ROOTS OF OROGRAPHIC CUMULI

Abstract

In an effort to disentangle the “orographic barrier” and “high-levelheat source” effects, as they may combine to lead to the developmentof summer convective clouds over mountains, a series of measurementswas undertaken in Arizona. With use of an instrumented airplane,measurements of temperature and dew point were obtained for a seriesof passes up- and downwind across a 9000-ft mountain range. Passesranged in altitude from 10,000 to 14,000 ft. Data obtained at sunriseshow very clearly the barrier effect which forced air to ascend about1000 ft in crossing the ridge. After the mountain slopes became heatedby insolation, a convection core formed over and slightly downwindfrom the ridge. This core served as the root of several small cumulusclouds which developed during the time of measurement.