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DaNa L. Carlis, Yi-Leng Chen, and Vernon R. Morris

Abstract

The fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) coupled with the Noah land surface model (LSM) is employed to simulate island-scale airflow and circulations over Maui County, Hawaii, under summer trade wind conditions, during July–August 2005. The model forecasts are validated by surface observations with good agreement.

In this study, it is shown that a previously known closed circulation over the Central Valley of Maui, or the Maui vortex, represents the northern cyclonic vortex of the dual-counter-rotating vortices in the lee of Haleakala, which extend up to the base of the trade wind inversion with a westerly reversed flow (>2 m s−1). At low levels, the northern cyclonic vortex is more pronounced than the southern anticyclonic vortex. The asymmetric structure of the dual vortices is related to the shape of Haleakala and the flow deflection by the West Maui Mountains. The Maui vortex has a relatively narrow east–west extent in the lowest levels, especially at night, due to the deflected strong northerly/northeasterly winds from the windward foothills of the West Maui Mountains. Unlike the lee vortices off the leeside coast of the island of Hawaii, the Maui vortex and the westerly return flow in low levels are mainly over land and are strongly modulated by the diurnal heating cycle. In addition, the location and horizontal and vertical extent are affected by the trade wind speed and latent heat release.

Over the West Maui Mountains, with their height below the trade wind inversion, dual-counter-rotating vortices are present below the 1-km level in the wake, with strong downslope flow on the leeside slopes followed by a hydraulic jump. In the afternoon, downslope winds are weak, with combined westerly return/sea-breeze flow along the leeside coast. Orographic blocking is also evident over eastern Molokai with strong downslope winds, especially at night.

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Jian Ma, Sara C. da Silva, Aaron Levine, Yang Yang, Paul Fuentes, Li Zhou, Chuan-Chi Tu, Jia Hu, I. M. Shiromani Jayawardena, Antti Pessi, and DaNa Carlis

A four-day educational cruise navigated around the leeward side of Oahu and Kauai to observe the thermodynamic and dynamic features of the trade-wind wakes of these small islands by using weather balloons and other onboard atmospheric and oceanographic sensors. This cruise was proposed, designed, and implemented completely by graduate students from the School of Ocean and Earth Science and Technology at the University of Hawaii. The data collected during the cruise show, for the first time, strong sea/land breezes during day/night and their thermal effects on the island wake. This cruise provided the students with a significant, valuable, and meaningful opportunity to experience the complete process of proposing and undertaking field observations, as well as analyzing data and writing a scientific article.

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