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| Titel |
Lagrangian analysis of the inter-hemispheric mass transport in the atmosphere |
| VerfasserIn |
Joakim Kjellsson, Kristofer Döös |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250032995
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| Zusammenfassung |
| The inter-hemispheric exchange of masses in the atmosphere is investigated by
Lagrangian analysis. In particular, we examine the timescales, paths and sizes of
mass transport from the two hemispheres to the equator, which can not be done by
conventional Eulerian methods. We present averages of residence times, transit residence
times and ages for different sections of each hemisphere (tropical troposphere,
stratosphere midlatitudes, etc.), and explore the spatial and temporal variability of these
timescales.
The Lagrangian trajectory code TRACMASS is extended to the atmosphere using fields
from the ERA-Interim reanalysis data set. The atmosphere is thus represented by ~ 2.5
million trajectories. The hemispheres are considered as two separate domains. The residence
time in a point, which is here the time it takes for a particle to go from that point to the
equator, is calculated by tracing trajectories forward in time. The age, which is
the time it takes for a particle to go from the equator to the point, is calculated by
tracing back in time. The transit residence time is then the sum of the residence time
and age. From this, we can calculate average age (AvA), average residence time
(AvR) and the average transit residence time (ATR) for different sections of each
hemisphere.
Preliminary results from trajectories traced from the northern hemisphere on 1 January
1989 show that the inter- hemispheric transport is much slower in the stratosphere than in the
troposphere. In the troposphere, the transit time is ~ 7 months at high latitudes and ~ 4
months in the subtropics. In the stratosphere, the transit time is ~ 2.5 years at high latitudes
and ~ 2 years in the subtropics. They also show a somewhat sharper transit time gradient in
the tropospheric subtropics that is tilted from the surface at 30-N to the tropopause
at the equator, indicating a transport barrier. Furthermore we find that surface air
over the Sahara Desert and East Pacific Ocean below 850 hPa has a shorter transit
time than the zonal average, which might be an effect of the subtropical highs. |
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