The Diurnal Variation of Large-Scale Inferred Rainfall over the Tropical Pacific Ocean during August 1979

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  • 1 Weather Research Program (WRP), Environmental Research Laboratories, NOAA, Boulder, CO 80303
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Abstract

Average diurnal variation of satellite-inferred rainfall for August 1979 was examined for five 15° longitudinal slices of the tropical Pacific Ocean. Over each area, averages were computed for each hour of the day over 30 days and examined in time series. The results illustrate the character of maritime convective rain over very large tropical areas and do not reflect the behavior of individual cumuli.

Time series over four of the five areas exhibited dual maxim one near dawn and the other in midafternoon. The remaining area's time series showed the test amount of rainfall in the morning. Harmonic analysis showed that the first harmonic (24-hour period), which peaked in the early afternoon over four of the arm accounted for most of the variance in the data over all areas. The second harmonic (12-hour period) significantly contributed to the variance, peaking near dawn and dusk over all areas, but, in most cases was of secondary importance. Higher frequency harmonics were unimportant. With the exception of the first harmonic of one area, the phase angles for the first two harmonies were coherent, suggesting that the same physical process (or processes) was at work.

Abstract

Average diurnal variation of satellite-inferred rainfall for August 1979 was examined for five 15° longitudinal slices of the tropical Pacific Ocean. Over each area, averages were computed for each hour of the day over 30 days and examined in time series. The results illustrate the character of maritime convective rain over very large tropical areas and do not reflect the behavior of individual cumuli.

Time series over four of the five areas exhibited dual maxim one near dawn and the other in midafternoon. The remaining area's time series showed the test amount of rainfall in the morning. Harmonic analysis showed that the first harmonic (24-hour period), which peaked in the early afternoon over four of the arm accounted for most of the variance in the data over all areas. The second harmonic (12-hour period) significantly contributed to the variance, peaking near dawn and dusk over all areas, but, in most cases was of secondary importance. Higher frequency harmonics were unimportant. With the exception of the first harmonic of one area, the phase angles for the first two harmonies were coherent, suggesting that the same physical process (or processes) was at work.

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