Pluto's atmosphere is really thin but its obviously thick and strong enough to move reddish tholin aerosols and the white methane snow into patterns resembling sastrugi on Earth. Knowing this really affects my view of what I see taking place at the polygonal cell troughs on Sputnik Planitia (SP).
I've said before that the warmest parts of SP are the troughs (page 80) not the cell center, NASA scientist's suggest the center of these large meandering hills of toothpaste consistency mounds called polygonal cells are raised by warm subsurface convection currents like lava lamps. But I've demonstrated how this is not a reasonable interpretation of the visual evidence. Convection currents are not raising the center of the cells as there are more aggressive signs of sublimation (evaporation) cups near the cells perimeter organized near the troughs. This increased heat at the cell's perimeter creates more frequent and larger sublimation cups along the edges.
Lets combine two concepts, viscous relaxation which increases with warmth and sastrugi ripples which are particles of frost or snow shaped by wind into wave patterns. The warmest surface areas of SP are the troughs or channels that run between the polygonal cells and they are the smoothest (most viscously relaxed). Along their edges we see sastrugi ripples emanating out from the trough toward the cell center until things become too cold too solid for the wind to shape and form sastrugi.
The center or most elevated part of the cell mounds are typically wind swept clean and smooth compared to their edges where methane/nitrogen snow collects and is organized into ripples.
While sublimation may be playing a role in this process the factor primarily influencing the landscape is wind. The wind is rolling down the hill shape of the polygonal cells being funneled and compressed, focused and channeled more rapidly through the troughs creating the rippled wave patterns. The channel of the trough's being warmer are less viscous so the surface relaxes quicker and becomes smooth or dissolves the nitrogen/methane frosty snow.
This image shows how far airborne tholin aerosols are blown by Pluto winds.
I don't know the exact scale but this wind blown tholin extends somewhere around 50 miles.
Tholins have to be heavier than the atmosphere else they wouldn't fall and deposit all over the place.
The atmosphere and wind must be dense and strong enough to migrate aerosol particulates many miles.
Sastrugi are just one other example of the winds density and strength as it carves features into the snow at Burney, makes ripples near the softer warmer troughs of nitrogen on SP and as it carries tholin aerosols for miles.
At the very least, I think its safe to say sublimation is not the only way to interpret the many bowl shaped cups and ripples on SP.
South of the mountain range tholin is making the ripples in the sastrugi appear more pronounced as the tholin accumulates into the sastrugi cups or bowls.
At first, I thought the mountain range was influencing the direction and speed of the wind creating sastrugi patterns but after studying the scene a little closer it appears as though the sastrugi exists primarily around the cell perimeter and is lacking in the center pretty much like we see elsewhere in SP.
The dark tholin swept off the mountain sized icebergs simply accentuates the darker divots making it appear as though the ripples are more pronounced along the direction of wind travel.
On the leeward side of the mountain the wind blown snow ripples are much less pronounced than on the windward side.
This is direct evidence that the sastrugi are snow blown wind patterns but their location is predominantly determined by the shape of the sloping cell mounds and mountains.
Four months after reading this page and stealing credit for it, NASA agreed with my interpretation even though they originally called all these wave patterns sublimation pits created by mass wasting.