Cloud shapes are influenced both by winds and by the shape of the Earth beneath. turbulent winds produce different cloud shapes. Mountains often create their own special clouds. Wave motion in the atmosphere can also produce interesting visual effects.
Lee-wave clouds - mountains often create standing waves in the atmosphere on the lee (downwind side).
Lenticular clouds may form at the top of each wave. These occur when air rises over mountains and remains stationary. So the clouds remain 'fixed' to the air over the mountains.
Rotor clouds are sometimes formed by turbulent circular motions in the vertical downwind of a mountain barrier.
Aircraft produce contrails (condensations trails) when flying through air at 30 degrees below freezing point. Water vapour condenses behind an aircraft's engines and the resulting water droplets freeze instantaneously into ice crystals.
Unusual Cloud Effects
Cumulus clouds sometimes form over power stations and are called "fumulus" clouds.
Mamma (or mammatocumulus) clouds are rounded structures that are sometimes seen on the lower surfaces of certain clouds, especially cumulonimbus (storm clouds).
Occasionally, clouds reveal wave motion in the atmosphere very clearly indeed. Kelvin-Helmholtz (K-H) waves are caused by differing wind-speeds in two adjacent levels of the atmosphere.
Banner cloud can sit on mountains and hills such as the well-known one over the over rock of Gibralter, or the 'table cloth' over Table Mountain in South Africa. These form because the air behind abrupt mountain slopes curls back upwards immediately behind the summit. The cloud forms in this upcurrent.
