Z-R Relationships for Weather Radar in Indonesia from the Particle Size and Velocity (Parsivel) Optical Disdrometer

The relationship between the radar reflectivity factor ( Z) and rainfall rate ( R), which is called the Z-R relationship (Z=AR
^b
), is important to convert Z from weather radar to R because a weather radar does not measure the rainfall amount directly. The Z-R relationship can be governed from raindrop size distribution (DSD) data. However, the DSD varies not only within a specific storm type but also across different storm types and climatic regimes. Therefore, the use of a single Z-R relation such as a climatological Z-R relationship type Z=200R
^1.6
(Marshall-Palmer) for converting radar reflectivity into R will underestimate or overestimate rainfall rate. In this research, the Z-R relationships for weather radar in Indonesia were governed through a network of the Particle Size and Velocity (Parsivel) optical disdrometer along equatorial Indonesia. The Parsivel were installed at Manado (Sulawesi) and Biak (Papua). In addition to the aforementioned sites, we have been conducting DSD observations at Padang, Sicincin, Kototabang (Sumatra) and Pontianak (Kalimantan). In general, the coefficients A and b of Z-R equations vary from 200-400 and 1.36-1.47, respectively. This value shows a significant diurnal variation. In Biak and Manado, coefficient A during 00-11 local time (LT) is larger than that during 12-23 LT. However, in Sicincin, Padang, Kototabang and Pontianak, coefficient A during 00-11 LT much smaller than that during 12-23 LT. It was also found that coefficient A in Pontianak is much larger than other sites which indicates a higher concentration of large size drop in this area as seen from a larger value of mass-weighted mean diameter (Dm).