| 1. |
- Asmus, H., et al.
(author)
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Charge balance for the mesosphere with meteoric dust particles
- 2015
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In: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 127, s. 137-149
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Journal article (peer-reviewed)abstract
- An aerosol particle charging model initially developed for noctilucent cloud ice particles has been extended in several steps in order to better explain the data for charged meteoric smoke particles (MSPs) obtained by the nighttime and daytime CHAMPS rockets launched from Andoya, Norway, in October 2011. Addition of photodetachment to the model shows that this process reduces the number density of positively charged MSPs as well as the number density of negatively charged MSPs as a consequence of the photodetached electrons neutralizing the positively charged MSPs. In addition, the model shows that the ionization rate can be deduced from the electron number density and the electron-ion recombination rate only at the highest altitudes (those with ionization rates above 20 cm(-3) s(-1)) as a consequence of recombination on the MSPs being dominant at lower altitudes. The differences between the daytime and the nighttime rocket data suggest a photodetachment rate between 0.1 and 0.01 s(-1). A further extension of the model to include the formation of negative ions and their destruction helps explain the ledge seen in the number density of the lightest negatively charged particles. The MSP number densities that are the inputs to the charging model are taken from the CARMA/CHEM2D model. The CHAMPS data are more consistent with number densities generated with an assumed input flux from ablation of 4 t d(-1) than with 44 t d(-1) assumed previously.
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| 2. |
- Christensen, Ole Martin, 1984, et al.
(author)
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The relationship between polar mesospheric clouds and their background atmosphere as observed by Odin-SMR and Odin-OSIRIS
- 2016
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In: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 16:19, s. 12587-12600
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Journal article (peer-reviewed)abstract
- In this study the properties of polar mesospheric clouds (PMCs) and the background atmosphere in which they exist are studied using measurements from two instruments, OSIRIS and SMR, on board the Odin satellite. The data comes from a set of tomographic measurements conducted by the satellite during 2010 and 2011. The expected ice mass density and cloud frequency for conditions of thermodynamic equilibrium, calculated using the temperature and water vapour as measured by SMR, are compared to the ice mass density and cloud frequency as measured by OSIRIS. We find that assuming thermodynamic equilibrium reproduces the seasonal, latitudinal and vertical variations in ice mass density and cloud frequency, but with a high bias of a factor of 2 in ice mass density. To investigate this bias, we use a simple ice particle growth model to estimate the time it would take for the observed clouds to sublimate completely and the time it takes for these clouds to reform. We find a difference in the median sublimation time (1.8 h) and the reformation time (3.2 h) at peak cloud altitudes (82-84 km). This difference implies that temperature variations on these timescales have a tendency to reduce the ice content of the clouds, possibly explaining the high bias of the equilibrium model. Finally, we detect and are, for the first time, able to positively identify cloud features with horizontal scales of 100 to 300 km extending far below the region of supersaturation (>2 km). Using the growth model, we conclude these features cannot be explained by sedimentation alone and suggest that these events may be an indication of strong vertical transport.
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| 3. |
- Gumbel, Jörg, et al.
(author)
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Charged meteoric smoke as ice nuclei in the mesosphere. Part 1 : A review of basic concepts
- 2009
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In: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 71:12, s. 1225-1235
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Journal article (peer-reviewed)abstract
- The role of meteoric smoke as condensation nuclei for mesospheric ice has recently been challenged by model simulations on the global transport of meteoric material. At the same time a considerable fraction of smoke particles is charged in the mesosphere. This has significant effects on nucleation processes as it can remove the Kelvin barrier. We suggest that in particular nucleation on negatively charged smoke is likely to be a dominant mechanism for mesospheric ice formation. This is in contrast to nucleation on positive ion clusters as the latter is largely hampered by efficient ion/electron recombination. Surprisingly, the large potential of nucleation on charged smoke has so far not been considered in mesospheric ice models. A challenging question concerns the fraction of mesospheric smoke that is actually charged. An improved understanding of mesospheric charging and nucleation will require laboratory experiments on nuclei in the transition regime between molecular and particulate sizes.
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| 4. |
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| 5. |
- Gumbel, Jörg, et al.
