Diurnal variation of precipitation in central Amazon Basin

ABSTRACT The diurnal variation of precipitation at four stations in and around Manaus (03°S, 60°W) is studied using hourly observations for the period 2006–2011. The rainfall at midforest stations is 20% greater than that at the city stations, especially in the afternoon hours. The frequency of rain events varies substantially with the hour of the day, but the mean intensity of rain events does not. Daytime [06–18 local time (LT)] frequency is more than two times the nighttime (19–05 LT) frequency. The hours with highest frequency are 12–17 LT. The wet season November through May (NDJFMAM) frequency is approximately three times that of the dry season June through October (JJASO) frequency at all hours and at all stations. The diurnal frequency peak in the afternoon is more pronounced at the forest stations than at city stations. For smaller intensities of hourly rainfall the afternoon peaks are very pronounced while larger intensities of rainfall (15 mm h−1 and above) do not show preference for any hour of the day. Higher rainfall totals in the rainy season are due to more frequent rainfall rather than higher intensities of the rain events. Higher frequencies in the early morning hours close to the river are possibly due to the river breeze effect.