Optimal width of hot spots for driving deep moist convective systems

In a recent study, Robinson et al. (2008) proposed a resonance mechanism for regulating the intensity of convection independently of classical instability measures, over heterogeneous surfaces. They predicted that the most efficient driving for deep moist convection occurs when the surface heating is confined to a scale close to the product of the environmental buoyancy frequency, the characteristic heating time scale and the thickness of the thermal boundary layer. The theory was tested with 2-D models and against lightning observations reported over islands, but the tests were qualitative since the models did not predict cloud electrification or lightning and were highly idealized. The robustness of this "resonance mechanism" is clarified by simulating in three dimensions and with more realistic surface heating and ice microphysics. Moreover, to establish more quantitatively the role of this mechanism in explaining observed behavior, we compare the more-realistic WRF model simulations against TRMM- observed effective radar reflectivities and brightness temperatures for a range of island sizes. Results suggest dry dynamics is more important than parcel theory in controlling convective vigor. This work is funded by NSF grant 'Physical and Dynamical Meteorology', award number NSF 078550