NUMERICAL-SIMULATION OF THE MAUI VORTEX IN THE TRADE WINDS

On the island of Maui, the dispersion of air pollutants associated wit h the field burning of biomass is complicated because the persistent M aui Vortex in the lee of Haleakala tends to trap smoke making pollutio n concentration worse in the central valley. In the present study we d escribe the spatially as well as temporally continuous short-term clim atology of the airflow in the central valley of Maui during a summer m onth under trade wind conditions; simulated by a high-resolution mesos cale model initialized and forced by large-scale objective analyses. T hese simulations are compared with station observations. Under persist ent trade wind conditions, an eddy would form in the central valley, a nd would remain steady and stationary regardless of the time of the da y with little indications of vortex shedding even if the Froude number Fr = U/NH < 0.4, where U is the uniform flow speed, H the height of t he obstacle, and N the Brunt-Vaisala frequency. However, vortex sheddi ng could occur if the West Maui mountains were removed. Two major fact ors contributing to formation, maintenance, and steadiness of the Maui Vortex, solar heating and the accelerated northerly flow over the val ley resulting from deflection of the trades by West Maui, are discusse d. Suggestions are made for preferred synoptic conditions for field bu rning.