Abstract
On the island of Maui, the dispersion of air pollutants associated with the field burning of biomass is complicated because the persistent Maui Vortex in the lee of Haleakala tends to trap smoke making pollution concentration worse in the central valley. In the present study we describe the spatially as well as temporally continuous short-term climatology of the airflow in the central valley of Maui during a summer month under trade wind conditions, simulated by a high-resolution mesoscale model initialized and forced by large-scale objective analyses. These simulations are compared with station observations. Under persistent trade wind conditions, an eddy would form in the central valley, and would remain steady and stationary regardless of the time of the day 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 the obstacle, and N the Brunt-Väisälä frequency. However, vortex shedding could occur if the West Maui mountains were removed. Two major factors contributing to formation, maintenance, and steadiness of the Maui Vortex, solar heating and the accelerated northerly flow over the valley resulting from deflection of the trades by West Maui, are discussed. Suggestions are made for preferred synoptic conditions for field burning.
