Datensatz

Zusammenfassung

The effects on the atmospheric circulation imposed by EI Nino-induced SST-
forcing („EI Nino—forcing“), by volcanic dust induced stratospheric heating and
reduction of solar radiation (,,volcanic forcing“) and by a combination of both
are investigated using permanent January runs of the low-resolution (T21)
ECHAM2—GCM. Considering zonally averaged quantities related to the
atmospheric energy cycle, we find two features that are unique for the forc-
ings: the Hadley circulation is increased with EI Nifio-forcing present, and the
stratospheric jet of the winter hemisphere is increased with volcanic forcing.
Combined forcing produces both anomalies simultaneously. Other anomaly
structures are excited no matter which forcing is active, and it is mostly the
local anomaly amplitudes that vary. Thus, the other zonal mean anomalies are
not suitable for a separation of signals.
One of the features common to both forcings is an increase of heat transports
by stationary eddies. It causes sinking tropospheric temperatures at 30°N. It
is in contrast to expectations from linear model studies that this modification of
the stationary waves is associated with opposing stratospheric wind anoma-
lies.
In accordance with the reduced temperature gradients poleward of 30°N,
local contributions to baroclinic energy conversions by transient eddies are
smaller than in the control run. This means that, with respect to the zonal
mean temperature signal, the transient eddies are counteracting the anomaly
imposed by the stationary eddies.