On the Dynamics of Hawaiian Cloud Bands: Comparison of Model Results with Observations and Island Climatology

Roy M. Rasmussen National Center for Atmospheric Research, Boulder, Colorado

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Piotr Smolarkiewicz National Center for Atmospheric Research, Boulder, Colorado

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John Warner National Center for Atmospheric Research, Boulder, Colorado

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Abstract

This paper presents a detailed comparison study of three-dimensional model results with an aircraft wind field mapping for the island of Hawaii. Model runs were initialized using an aircraft sounding from 1 August 1985, and detailed predictions from the model are compared with observations from that day.

The strength and location of the upwind convergence zone were well simulated, as well as the strong deflection and deceleration of the flow around the island and the geometry and location of the upstream cloud bands. The good agreement between the model results and observations supports the results of our previous study in which we show that the flow pattern and associated cloud processes around the island of Hawaii can be understood by considering the flow of a stably stratified fluid around a large three-dimensional obstacle.

Model runs with different wind directions showed that increasing northerly tradewind flow resulted in the band clouds moving closer to the shore line, and the large scale flow pattern rotating counterclockwise. Model results were also compared with various aspects of the island climatology, and good agreement was found in both the temporal and spatial distribution of precipitation on the island.

Abstract

This paper presents a detailed comparison study of three-dimensional model results with an aircraft wind field mapping for the island of Hawaii. Model runs were initialized using an aircraft sounding from 1 August 1985, and detailed predictions from the model are compared with observations from that day.

The strength and location of the upwind convergence zone were well simulated, as well as the strong deflection and deceleration of the flow around the island and the geometry and location of the upstream cloud bands. The good agreement between the model results and observations supports the results of our previous study in which we show that the flow pattern and associated cloud processes around the island of Hawaii can be understood by considering the flow of a stably stratified fluid around a large three-dimensional obstacle.

Model runs with different wind directions showed that increasing northerly tradewind flow resulted in the band clouds moving closer to the shore line, and the large scale flow pattern rotating counterclockwise. Model results were also compared with various aspects of the island climatology, and good agreement was found in both the temporal and spatial distribution of precipitation on the island.

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