熱帶雷雨系統降雨強度閃電次數與系統大小之關係

Relationships among Maximum Rain Rate, Flash Counts, and System Size of Tropical Thunderstorms

簡弘文(Hong-Wen Jian)

指導教授 ： 陳維婷

國立臺灣大學/理學院/大氣科學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201802493

摘要

熱帶雷雨系統是垂直發展很強的對流系統並在全球能量收支與水循環扮演重要角色。熱帶雷雨系統伴隨的雷擊與強降水可能造成巨大的經濟損失。過往研究指出劇烈地面降雨與系統尺寸之間有正關聯，但並沒有特別針對有發生閃電的降雨系統進行分析。為了探討發生閃電的降雨系統特性如系統尺寸與降雨和閃電次數之間的關係以及熱帶雷雨的時空變化，本研究使用1998-2014 年TRMM 衛星上降雨雷達(PR)以及閃電成像儀(LIS)的資料，將近地面降水與閃電次數進行共同定位建立熱帶降水系統資料庫。在九千三百萬個降雨系統中，其中僅有1%的系統具有閃電活動。結果顯示熱帶雷雨系統比無閃電的降水系統尺寸更大以及具有更極端的降水。雷雨系統的大小以及最大閃電次數都與最大降雨強度成正相關，而熱帶海洋上的雷雨系統比陸地上的系統更容易發生尺寸較大、強降雨但閃電次數偏少的系統。雷雨系統的特性在海洋大陸地區並不像一般發生在陸上的雷雨系統，他們更傾向發生尺寸更大且降雨強度更高的雷雨。在海洋大陸中，海洋上的極端的雷雨系統(尺寸大於83.2 km、降雨大於23.67mm hr-1、閃電大於54 次)有很明顯的日夜變化，且主要發生在晚間。環境條件取樣分析顯示此類極端雷雨系統容易發生在微弱底層(850 至1000 hPa)垂直風切(1 至2 m s-1)、中等850hPa 以下的濕靜能(338 至342 K)搭配中低層(900 至600 hPa)較少的水氣(30 至35 mm)及高層(600 至200 hPa)較多的水氣(4 至6 mm)。在此區中，麻六甲海峽上好發此類極端雷雨並且主要發生在5 至11 月。環境分析顯示此季節午夜至清晨期間來自蘇門答臘島與馬來半島的兩支陸風在此區輻合提供水氣有利於高度組織性極端雷雨系統的產生。

關鍵字

熱帶雷雨系統 ； 熱帶降雨觀測任務(TRMM) ； 共同定位

並列摘要

Tropical thunderstorms are deep convective systems, which play a crucial role in the global energy balance and hydrological cycle. The severe rainfall accompanied with the intense lightning activity of the thunderstorm can cause enormous economic damage. Previous studies showed that extreme surface rain rate is associated with system size but they did not distinguish the rainy systems according to lightning. In order to investigate the characteristics of the extreme systems with the consideration of lightning occurrence, the present study analyzes the relationships among maximum flash counts, surface rain rate, and size of rainy systems, as well as the spatial and temporal variations over the Tropics. The data from Precipitation Radar (PR) and Lightning Imaging Sensor (LIS) of Tropical Rainfall Measurement Mission (TRMM) are co-located to identify rainy systems. There are over ninety-three million rainy systems from 1998 to 2014 in this database but only one percent of rainy systems exhibits lightning activity. The result shows that tropical thunderstorms have larger size and more intense maximum rain rate compared with the non-flash rainy systems. For thunderstorm systems, larger system size and frequent flash counts are associated with heavier maximum rain rate. Thunderstorm systems over tropical ocean are more organized and exhibit more intense rainfall, but weaker in flash counts. Unlike the characteristics of thunderstorms over land, Maritime Continent has comparable thunderstorms occurrences with landmass but systems tend to be larger and heavier-rainfall here. The most extreme thunderstorms (size > 83.2 km, rain rate > 23.67 mm hr-1, flash > 54 counts) over ocean in Maritime Continent exhibit strong nocturnal signals. From the conditional sampling of environmental conditions, these systems favor weak low-level (850 hPa – 1000 hPa) vertical wind shear (1-2 m s-1), moderate low-level (below 850 hPa) moist static energy (338-342 K), weaker mid-level (900 hPa – 600 hPa) moisture (30 – 35 mm) and higher upper-level (600 hPa – 200 hPa) moisture (4 – 6 mm). These highly organized extreme thunderstorms over ocean occur frequently in the Strait of Malacca from the midnight to the early morning, when the convergence of land breezes from Sumatra and Malay Peninsula bringing abundant moisture into the strait, especially from May to November.

並列關鍵字

Tropical Thunderstorms ； TRMM ； Co-location

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