O2 and OH airglow in the mesosphere through the lens of Odin/OSIRIS Infrared Imager
Doctoral thesis, 2022
Observing airglow emissions allows us to explore the chemical composition and dynamics of the upper mesosphere. The Odin satellite has routinely measured O2(a1∆g) and OH Meinel band airglow emissions from 2001 until 2015. In this thesis, the Odin/OSIRIS infrared imager data have been studied in some depth for the first time. Numerical inversions of the observed radiances have been carried out to retrieve the volume emission rates and, thereafter, the mesospheric ozone density. This resulted in a new, long-term high-resolution airglow and ozone datasets of the middle atmosphere.
The photolysis reactions are affected by periodic changes in solar irradiance. Thus, the OHv emission should vary with the solar cycle. In terms of the 11-year solar cycle, as expected, we observed that the vertically integrated intensity of OHv correlates positively with the Lyman-α flux and that the emission height correlates negatively at most latitudes except near the equator. Employing a time-dependent photochemical model, we showed that the changing local time sampling of the Odin satellite was the cause of the observed distortion of the solar cycle signature near the equator.
We also observed the episodic signatures in the two airglow emissions of sudden stratospheric warming (SSW) events. With the aid of the temperature and H2O measured from Odin-SMR, we qualitatively assessed the events that occurred in 2009, 2012, and 2013. Using analytical expressions, we derived proxy O and OHv number densities. A significant amount of atomic oxygen-rich air descends into the mesosphere a few days after the SSW onsets, resulting in unusually intense airglow emissions at a much lower altitude than average. The modelled OHv largely resembles the temporal evolution of the observed OHv. The synchronous structure of the two airglow emissions indicates that the vertical transport of O plays a dominant role in the observed changes.
This thesis work has set a valuable foundation as part of the preparations for the future MATS mission.
The photolysis reactions are affected by periodic changes in solar irradiance. Thus, the OHv emission should vary with the solar cycle. In terms of the 11-year solar cycle, as expected, we observed that the vertically integrated intensity of OHv correlates positively with the Lyman-α flux and that the emission height correlates negatively at most latitudes except near the equator. Employing a time-dependent photochemical model, we showed that the changing local time sampling of the Odin satellite was the cause of the observed distortion of the solar cycle signature near the equator.
We also observed the episodic signatures in the two airglow emissions of sudden stratospheric warming (SSW) events. With the aid of the temperature and H2O measured from Odin-SMR, we qualitatively assessed the events that occurred in 2009, 2012, and 2013. Using analytical expressions, we derived proxy O and OHv number densities. A significant amount of atomic oxygen-rich air descends into the mesosphere a few days after the SSW onsets, resulting in unusually intense airglow emissions at a much lower altitude than average. The modelled OHv largely resembles the temporal evolution of the observed OHv. The synchronous structure of the two airglow emissions indicates that the vertical transport of O plays a dominant role in the observed changes.
This thesis work has set a valuable foundation as part of the preparations for the future MATS mission.
Satellite limb observation
mesospheric ozone
photochemistry
airglow
atmospheric waves
mesosphere
Author
Anqi Li
Chalmers, Space, Earth and Environment, Geoscience and Remote Sensing
11-year solar cycle influence on OH (3-1) nightglow observed by OSIRIS
Journal of Atmospheric and Solar-Terrestrial Physics,;Vol. 229(2022)
Journal article
The OH (3-1) nightglow volume emission rate retrieved from OSIRIS measurements: 2001 to 2015
Earth System Science Data,;Vol. 13(2021)p. 5115-5126
Journal article
Retrieval of daytime mesospheric ozone using OSIRIS observations of O2 (a1Δg) emission
Atmospheric Measurement Techniques,;Vol. 13(2020)p. 6215-6236
Journal article
Anqi Li, Kristell Pérot and Donal Murtagh. Case studies of the OH and O2 airglow response to sudden stratospheric warmings with elevated stratopause
The mesosphere (from Greek `mesos', middle) is one of the `spheres' in the atmosphere, and it ranges approximately from 50 -100 km altitude. A distinct feature of the mesosphere is the existence of a shining gas known as airglow resulting from the chemical interactions with the solar light. The analysis of the airglow distribution in altitude and around the globe helps us understand the internal and external sources of disturbances such as atmospheric waves and seasonal and solar cycles.
Since 2001 the Odin satellite has been orbiting the Earth. One of the instruments onboard is OSIRIS, which has measured airglow emissions that originated from two species of gases: O2 and OH. In this thesis, the Odin/OSIRIS infrared imager data have been studied in some depth for the first time.
We first processed the raw data using a statistical method. This resulted in a new, long-term high-resolution airglow and ozone datasets of the middle atmosphere. Then, we analysed the variations seen in the data and interpreted their causes behind. One of which is the changes following the 11-year solar cycle. Because the gas concentrations in the mesosphere change according to the radiation from the sun. We also analysed the extreme events caused by the unusual atmospheric behaviour called sudden stratospheric warming in the polar night region.
Overall, this thesis work has set a valuable foundation as part of the preparations for the future satellite mission MATS, which has similar sensors onboard.
Since 2001 the Odin satellite has been orbiting the Earth. One of the instruments onboard is OSIRIS, which has measured airglow emissions that originated from two species of gases: O2 and OH. In this thesis, the Odin/OSIRIS infrared imager data have been studied in some depth for the first time.
We first processed the raw data using a statistical method. This resulted in a new, long-term high-resolution airglow and ozone datasets of the middle atmosphere. Then, we analysed the variations seen in the data and interpreted their causes behind. One of which is the changes following the 11-year solar cycle. Because the gas concentrations in the mesosphere change according to the radiation from the sun. We also analysed the extreme events caused by the unusual atmospheric behaviour called sudden stratospheric warming in the polar night region.
Overall, this thesis work has set a valuable foundation as part of the preparations for the future satellite mission MATS, which has similar sensors onboard.
Subject Categories
Physical Sciences
Earth and Related Environmental Sciences
ISBN
978-91-7905-654-4
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5120
Publisher
Chalmers