Abstract
Sodium airglow is generated when excited sodium atoms emit electromagnetic radiation while they are relaxing from an excited state into a lower energetic state. This electromagnetic radiation, the two sodium D-lines at 589.0 nm and 589.6 nm, can usually be detected from space or from ground. Sodium nightglow occurs at times when the sun is not present and excitation of sodium atoms is a result of chemical reaction with ozone. The detection of sodium nightglow can be a means to determine the amount of sodium in the earths' mesosphere and lower thermosphere (MLT). In this study, we present time series of monthly mean sodium concentration profiles, by utilizing the large spatial and temporal coverage of satellite sodium D-line nightglow measurements. We use the OSIRIS/Odin mesospheric limb measurements to derive sodium concentration profiles and vertical column densities and compare those to measurements from SCIAMACHY/Envisat and GOMOS/Envisat. Here we show that the Na D-line Limb Emission Rate (LER) and Volume emission rate (VER) profiles calculated from the OSIRIS and SCIAMACHY measurements, although the OSIRIS LER and VER profiles are around 25 % lower, agree very well in shape and overall seasonal variation. The sodium concentration profiles also agree in shape and magnitude, although those do not show the clear semi-annual cycle which is present in the LER and VER profiles. The comparison to the GOMOS sodium vertical column densities (VCD) shows that the OSIRIS VCDs are in the same order of magnitude although again the semi-annual cycle is not as clear. We attribute the differences in the LER, VER and sodium profiles to the differences in spatial coverage between the two satellite measurements, the lower signal-to-noise ratio (SNR) of the SCIAMACHY measurements and differences in local time between the measurements of the two satellites.
Highlights
It has been known for a long time that the night sky, even in moonless nights, is sometimes not completely dark
We show that the Na D-line Limb Emission Rate (LER) and Volume emission rate (VER) profiles calculated from the 10 Optical Spectrograph and Infrared Imager System (OSIRIS) and SCIAMACHY measurements, the OSIRIS LER and VER profiles are around 25 % lower, agree very well in shape and overall seasonal variation
The sodium concentration profiles agree in shape and magnitude, those do not show the clear semi-annual cycle which is present in the LER and VER profiles
Summary
It has been known for a long time that the night sky, even in moonless nights, is sometimes not completely dark. M. Shrum found the green emission line of oxygen which could explain the two apparently related phenomena in the night sky (McLennan and Shrum, 1925). Less than a decade later, V.M. Slipher found that in addition to the oxygen green line, the night sky emissions contained features at wavelengths corresponding to the sodium doublet. Slipher found that in addition to the oxygen green line, the night sky emissions contained features at wavelengths corresponding to the sodium doublet He concluded that there has to be a layer of sodium atoms in the upper atmosphere (Slipher, 1929). To determine the background atmosphere, temperature, O2 and N2 profiles are taken from the NRLMSIS-00 atmosphere model (Picone et al, 2002). The data was filtered for the latitude band described previously and we took one profile for every month at 06:00 pm or 10:00 pm for OSIRIS and SCIAMACHY, respectively
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
