Triggered convection and orographic precipitation in the tropics: control parameters and predictability

The Dominica Experiment field campaign (DOMEX) in April/May 2011 examined triggered moist convection and orographic precipitation in the tropics. Flight-level data from 20 flights of the Wyoming King Air , along with surface, balloon, radar and satellite data during DOMEX were used to document upstream airflow properties that might control precipitation on Dominica. Using these data, we tested several hypotheses concerning upwind control.

Previous analysis of balloon data has shown that low troposphere relative humidity and wind speed correlate positively with island precipitation. Previous numerical modeling suggests that the scale and amplitude of humidity and temperature perturbations in the upstream flow may also be important. These parameters, along with upstream cloudiness, regional subsidence and the strength of oceanic heat and moisture fluxes were evaluated as control parameters. The physical mechanism behind upwind control was sought.

The properties of the upstream airflow influence precipitation on Dominica, but Dominica also influences the properties of the airflow. A detailed comparison of upwind and downwind air mass properties was carried out. Attention was given to profiles of wind speed, static stability, humidity and aerosol concentration, as indicators of air mass transformation by the island. We have tried to understand air mass changes in relation to the precipitation and mixing processes happening over the island.