Both, actually. The vertical motion of the storm lifts the sand vertically, and the winds advect the sand laterally.
A picture at:
http://www.osei.noaa.gov/IOD/OSEIiod.jpg
has some arrows to point out the sand.
Both, actually. The vertical motion of the storm lifts the sand vertically, and the winds advect the sand laterally.
Yes, the sand is of course lifted off the ground, but the amount would not be visible in this photo. Even if it were lifted up into the air as high as the top of Mount Everest, the vertical component would only be equal to five pixels of this image (less than 1% of its width).
It's easy to overestimate the "thickness" of the Earth's atmosphere, or geographic "roughness". If the Earth were the size of a billiard ball, it would be about as smooth *as* a billiard ball, even taking into account such "imperfections" as the depth of the Marianas Trench and the height of Everest. At billiard-ball size, the difference in heights of those features would amount to imperfections no greater than a few one-thousandths of an inch.