Electron temperature enhancement beneath the magnetospheric cusp
Electron temperature enhancement beneath the magnetospheric cusp
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DOI：
10.1029/2006ja011618
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发表时间：
2006-07
影响因子：
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通讯作者：
G. W. Prölss
中科院分区：
文献类型：
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作者：
G. W. Prölss
在昼侧极区，软电子沉淀和热传导导致电离层上部电子温度显著升高。利用DE-2卫星数据，研究了这种显著的尖峰特征的性质。首先，确定温度增强的位置。发现该位置主要取决于亚暴活动。在地磁平静条件下（AE≃0），温度峰值位于不变纬度79°附近。声发射指数每增加100 nT，它就向赤道方向移动约1度。在强烈扰动条件下，它可以在低至61度的纬度上观察到。由于亚暴活动受行星际磁场的Bz分量控制，因此温度峰值的位置也依赖于该参数。除了位置之外，温度升高的幅度也令人感兴趣。这个量级被发现强烈依赖于海拔高度。在280至940公里的高度范围内，它几乎增加了5倍。与海拔高度相比，太阳风动压或地磁活动等其他参数只是次要的。为了得到尖峰相关温度增强的平均纬向剖面图，采用了叠加历元型平均方法。这样就保留了这个狭窄地貌的基本纬度结构。在海拔700 km处，可以得到如下的平均性质：幅度≃1200 K；宽度在该最大值的一半处≃2.5度；赤道边界到最高升温点的距离≃3.5度。一般来说，在温度峰值的位置观察到电子密度的下降。平均而言，只有在最上层电离层和地磁安静的情况下，密度才会增加。本研究所得的结果将被证明对日侧极地电离层的经验和理论建模非常有用。它们也可能对亚暴活动期间尖峰区磁层的重新配置提供一些启示。
[1] In the dayside polar region, soft electron precipitation and heat conduction cause a significant increase in the electron temperature of the upper ionosphere. Using DE-2 satellite data, the properties of this remarkable cusp signature are investigated. First, the location of the temperature enhancement is determined. It is found that this location is primarily dependent on the substorm activity. For geomagnetically quiet conditions (AE ≃ 0) the temperature peak is located near 79° invariant latitude. For each increase in the AE index by 100 nT it moves equatorward by about 1 degree. During strongly disturbed conditions it may be observed at a latitude as low as 61 degrees. Since the substorm activity is controlled by the Bz component of the interplanetary magnetic field, the location of the temperature peak is also dependent on this parameter. Besides the location, the magnitude of the temperature increase is of interest. This magnitude is found to be strongly dependent on altitude. Within the height range 280 to 940 km it increases by a factor of almost 5. Compared with altitude, other parameters like the dynamic pressure of the solar wind or the geomagnetic activity are only of secondary importance. To obtain mean latitudinal profiles of the cusp-related temperature enhancement, a superposed epoch type of averaging procedure is used. This way the basic latitudinal structure of this narrow feature is preserved. For an altitude of 700 km the following mean properties are derived: amplitude ≃1200 K; width at half this maximum value ≃2.5 degrees; distance between equatorward boundary and maximum of the temperature increase ≃3.5 degrees. In general, a decrease in the electron density is observed at the location of the temperature peak. Only in the uppermost ionosphere and during geomagnetically quiet conditions is the density observed to increase, on average. The results obtained in this study should prove very useful for both empirical and theoretical modeling of the dayside polar ionosphere. They may also shed some light on the reconfiguration of the magnetosphere in the cusp region during substorm activity.