This seems as good of a thread as any to ponder the disconnect between a near vacuum and global dust storms. The sound waves would be no stretch as sound waves will travel, they just will be weak. We will see about that if they turn it on and if they release the data.
There is a growing interest to vortex formation on Earth and the connection to electrical fields. I suppose when I am long gone they will come to the realization that Mars dust devils and global dust storms are at least assisted by an atmospheric electric discharge phenomenon.
That being said the wind does blow. We have seen it whip the instrumentation and solar panels on Phoenix. Most global dust storms begin in Hellas Basin. This is an area of higher surface pressures that would give the wind more force. We have seen great dust plumes rise on the northern scarp along the thermal boundary just north of Phoenix.
I believe once the dust is airborne it sets up a thermal gradient. Temperatures during dust storms can rise by 40C on a global level. Just as the thermal gradient forms storms on the local level they would propagate the dust storm by creating more thermal boundaries.
The next question is why would not all dust storms become global. This is were the mind must wonder. The universe does have more secrets to come, some may shock you, pun intended.