Abstract
Convection and cloud formation over mountains during weak winds and strong insolation were studied using an instrumented aircraft. Previous studies in cloudless situations had shown the existence of convergence over the mountain range at low levels, and divergence aloft. The present observations indicate that cumulus clouds and even thunderstorms in their early stages do not significantly affect the strength of the low level convergence. Furthermore, net divergence was found around clouds up to at least 6 km MSL. This favors the vertical mixing model of a cumulus cloud over the lateral entrainment model. In one case, the convergent low level heat island circulation over the mountain was observed to change to an almost non-divergent, asymmetric circulation as a thunderstorm over the mountain reached maturity.
