Diurnal variation of precipitation from the perspectives of precipitation amount, intensity and duration over Sumatra from rain gauge observations

The characteristics of diurnal variation of precipitation in terms of amount (PA), frequency (PF), and intensity (PI) over Sumatra have been investigated using rain-gauge data from 186 stations. Mean PA and PF show spatial variations significantly affected by the terrain elevation and stations' distance to the west coastline of Sumatra. A slightly larger PA and PF appear over the middle and western sections of the Barisan mountains, in which the mean PI is smaller in these regions. Most stations with large rainfall amount also have large rainfall frequencies, indicated by a strong correlation between PA and PF. The timing of the diurnal peak of PA, PF, and PI also has prominent regional characteristics. The cluster analysis reveals different grouping of stations with distinctive diurnal peaks. The prevailing afternoon and early-evening peaks, that is, 1500-2000 LST, appear mostly over mountain ranges where amplitude of PA and PF tended to increase with elevation. Moreover, the amplitude of diurnal cycles tended to decrease as distance from the Sumatra's west coastline increases. On the western side of Barisan's mountain range, high amplitude of diurnal cycle prevails compared to the eastern side. We also found a strong relationship between rain event duration with diurnal cycle pattern. Generally, rain event with a long duration tended to have a peak occurring at a later time compared with those events of shorter duration. The diurnal variation of precipitation corresponds to the temporal evolution of the low-level convergences and wind vectors, and cloud migration modulated by land-sea breeze system.

Automated summary

The diurnal variation of precipitation in Sumatra shows spatial variations in amount, frequency, and intensity, influenced by terrain elevation and distance to the coastline. Stations with high rainfall amount also tend to have high rainfall frequencies, with regional differences in timing of diurnal peaks. The amplitude of diurnal cycles tends to increase with elevation and decrease with distance from the coastline.