Secular variability of the geocoronal Balmer-alpha brightness: magnetic activity and possible human influences
Secular variability of the geocoronal Balmer-alpha brightness: magnetic activity and possible human influences
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地冕巴尔默-α 亮度的长期变化：磁活动和可能的人类影响
DOI：
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
B. McCormack
中科院分区：
文献类型：
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作者：
R. Kerr;R. Garcia;X. He;J. Noto;R. Lancaster;C. Tepley;S. González;J. Friedman;R. Doe;M. Lappen;B. McCormack
1983年至1994年间，在阿雷西博天文台（18.35° N，66.75° W）对地冠Balmer-alpha（Hα）亮度的测量偶尔显示出非周期性的亮度变化，我们将其归因于外逸层氢丰度对地磁活动的局部响应。在中等风暴爆发条件下的几天中，Hα亮度增强了大约两倍，并且这些事件期间的绝对亮度明显大于基于平静地磁条件的模拟亮度。虽然没有直接测量在这些事件中泵出Hα的线中心太阳莱曼β（Ly β）通量，亮度增强的幅度和现象的时间再现性（在我们的数据中所有风暴发生后）这使得Hα亮度的增强可能是由于阿雷西博上方散逸层中氢柱丰度的增强，而不是由于太阳Ly β的零星增加通量由于极光加热事件传播后中纬度大气热膨胀而导致的氢丰度增加不能解释整个增强。数据还表明，Hα.从1984年到1994年，亮度有系统地变强，与太阳周期的变化或地磁活动引起的变化无关。每年增加0.3%，可能是由于在此期间地冠氢柱丰度的真实的变化，并可能是低层大气中含氢物质浓度增加的结果。1984年至1994年期间地冠Hα亮度的增强可能是对流层中甲烷增加的结果，并可能表明低层大气中甲烷沉积的影响已经传播到整个大气。
Measurements of the geocoronal Balmer-alpha (Hα) brightness taken between 1983 and 1994 at the Arecibo Observatory (18.35° N, 66.75° W) occasionally display aperiodic brightness variations that we attribute to a local response of exospheric hydrogen abundance to geomagnetic activity. Approximately twofold Hα brightness enhancements in the days following moderate storm onset conditions are demonstrated, and the absolute brightness during these events is significantly greater than modeled brightness based on quiet geomagnetic conditions. Although there are no direct measurements of the line center solar Lyman beta (Ly β) flux that pumps Hα during these events, the magnitude of the brightness enhancements and the temporal reproducibility of the phenomena (following onset of all storms in our data) make it likely that the enhanced Hα brightness is due to enhanced column abundances of hydrogen in the exosphere above Arecibo and not to sporadic increases in the solar Ly β flux. Increased hydrogen abundance due to thermal expansion of the midlatitude atmosphere following propagation of the auroral heating event cannot account for the entire enhancement. The data also suggest that Hα. brightness has become systematically stronger from 1984 to 1994, independent of solar cycle variability or variations due to geomagnetic activity. An increase of ∼ 3% per year, may be attributable to real change in the geocoronal hydrogen column abundance during the period, and is possibly a consequence of increasing hydrogenous species concentrations in the lower atmosphere. The enhancement of geocoronal Hα brightness between 1984 and 1994 may be the consequence of increasing methane in the troposphere and may signal that the effects of methane deposition in the lower atmosphere have propagated throughout the atmosphere.