| 1. |
- Gumbel, Jörg, et al.
(författare)
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The MATS satellite mission - gravity wave studies by Mesospheric Airglow/Aerosol Tomography and Spectroscopy
- 2020
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Ingår i: Atmospheric Chemistry And Physics. - : COPERNICUS GESELLSCHAFT MBH. - 1680-7316 .- 1680-7324. ; 20:1, s. 431-455
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Tidskriftsartikel (refereegranskat)abstract
- Global three-dimensional data are a key to understanding gravity waves in the mesosphere and lower thermosphere. MATS (Mesospheric Airglow/Aerosol Tomography and Spectroscopy) is a new Swedish satellite mission that addresses this need. It applies space-borne limb imaging in combination with tomographic and spectroscopic analysis to obtain gravity wave data on relevant spatial scales. Primary measurement targets are O-2 atmospheric band dayglow and nightglow in the near infrared, and sunlight scattered from noctilucent clouds in the ultraviolet. While tomography provides horizontally and vertically resolved data, spectroscopy allows analysis in terms of mesospheric temperature, composition, and cloud properties. Based on these dynamical tracers, MATS will produce a climatology on wave spectra during a 2-year mission. Major scientific objectives include a characterization of gravity waves and their interaction with larger-scale waves and mean flow in the mesosphere and lower thermosphere, as well as their relationship to dynamical conditions in the lower and upper atmosphere. MATS is currently being prepared to be ready for a launch in 2020. This paper provides an overview of scientific goals, measurement concepts, instruments, and analysis ideas.
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| 2. |
- Li, Anqi, 1990, et al.
(författare)
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11-year solar cycle influence on OH (3-1) nightglow observed by OSIRIS
- 2022
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Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826. ; 229
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Tidskriftsartikel (refereegranskat)abstract
- In the mesosphere, the vibrationally excited hydroxyl layer is sensitive to changes in incoming solar flux. An enhanced photodissociation of molecular oxygen will lead to more atomic oxygen production, thus we expect the OH layer emission rate to be positively with the Lyman-α flux and the emission height to be negatively correlated. The Optical Spectrograph and InfraRed Imager System (OSIRIS) has recorded the Meinel band centred at 1.53 μm from 2001 to 2015. In this study, we show how the 11-year solar cycle signature manifests itself in this data set, in terms of OH zenith emission rate and emission height. As expected, the emission height is negatively correlated with the Lyman-α flux at all latitudes. The zenith emission rate is positively correlated with the Lyman-α flux at most latitudes except near the equator. By the means of a time dependent photochemical model, we show 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.
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| 3. |
- Li, Anqi, 1990
(författare)
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New perspectives in mesospheric wave dynamics and oxygen photochemistry
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The mesosphere is the region of the atmosphere between 50km to 100km, where both dynamical and photochemical aspects play important roles for the thermal balance. This thesis focuses on the following three areas for mesospheric studies: wave dynamics, oxygen photochemistry and retrieval using the optimal estimation method. Atmospheric gravity waves are internal disturbances in the medium that propagate horizontally and vertically. Based on linear wave theory, this thesis attempts to enhance our understanding of the relationships between the wave characteristics, the mean flow and the sources. We try to emphasise the frequency change due to the Doppler effect in several reference frames. This thesis proposes a consistent framework for deriving those wave parameters that cannot be obtained from a single type of instrument due to their particular observational geometry. Finally, a plausible interpretation of a readily available ground-based lidar observation is given as an example. Oxygen photochemistry is another important aspect in this thesis. The underlying chemical reactions are affected by disturbances in the local temperature and density, which in turn changes the distribution of the excited oxygen species. In this work, a photochemical model has been implemented, which describes most of the important processes such as O3 photolysis that are related to the production and loss of O(1D), O2(b1Σg+ ) and O2(a1∆g). The observation of airglow emissions provides an opportunity to explore the chemical composition and wave dynamics in the upper mesosphere. The Odin satellite has been routinely measuring O2(a1∆g) airglow emissions since 2001. In this thesis, data collected by OSIRIS are explored. Inversions are carried out in order to retrieve the volume emission rate of O2(a1∆g) as well as the mesospheric ozone density. The resulting ozone profiles are shown to be consistent with other independent ozone datasets collected by instruments aboard the same spacecraft as well as ACE-FTS and MIPAS, despite intrinsically different measurement principles. The overall good agreement between them illustrates the good performance of the retrieval technique. Furthermore, these investigations serve well as a preparatory activity for the upcoming satellite mission MATS, set for launch later this year.
