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The main reference simulation, hereafter labeled GWRF1, is carried
out with the MAECHAM4 model with the abovementionned parameterization
of the gravity wave emission from frontal disturbances applied
to the input source spectrum of the Hines parameterization (Hines
1997a,b). The GWRF1 employs T30 truncation and includes a few
other modifications to the input source spectrum with respect
to the configuration used by Manzini and McFarlane (1998). As
the GWRF1 simulation evolves, the right-hand side of Eq. 1 is
computed at each grid point and time step at the launching level
near 600 hPa in order to determine whether or not conditions favorable
to frontogenesis are met and to specify the gravity wave variance
and directions of propagation accordingly.
In addition, two sensitivity simulations have been carried out
with MAECHAM4, respectively labeled UNI1 and UNI2. They serve
as a mean of directly evaluating the impact of including a representation
of fronts in the gravity wave source. Both UNI1 and UNI2 simulations
are carried out at T30 truncations. The source spectrum of the
UNI1 and UNI2 simulations is assumed to be isotropic. The total
gravity wave wind variance at the same launching level as GWRF1
is set to 0.64 m2 s-2 for UNI1 and to 1 m2 s-2 for UNI2, uniform
in space and constant time. The UNI1 source spectrum would therefore
be identical to the one specified in simulation GWRF1 if the minimum
threshold of the frontogenesis function was never reached in this
latter simulation. The UNI2 source spectrum is very close to the
monthly zonal mean source spectrum of GWRF1 in the extra-tropics.
The results from the GWRF1, UNI1, and UNI2 simulations are each
one from 12 year integrations.