Trade Wind Rainfall near the Windward Coast of Hawaii: Corrected Data Yield Improved Results

John D. Tuttle National Center for Atmospheric Research, Boulder, Colorado

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Richard E. Carbone National Center for Atmospheric Research, Boulder, Colorado

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J. J. Wang Department of Atmospheric Sciences, University of Illinois, Urbana–Champaign, Urbana, Illinois

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Abstract

This note documents the effects of a radar calibration error that affected 5% of the data used in an earlier study by Carbone et al. While the original intent of this correction was merely to set the record straight, a significant finding emerged from the revised time series.

The main impact is to reveal a more rapid spatial decorrelation between island Froude number (Fr) and oceanic rainfall, a measure of the dynamical blocking effects upstream of Hawaii. There no longer exists a residual correlation between Fr and cumulative rainfall over the remote ocean, defined in this instance as distances >50 km from shore. This result both simplifies and strengthens the conclusions of the original work, which was based on a very short time series. The strong dependence of rainfall on Fr over the coastal lowlands and near shore remains unchanged from the results presented by Carbone et al. To the extent that remote oceanic rainfall is expected to be uncorrelated with Fr, there is increased confidence with respect to the causes and effects of island blocking on rainfall production over and near the island.

Current affiliation: Joint Center for Earth Systems Technology, University of Maryland, Baltimore County, Baltimore, Maryland.

Corresponding author address: John Tuttle, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307.

Email: tuttle@ncar.ucar.edu

Abstract

This note documents the effects of a radar calibration error that affected 5% of the data used in an earlier study by Carbone et al. While the original intent of this correction was merely to set the record straight, a significant finding emerged from the revised time series.

The main impact is to reveal a more rapid spatial decorrelation between island Froude number (Fr) and oceanic rainfall, a measure of the dynamical blocking effects upstream of Hawaii. There no longer exists a residual correlation between Fr and cumulative rainfall over the remote ocean, defined in this instance as distances >50 km from shore. This result both simplifies and strengthens the conclusions of the original work, which was based on a very short time series. The strong dependence of rainfall on Fr over the coastal lowlands and near shore remains unchanged from the results presented by Carbone et al. To the extent that remote oceanic rainfall is expected to be uncorrelated with Fr, there is increased confidence with respect to the causes and effects of island blocking on rainfall production over and near the island.

Current affiliation: Joint Center for Earth Systems Technology, University of Maryland, Baltimore County, Baltimore, Maryland.

Corresponding author address: John Tuttle, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307.

Email: tuttle@ncar.ucar.edu

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  • Carbone, R. E., J. D. Tuttle, W. A. Cooper, V. Grubisic, and W. C. Lee, 1998: Trade wind rainfall near the windward coast of Hawaii. Mon. Wea. Rev.,126, 2847–2863.

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