5:15 PM - 6:45 PM
[PEM12-P03] Investigation on sodium D1 and D2 lines in the mesospheric nightglow
based on spectroscopic observations at Tromsø, Norway
Keywords:Na nightglow, Spectrograph, Tromsø
The emission layer of Na nightglow is normally located at an altitude of approximately 90 km, offering valuable insights into the atmosphere near the mesopause region. The emission mechanism of Na nightglow is well known as the Chapman mechanism. During this process, Na splits into two excited states with different energy levels, leading to the double lines in the emission spectrum: the D1 line, 589.6 nm (in air), and the D2 line, 589.0 nm (in air). While the ratio branching to the two excited states is theoretically considered to be constant, some recent works reported that the intensity ratio of the D1 and D2 lines (RD) was variable (not constant) from their observations. As an interpretation for the variable RD, a modification in the Chapman mechanism has been proposed, in which RD can vary with the balance between reactions with O and quenching with O2. To verify the interpretation, we need more detailed investigations based on more observations.
In this study, we conducted experimental observations of RD using a compact spectrograph at Tromsø, Norway (69.6N, 19.2 E), during approximately five months from October 2017 to March 2018. To enhance the resolution of our spectrograph, we replaced the diffraction grating with one that has four times higher resolution. Although this made it possible to separate the Na D1 and D2 lines more effectively, the separation was not perfect. To separate D1 and D2 lines, we performed a double-gaussian fitting in the data analysis, and subsequently obtained RD. Additionally, we analyzed all-sky images obtained during observations to examine the weather conditions and the surrounding environment affecting the observations. Such conditions over Tromsø were determined through both manual inspection and deep learning methods. We made data selections based on the determined conditions. After that, 168-hour RD data during the five months were obtained by the data analysis including the double-gaussian fitting. In the presentation, we will show the observed RD variations and discuss their relationships with O and O2 effects.
In this study, we conducted experimental observations of RD using a compact spectrograph at Tromsø, Norway (69.6N, 19.2 E), during approximately five months from October 2017 to March 2018. To enhance the resolution of our spectrograph, we replaced the diffraction grating with one that has four times higher resolution. Although this made it possible to separate the Na D1 and D2 lines more effectively, the separation was not perfect. To separate D1 and D2 lines, we performed a double-gaussian fitting in the data analysis, and subsequently obtained RD. Additionally, we analyzed all-sky images obtained during observations to examine the weather conditions and the surrounding environment affecting the observations. Such conditions over Tromsø were determined through both manual inspection and deep learning methods. We made data selections based on the determined conditions. After that, 168-hour RD data during the five months were obtained by the data analysis including the double-gaussian fitting. In the presentation, we will show the observed RD variations and discuss their relationships with O and O2 effects.