  We carry out local three dimensional (3D) hydrodynamic simulations of
planet-disk interaction in stratified disks with varied thermodynamic
properties. We find that whenever the Brunt-Vaisala frequency (N) in the disk
is nonzero, the planet exerts a strong torque on the disk in the vicinity of
the planet, with a reduction in the traditional "torque cutoff". In particular,
this is true for adiabatic perturbations in disks with isothermal density
structure, as should be typical for centrally irradiated protoplanetary disks.
We identify this torque with buoyancy waves, which are excited (when N is
non-zero) close to the planet, within one disk scale height from its orbit.
These waves give rise to density perturbations with a characteristic 3D spatial
pattern which is in close agreement with the linear dispersion relation for
buoyancy waves. The torque due to these waves can amount to as much as several
tens of per cent of the total planetary torque, which is not expected based on
analytical calculations limited to axisymmetric or low-m modes. Buoyancy waves
should be ubiquitous around planets in the inner, dense regions of
protoplanetary disks, where they might possibly affect planet migration.
