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Trends and variability in stratospheric mixing: 1979–2005

Garny, Hella and Bodeker, Greg and Dameris, Martin (2007) Trends and variability in stratospheric mixing: 1979–2005. Atmospheric Chemistry and Physics, 7, pp. 5611-5624.

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Official URL: http://www.atmos-chem-phys.net/7/5611/2007/

Abstract

Changes in climate are likely to drive changes in stratospheric mixing with associated implications for changes in transport of ozone from tropical source regions to higher latitudes, transport of water vapour and source gas degradation products from the tropical tropopause layer into the mid-latitude lower stratosphere, and changes in the meridional distribution of long-lived trace gases. To diagnose long-term changes in stratospheric mixing, global monthly fields of Lyapunov exponents were calculated on the 450 K, 550 K, and 650K isentropic surfaces by applying a trajectory model to wind fields from NCEP/NCAR reanalyses over the period 1979 to 2005. Potential underlying geophysical drivers of trends and variability in these mixing fields were investigated by applying a least squares regression model, which included basis functions for a mean annual cycle, seasonally dependent linear trends, the quasibiennial oscillation (QBO), the solar cycle, and the El Ni˜no Southern Oscillation (ENSO), to zonal mean time series of the Lyapunov exponents. Long-term positive trends in mixing are apparent over southern middle to high latitudes at 450K through most of the year, while negative trends over southern high latitudes are apparent at 650K from May to August. Wintertime negative trends in mixing over northern mid-latitudes are apparent at 550K and 650 K. Over low latitudes, within 40<sup>o</sup> of the equator, the QBO exerts a strong influence on mixing at all three analysis levels. This QBO influence is strongly modulated by the annual cycle and shows a phase shift across the subtropical mixing barrier. Solar cycle and ENSO influences on mixing are generally not significant. The diagnosed long-term changes in mixing should aid the interpretation of trends in stratospheric trace gases.

Document Type:Article
Title:Trends and variability in stratospheric mixing: 1979–2005
Authors:
AuthorsInstitution or Email of Authors
Garny, HellaLMU München, München
Bodeker, GregNIWA, Lauder, NZ
Dameris, MartinUNSPECIFIED
Date:14 November 2007
Journal or Publication Title:Atmospheric Chemistry and Physics
Volume:7
Page Range:pp. 5611-5624
Status:Published
Keywords:Lyapunov exponents, NCEP reanalyses
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EO - Erdbeobachtung
DLR - Research area:Space
DLR - Program:W EO - Erdbeobachtung
DLR - Research theme (Project):W - Vorhaben Atmosphären- und Klimaforschung (old)
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Atmospheric Dynamics
Deposited By: Prof. Dr. rer. nat. Martin Dameris
Deposited On:17 Dec 2007
Last Modified:12 Dec 2013 20:28

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