Absent due to some local drama, this Caribbean island article about the 'mystery' of rainfall was a good starter for yet another rant on how little we see as we watch both planets. The internal bright spots in the dark areas of the barchans in the HiRISE image is so curious, as the bright small spots have fan and differing directionality, showing daily variations, even hourly perhaps, during the events we see from such a great distance. These are one to two hundred miles distant, have little detail we can see at human scale, and are house lot to building size lots with little overlap of the local units of action.
Hoping the next HiRISE satellite equivalents have even better optical resolution.
I haven't presented the images of near equatorial craters with blue color band semi-transparent or translucent structures which resemble 'clear' ice of a 3D shape covering portions of the crater floors and walls, as it is nearly impossible to transfer the subtle shape patterns after producing the images on my computer. It appears we have something like ice at some craters. Not supposed to be there as ice, and it may remain a mystery like many others.
Often the blue channel is confusing and has substantial appearance differences from the other bands.
This link to a story of clouds with heavy downpours in just minutes from apparent clear skies shows we can see only a portion of our world, and much is not apparent. I live in a dry core city with a series of 'micro climate lanes' around the city, prevailing wind directions, and within a few miles west and north, and south and east, we see both rainfall and tornado differences which create farming on both lanes, leaving the city often dry or nearly so. We actually feel safe from tornado's here in the city proper whereas local suburb cities are unsafe to live in and are shunned by many.
The conditions of the available pressurized CO2 and water/ice H2O, the actions of seasonal change are just a degree or a few degrees variation perhaps. The same condition degrees of variation control the dust devils in patterned behavior, providing differing opportunities for life possibly.
I lived in a forested area for a time, outside, and life has very distinct domains of activity. Under a tree, in short shrubs, at patches of grass, each climate at small scale is unique and 'just right' for particular life types. Surely Mars has spots that can allow survival for even Earth type life?
CO2 is twenty times as soluble in water as oxygen, and expansion of the ice sheets as they volatize would power a localized climate for seasonal and even daily conditions completely different from open atmosphere Mars. Massive local opportunities in pockets of local conditions, especially at dunes with confined water and ice? Just surmising what we cannot see as yet.
The layering may provide a very different environment even beyond seasons, with repeated conditions routine.
Perhaps it is just refreezing CO2 showing us light core spots when the pressure is reduced? Too much drift in my thinking about both water and CO2 ices outgassing and being pressurized.
In the red dirt 'sand' around me in Oklahoma, much of the concentration of minerals is calcium and iron, with the older layers not showing residual fossils. It was always a curious written mystery as to why so few fossils and where the red dirt 'sand' originated geologically. Other details resemble Mars layering somewhat.
Dunes often begin at points of shaped objects, active zones which are causing the dunes, and on Mars we see the patterned ground effects with fractures , cones, and vertical mixing opportunities from deeper underground through layers.