  The atmosphere of Venus is characterized by strong superrotation, in which
the wind velocities at cloud heights are around 60 times faster than the
surface rotation rate. The reasons for this strong superrotation are still not
well understood. Motions in the atmosphere below the thick cloud deck are hard
to determine remotely and in-situ measurements of the circulation below 40 km
altitude are scarce. No model to date has been able to simulate superrotating
winds with magnitudes comparable with those measured by entry probes, in the
dense atmosphere between the surface and the clouds. However, important
information on the dynamics and circulation of Venus' atmosphere can be
determined by studying the atmosphere at cloud levels, where there are
significantly more measurements than in the sub-cloud region, including the
many recent observations made during the Venus Express and Akatsuki missions.
In this work we describe a new Venus Middle atmosphere general circulation
Model (VMM) to study the dynamics of the atmosphere at cloud altitudes. The
model simulates the atmosphere from just below cloud deck to around 95 km
altitude. We present simulations using the VMM with a simplified Newtonian
cooling radiation scheme. Sensitivity studies have been performed to determine
the most appropriate values for model parameters and the model has been
validated by comparison with observations, including those from Venus Express
and Akatsuki. The validated model provides some constraints on parameters which
are poorly measured close to the boundary such as the mean winds and
temperatures, and provides a basis for further investigations of the dynamics
of Venus' cloud-level atmosphere. In future studies we will also investigate
the influence of atmospheric waves, such as Kelvin and Rossby waves, to
determine the role they play in generating the poorly-understood cloud-level
structure at all latitudes.
