Sensitivity of eddies to the vertical structure of baroclinicity

Abstract
The relation between the mean meridional temperature gradient and eddy
fluxes has been addressed by several eddy flux closure theories.
However, these theories give little information on the dependence of
eddy fluxes on the vertical structure of the temperature gradient. The
response of eddies to changes in the vertical structure of the
temperature gradient is especially interesting since global circulation
models suggest that as a result of greenhouse warming, the
lower-tropospheric temperature gradient will decrease whereas the
upper-tropospheric temperature gradient will increase. The sensitivity
of eddies to changes in the vertical structure of baroclinicity and the
relation between the mean available potential energy and eddy quantities
are studied for cases where the vertical structure of the lapse rate and
meridional temperature gradient are modified.
An idealized global circulation model with a modified Newtonian
relaxation schemes is used. We use two different schemes that allows for
any chosen zonally mean state to be obtained with good precision. The
results indicate that eddy activity is more sensitive to temperature
gradient changes in the upper troposphere. It is suggested that the
larger eddy sensitivity to the upper-tropospheric temperature gradient
is a consequence of large baroclinicity concentrated in upper levels.
This result is consistent with a 1D Eady-like model with nonuniform
shear showing more sensitivity to shear changes in regions of larger
baroclinicity. Furthermore, when the vertical structure of the lapse
rate or the meridional temperature gradient are modified, we find that
there is no universal linear relation between the mean available
potential energy and eddy quantities.

Date

10.04.2017

Speaker

Janni Yuval

Organizers

Marco Giorgetta

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