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    Title: 全球暖化下季風亞洲降水的變化;Changes of precipitation in Monsoon Asia under Global Warming
    Authors: 葉芳利;Yeh, Fang-Li
    Contributors: 大氣科學學系
    Keywords: 全球暖化;降水強度;降水頻率;水氣收支方程;Global warming;precipitation intensity;precipitation frequency;moisture budget equation
    Date: 2018-05-01
    Issue Date: 2018-08-31 11:24:30 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 20世紀中期以後是人類溫室效應造成全球暖化最劇烈階段,全球平均地面氣溫在這短短50餘年間增加0.6℃以上。本研究應用1951-2007年間,日本氣象廳氣象研究所和日本綜合地球環境學研究所研發的【亞洲降水高解析度陸地日降雨網格資料】(APHRODITE,V1101)來分析亞洲季風區之降雨量、降雨日、雨跡日及無降水日在全球暖化下的變化。資料分析顯示,沿海地區、海島地區及熱帶地區的年降雨量較豐沛,但可以發現降雨量豐沛的地區,其降雨日天數並不一定也很多,這意味著各地區降雨強度不盡相同。全球暖化可能使得熱帶赤道地區降水強度下降、中國東北部降水量及降水強度皆下降、中國東南部降水強度增加、印度地區降水強度下降。
    不同降雨事件發生的頻率在地理分布上的變化顯示,前十年(1951-1960年)與後十年(1998-2007年)絕對變化差異大的事件為強度偏弱的降水事件。也可以知道不論是何種氣候區,整個亞洲季風區主要的降水量變化皆來自非常弱及弱降水事件。以非常弱(0.1~1 mm/day)、弱(1~10 mm/day)、中等(10~25 mm/day)、強(25~50 mm/day)及非常強(大於50 mm/day)降水事件來分析降雨量、降雨日的各種變化,發現九個氣候區中以熱帶雨林氣候區、副熱帶季風氣候區、溫帶海洋氣候區的降雨事件變化情況比較顯著。
    受到全球暖化的影響,亞洲季風區中各氣候分區的降水量變化皆呈現下降的趨勢,其中以熱帶雨林氣候區下降最明顯;降水頻率變化主要集中在中、強降水範圍,其中溫帶海洋氣候區的降水頻率在強、非常強降水增加幅度最大,相對變化率可達100-300%。反之熱帶雨林氣候區與溫帶乾燥氣候區的降水頻率相對變化在強、非常強降水強度可下降20-80%。降水強度的相對變化同樣是溫帶海洋氣候區的強降水強度增加最多,而熱帶雨林氣候區的強度是減少最明顯的。因此可以明顯地了解到降水的變化趨勢在各氣候區是非常不均勻的分布,這樣的現象與環境場有著密切的相關性。
    在定量分析上,利用水氣收支方程來探討熱帶雨林、副熱帶季風及溫帶海洋氣候區降雨變化的物理機制。熱帶雨林、副熱帶季風及溫帶海洋氣候區主要是由擾動垂直速度的垂直平流項為影響降雨擾動項變化的主要貢獻項,熱帶雨林、副熱帶季風及溫帶海洋氣候區為上升運動減弱而造成降雨的減少。
    整體而言,整個亞洲季風區受到全球暖化的影響,降雨的變化在地理位置分佈上非常不均勻,並不完全遵守【濕者愈濕、乾者愈乾】假說。基本上可以發現降雨變化主要是由垂直上升運動增加或減少所控制。至於九個氣候區在各種降雨事件上的變化皆不盡相同,未來可以再使用不同降雨資料來分析暖化氣候對降雨的影響及造成變化的機制。
    ;Since the 2nd half of the 20th century, anthropogenic greenhouse effect has caused the rapidest global warming trend ever in human history. The global-mean surface air temperature increased greater than 0.6℃ in the past fifty years. In this thesis research, we used a high-resolution precipitation reanalysis data, the “Asian Precipitation - Highly - Resolved Observational Data Integration Towards Evaluation” (APHRODITE,V1101) to examine changes of precipitation amount, precipitation days, trace days and dry days in Monsoon Asia over the period from 1951 to 2007. The results showed that precipitation intensity is larger over coastal areas of Asian continent and maritime continent. Precipitation day shows a significant non-homogeneous distribution in Monsoon Asia which also implies the strong non-homogeneity of precipitation intensity. Under global warming, the precipitation intensity tends to weaken in tropical equator, the precipitation amount and precipitation intensity appears to decrease in northeast China, the precipitation intensity tends to strengthen in southeast China, and the precipitation intensity appears to weaken in India.
    Examining changes in frequency of five precipitation categories showed that differences in precipitation intensity of very light and light precipitation events are largest over the study period. We also found that, no matter in which climatic zones, the very light and light precipitation events mainly contribute to changes in precipitation amount in Monsoon Asia. We also used five precipitation categories (very light, light, moderate, heavy, and very heavy) to analyze changes of precipitation amount and precipitation days. Only modest changes of precipitation amount were found over the study period in nine climate zones except for the tropical rainforest climate, subtropical monsoon climate, and temperate maritime climate zones.
    Under global warming, trends of precipitation amount were all reduced in nine climate zones. Trend of precipitation amount in Tropical rainforest climate was obviously reduced among nine climate zones. Changes in precipitation frequency were found mainly on moderate and heavy precipitation events. the relative change of precipitation frequency increases in temperate maritime climate, with values around 100-300%. Conversely, the relative change of precipitation frequency decreases in Tropical rainforest climate and subtropical monsoon climate, with values around 20-80%. Next, relative changes of precipitation intensity are similar to relative changes of precipitation frequency, i.e., the relative change of intensity largely increases for heavy precipitation among all precipitation events in temperate maritime climate, and largest decrease in tropical rainforest climate. Consequently, it is expected that changes of precipitation trend and the associated non-uniform distribution for all climate regions must be related to environment factors.
    For the quantitative analysis, we used the moisture budget equation to explore mechanism responsible for changes of precipitation amount in tropical rainforest climate, subtropical monsoon climate, and temperate maritime climate. The vertical moisture advection due to convection change is the main contribution effect leading to precipitation changes term in the tropical rainforest climate, subtropical monsoon climate, and temperate maritime climate. In other words, anomalous divergence and subsidence lead to reduce rainfall in tropical rainforest climate, subtropical monsoon climate, and temperate maritime climate.
    In conclusion, changes of precipitation showed a non-uniform geographical distribution in Monsoon Asia, in general, disobeying the “wet-get-wetter and dry-get-drier” hypothesis. Specifically, changes in precipitation are controlled by changes in convection. As for the nine climate zones, changes of various rainfall events are not always the same in all climate zones. In the future, we will use different data to analyze how global warming impacts precipitation frequency and intensity.
    Appears in Collections:[Department of Atmospheric Sciences and Graduate Institute of Atmospheric Physics ] Department of Earth Sciences

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