(author)
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The MATS satellite mission - gravity wave studies by Mesospheric Airglow/Aerosol Tomography and Spectroscopy
- 2020
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In: Atmospheric Chemistry And Physics. - : COPERNICUS GESELLSCHAFT MBH. - 1680-7316 .- 1680-7324. ; 20:1, s. 431-455
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Journal article (peer-reviewed)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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| 6. |
- Harvey, V. Lynn, et al.
(author)
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Improving ionospheric predictability requires accurate simulation of the mesospheric polar vortex
- 2022
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In: Frontiers in Astronomy and Space Sciences. - : Frontiers Media SA. - 2296-987X. ; 9
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Journal article (peer-reviewed)abstract
- The mesospheric polar vortex (MPV) plays a critical role in coupling the atmosphere-ionosphere system, so its accurate simulation is imperative for robust predictions of the thermosphere and ionosphere. While the stratospheric polar vortex is widely understood and characterized, the mesospheric polar vortex is much less well-known and observed, a short-coming that must be addressed to improve predictability of the ionosphere. The winter MPV facilitates top-down coupling via the communication of high energy particle precipitation effects from the thermosphere down to the stratosphere, though the details of this mechanism are poorly understood. Coupling from the bottom-up involves gravity waves (GWs), planetary waves (PWs), and tidal interactions that are distinctly different and important during weak vs. strong vortex states, and yet remain poorly understood as well. Moreover, generation and modulation of GWs by the large wind shears at the vortex edge contribute to the generation of traveling atmospheric disturbances and traveling ionospheric disturbances. Unfortunately, representation of the MPV is generally not accurate in state-of-the-art general circulation models, even when compared to the limited observational data available. Models substantially underestimate eastward momentum at the top of the MPV, which limits the ability to predict upward effects in the thermosphere. The zonal wind bias responsible for this missing momentum in models has been attributed to deficiencies in the treatment of GWs and to an inaccurate representation of the high-latitude dynamics. In the coming decade, simulations of the MPV must be improved.
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| 7. |
- Hendrickx, Koen, 1990-, et al.
(author)
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Observation of 27-day solar cycles in mesospheric production and descent of EPP-produced NO
- 2015
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In: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 120:10, s. 8978-8988
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Journal article (peer-reviewed)abstract
- Nitric oxide (NO) is produced by energetic particle precipitation (EPP) in the mesosphere-lower thermosphere (MLT) region, and during the polar winter, NO can descend to stratospheric altitudes where it destroys ozone. In this paper, we study the general scenario, as opposed to a case study, of NO production in the thermosphere due to energetic particles in the auroral region. We first investigate the relationship between NO production and two geomagnetic indices. The analysis indicates that the auroral electrojet index is a more suitable proxy for EPP-produced NO than the typically used midlatitude Ap index. In order to study the production and downward transport of NO from the lower thermosphere to the mesosphere, we perform superposed epoch analyses on NO observations made by the Solar Occultation For Ice Experiment instrument on board the Aeronomy of Ice in the Mesosphere satellite. The epoch analysis clearly shows the impact of the 27 day solar cycle on NO production. The effect is observed down to an altitude range of about 50 km to 65 km, depending on the hemisphere and the occurrence of stratospheric warmings. Initially, a rapid downward transport is noted during the first 10 days after EPP onset to an altitude of about 80–85 km, which is then followed by a slower downward transport of approximately 1–1.2 km/d to lower mesospheric altitudes in the order of 30 days.
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| 8. |
- Hendrickx, Koen, et al.
(author)
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Production and transport mechanisms of NO in observations and models
- 2018
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In: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 18:12, s. 9075-9089
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Journal article (peer-reviewed)abstract
- A reservoir of Nitric Oxide (NO) in the lower thermosphere efficiently cools the atmosphere after periods of enhanced geomagnetic activity. Transport from this reservoir to the stratosphere within the winter polar vortex allows NO to deplete ozone levels and thereby affect the middle atmospheric heat budget. As more climate models resolve the mesosphere and lower thermosphere (MLT) region, the need for an improved representation of NO related processes increases. This work presents a detailed comparison of NO in the Antarctic MLT region between observations made by the Solar Occultation for Ice Experiment (SOFIE) instrument onboard the Aeronomy of Ice in the Mesosphere (AIM) satellite and simulations performed by the Whole Atmosphere Community Climate Model with Specified Dynamics (SD-WACCM). We investigate 7 years of SOFIE observations and focus on the Southern hemisphere, rather than on dynamical variability in the Northern hemisphere or a specific geomagnetic perturbed event. The morphology of the simulated NO is in agreement with observations though the long term mean is too high and the short term variability is too low. Number densities are more similar during winter, though the altitude of peak densities, which reaches between 102–106 km in WACCM and between 98–104 km in SOFIE, is most separated during winter. Using multiple linear regressions and superposed epoch analyses we investigate how well the NO production and transport are represented in the model. The impact of geomagnetic activity is shown to drive NO variations in the lower thermosphere similarly across both datasets. The dynamical transport from the lower thermosphere into the mesosphere during polar winter is found to agree very well, with a descent rate of about 2.2 km/day in the 80–110 km region in both datasets. The downward transported NO fluxes are however too low in WACCM, which is likely due to medium energy electrons and D-region chemistry that are not represented in the model.
