The impact of soil moisture on the diurnal evolution of the PBL and on orographic cumulus development over the Santa Catalina Mountains during the 2006 Arizona monsoon

During the 2006 monsoon season, the Cumulus Photogrammetric, In Situ, and Doppler Observations (CuPIDO) experiment was carried out over the Santa Catalina Mountains in Arizona. The dataset was used to assess the influence of soil moisture on the planet boundary layer (PBL) evolution and orographic cumulus development over complex terrain. Also, a two month simulation (Jul 01 – Aug 29) over the same mountain range was conducted using the Weather, Research and Forecasting (WRF) model with 1km horizontal resolution and a high vertical resolution for the lowest 3.5 km above ground.

Both the observation and simulation reveal the dry soil period (DSP) and wet soil period (WSP) with distinct characters in terms of net surface radiation, Bowen Ratio, PBL height, LCL, LFC, CAPE, CIN, mountain scale convergence and the diurnal evolution of PBL parameters. Results show that the increased soil moisture tends to suppress the PBL depth during the daytime as well as mountain-scale convergence, and a stable PBL makes it more difficult for cumulus convection. But, the moist static energy and CAPE are larger during WSP, which makes the convection to initiate earlier and last longer. The simulation successfully reveals the wet/dry soil periods and their characteristics, but the precipitation and soil moisture related parameters were less well captured in terms of magnitude and duration, which may lead to a different condition for PBL development and convection initiation.