A new paper in Science is making the news for its very interesting findings on the Marsian water cycle. Ars Technica has a longer story that quotes this summary:
The authors of one paper sum up the cycle as follows: “This diurnal cycle deposited ice onto the surface at night, reducing the vapor pressure to low values, sublimated it in the morning, and redistributed it throughout the planetary boundary layer in the turbulent afternoon. Near midnight, ice clouds formed and precipitated a portion of the atmospheric H2O back to the surface in the early morning.”
National Geographic also writes about it.