Numerical Simulations and Observations of Airflow through the Alenuihaha Channel

Airflow characteristics in the coastal waters of the Hawaiian archipelago, particular the Alenuihaha Channel between the island of Hawaii and the Island of Maui, are examined using observations and model simulations from the Advanced Research WRF (ARW) Modeling System. Airflow features related to interaction with the archipelago, including seasonal and diurnal changes, are presented using data from the QuikSCAT satellite, various buoys and ship data gathered in the Alenuihaha Channel. Verifications of the WRF model is made through comparisons of several years of buoy data with respective years of a WRF model hindcast. Special attention is paid to the Alenuihaha Channel, the site of two historical buoys, where a notable acceleration of wind occurs in conjunction with a sinking of the trade-wind inversion. WRF simulations for July 2005 provides model support for the existence of accelerated winds, a lowering of the trade-wind inversion and a hydraulic jump within the channel, delineating their magnitude, degree of deflection, diurnal variations, and placement while elucidating their mechanics. Topographical influences of Maui on the airflow through the Alenuihaha Channel are explored by comparing WRF runs with Maui County with those in which it has been removed. These influences include island blocking/orographic lifting on the windward side and adiabatic descent on the lee side, which augment the pressure gradient through the channel.