Comparison Studies on the Observation of Raindrop Size Distribution in Strong Precipitation Frontal Case in Northern Taiwan
| Autor: | Ying-jhen Chen, 陳盈臻 |
|---|---|
| Rok vydání: | 2013 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 101 In the nighttime of 11th June 2012, a mature Mai-Yu front passed through the northern Taiwan. The extreme rainfall event caused multiple areas flooding. In order to investigate the characteristic of drop size distribution (DSD) accompanied with this heavy rainfall event, we used JWD, Parsivel and 2DVD collocated at NCU, and three JWDs in FeiCui, NanGang and XiaYung to investigate the frontal precipitation. In order to get the complete data, my discussion is organized as follows: Part 1 is focused on the weak precipitation period. Part 2 is focused on the strong precipitation period. Part 3 is the whole period as the front passing through the northen Taiwan. In the weak precipitation period, we made sure that before the strong precipitation happens, the three type disdrometers (JWD, 2DVD and Parsivel) operate consistently.During strong precipitation period, a significant DSD variation characteristic had been found. Due to the limitation of instrument, Parsivel tended to overestimate the concentration of medium to large drops in the strong rainfall intensity. Comparing the rain drops concentration with the rain rate varies with time, Parsivel showed a good agreement but JWD even did not get the most significant characteristic as the strongest rainfall occurred. The rain rates of JWD and Parsivel varied in the same trend, but compared the rain rates with the rain gauge observation in the 10 m tower at NCU, both of them showed obvious underestimation. We suspected the limitation of instrument made the rain rate underestimated. We analyzed whole two days’ data of JWD at FeiCui, NanGang and XiaYung on 11th-12th June 2012. The accumulated rainrates of these three stations were similar to the tipping buckets nearby. For the DSD variation, we found the concentration of small raindrops at XiaYung was the most in weak precipitation period but the least in strong precipitation. The DSD variations of FeiCui were similar to NanGang. The largest size of the raindrop detected at NCU was the smallest but the concentration is the highest amont the four JWD stations. For quantitative precipitation estimation (QPE) of radar, we used the WuFenShan radar data and disdrimeter data to estimate the rain rates based on the Z-R relationship. We also used the C-Pol radar data of NCU to estimate the rain rates based on the K_DP-R relationship. According to the analysis results, the K_DP-R relationship showed a good proformance on the rain rate estimation. The reflactivity of the WuFenShan radar needed to add 3 dBZ for the better rain rate estimation. Besides, the rain rate estimation showed the worst result at the station of NCU. The reason was the rain rate of disdromters underestimated seriously so the performance of the Z-R relationship was bad. To avoid these bad results happening again, we should confirm the disdrometer shows consistency well with tipping buckets before we use the disdromter data. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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