Numerical Simulations of Airflow and Cloud Distributions over the Windward Side of the Island of Hawaii. Part I: The Effects of Trade Wind Inversion

Abstract

Initialized by the composite upstream sounding during the Hawaiian Rainband Project, high-resolution numerical experiments are conducted using the Pennsylvania State University?National Center for Atmospheric Research fifth generation Mesoscale Model to study the island-scale airflow and cloud distributions over the island of Hawaii without considering the diurnal heating cycle. The observed mean patterns of island airflow and weather under the summer trade wind conditions are well simulated. These features include orographic clouds on the windward slopes, flow deceleration and splitting on the windward side, leeside vortices, and cool and moist (warm and dry) conditions on the windward (lee) side. In addition to Fr (Froude number), the simulated island airflow and cloud distributions are sensitive to net diabatic heating associated with clouds and precipitation and rain evaporative cooling. The trade wind inversion height determines the depth of the moist trade wind layer, which also affects the island airflow. The orographic clouds in the high-inversion days and the coastal band clouds in the low-inversion days are simulated in the model with the same Fr upstream. It is apparent that accurate representation of the moisture profile upstream and convective feedback effects in the model is crucial for the simulation of island airflow and cloud distributions under the trade wind weather over the Hawaiian Islands.