Lidar observations of thermospheric Na layers up to 170 km with a descending tidal phase at Lijiang (26.7°N, 100.0°E), China
Lidar observations of thermospheric Na layers up to 170 km with a descending tidal phase at Lijiang (26.7°N, 100.0°E), China
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DOI：
10.1002/2015ja021808
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发表时间：
2015-10
期刊：
影响因子：
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通讯作者：
Q. Gao;X. Chu;X. Xue;X. Dou;Tingdi Chen;Jinsong Chen
中科院分区：
文献类型：
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作者：
Q. Gao;X. Chu;X. Xue;X. Dou;Tingdi Chen;Jinsong Chen
我们报告了2012年3月、4月和12月在中国丽江（地磁21.6°N，171.8°E）首次对热层Na层进行了激光雷达观测，该层长达170公里。层内的Na密度较低，在海拔130-170 km处为约1至约6 cm−3，比中层顶区域的Na峰值密度低约3个数量级。所有这些层都表现出明显的下降阶段进展，下降速率为 11-12 km/h 或 ~3 m/s，与 140 km 左右半日潮汐的垂直阶段速度一致。我们从总共 37 个晚上的激光雷达观测中识别出至少 12 个事件，其中本报告中显示了 4 个事件，丽江上空的发生频率约为 33%。这些热层事件对应于强到中度的赤道喷泉效应，支持了我们的假设，即金属离子通过喷泉效应从赤道地区沉积到低纬度地区，提供了丽江上空热层中的Na+离子。采用 Chu 等人的理论。 (2011) 和 Tsuda 等人的假设。 （2015），我们进一步假设热层Na层是通过直接电子-Na+复合Na+ + e−→Na + hν中和潮汐风切变汇聚的Na+层而形成的。使用合理的离子和电子密度进行的包络计算显示与观察结果具有良好的一致性。
We report the first lidar observations of thermospheric Na layers up to 170 km at Lijiang (geomagnetic 21.6°N, 171.8°E), China, in March, April, and December 2012. The Na densities inside the layers are low, ranging from ~1 to ~6 cm−3 at altitudes of 130–170 km, about 3 orders of magnitude lower than the Na peak density in the mesopause region. All of these layers exhibit an apparent downward phase progression with a descending rate of 11–12 km/h or ~3 m/s, consistent with the vertical phase speed of semidiurnal tides around 140 km. We have identified at least 12 events from the total 37 nights of lidar observations with four shown in this report, giving an occurrence frequency of ~33% over Lijiang. These thermospheric layer events correspond to strong to moderate equatorial fountain effects, bolstering our hypothesis that the deposit of metallic ions from the equatorial region to low latitudes via the fountain effect provides the Na+ ions in the thermosphere over Lijiang. Adopting the theory by Chu et al. (2011) and the hypothesis by Tsuda et al. (2015), we further hypothesize that the thermospheric Na layers are formed through the neutralization of the tidal‐wind‐shear‐converged Na+ layers via direct electron‐Na+ recombination Na+ + e− → Na + hν. An envelope calculation using reasonable ion and electron densities shows good consistency with the observations.