A Three-Dimensional Study of Cumulus Clouds by the Use of Aerial Photographs of the Clouds and Their Shadows

Abstract

A three-dimensional study of cumulus clouds was made by the use of aerial photographs of the clouds and their shadows. The side views of the clouds were obtained from photographs taken from an aircraft at a height slightly above cloud base level. Plan views were estimated from the rectified shapes of the cloud shadows. The map position of the clouds and height of cloud base were determined from the map position of their shadows and the. direction of the sun, by the use of Fujita' technique of single image photogrammetry. It was found that the long axis of flat cumulus cloud showed an apparent rotation in a wind field turning with height. In the case of fairly deep cumulus clouds, the forward edge of their upper part moved in the same direction and with nearly the same speed as the wind at the man level of the clouds; the forward edge of their lower part moved with the wind at the cloud base level but with a lower speed. The formation of new cumulus towers was observed on the up-shear side of the clouds.