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Observation of 27-day solar cycles in mesospheric production and descent of EPP-produced NO
Stockholm University, Faculty of Science, Department of Meteorology .ORCID iD: 0000-0003-3679-6744
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
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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.

Place, publisher, year, edition, pages
2015. Vol. 120, no 10, p. 8978-8988
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-122156DOI: 10.1002/2015JA021441ISI: 000366135200058OAI: oai:DiVA.org:su-122156DiVA, id: diva2:865230
Available from: 2015-10-27 Created: 2015-10-27 Last updated: 2018-01-23Bibliographically approved
In thesis
1. Solar Forcing of Nitric Oxide in the Upper Atmosphere
Open this publication in new window or tab >>Solar Forcing of Nitric Oxide in the Upper Atmosphere
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
Keyword
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:nbn:se:su:diva-152065 (URN)978-91-7797-139-9 (ISBN)978-91-7797-140-5 (ISBN)
Public defence
2018-03-09, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
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Supervisors
Available from: 2018-02-14 Created: 2018-01-23 Last updated: 2018-02-12Bibliographically approved

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