Spherical particle terminal velocities in the Martian daytime atmosphere from 0 to 50 kilometers

The terminal velocities of spherical particles (density = 3.0 g cm−3), with diameters from one to 10,000 microns, are presented for three Martian daytime model atmospheres from 0 to 50 km, based on two different surface pressures (5.55 and 10 mb). The model atmospheres are founded on results from the Mariner 4 occultation experiment, which gave densities in the Martian atmosphere that were much lower than previous estimates. The following conclusions are reached concerning the yellow (dust) clouds: (1) the vertical velocities required to keep yellow-cloud particles of sizes 10 microns or less aloft are greater on Mars than on earth. (2) The minimum size of the grains primarily responsible for the local surface yellow-cloud obscurations is about 20 microns. This falls within the range of estimates in the literature (1–20 microns) as to the size primarily responsible for the surface obscurations. (3) Particles as small as 3 microns could be responsible for the rarer planet-wide obscurations lasting a month or more. The above conclusions are compared with those of Ryan who based his analysis on a denser Martian model atmosphere (25 mb).