A Stormy Forecast for the Upcoming Dust Storm Season on Mars

The dust storm season on Mars is centered on the time of Mars' perihelion, which occurs late in the southern spring. The dust storm season of the current Mars year (MY 33) will begin on 1 June 2016 (Ls=160°) and will end on 28 March 2017 (Ls=340°). Mars will reach perihelion in late October 2016, about a month after the planned landing of the Mars InSight Lander. Spectacular global-scale dust storms (GDS) occur during the dust storm season in some Mars years but not in others. In a prior study (Shirley, 2015; Icarus 251, 128-144), systematic relationships were found linking the occurrence of historic global-scale dust storms on Mars with the variability of the orbital angular momentum of the planet with respect to the solar system barycenter. Conditions favorable to the occurrence of a future GDS in the current Mars year were noted in that study. A physical model that may account for the observed relationships has subsequently emerged. In this model, a weak coupling of the orbital and rotational motions of extended bodies is effected through a modulation of circulatory flows of atmospheres. The formal derivation yields a coupling term, which in turn prescribes an acceleration field that may constructively or destructively interfere with large-scale atmospheric motions driven by other means. This coupling term has been incorporated within the MarsWRF Global Circulation Model, and the GCM thus modified has undergone extensive validation and testing. The GCM "retrodicts" accelerations and circulation patterns favorable for the occurrence of southern summer solstice season global-scale dust storms in all of the prior years (n=7) in which such storms are known to have occurred (Mischna and Shirley, this meeting). The forcing function for the upcoming dust storm season exhibits amplitude and phasing that largely replicates the dynamical conditions prevailing prior to and during the MY 9 GDS of 1971. We conclude that a global-scale dust storm is likely to occur during the dust storm season of Mars year 33.