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| Titel |
Using finite-time Lyapunov exponents to investigate the effect of stratospheric sudden warmings on the polar vortices |
| VerfasserIn |
M. Smith, A. J. McDonald |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250061811
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| Zusammenfassung |
| Finite-time Lyapunov exponents are often used to measure mixing in the stratosphere and
have been used to investigate the horizontal transport of trace gases near the polar vortices. A
better understanding of the dynamics of the polar vortices should provide insight into the
circumstances under which odd nitrogen and hydrogen produced by energetic particle
precipitation (EPP) in the mesosphere and lower thermosphere (MLT) can be transported to
lower levels of the atmosphere.
A climatology of finite-time Lyapunov exponents for isentropic surfaces in the
stratosphere ranging from 550-2300K for both the northern and southern hemispheres has
been created for the observational period of the EOS-MLS instrument.The Lyapunov
exponents are derived by using output from a Lagrangian trajectory model forced by data
from the MERRA reanalysis. They are calculated at each point on a 2Ë x 4Ë global grid by
running trajectories for two neighbouring parcels which are initially 1km apart and measuring
their separation after a period of time. In order to ensure that the parcel trajectories
remain close enough to each other for the exponents to be a good measure of local
mixing, the distance between the parcels is periodically reset to 1km. In order to
provide a consistency check Lyapunov exponents and trajectories have also been
calculated at 550K using NCEP/NCAR reanalysis data. Initial comparisons suggest that
the qualitative agreement is quite good between the results using the two different
reanalyses.
Comparison of the variations in the Lyapunov exponents and trace gas distributions
using EOS-MLS data during periods where the stratospheric polar vortices are
undisturbed and periods which are disturbed by stratospheric sudden warmings are
also discussed. Studying how stratospheric sudden warmings (SSWs) affect the
atmospheric dynamics in polar regions is particularly worthwhile since recent studies have
shown that they have a significant modulating influence upon the EPP indirect effect
in the stratosphere. Variations in the impacts of planetary waves on the position
and strength of the polar vortices in the middle and upper stratosphere will also be
discussed. Differences between the generally undisturbed Southern hemisphere vortices
and the dynamically disturbed Northern hemisphere vortices will also be detailed. |
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