方向是反向的。我们表明，西部的电流楔的中纬度和低纬度之间的最大的相位变化发生在H分量，我们讨论了如何反转极化和H分量的相位变化与现有的模型产生的Pi 2脉动。
Mid-latitude observations of substorm-related Pi 2 waves have established a pattern in the orientation of the major axis of the polarization ellipse relative to the substorm current wedge. The purpose of this paper is to relate the mid-latitude observations to those at lower latitudes. Pi 2 wave polarization parameters (ellipticity, sense of polarization, and the orientation of the major axis, or azimuth, of the horizontal wave ellipse) were measured at the two southern stations of the Air Force Geophysics Laboratory (AFGL) Magnetometer Network located at 40°N magnetic latitude. For the same events the H and D component bays at the five northern stations of the AFGL network located at 55°N were used to locate the position of the substorm current wedge. Then the ellipticity and the azimuth of the waves were examined with respect to the current wedge. We find that inside the current wedge the longitudinal pattern of the polarization azimuth of the low-latitude (40°N) stations agrees with the observed mid-latitude (55°N) azimuth pattern without exception. However, outside the wedge near the longitudes of the field-aligned currents, the azimuth does not change at low latitudes as it does at 55°N. The difference between the mid- and low-latitude observations can be partially explained by the additional observation of positive H component bays at the low-latitude stations, which suggests that the ground-based signature of the current wedge increases in longitudinal extent with decreasing latitude. In agreement with these observations a model calculation of the current wedge shows that the region of the low-latitude H component positive bay is wider at low latitudes than at mid latitudes. With regard to sense of polarization, inside and east of the wedge the sense is predominantly counterclockwise, just as it is at mid latitudes. However, in contrast to mid-latitude observations, west of the wedge the polarization is predominantly clockwise, which implies a reversal in the sense of polarization between 55°N and 40°N. We show that west of the current wedge the largest phase change between the mid and low latitudes occurs in the H component, and we discuss how the reversal in polarization and the H component phase change are related to the existing models for the generation of Pi 2 pulsations.