臺灣西南海域總閃電頻率之模擬研究

The simulation of total lightning frequency over south-west coast of Taiwan

吳依璇(Yi-Hsuan Wu)

指導教授 ： 林博雄

國立臺灣大學/理學院/大氣科學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.03035

摘要

本研究結合臺灣電力公司TLDS（Total Lightning Detection System）系統的閃電資料與WISCDYMM（Wisconsin Dynamic-Microphysical Model）雲模式所輸出的水象粒子資訊，針對5、6月份臺灣西南海域位置，進行2005年~2008年的閃電及天氣特徵分析，並再針對2007年5月23日10:00~12:00UTC以及2008年5月22日22:00 UTC~5月23日00:46UTC兩個弱綜觀天氣的海上對流個案進行雲模式四種水象粒子質量與總閃電頻率進行分析診斷，我們期望藉由「水象粒子質量百分比與閃電數量的時序列關係」，以及「水象粒子所占質量百分比與閃電數量的相關性」等分析，對於閃電機制與雲微物理的關聯能夠更加認識與提供閃電參數化的可行方向。
針對2005 ~ 2008年5、6月份臺灣西南海域閃電與天氣特徵分析，結果顯示2007年為閃電相當活躍的一年，而2008年情況相仿，2005年及2006年相對的微弱許多；由天氣特徵分析，可發現5、6月份造成閃電發生主要是鋒面系統，然而由高溫熱對流所造成的閃電現象仍不容小覷，在2007年甚至可達到34.4%。
探討閃電數量與水象粒子質量百分比的關係，可發現高層大氣（7.2 ~ 11公里）相關性較佳，若分析這些參數的時間序列特徵，可發現中層大氣（3.2 ~ 7公里）與高層大氣高度中，軟雹與冰晶分別與閃電發生有明顯的相關性存在，符合雲中粒子帶電之理論。
在研究進行過程中，使用WISCDYMM模式時發覺熱胞的設定有其敏感度在，因此本研究再針對熱胞的「溫度、寬度、深度、離地高度」等10種設定進行敏感度測試，結果確實顯示熱胞對於「是否離地（中心距離地表高度）」、「厚度」以及「降溫」的敏感度甚大。

關鍵字

閃電 ； 雲模式 ； 帶電機制

並列摘要

This study analyzed the lightning and weather characteristics in southwest coast of Taiwan on May & June, from 2005 to2008. Data used in this study are the TLDS (Total Lightning Detection System, Taiwan Power Company) lightning data and hydrometers output of WISCDYMM (Wisconsin Dynamic-Microphysical Model) simulation. Two case studies on 10:00 ~ 12:00UTC, May 23 of 2007 and 22:00UTC May 22 to 00:46UTC, May 23, 2008 provided the detail analysis between these hydrometeors mass and the total lightning frequency. Through the studies of "time sequence relationship between hydrometeor mass percentage and lightning number" and "correlation ship between hydrometeor mass percentage and lightning number", the lightning mechanism related to cloud microphysics could be explored and provides a possible parameterization of lightning in cloud model.
In the result of lightning characteristic in May-June season, we found that lightning has higher frequency in 2007 & 2008. The lightning number of 2005 & 2006 is relatively less than the former. Frontal system is the major favor weather condition for lightning activity. Nevertheless, local thermal convection due to high temperature cannot be negligible with its 34.4% rate in 2007.
There is better correlation between hydrometeor mass and lightning number in upper atmosphere (7.2~11km). Further analysis showed that lightning was closely related to graupel and ice in middle atmosphere (3.2~7km) and upper atmosphere. This result is consistent to the charge mechanism of lightning.
Meanwhile, this study went through the sensitivity of WISCDYMM settings on thermal bubble condition of triggering cloud growth. Ten types of thermal-bubble setting such as core temperature, width, depth, AGL (Above Ground Level) and so on were tested in this study. By comparing different thermal bubbles with various settings, the result concluded that thermal bubble setting of WISCDYMM cloud model is sensitive to the result.

並列關鍵字

TLDS ； WISCDYMM cloud model ； Lightning

參考文獻

Fehr T, Dotzek N, Holler H. 2005. Comparison of lightning activity and radar-retrieved microphysical properties in EULINOX storms. Atmospheric research 76(1-4):167-189.

Gish O. 1944. Evaluation and interpretation of the columnar resistance of the atmosphere. Journal of Geophysical Research 49(3):159-168.

Helsdon Jr J, Farley R. 1987. A numerical modeling study of a Montana thunderstorm: 2. Model results versus observations involving electrical aspects. Journal of Geophysical Research-Atmospheres 92(D5).

Helsdon Jr J, Wu G, Farley R. 1992. An intracloud lightning parameterization scheme for a storm electrification model. Journal of Geophysical Research-Atmospheres 97(D5).

Jayaratne E, Saunders C, Hallett J. 1983. Laboratory studies of the charging of soft-hail during ice crystal interactions. Quarterly Journal of the Royal Meteorological Society 109(461).