|dc.description.abstract||Characterization of variations in the raindrop size distribution (DSD) is required for microphysical studies. The DSD varies in different rain types and different spatial distribution. And variations in reflectivity-rainfall (Z-R) relations are strongly dependent on DSD variations. Other integral rainfall parameters such as liquid water content, reflectivity, and rain-rate are also functions of DSD. For these reason, it is important to analyze the DSD in different places and rain types.
DSD data collected with a Joss-Waldvogel disdrometer (JWD) and a 2d-video disdrometer (2DVD) in NCU from February, 2002 to May, 2006, is used to analyze the variations in gamma parameters of raindrop spectra. Besides, to compare the spatial difference of DSD, we also analyzed JWD data in five stations (i.e. Feitsui, Nankang, NCU, Shiyun and Suiman) from June, 2004 to May, 2006.
On average, as the rain-rate increased, more large drops were found in 2DVD and JWD. Although JWD underestimated the small drops, the small drops had little impact on the rain-rate and reflectivity differences between the 2DVD and JWD. For the comparison between five stations in northern Taiwan, the rainfall characteristics of Feitsui were more light rain and more small drops. Nankang had less small drops because small drops were masked by background noise. More heavy rainfall events occurred in Suiman and Shiyun due to its geographical features. And the average raindrop size in Suiman and Shiyun was larger than the other three stations.
DSD data from 2DVD and JWD had been analyzed to determine the variability of drop size in different seasons and precipitation types. For winter and front type, the rain-rate was smaller and the raindrops tended to smaller drop size. For Mei-yu front, the raindrop spectra were broader than the other seasons or types except the afternoon thundershower type. And the raindrop size was larger than winter. For typhoon type, the raindrops tended to medium size. As rain-rate greater than 60(mm/hr), the right side of raindrop spectra became narrow and the concentration of large drops decreased. For afternoon thundershower, it had more heavy rainfall events. The drop size was the largest and its spectra were the broadest of all types.
The composite statistics based on disdrometer suggested that the median volume diameter and generalized intercept for rain-rate less than 10(mm/hr) lied on a straight line with negative slope, which similar to stratiform rain type discussed by Bringi et al. (2003). And as rain-rate larger than 10(mm/hr), the two parameters lied between “maritime-like” and “continental-like” clusters.
In squall line case study, the analysis showed that stratiform precipitation has weaker reflectivity, narrower raindrop spectra, and smaller drop size. For convective precipitation, it had stronger reflectivity, broader raindrop spectra, and larger drop size. In typhoon Aere case, during the spiral band passage, the raindrop spectra became broader and the raindrop size was larger compared to the raindrop size during the passage of eye wall.||en_US|