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| 4. |
- Li, Anqi, 1990
(författare)
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O2 and OH airglow in the mesosphere through the lens of Odin/OSIRIS Infrared Imager
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 5. |
- Li, Anqi, 1990, et al.
(författare)
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Retrieval of daytime mesospheric ozone using OSIRIS observations of O2 (a1Δg) emission
- 2020
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 13:11, s. 6215-6236
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Tidskriftsartikel (refereegranskat)abstract
- This work is distributed under the Creative Commons Attribution 4.0 License. Improving knowledge of the ozone global distributions in the mesosphere-lower thermosphere (MLT) is a crucial step in understanding the behaviour of the middle atmosphere. However, the concentration of ozone under sunlit conditions in the MLT is often so low that its measurement requires instruments with very high sensitivity. Fortunately, the bright oxygen airglow can serve as a proxy to retrieve the daytime ozone density indirectly, due to the strong connection to ozone photolysis in the Hartley band. The OSIRIS IR imager (hereafter, IRI), one of the instruments on the Odin satellite, routinely measures the oxygen infrared atmospheric band (IRA band) at 1.27 μm. In this paper, we will primarily focus on the detailed description of the steps done for retrieving the calibrated IRA band limb radiance (with <10 % random error), the volume emission rate of O2 ( a 1i"g) (with <25 % random error) and finally the ozone number density (with <20 % random error). This retrieval technique is applied to a 1-year sample from the IRI dataset. The resulting product is a new ozone dataset with very tight along-track sampling distance (<20 km). The feasibility of the retrieval technique is demonstrated by a comparison of coincident ozone measurements from other instruments aboard the same spacecraft, as well as zonal mean and monthly average comparisons between Odin-OSIRIS (both spectrograph and IRI), Odin-SMR and Envisat-MIPAS. We find that IRI appears to have a positive bias of up to 25 % below 75 km, and up to 50 % in some regions above. We attribute these differences to uncertainty in the IRI calibration as well as uncertainties in the photochemical constants. However, the IRI ozone dataset is consistent with the compared dataset in terms of the overall atmospheric distribution of ozone between 50 and 100 km. If the origin of the bias can be identified before processing the entire dataset, this will be corrected and noted in the dataset description. The retrieval technique described in this paper can be further applied to all the measurements made throughout the 19 year mission, leading to a new, long-term high-resolution ozone dataset in the middle atmosphere.
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| 6. |
- Li, Anqi, 1990, et al.
(författare)
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The OH (3-1) nightglow volume emission rate retrieved from OSIRIS measurements: 2001 to 2015
- 2021
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Ingår i: Earth System Science Data. - : Copernicus GmbH. - 1866-3516 .- 1866-3508. ; 13:11, s. 5115-5126
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Tidskriftsartikel (refereegranskat)abstract
- The OH airglow has been used to investigate the chemistry and dynamics of the mesosphere and the lower thermosphere (MLT) for a long time. The infrared imager (IRI) aboard the Odin satellite has been recording the night-time 1.53 mu m OH (3-1) emission for more than 15 years (2001-2015), and we have recently processed the complete data set. The newly derived data products contain the volume emission rate profiles and the Gaussian-approximated layer height, thickness, peak intensity and zenith intensity, and their corresponding error estimates. In this study, we describe the retrieval steps for these data products. We also provide data screening recommendations. The monthly zonal averages depict the well-known annual oscillation and semi-annual oscillation signatures, which demonstrate the fidelity of the data set (https://doi.org/10.5281/zenodo.4746506, Li et al., 2021). The uniqueness of this Odin IRI OH long-term data set makes it valuable for studying various topics, for instance, the sudden stratospheric warming events in the polar regions and solar cycle influences on the MLT.
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