ROOTS OF OROGRAPHIC CUMULI

Abstract

In an effort to disentangle the ?orographic barrier? and ?high-level heat source? effects, as they may combine to lead to the development of summer convective clouds over mountains, a series of measurements was undertaken in Arizona. With use of an instrumented airplane, measurements of temperature and dew point were obtained for a series of passes up- and downwind across a 9000-ft mountain range. Passes ranged in altitude from 10,000 to 14,000 ft. Data obtained at sunrise show very clearly the barrier effect which forced air to ascend about 1000 ft in crossing the ridge. After the mountain slopes became heated by insolation, a convection core formed over and slightly downwind from the ridge. This core served as the root of several small cumulus clouds which developed during the time of measurement.