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Impact of Trade Wind Strength on Precipitation and Circulation of the island of Hawaii

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Title:Impact of Trade Wind Strength on Precipitation and Circulation of the island of Hawaii
Authors:Esteban, Mary Ann B.
Contributors:Chen, Yi-Leng (advisor)
Meteorology (department)
Date Issued:Dec 2002
Publisher:University of Hawaii at Manoa
Abstract:The relation between different trade wind regimes and rainfall patterns on the windward side of the island of Hawaiʻi was studied using several data sources, mainly from the Hawaiian Rainband Project (HaRP). Previous modeling studies have emphasized that stronger trade winds are anticipated to produce more rainfall over the windward coast of the island of Hawaiʻi due to a dynamically induced return flow reversing direction as a result of island blocking and interacting with incoming trades; thus, higher rainfall production is dependent upon higher Froude numbers. However, analysis of Portable Automated Mesonet (PAM) data of the 12 strongest and 12 weakest trade wind days during HaRP throughout the diurnal cycle shows that stronger trade winds produce higher rainfall amounts at night, while weaker trade winds produce higher rainfall amounts during the daytime in relation to thermal contrasts between the land and sea. Expanding this dataset to the same HaRP period (11 July - 24 August) for 1997-2000 using NCEP/NCAR Reanalysis wind data and rainfall data from the National Weather Service Hydronet and National Climatic Data Center rain gauges show similar results. Rainfall over the windward side of the island of Hawaiʻi is a result of the complex interaction among island blocking, orographic lifting and the diurnal heating cycle and not primarily a result of stronger trade winds. In addition, an elevated Froude number of 0.35 can be reproduced at Kauaʻi which has a lower mountain height of 1598 m. Rainfall analysis of Kauaʻi shows that the rainfall axis occurs at the mountain top, not over the coastal regions. Rainfall, wind, and temperature data were also analyzed over the less frequently studied southeastern flank of the island of Hawaiʻi. Weaker trade days during HaRP produce higher rainfall amounts over the upper slopes in the afternoon as a result of orographic lifting and less flow deflection of incoming trades. Analysis of aircraft data and HHo soundings from HaRP reveal that flow deceleration upstream has a strong diurnal signal. The offshore extension of the downslope katabatic flow has a more dominant effect on the rate at which upstream air flow decelerates. In addition, with the development of katabatic flow at the lowest levels due to nocturnal cooling, winds aloft are stronger than during the daytime.
Description:xiv, 188 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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