Wispy, white and made of ice crystals cirrus clouds are usually found at altitudes of 5000m or more in New Zealand. In certain conditions cirrus and cirrostratus clouds can produce optical effects, such as halos and rainbow like patterns. Light from the sun passes through plate shaped ice crystals at specific angles, then refracts, producing a bright halo, or rainbow colours. Photo taken by Alan Blacklock in 2005.
