Thermally-driven circulation and convection over a mountainous tropical island

English Abstract:

Observational data from the 2011 Dominica Experiment (DOMEX) and cloud-resolving numerical simulations are exploited to gain a better understanding of controlling parameters of thermally-driven convection over a mountainous tropical island. A “golden” case from DOMEX with a clear diurnal cycle in cumulus convection and quasi-steady large-scale conditions is studied using observations and cloud-resolving numerical simulations. The simulations are quasi-idealized in that they use full model physics and the real Dominica terrain, along with a horizontally homogeneous initial flow based on a single observed sounding. Simulations at different grid resolutions reveal that large-eddy resolution (~100 m) provides the most accurate representation of the in-situ measurements from DOMEX and the radar-derived island precipitation. However, regardless of grid resolution, the simulations robustly under-predict the island diurnal cycle and over-predict the precipitation, which stem from biases in land-surface and subgrid microphysics parameterizations. Sensitivity tests reveal the importance of key factors including island terrain height, land-surface type, cloud-radiative feedbacks, moist stability, and background wind velocity in controlling the thermally-driven convection.