An observational study of thermally-forced, orographic energy transport and cumulus development

Aircraft and surface measurements of the boundary-layer transport of mass and energy towards an isolated mountain are presented. The data were collected around the Catalina Mountains, about 20 km in diameter, during Arizona's summer monsoon, as part of the CuPIDO_2006 campaign. During the morning an anabatic wind developed, about 1-2 m/s in magnitude, which is comparable to the strength of the mean advective wind in the boundary-layer. On all days cumulus congestus developed over the mountain, on some days thunderstorms formed. There is some evidence of a toroidal heat-island circulation, although the vertical profile of the anabatic wind or mountain-mean convergence appears quite variable. The transport of energy by the toroidal circulation was almost entirely driven by the mean anabatic wind, rather than by eddies in the horizontal flow. During times of anabatic flow, the horizontal influx of latent and sensible heat (averaged over the mountain footprint area, and integrated of the inflow depth) is far larger than the vertical influx of the same at the surface, although the start of anabatic flow lags sunrise by 2-4 hours.