  We employ the MarsWRF general circulation model (GCM) to test the predictions
of a new physical hypothesis: a weak coupling of the orbital and rotational
angular momenta of extended bodies is predicted to give rise to cycles of
intensification and relaxation of circulatory flows within atmospheres. The
dynamical core of the GCM has been modified to include the orbit-spin coupling
accelerations due to solar system dynamics for the years 1920-2030. The
modified GCM is first subjected to extensive testing and validation. We compare
forced and unforced model outcomes for large-scale zonal and meridional flows,
and for near-surface wind velocities and surface wind stresses. The predicted
cycles of circulatory intensification and relaxation within the modified GCM
are observed. Most remarkably, the modified GCM reproduces conditions favorable
for the occurrence of perihelion-season global-scale dust storms on Mars in
years in which such storms were observed. A strengthening of the meridional
overturning (Hadley) circulation during the dust storm season occurs in the GCM
in all previously known years with perihelion-season global-scale dust storms.
The increased upwelling produced in the southern hemisphere in southern summer
may facilitate the transport of dust to high altitudes in the Mars atmosphere
during the dust storm season, where radiative heating may further strengthen
the circulation. Significantly increased surface winds and surface wind
stresses are also obtained. These may locally facilitate saltation and dust
lifting from the surface. The numerical simulations constitute proof of concept
for the orbit-spin coupling hypothesis under evaluation.
