Abstract
Equipped with a 1-meter Cassegrain telescope with 6.2 meter focal length and an electronically gated Intensified Charge-Coupled Device (ICCD), a multilayer Na imager is designed and developed at Wuhan in China. This novel instrument has successfully achieved the first preliminary 3-D image of the mesospheric Sodium (Na) layer when running alongside a Na lidar. The vertical Na layer profile is measured by the lidar, while the horizontal structure of the layer at different altitudes is measured by the ICCD imaging with a horizontal resolution of ~3.7 urad. In this experiment, controlled by the delay and width of the ICCD gating signal, the images of the layer are taken with three-second temporal resolution for every 5 km. The results show highly variable structures in both the vertical and horizontal directions within the Na layer. Horizontal images of the Na layer at different altitudes near both the permanent layer (80–100 km) and a sporadic Na layer at 117.5 km are obtained simultaneously for the first time. The Na number density profiles measured by the lidar and those derived from this imaging technique show excellent agreement, demonstrating the success of this observational technique and the first 3-D imaging of the mesospheric Na layer.
Highlights
The mesospheric Sodium (Na) layer in the mesosphere and lower thermosphere (MLT) at an altitude of between ~80 km and 110 km is mainly generated through the combination of meteor ablation and multibody chemical reactions involving several Na compounds and ion species in this region [1]
Due to the high abundance and large scattering cross section of this metallic Na, the layer has become an ideal target for laser guide star systems [2] and for Na lidars measuring the temperature and wind field variations in the MLT [3,4]
Na lidar measurements over the past a few decades have significantly advanced our understanding of the dynamics and chemistry in this region [5]
Summary
The mesospheric Sodium (Na) layer in the mesosphere and lower thermosphere (MLT) at an altitude of between ~80 km and 110 km is mainly generated through the combination of meteor ablation and multibody chemical reactions involving several Na compounds and ion species in this region [1]. Passive airglow imaging instruments can measure the horizontal variations within their field of view (FOV) around the peak altitudes of the layer of hydroxyl (OH), Na and atomic oxygen (O) in the MLT [10]. Their receiving signals, have to be averaged throughout the whole layer vertically due to relatively weak airglow signals, losing critical information regarding vertical variations. The system, running alongside a high power Na lidar, consists of a large aperture telescope and an electronically gated, high sensitivity Intensified Charge-Coupled Device (ICCD) This new observation capability further advances our understanding of some of the most fundamental small-scale atmospheric processes.
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