Raindrop distribution in the Eastern Coast of Northeastern Brazil using disdrometer data

Abstract

Usually a single literature-suggested Z-R relationship, where Z the radar reflectivity factor and R the rain rate, is used for weather radar data interpretation. It is desirable to calculate a Z-R relationship by precipitation type to improve the accuracy of quantitative rainfall rate in case of coexistence of different precipitation types, such as, in the area of precipitation produced from a Mesoscale Convective System (MCS). In general, in the MCS trailing anvil, the stratiform precipitation does not fall as drizzle. Rather, the rainfall can assume significant intensity (~10 mm h-1) with showery character. For that reason, in this study, the precipitations were classified into convective and stratiform type, to produce optimum rainfall estimates. Therefore, Z-R relationships were developed for the Eastern Coast of Northeastern Brazil (NEB) using rainfall raindrop size distribution (DSD) data collected with a disdrometer RD-69, aiming their utilization to start the operation of a weather radar system. In this study, due to operation and maintenance facilities, the disdrometer was installed in the Campus of the Universidade Federal de Alagoas (The Federal University of Alagoas) in Maceió in 2001, 12 months before the complete installation of a new radar system. The DSD was stratified by rainfall rate classes. It is found that the DSD are clearly dependent on the parameters of the analytical distribution functions are, and show a marked monthly variability. The parameters of the frequency distributions are dependent on R. The forms of DSDs are similar but the amount of droplets in each one very strongly. This may be possible due to the short period of data collection or to the intraseasonal rainfall variability. The general relationship for the Eastern Coast of NEB was found to be Z = 176.5 R1.29, with correlation coefficient equal to 0.83. This equation is in accordance with the ones for stratiform rain reported in the literature. We found that the convective rain observed is produced by convective cells imbedded into stratiform cloud layers. However, when separating stratiform and convective rainfall we found that the linear coefficient of the Z-R relation is significantly smaller for convective rainfall than for stratiform one (65 and 167 respectively), but the exponential coefficient is higher for convective than for stratiform (1.69 and 1.26 respectively).

Rainfall Microstructural Analysis for Microwave Link Networks: Comparison at Equatorial and Subtropical Africa

“…Again, the predominance of stratiform precipitation at the two sites is consistent with observations at mid-latitude areas, especially tropical regions [6,24,25]. By fitting the reflectivity samples at both sites for stratiform and convective regimes, it is found that A coefficients of the Z-R function for former regime is higher than that of the latter regime (see Table 3).…”

“…Ground or space-borne radar measurements both estimate reflectivity parameters with background information on rain DSD and droplet densities [6,7].…”

Precipitation Diurnal Cycle Assessment of Satellite-Based Estimates over Brazil

“…In some cases like INMET, CEMIG and SIMEPAR data are flagged as 9999.99 while the other networks use a spurious value (i.e., 650 mmh −1 ); 2. A threshold between 10 mmh −1 and 120 mmh −1 was established for convective rainfall (also adopted at SIMEPAR) to apply specific quality control tests, according to [16]; 3. For rainfall rates within this interval, the physical characteristics of the convective clouds were compared with the correspondent satellite imagery [17] using different channels (mainly infrared and visible, when available) from GOES 13 and 16.…”

Quality Control Algorithms Applied on Weather Radar Reflectivity Data

“…There are approaches that use tuned Z-R relationships for different meteorological situations. It requires the different types of precipitation to be identified on the basis of dedicated algorithms, which is easier if disdrometer measurements are available (Tenório et al, 2010). Improvement in precipitation rate R estimation is noticeable using dual-polarization parameters, especially for heavy rainfall.…”