Formation of a bottomside secondary sodium layer associated with the passage of multiple mesospheric frontal systems
Formation of a bottomside secondary sodium layer associated with the passage of multiple mesospheric frontal systems
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DOI：
10.5194/acp-2020-803
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发表时间：
2020-09
影响因子：
6.3
通讯作者：
V. L. Narayanan;Satanori Nozawa;S. Oyama;I. Mann;K. Shiokawa;Y. Otsuka;N. Saito;S. Wada;T. Kawahara;Toru Takahashi
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作者：
V. L. Narayanan;Satanori Nozawa;S. Oyama;I. Mann;K. Shiokawa;Y. Otsuka;N. Saito;S. Wada;T. Kawahara;Toru Takahashi
抽象的。2014年12月19日晚，我们在挪威特罗姆瑟附近的Ramfjordmoen进行了钠激光雷达和气辉成像仪测量，详细调查了主钠层以下79-85公里高度处第二钠层的形成。的气辉成像仪观测OH排放揭示了四个通过锋面系统，类似于中层孔，通常发生在上层中层的管道区域。在大约1.5小时的时间里，低海拔钠层的密度与主层的密度相似，峰值在90公里左右。低海拔的钠层减弱，在第四前线通过后不久就消失了。当第四波锋接近激光雷达光束区域时，其强度已经减弱，并很快消失。在低海拔钠层形成过程中，柱积分钠浓度逐渐增加。激光雷达测得的温度表明，在87至93公里之间存在强烈的热导管结构。85公里以下气温升高。从激光雷达估计的水平风速显示出93公里以上的强风切变。我们的结论是，由于温度廓线和强烈的风切变的增强的稳定区域的组合提供了理想的条件，显示在OH图像中的锋面系统的多个中层孔的演变。与锋面相关的向下运动似乎将富含H和O的空气从较高高度带入85公里以下的区域，其中温度也相对较高。这将使钠原子从储层物质中释放出来，并抑制钠原子重新转化为储层物质，从而可以形成低海拔钠层，并增加柱丰度。所提出的意见也揭示了中层锋面系统的重要性，在较短的时间间隔内带来显着的变化的次要物种。
Abstract. We present a detailed investigation of the formation of a secondary sodium layer at altitudes of 79–85 km below the main sodium layer based on sodium lidar and airglow imager measurements made at Ramfjordmoen near Tromsø, Norway on the night of 19 December 2014. The airglow imager observations of OH emission revealed four passing frontal systems that resembled mesospheric bores which typically occur in ducting regions of the upper mesosphere. For about 1.5 hours, the lower altitude sodium layer had densities similar to that of the main layer with a peak around 90 km. The lower altitude sodium layer weakened and disappeared soon after the fourth front had passed. The fourth front had weakened in intensity by the time it approached the region of lidar beams and disappeared soon afterwards. The column integrated sodium densities increased gradually during formation of the lower altitude sodium layer. Temperatures measured with the lidar indicate that there was a strong thermal duct structure between 87 and 93 km. Furthermore, the temperature was enhanced below 85 km. Horizontal wind magnitudes estimated from the lidar showed strong wind shears above 93 km. We conclude that the combination of an enhanced stability region due to the temperature profile and intense wind shears have provided ideal conditions for evolution of multiple mesospheric bores revealed as frontal systems in OH images. The downward motion associated with the fronts appeared to have brought air rich in H and O from higher altitudes into the region below 85 km wherein the temperatures were also relatively high. This would have liberated sodium atoms from the reservoir species and suppressed the re-conversion of atomic sodium into reservoir species so that the lower altitude sodium layer could form and the column abundance could increase. The presented observations also reveal the importance of mesospheric frontal systems in bringing about significant variation of minor species over shorter temporal intervals.