  Airborne dust is an important constituent in the Martian atmosphere because
of its radiative interaction with the atmospheric circulation, and dust size is
one crucial factor in determining this effect. In numerical modeling of the
dust processes, description of the dust size is usually dependent on the choice
of a particular size distribution function, or with fixed values of effective
radius (ER) and effective variance (EV) though they are variable in reality. In
this work, analytical expressions have been derived to specify ER and EV for
N-bin dust schemes based on the model calculated dust mixing ratio. Numerical
simulations based on this approach thus consider the effects of variable ER on
the atmospheric radiation and their interaction. The results have revealed some
interesting features of the dust distribution parameters such as the seasonal
and spatial variation of ER and EV, which are generally consistent with some
previous observational and modeling studies. Compared with the usual approach
of using fixed ER, simulation results with the present approach suggest that
the variability of ER can have significant effect on the simulated thermal
field of the Martian atmosphere.
