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Noctilucent clouds in a coupled atmosphere
Stockholm University, Faculty of Science, Department of Meteorology.
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Noctilucent clouds (NLC) at altitudes around 80 km are the highest clouds in our atmosphere. They have been a subject of research ever since their discovery in the late 19th century. This thesis takes an important step towards using NLC as a tool for studying dynamic coupling processes in the atmosphere on a global scale.

Six years of NLC observations by the Odin satellite have provided information on global distribution, seasonal variation and hemispheric differences in cloud properties. Spectroscopic measurements by the OSIRIS instrument onboard Odin are used to retrieve cloud particle sizes. The ideas and challenges behind these retrievals are discussed in detail. A study of the latitudinal dependence of NLC shows a general increase of cloud occurrence, brightness, and particle sizes towards the pole. Microphysical modelling suggests that the particles grow larger near the pole because of a combined effect of colder temperature, availability of water vapour, and meridional transport times.

To investigate the relationship between the cold summer mesopause region and the dynamics in the stratosphere, NLC properties derived from Odin have been used as a proxy for the state of the summer mesosphere. These data have been co-analysed with ECMWF temperatures as a proxy for the residual circulation in the stratosphere. The results of this study reveal a surprising coupling between the winter stratosphere and the summer mesopause. This interhemispheric link is suggested to be the principal cause for both year-to-year variability and hemispheric differences in summer mesosphere conditions. Further studies of the underlying dynamic coupling mechanisms were carried out using a comprehensive middle atmospheric model. As a conclusion from this study, the interannual variability in the summer polar mesopause region can be traced back to the planetary wave flux entering the winter stratosphere from the troposphere.

Place, publisher, year, edition, pages
Stockholm: Meteorologiska institutionen (MISU) , 2008. , 71 p.
Keyword [en]
Noctilucent clouds, atmospheric dynamics
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences
Identifiers
URN: urn:nbn:se:su:diva-7415ISBN: 978-91-7155-604-2 (print)OAI: oai:DiVA.org:su-7415DiVA: diva2:198229
Public defence
2008-04-04, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 10:00
Opponent
Supervisors
Available from: 2008-03-13 Created: 2008-03-13Bibliographically approved
List of papers
1. Challenges in the limb retrieval of noctilucent cloud properties from Odin/OSIRIS
Open this publication in new window or tab >>Challenges in the limb retrieval of noctilucent cloud properties from Odin/OSIRIS
2005 In: Adv. Space Res., Vol. 36, 935-942 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24740 (URN)
Note
Part of urn:nbn:se:su:diva-7415Available from: 2008-03-13 Created: 2008-03-13Bibliographically approved
2. Latitudinal dependence of noctilucent cloud growth
Open this publication in new window or tab >>Latitudinal dependence of noctilucent cloud growth
2006 In: Geophys. Res. Lett., Vol. 33, no L11812Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24741 (URN)
Note
Part of urn:nbn:se:su:diva-7415Available from: 2008-03-13 Created: 2008-03-13Bibliographically approved
3. Evidence for interhemispheric stratosphere-mesosphere coupling derived from noctilucent cloud properties
Open this publication in new window or tab >>Evidence for interhemispheric stratosphere-mesosphere coupling derived from noctilucent cloud properties
2007 In: Geophys. Res. Lett., Vol. 34, no L16806Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24742 (URN)000248896800003 ()
Note
Part of urn:nbn:se:su:diva-7415Available from: 2008-03-13 Created: 2008-03-13Bibliographically approved
4. Inter-hemispheric mesospheric coupling in a comprehensive middle atmosphere model
Open this publication in new window or tab >>Inter-hemispheric mesospheric coupling in a comprehensive middle atmosphere model
2009 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 71, no 3-4, 518-530 p.Article in journal (Refereed) Published
Abstract [en]

Observations of noctilucent clouds have revealed a surprising coupling between the winter stratosphere and the summer polar mesopause region. In spite of the great distance involved, this inter-hemispheric link has been suggested to be the principal reason for both the year-to-year variability and the hemispheric differences in the frequency of occurrence of these high-altitude clouds. In this study, we investigate the dynamical influence of the winter stratosphere on the summer mesosphere using simulations from the vertically extended version of the Canadian Middle Atmosphere Model (CMAM). We find that for both Northern and Southern Hemispheres, variability in the summer polar mesopause region from one year to another can be traced back to the planetary-wave flux entering the winter stratosphere. The teleconnection pattern is the same for both positive and negative wave-flux anomalies. Using a composite analysis to isolate the events, it is argued that the mechanism for inter-hemispheric coupling is a feedback between summer mesosphere gravity-wave drag (GWD) and zonal wind, which is induced by an anomaly in mesospheric cross-equatorial flow, the latter arising from the anomaly in winter hemisphere GWD induced by the anomaly in stratospheric conditions.

Keyword
Inter-hemispheric coupling; Middle atmosphere; Dynamics; Noctilucent clouds
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:su:diva-24743 (URN)10.1016/j.jastp.2008.08.006 (DOI)000265231700024 ()
Note
Part of urn:nbn:se:su:diva-7415Available from: 2008-03-13 Created: 2008-03-13 Last updated: 2017-12-13Bibliographically approved

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