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Solar Forcing of Nitric Oxide in the Upper Atmosphere
Stockholm University, Faculty of Science, Department of Meteorology .ORCID iD: 0000-0003-3679-6744
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University , 2018. , p. 38
Keywords [en]
nitric oxide, NO, mesosphere, lower thermosphere, MLT, energetic particle precipitation, EPP, medium energy electrons, MEE, SOFIE, SNOE, WACCM, POES
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-152065ISBN: 978-91-7797-139-9 (print)ISBN: 978-91-7797-140-5 (electronic)OAI: oai:DiVA.org:su-152065DiVA, id: diva2:1176968
Public defence
2018-03-09, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2018-02-14 Created: 2018-01-23 Last updated: 2018-02-12Bibliographically approved
List of papers
1. Observation of 27-day solar cycles in mesospheric production and descent of EPP-produced NO
Open this publication in new window or tab >>Observation of 27-day solar cycles in mesospheric production and descent of EPP-produced NO
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2015 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 10, p. 8978-8988Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-122156 (URN)10.1002/2015JA021441 (DOI)000366135200058 ()
Available from: 2015-10-27 Created: 2015-10-27 Last updated: 2018-01-23Bibliographically approved
2. Relative Importance of Nitric Oxide Physical Drivers in the Lower Thermosphere
Open this publication in new window or tab >>Relative Importance of Nitric Oxide Physical Drivers in the Lower Thermosphere
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2017 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 19, p. 10081-10087Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-149006 (URN)10.1002/2017GL074786 (DOI)000413921300062 ()
Available from: 2017-11-22 Created: 2017-11-22 Last updated: 2020-01-30Bibliographically approved
3. Direct and indirect electron precipitation effect on nitric oxide in the polar middle atmosphere, using a full-range energy spectrum
Open this publication in new window or tab >>Direct and indirect electron precipitation effect on nitric oxide in the polar middle atmosphere, using a full-range energy spectrum
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 8, p. 8679-8693Article in journal (Refereed) Published
Abstract [en]

In April 2010, a coronal mass ejection and a corotating interaction region on the Sun resulted in an energetic electron precipitation event in the Earth’s atmosphere. We investigate direct and indirect nitric oxide (NO) response to the electron precipitation. By combining electron fluxes from the Total Energy Detector and the Medium Energy Proton and Electron Detector on the National Oceanic and Atmospheric Administration’s Polar-orbiting Operational Environmental Satellites, we obtain a continuous energy spectrum covering 1–750 keV. This corresponds to electrons depositing their energy at atmospheric altitudes 60–120 km. Based on the electron energy deposition, taking into account loss due to photolysis, the accumulated NO number density is estimated. When compared to NO measured at these altitudes by the Solar Occultation for Ice Experiment instrument on board the Aeronomy of Ice in the Mesosphere satellite, the NO direct effect was detected down to 55 km. The main variability at these altitudes is, however, dominated by the indirect effect, which is downward transported NO. We estimate the source of this descending NO to be in the upper mesosphere at ~75–90 km.

Keywords
energetic electron precipitation, nitric oxide, direct and indirect effect
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-147552 (URN)10.1002/2017JA024364 (DOI)000411788800056 ()
Available from: 2017-10-03 Created: 2017-10-03 Last updated: 2018-01-23Bibliographically approved
4. Production and transport mechanisms of NO in observations and models
Open this publication in new window or tab >>Production and transport mechanisms of NO in observations and models
2018 (English)In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 18, no 12, p. 9075-9089Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Earth and Related Environmental Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-152063 (URN)10.5194/acp-2017-1188 (DOI)000436579500009 ()
Available from: 2018-01-23 Created: 2018-01-23 Last updated: 2018-07-23Bibliographically approved

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