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Precipitation and the Lunar Synodic Cycle: Phase Progression across the United States

Kirby HansonNational Oceanic and Atmospheric Administration, Miami, FL 33149

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George A. MaulNational Oceanic and Atmospheric Administration, Miami, FL 33149

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William McLeishNational Oceanic and Atmospheric Administration, Miami, FL 33149

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Abstract

The question of whether there is significant variation in precipitation in the United States at the lunar synodic period (29.531 days) has been examined, based on daily precipitation data for the period 1900–80. Our results confirm previous studies and indicate by a new method that there is statistically significant variation in precipitation at this lunar frequency. We also show for the first time that there is spatial progression over the United States in the phase of the lunar-precipitation relationship. During spring, a precipitation maximum occurs first when the moon is gibbous in the northwestern United States, progressively later during the lunar cycle in the Midwest, and, finally, about the time of the new moon in the East. The recognition of spatial progression in phase raises questions about the reality of previously proposed global, lunar-precipitation mechanisms. We suggest, instead, the actual cause-effect relationship may involve the long-wave circulation of the atmosphere.

Abstract

The question of whether there is significant variation in precipitation in the United States at the lunar synodic period (29.531 days) has been examined, based on daily precipitation data for the period 1900–80. Our results confirm previous studies and indicate by a new method that there is statistically significant variation in precipitation at this lunar frequency. We also show for the first time that there is spatial progression over the United States in the phase of the lunar-precipitation relationship. During spring, a precipitation maximum occurs first when the moon is gibbous in the northwestern United States, progressively later during the lunar cycle in the Midwest, and, finally, about the time of the new moon in the East. The recognition of spatial progression in phase raises questions about the reality of previously proposed global, lunar-precipitation mechanisms. We suggest, instead, the actual cause-effect relationship may involve the long-wave circulation of the atmosphere.

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