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| 9. |
- Hendrickx, Koen, et al.
(author)
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Relative Importance of Nitric Oxide Physical Drivers in the Lower Thermosphere
- 2017
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 44:19, s. 10081-10087
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Journal article (peer-reviewed)abstract
- Nitric oxide (NO) observations from the Solar Occultation for Ice Experiment and Student Nitric Oxide Explorer satellite instruments are investigated to determine the relative importance of drivers of short-term NO variability. We study the variations of deseasonalized NO anomalies by removing a climatology, which explains between approximately 70% and 90% of the total NO budget, and relate them to variability in geomagnetic activity and solar radiation. Throughout the lower thermosphere geomagnetic activity is the dominant process at high latitudes, while in the equatorial region solar radiation is the primary source of short-term NO changes. Consistent results are obtained on estimated geomagnetic and radiation contributions of NO variations in the two data sets, which are nearly a decade apart in time. The analysis presented here can be applied to model simulations of NO to investigate the accuracy of the parametrized physical drivers.
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| 10. |
- Hendrickx, Koen, 1990-
(author)
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Solar Forcing of Nitric Oxide in the Upper Atmosphere
- 2018
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Doctoral thesis (other academic/artistic)abstract
- The forcing of the Sun on Earth's atmosphere manifests itself via solar radiation and energetic particle precipitation (EPP), which variations are most noticeable in the upper regions of the atmosphere. A key species in the lower thermosphere, which is influenced by solar forcing, is nitric oxide (NO). An NO reservoir is present in the lower thermosphere, from which NO-rich air can be transported downward into the mesosphere and stratosphere, where it takes part in catalytic ozone destruction cycles. For climate models to correctly simulate the solar forcing on our climate, the processes of NO production and destruction, as well as the descent into the lower atmosphere, must be understood and accurately represented.In this thesis, observations from the Solar Occultation For Ice Experiment (SOFIE) instrument onboard the Aeronomy of Ice in the Mesosphere (AIM) satellite are used to investigate temporal characteristics of NO in the mesosphere and lower thermosphere. We have developed a diagnostic method to determine the relative importance of the NO physical drivers throughout the lower thermosphere. The method shows that, at high latitudes, precipitating auroral electrons dominantly drive NO variations. Comparisons with NO measurements by the Student Nitric Oxide Experiment (SNOE), made almost a decade earlier, reveal that the impact of this forcing on NO appears to be invariant throughout the 11 year solar cycle.On shorter timescales, we have shown a clear signature of the reoccurring 27 day geomagnetic impact on NO concentrations during summer and winter, with subsequent descent into the lower mesosphere during winter. The occurrence of medium energy electrons, which precipitate to mesospheric altitudes, results in a further increase of the descending NO flux. This complicates the determination of the relative contribution of the EPP direct and indirect effect on NO, i.e. separating direct NO production from downwards transported NO, respectively, in NO enhancements at a certain altitude. Using a full-range energy spectrum from the Polar-orbiting Operational Environmental Satellites (POES), we have been able to disentangle the direct and indirect EPP effect on Southern hemispheric NO during a geomagnetic storm in 2010.Simulations of NO by the Whole Atmosphere Community Climate Model with Specified Dynamics (SD-WACCM) model reveal that the model predicts a too high climatological mean, while the short term variability is too low, as compared to SOFIE. However, even though the dynamical transport in both model and observations agrees very well, the descending NO fluxes are too low in the model.In conclusion, the results of this thesis provide a better understanding of NO variability from an observational standpoint and will enable better model representations in the future.
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