A positive radiative-dynamic feedback mechanism for the maintenance and growth of Martian dust storms

摘要

Atmospheric dust disturbances ranging in size from dust devils to planet-encircling dust storms are ubiquitous on Mars. After dust devils, the most common disturbances are local- or regional-scale disturbances. The origin of some of these mesoscale systems has been previously investigated and found to be linked to lifting along frontal systems or cap edge circulations. Very little attention has been given to whether the lifted dust in these systems result in radiative forcing that might modulate the local system dynamics with an amplitude large enough to affect local dust-lifting processes. Idealized numerical modeling results presented herein show that a positive feedback process between local dynamics and radiative forcing of lifted dust can occur under some conditions. The feedback process is distinctly different than an enhancement of the general circulation by increasing atmospheric dust loading because the dynamical effects of this feedback process occur locally, within the disturbance itself. Optimal conditions for growth of initial atmospheric dust perturbations include (1) subtropical latitudes associated with relatively large solar insolation and moderate coriolis force; (2) modest dust-lifting thresholds and dust-lifting efficiencies; (3) relatively large initial dust perturbations; (4) steep background lapse rates; and (5) a barotropic environment. The positive feedback process is explained by a combination of geostrophic adjustment theory and a Carnot engine-like mechanism related to the Wind-Induced Sensible Heat Exchange hypothesis for tropical cyclones on Earth.