Seasonal effects on auroral particle acceleration and precipitation
Seasonal effects on auroral particle acceleration and precipitation
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DOI：
10.1029/1999ja000391
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发表时间：
2001-04-01
影响因子：
2.8
通讯作者：
Meng, CI
中科院分区：
文献类型：
--
作者：
Liou, K;Newell, PT;Meng, CI
利用1996年冬季和1997年夏季（至日前后4周）北方半球极地紫外成像仪获得的全球非道德图像，研究了极光加速和降水的季节效应。根据N-2 Lyman-Birge-Hopfield（LBH 1）极光发射的长波段（1600-1800埃）的极光亮度推断出沉淀电子的能量通量，根据LBH 1与LBHs（LBH 1波段中较短的波长）极光发射的强度比推断出沉淀电子的平均能量。结果表明，极光的昼侧和夜侧区域表现出不同的季节效应：夜侧（类似于1900-0300 MLT）极光功率在夏季受到抑制，而昼侧极光功率在夏季增强，并形成所谓的午后极光热点，所有因素均接近2。沉淀电子的平均能量是在黑暗中高于在阳光照射的半球，而在黑暗中比在阳光照射的半球的所有区域的数量通量较低。这些变化，最多可达3倍，与当地时间和纬度有关。在夏季的夜侧极光功率的抑制与电子能量的大幅下降，而在夏季的昼侧极光的增强与电子数通量的大幅增加。夏季昼侧极光功率的增加可能与夏季出现的大规模向上场向流有关。结果也讨论了电导率反馈不稳定性和回旋脉塞不稳定性的背景下。对昼侧和夜侧极光的不对称季节效应表明，昼侧磁层有一个电压发生器，夜侧磁层有一个电流发生器。
Global amoral images acquired from the Polar ultraviolet imager in the Northern Hemisphere during the winter of 1996 and the summer of 1997 (4 weeks before and after solstice) are used to study seasonal effects on auroral acceleration and precipitation. The energy flux of precipitating electrons is inferred from auroral luminosity in the long-wavelength bands (1600-1800 Angstrom) of N-2 Lyman-Birge-Hopfield (LBHl) auroral emissions, and the mean energy of precipitating electrons is inferred from the intensity ratio of LBHl to LBHs (1400-1600 Angstrom, the shorter wavelength of LBH bands) auroral emissions. Results indicate that dayside and nightside regions of aurora reveal different seasonal effects: nightside (similar to 1900-0300 MLT) auroral power is suppressed in summer, while dayside auroral power is enhanced in summer and forms the so-called postnoon auroral hot spots, all by a factor of similar to2. The average energy of precipitating electrons is higher in the dark than in the sunlit hemisphere, while the number flux is lower in the dark than in the sunlit hemisphere for all regions. These changes, up to a factor of similar to3, are local time and latitude dependent. The suppression of the nightside auroral power in summer is associated with a large decrease in the electron energy, whereas the enhancement of dayside aurora in summer is associated with a large increase in the electron number flux. The increase of dayside auroral power in summer may be associated with the large-scale upward field-aligned currents, which peak in summer. Results are also discussed in the context of a conductivity feedback instability and a cyclotron maser instability. The asymmetric seasonal effects on the dayside and nightside auroras suggest a voltage generator for the dayside magnetosphere and a current generator for the nightside magnetosphere.