Airglow originating from metastable helium He($2^3$S) at 1,083 nm has been used to study the upper thermosphere since its discovery in 1959, yielding insights into, for example, solar EUV intensities and thermospheric photoelectron densities. For over 6 decades, these measurements were made passively, relying on solar illumination of the He($2^3$S) layer to produce a detectable signal, resulting in a column integration of the He($2^3$S) layer. Recently, the first height-resolved measurements of He($2^3$S) density were made by fluorescence lidar, opening a new window for studying the upper thermosphere. We report on a series of 51 measurements by this instrument spanning an entire winter season and extending to an altitude of 1,000 km, revealing a broad He($2^3$S) layer that peaks at higher altitudes than previously expected.

中文翻译：

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荧光激光雷达测量的热球亚稳态氦密度的季节和高度依赖性


自 1959 年发现以来，源自 1,083 nm 的亚稳态氦 He（ $2^3$ S） 的气辉一直被用于研究上热层，从而深入了解了太阳 EUV 强度和热球层光电子密度等问题。6 多年来，这些测量都是被动进行的，依靠 He（ $2^3$ S） 层的太阳照明来产生可检测的信号，从而产生 He（ $2^3$ S） 层的列积分。最近，荧光激光雷达首次对 He（ $2^3$ S） 密度进行了高度分辨测量，为研究上层热层打开了一扇新窗口。我们报告了该仪器的 51 次测量，跨越整个冬季并延伸到 1,000 公里的高度，揭示了一个宽阔的 He（ $2^3$ S） 层，其峰值高于先前的预期。