Observations of detrainment signatures from non-precipitating orographic cumulus clouds

This study uses aircraft in-situ data, airborne mm-wavelength radar data, time lapse photography, and close-proximity radiosonde data to describe the signature of a lifecycle of non-precipitating moist convection left onto the ambient free tropospheric air. The data were collected as part of the 2006 Cumulus Photogrammetric, In-situ and Doppler Observations (CuPIDO-06) campaign, which was centered over the Santa Catalina Mountains, a natural laboratory for the study of the formation and decay of cumulus clouds. This study focuses on one case study, on 8 August 2006, when a series of Cu mediocris formed on the upwind side of the mountain, and decayed on the downwind side. Because these clouds were not precipitating, convective downdrafts were too weak to significantly affect the boundary-layer air downwind of the mountain. The layer containing orographic cumuli clearly became enriched with moist static energy immediately downwind of the mountain. This enrichment was due to the transport of boundary-layer air by moist convection, and not an artifact of stratified flow over a mountain, since it was mostly caused by an increase in water vapor. Some downwind plumes contained over 50% of the water vapor and moist static energy excess found in orographic cumuli over base values in the upstream environment in the orographic cumulus layer. This enrichment reduces potential instability but increases ambient humidity. This may facilitate successive cumulus growth, although this process of convective conditioning is unlikely to be important for meso-γ scale (~. 20. km) orographic convection.