Observational study on diurnal precipitation cycle in equatorial Indonesia using 1.3-GHz wind profiling radar network and TRMM precipitation radar

Abstract Variations in the diurnal precipitation cycle over equatorial Indonesia was investigated using 1.3-GHz wind profiling radars (WPRs) and rain gauges installed at Pontianak (109.37°E, 0.00°S), Manado (124.92°E, 1.55°N), and Biak (136.10°E, 1.18°S). The horizontal scale of the landmass around Pontianak is more than 100 km, while those of Manado and Biak are 10–100 km. At all three WPR sites, peak rain rate was detected during 1300–1500 local time (LT) by rain gauges. WPR observations showed that deep convective clouds were predominant during that period. There was a clear difference in the afternoon-to-evening precipitation among the three WPR sites. At Pontianak, the afternoon-to-evening precipitation has the characteristics of a mesoscale convective system (MCS). Stratiform precipitation after the peak deep convective rain rate was predominant, and the transition from convective precipitation to stratiform precipitation was clearly apparent during 1500–2000 LT. Black body brightness temperature (Tbb) observed by MTSAT-1R satellite also indicated that the precipitation clouds had enough horizontal scale to be well organized as an MCS. At Manado and Biak, the peak rain rate in the early afternoon was characterized by a short period (1–2 h), and the precipitation after the convective precipitation was not clear. Tbb data showed that the convective precipitation had a horizontal scale of 10–100 km. The difference of precipitation features among the three WPR sites is considered to be caused by the difference of horizontal scales of the respective landmasses. The diurnal precipitation cycle was also investigated using 11 years of Tropical Rainfall Measuring Mission (TRMM) data. A 3G68 product with a horizontal resolution of 0.5° could not resolve peak rain rate in the early afternoon at Manado and Biak, where convective clouds developed with the 10–100 km horizontal scale. Surface rain data with a horizontal resolution of 0.1° were produced using the TRMM precipitation radar (PR) 2A25 product. This high-horizontal-resolution data set successfully detected the peak convective rain rate in the early afternoon at Manado and Biak.