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High resolution mesoscale modeling of Kauai wintertime weather

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Title:High resolution mesoscale modeling of Kauai wintertime weather
Authors:Chambers, Christopher R.S.
Contributors:Stevens, Duane E (advisor)
Meteorology (department)
Date Issued:Dec 2003
Publisher:University of Hawaii at Manoa
Abstract:Across the island of Kauai there are enormous gradients of rainfall, and in the center of the island Mt Waialeale is considered one of the wettest spots on Earth. Five high resolution MM5 case studies under different wintertime synoptic flow regimes have been performed to investigate the processes that lead to the observed rainfall distributions across the island. There is good agreement between the mOdeled rainfall and 3 day rain gauge totals for 4 out of the 5 case studies presented. This suggests that rainfall distributions and gradients across the island are to some extent realistically simulated. Analysis of the easterly wind case reveals significant structural changes to the trade wind layer as it passes over the island. On approach to the central mountains, there is a general deepening of the moist layer and a corresponding deepening of clouds associated with flow over, rather than around, the island. On the lee side downward moving air mixes dry air from above the inversion with the moist air below, leading to a drying of the moist layer over leeward areas. Trajectory analysis suggests that, aided by latent heat release, air from low levels under partially cloudy (i.e. trade cumulus) easterly wind conditions can lift up the windward slopes and flow over the top of Waialeale. Persistent heavy rainfall out of the consequent deep orographic clouds is triggered as upward motion shifts to downward motion over the summit. Wind flow changes over the summit crest are in turn likely to be largely dependent on the characteristics of the trade wind inversion. Other case studies under different synoptic flow also produce a maximum in rainfall over Waialeale. Results suggest, but do not prove, general intuitions about the conditions that favor the production of orographic rain. A deeper moist layer allows the development of deeper clouds leading to greater rainfall. Latent heat aided uplift within orographic clouds supports the flow of air over the mountains. Model testing of sensitivity to vegetation specification reveals that changing the vegetation type in the model leads to different total rainfall patterns across the island. These differences result as (either) a local island consequence of the altered surface fluxes associated with the vegetation changes made, and (or) the simulations producing different cloud and rain distributions generated by a separate forecast.
Description:x, 104 leaves
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: M.S. - Meteorology

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