A Photogrammetric Study of the Initiation of Cumulus Clouds over Mountainous Terrain

Abstract

The initiation of cumulus clouds over mountainous terrain is investigated photogrammetrically. Stereo pairs taken at one- and two-minute intervals are analyzed for four days of cumulus initiation over the Santa Catalina Mountains, northeast of Tucson, Arizona. Charts of growth rates, cloud position, and tracings of clouds over the mountain ridges are presented. The environmental conditions, represented by the Tucson radiosonde and rawin soundings, are related to the growth characteristics. Two days with easterly components in the wind and two with westerly components are analyzed. The growth characteristics can be vastly different, depending upon the water vapor content of the air and the ambient winds. There is no obvious effect of the lapse rate on the initial growth rates. The clouds form over the principal mountain ridges with their base topography in general agreement with the ridge topography on three of the four days. The ambient winds determine the position of the clouds with respect to the ridge line. The days with fairly strong winds show evidence of cloud formation in suspected lee waves. The growths in the waves are more vigorous and extend to greater heights.