Cumulus cloud
Cumulus clouds are often precursors of other types of clouds, such as cumulonimbus, when influenced by weather factors such as instability, moisture, and temperature gradient. Normally, cumulus clouds produce little or no precipitation, but they can grow into the precipitation-bearing congestus or cumulonimbus clouds. Cumulus clouds can be formed from water vapor, supercooled water droplets, or ice crystals, depending upon the ambient temperature. They come in many distinct subforms, and generally cool the earth by reflecting the incoming solar radiation. Cumulus clouds are part of the larger category of free-convective cumuliform clouds, which include cumulonimbus clouds. The latter genus-type is sometimes categorized separately as cumulonimbiform due to its more complex structure that often includes a cirriform or anvil top. There are also cumuliform clouds of limited convection that comprise stratocumulus (low-étage), altocumulus (middle-étage) and cirrocumulus (high-étage). These last three genus-types are sometimes classified separately as stratocumuliform.
Dune
Five basic dune types are recognized: crescentic, linear, star, dome, and parabolic. Dune areas may occur in three forms: simple (isolated dunes of basic type), compound (larger dunes on which smaller dunes of same type form), and complex (combinations of different types). 
Barchan dunes are crescent-shaped mounds which are generally wider than they are long. The lee-side slipfaces are on the concave sides of the dunes. These dunes form under winds that blow consistently from one direction (unimodal winds). They form separate crescents when the sand supply is comparatively small. When the sand supply is greater, they may merge into barchanoid ridges, and then transverse dunes (see below).