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Observations of the mesospheric semi-annual oscillation (MSAO) in water vapour by Odin/SMR
Stockholm University, Faculty of Science, Department of Meteorology .
Chalmers University of Technology, Department of Radio and Space Science.
Stockholm University, Faculty of Science, Department of Meteorology .
Chalmers University of Technology, Department of Radio and Space Science.
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2008 (English)In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 8, 6527-6540 p.Article in journal (Refereed) Published
Abstract [en]

Mesospheric water vapour measurements taken by the SMR instrument aboard the Odin satellite between 2002 and 2006 have been analysed with focus on the mesospheric semi-annual circulation in the tropical and subtropical region. This analysis provides the first complete picture of mesospheric SAO in water vapour, covering altitudes above 80 km where previous studies were limited. Our analysis shows a clear semi-annual variation in the water vapour distribution in the entire altitude range between 65 km and 100 km in the equatorial area. Maxima occur near the equinoxes below 75 km and around the solstices above 80 km. The phase reversal occurs in the small layer in-between, consistent with the downward propagation of the mesospheric SAO in the zonal wind in this altitude range. The SAO amplitude exhibits a double peak structure in the equatorial region, with maxima at about 75 km and 81 km. The observed amplitudes show higher values than an earlier analysis based on UARS/HALOE data. The upper peak amplitude remains relatively constant with latitude. The lower peak amplitude decreases towards higher latitudes, but recovers in the Southern Hemisphere subtropics. On the other hand, the annual variation is much more prominent in the Northern Hemisphere subtropics. Furthermore, higher volume mixing ratios during summer and lower values during winter are observed in the Northern Hemisphere subtropics, as compared to the corresponding latitude range in the Southern Hemisphere.

Place, publisher, year, edition, pages
2008. Vol. 8, 6527-6540 p.
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences
Identifiers
URN: urn:nbn:se:su:diva-25444ISI: 000260927800015OAI: oai:DiVA.org:su-25444DiVA: diva2:199729
Note
Part of urn:nbn:se:su:diva-8167Available from: 2008-09-10 Created: 2008-09-10 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Observations of water vapour in the middle atmosphere
Open this publication in new window or tab >>Observations of water vapour in the middle atmosphere
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Water vapour is the most important greenhouse gas and plays a fundamental role in the climate system and for the chemistry of the Earth's atmosphere. This thesis presents observations of water vapour in the middle atmosphere with a particular focus on the mesosphere. The majority of these observations presented in this thesis have been performed by the Swedish satellite Odin, providing global observations since 2001. Further observations come from the Hygrosonde-2 campaign in December 2001 based on balloon and rocket-borne measurements. A general overview of Odin's water vapour measurements in the middle atmosphere is given. The optimisation of the mesospheric water vapour retrieval is presented in detail.

The analysis of the observations has focused mainly on different dynamical aspects utilising the characteristic of water vapour as a dynamical tracer in the middle atmosphere. One application is the mesospheric part of the semi-annual oscillation (SAO). The observations reveal that this oscillation is the dominant pattern of variability between 30°S and 10°N in the mesosphere up to an altitude of 80 km. Above 90 km the SAO is dominating at all latitudes in the tropics and subtropics. It is shown that the SAO exhibits a distinct phase change between 75 km and 80 km in the tropical region.

This thesis also presents the first satellite observations of water vapour in the altitude range between 90 km and 110 km, extending the observational database up into the lower thermosphere. In the polar regions water vapour exhibits the annual maximum during winter time above 95 km, mainly caused by upwelling during this season. This behaviour is different from that observed in the subjacent part of the mesosphere where the annual maximum occurs during summer time.

The Hygrosonde-2 campaign provided a high resolution measurement of water vapour in the vicinity of the polar vortex edge. This edge prevents horizontal transport causing different water vapour characteristics inside and outside the polar vortex. The observations show that this separating behaviour extends high up into the mesosphere. Small scale transitions in the Hygrosonde-2 profile between conditions inside and outside the vortex coincided with wind shears caused by gravity waves.

Place, publisher, year, edition, pages
Stockholm: Meteorologiska institutionen (MISU), 2008. 63 p.
Keyword
water vapour, mesosphere, stratosphere, dynamics, Odin satellite, limb sounding, microwave, tropics, polar winter
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:su:diva-8167 (URN)978–91–7155–721–6 (ISBN)
Public defence
2008-09-19, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 13:00
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Available from: 2008-09-10 Created: 2008-09-10Bibliographically approved

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