A paper from the 2017 meeting Lunar and Planetary Sciences XLVIII describes a systematic observation of the Martian sky, with a sequence of eight taken every day at zenith and near-horizon angles. They show tenuous clouds, often with a wavy gravity wave pattern (that's gravity wave, not gravitational wave).
The images are very grainy compared to the one's I'm used to seeing of the Martian sky or surface. Are they taken before sunrise when it is very dark? Since nothing is moving couldn't they just use a longer exposure? Or does it have to do with noise from some enhancement processing? If so, what is the enhancement process?
Isn't extensive cloud cover quite rare on Mars, and not a daily occurrence?
Note: the GIF below is made from only four frames of the first 8-frame GIF of three, shown in this news item in Science. They look much better there - the stackexchange image size restriction prevents the direct posting of the 2.7 MB images. You can direct-link to them: here, here, and here.
For contrast, here is a tweeted image.