Abstract
Secular variability of the coupled tropospheric and
stratospheric circulation in the GCM ECHAM3/LSG
Frauke Feser, Hans-F. Graf and Judith Perlwitz
Secular or multi-decadal variability is a widely observed phenomenon, apparent in
instrumental and paleo climatic records. These long time oscillations
are found in many variables of the climate system. The ocean especially
experiences low frequency variations. But also atmospheric variables such
as
temperature, wind velocity and sea level pressure can show secular
variability.
The low frequency variability here is examined in the coupled
atmosphere-ocean model ECHAM3/LSG T21. A coupled stratospheric and
tropospheric mode is detected oscillating with a period of approximately
100 years. The atmospheric pressure system mainly involved in this
oscillation is the northern hemispheric winter stratospheric polar vortex. The near surface
temperature experiences variations of the same magnitude as the observed
temperature trends of the last decades. Multi decadal variability is also
shown in the North Atlantic Oscillation Index.
A shift of the length of the oscillation period between longer and shorter
time scales indicates that chaotic processes might be responsible for the
variability.
Time series [years] of the first PC of winterly zonal mean zonal wind
of the northern hemisphere (20 degrees N - 85.76 degrees N; control run)
smoothed with a two year running mean filter (blue line). The black line represents the 30 year running mean of the second PC's time series. Horizontal lines indicate one positive and one negative standard deviation of the smoothed time series.
Secular variability of the coupled tropospheric and stratospheric circulation in the GCM ECHAM3/LSG
F. Feser, H.-F. Graf and J. Perlwitz
Theor Appl Climatol 65 (2000) 1/2, 1-15
[Download paper in PDF-format] (~4.2 MB)
Download PDF-file of my Diploma Thesis "Dekadische Variabilitaet der gekoppelten troposphaerischen und stratosphaerischen Zirkulation"
(Sorry, only in german)