Unraveling Local Dust Storm Structure on Mars: The Case of Northern Amazonis During Mars Year 24

Abstract:

On an average Martian afternoon, two or three local dust storms are taking place somewhere on the planet. By definition, these storms range in area from a few square kilometers to hundreds of thousands, rarely surviving from sol to the next. After more than 40 years of observation, a great deal is known about where and when they occur, but very little is known about the structure and dynamics of individual storms.

This contrast in our knowledge about local dust storms results from how they are observed. Daily global mapping of Mars in the visible has enabled an accurate census of storms as well as observation of their morphological diversity. However, even under ideal conditions, an individual storm is only observed by sounder-type instrumentation once or twice (if it is a large enough), providing an incomplete picture of structure of an individual storm.

Early studies of cyclogenesis on Earth had a similar problem. Cyclones were many, but observations of individual cyclones, especially over the ocean, were sparse. The structure and dynamics of cyclones was unraveled by noting similarities in properties between certain classes of cyclones and using observational data to generate composite cyclones that could be analyzed and modeled. Variability within the composite also could be studied.

Here I establish the existence of a well-defined class of Martian local dust storms defined by: (1) occurrence along the axis of the dark albedo feature in northern Amazonis Planitia (36 N, 155 W); (2) not being associated with lifting or cloudiness due to a baroclinic wave/frontal boundary at higher latitude; (3) being textured, that is, having dust clouds with sharp, well-defined features that are thought to indicate their clouds are supplied by the active lifting of dust; (4) having dust clouds organized in well-defined streets indicative of convective rolls. In Mars Year 24, such storms developed on thirteen occasions in northern fall and autumn.
Using data from the Mars Orbiter Camera, Thermal Emission Spectrometer, and Mars Orbiter Laser Altimeter on Mars Global Surveyor, I will present a composite description of the structure of an individual storm of this class and its variability.

This work is supported by NASA's Mars Data Analysis Program (NNX14AM32G).