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標題: | 全球暖化之下北大西洋海洋條件改變對颶風活動影響之探討 Change of the North Atlantic Ocean Condition under Global Warming and Implication on Hurricane Activity |
作者: | Shuo-Fu Geng 耿碩甫 |
指導教授: | 林依依 |
關鍵字: | 颶風強度,北大西洋,模態水,沉潛作用, Hurricane Intensity,North Atlantic,Mode Water,Subduction, |
出版年 : | 2015 |
學位: | 碩士 |
摘要: | Bender et al. 2010 利用第三期耦合氣候模式數值實驗計畫(Coupled Model Intercomparison Project Phase 3, Special Report on Emissions Scenarios A1B)探討北大西洋颶風的強度與個數,其研究發現風速大於65m/s的颶風個數,從二十世紀末(1980-2006)的六個上升到二十一世紀末(2081-2100)的二十一個,其中颶風強度達到category-4以上出現個數增加最多的區域為80°W-50°W,20°N-30°N,本研究將這個區域命名為boosting zone以做接續的討論。目前北大西洋颶風的主要發展區域(Main Development Region, MDR)為80°W-20°W,10°N-20°N,在MDR中,二十一世紀末颶風強度達到category-4以上的個數沒有明顯增加的趨勢。
本研究利用第五期耦合氣候模式數值實驗計畫(Coupled Model Intercomparison Project Phase 5, CMIP5) 19個模式的多模式系集(Multi-Model Ensemble, MME), Representative Concentration Pathways 8.5 (RCP8.5) 探討二十一世紀末(2091-2100)與二十一世紀初(2006-2015)海洋溫度場的變化。在全球暖化之下,MDR與boosting zone的次表層海水升溫不一致,在MDR中,表層海水溫度上升較多,次表層海水則上升較少,但是在boosting zone,次表層海水與表層海水溫度上升近乎一致,甚至更多。如此表示在全球暖化之下,boosting zone暖水層的厚度會增加,有利於熱帶氣旋增強。在MDR中,因為層化作用增加,將不利於熱帶氣旋的增強。因此,本研究將探討在boosting zone可能造成次表層溫度增加的因素。 根據前人研究的結果指出,副熱帶表層海水經過沉潛作用(Subduction)能夠將表層溫度異常,沿著等位密度線帶至熱帶次表層,造成次表層溫度的改變。此外,boosting zone次表層名為副熱帶模態水(North Atlantic Subtropical Mode Water, NASTMW, Masuzawa 1969)的水平移動也會造成次表層溫度的改變(Xie et al. 2000)。NASTMW的存在會擠壓到上層海水的等溫線,使表層至次表層海水的垂直溫度梯度增加,本研究將此現象命名為Compression;當NASTMW移動之後,上層海水的等溫線不在受到擠壓,等溫線向下沉,因此上層可以容納更多暖水,將此現象稱為Relaxation。結果顯示,在全球暖化下,除了輻射驅動力的增加之外,boosting zone次表層的升溫與Relaxation機制和Subduction機制有關。 Hurricane frequency and intensity in a globally warmed, late-21st-century climate were investigated in (Bender et al., 2010) by an ensemble-mean (18 models). The 18 models are from the World Climate Research Program coupled model intercomparison project 3 (CMIP3) and use the Intergovernmental Panel on Climate Change (IPCC) A1B emissions scenario. Bender et al. found that the total number of hurricanes with winds greater than 65 m/s increased from 6 (1980-2006) to 21 (2081-2100). The largest increase of the number is in the region (0°W-50°W,20°N-30°N) named as “boosting zone” for following discussions. However, there was no significant trend of the number in main development region (MDR; 80°W-20°W,10°N-20°N). The research objective of this study is to investigate the change of North Atlantic upper ocean condition between early-21-century (2006-2015) and late-21-century (2091-2100) under global warming. In this study, Multi-Model Ensemble (MME, 19 models) is used. The 19 models are from Coupled Model Intercomparison Project Phase 5 (CMIP5), and use the IPCC Representative Concentration Pathways 8.5 (RCP 8.5) emissions scenario. It was found that the temperature of subsurface increased as more as surface temperature or even more in boosting zone, but in the MDR, surface temperature increased more than subsurface temperature. Furthermore, the warm layer gets thicker in boosting zone under global warming, and it is conducive to tropical cyclone’s intensification. Via the subduction process, surface thermal anomalies may be transmitted from the surface to the upper thermocline. The shifting of water mass called North Atlantic Subtropical Mode Water (NASTMW, Masuzawa 1969) also makes temperature change in subsurface (Xie et al. 2000). Associated with this shift of NASTMW, the upper isotherm sinks, giving rise to large subsurface temperature anomalies. In this research, this mechanism is called “Relaxation”. Before shifting, it is called “Compression”. It is found that the increase subsurface warming in boosting zone may be related to the shifting of NASTMW in the subsurface ocean and the subduction of surface thermal anomalies. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/19932 |
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