2 Mar 2018

At http://spaceweather.com (March 2nd 2018) we have a fine image of saucer clouds over Brasilia ....

   ... these are pileus clouds. On warm summer afternoons (it is summer in Brazil) cumulus clouds push upwards and move layers of moist air above them even higher in the atmosphere where they condense to form cloud caps - which in Latin is pileus. Pileus clouds form quickly and internal water droplets tend to be all of the same size and diffract passing sunlight into vivid pastel colours. The saucer shape id due to a layer of wind above the cumulus which sculpts the colourful clouds into starship shapes (or flying saucers).