The 2018 opposition of Mars & the global dust storm: Part I.

The perihelic opposition that occurred on 2018 Jul 27 at areocentric longitude (Ls) 219° was monitored by 121 observers, yielding nearly 9,000 observations. Part I of this paper focuses upon the global dust storm that arose on 2018 May 30 in early southern spring, at Ls = 184°. The event was unprecedented in having commenced in the northern hemisphere, and the process of encirclement (over 25 days) was unusually slow. The expansion of the storm in both the northern and southern hemispheres was faster to the east than to the west. Its effects were still apparent in mid-August, and there were striking and long-lasting albedo changes including the reappearance of Phasis, the unprecedented distortion of the N. part of Margaritifer Sinus - Oxia Palus, and the intensification of Indus at SE Mare Acidalium - Niliacus Lacus. The global storm deposited dust upon the S. polar cap, accelerating its early recession, though the majority of the recession curve followed that of 2003 (a year without an encircling storm) extremely closely. Other global storm phenomena included terminator projections - due to suspended dust - up to some 80km in altitude, increased activity of the N. polar hood, and the presence of a bright morning limb cloud arc adjacent to the S. polar cap. Dust velocities of up to 118km h-1 were measured. In Part II, other local and regional dust storms are described, as well as white cloud activity and the behaviour of the polar regions. [ABSTRACT FROM AUTHOR]