發(fā)布時(shí)間：2018-04-24 06:12

  本文選題：中尺度渦旋 + 渦旋自動識別方法��； 參考：《南京大學(xué)》2017年碩士論文

【摘要】：中尺度渦旋是造成長江中下游地區(qū)暖季暴雨災(zāi)害的主要天氣系統(tǒng)之一,它是出現(xiàn)在對流層中低層的,水平尺度在幾十到幾百公里之間的氣旋性環(huán)流,并常常與對流活動相伴隨。為了加深對中尺度渦旋的認(rèn)識,本文采用水平分辨率為0.5°×0.5°、時(shí)間分辨率為 6h 的 CFSR(Climate Forecast System Reanalysis)再分析資料,利用神經(jīng)網(wǎng)絡(luò)算法對1996-2015年共20年長江中下游地區(qū)暖季的中尺度渦旋進(jìn)行了普查,共得到309個(gè)中尺度渦旋樣本,并從渦旋發(fā)生頻數(shù)的年際、月際變化、生成源地、水平尺度、垂直厚度、生成時(shí)刻、持續(xù)時(shí)間、移動路徑、渦旋干濕性質(zhì)等方面著手進(jìn)行了統(tǒng)計(jì)特征研究。對2015年長江中下游地區(qū)暖季的MCS(Mesoscale Convective System)進(jìn)行了普查,找出了形成于 MCS 中的 5 例濕渦旋,對這5例渦旋進(jìn)行了合成分析,研究其結(jié)構(gòu)特征;對其中1例持續(xù)時(shí)間最長的渦旋進(jìn)行了個(gè)例分析,詳細(xì)地展示了渦旋的演變過程,探討其發(fā)生發(fā)展的機(jī)制。分析結(jié)果表明:長江中下游地區(qū)的中尺度渦旋在5、6、7月出現(xiàn)頻率基本相同,而8月明顯偏少。大多數(shù)的渦旋是局地新生的渦旋,凌晨02:00(北京時(shí)間,下同)為渦旋的高發(fā)期,午后14:00時(shí)為渦旋生成的第二個(gè)高峰期。大部分渦旋的維持時(shí)間較短(30h以內(nèi)),半徑在100km左右,垂直厚度大多小于250hPa,閉合環(huán)流最明顯的高度在850hPa。因此,長江中下游地區(qū)暖季的中尺度渦旋是位于較低層次的淺薄系統(tǒng)。渦旋的移動路徑主要有偏北、偏南、向東和準(zhǔn)靜止四種,其中偏北路徑最多。按照渦旋的干濕性質(zhì)可以分為:濕渦旋、干渦旋和MCV(Mesoscale Convective Vortex,MCV可看作濕渦旋的一種特例)。識別到的渦旋中濕渦旋的數(shù)目遠(yuǎn)多于干渦旋,說明大部分中尺度渦旋的形成都離不開水汽,相態(tài)變化和潛熱釋放在渦旋的形成中占主導(dǎo)作用,干渦旋的水平尺度和持續(xù)時(shí)間都較小,其形成主要是動力作用的結(jié)果。對2015年5個(gè)形成于有組織的對流系統(tǒng)中的濕渦旋進(jìn)行合成分析發(fā)現(xiàn),這些渦旋是上暖下冷的結(jié)構(gòu)分布,它們與成熟期的溫帶氣旋的冷心結(jié)構(gòu)不同,與熱帶氣旋的強(qiáng)暖心結(jié)構(gòu)也不同,而是一類弱暖心的結(jié)構(gòu),這可能是屬于東亞季風(fēng)區(qū)與副熱帶地區(qū)中尺度渦旋熱力結(jié)構(gòu)的特點(diǎn);渦旋的強(qiáng)輻合區(qū)、高層的強(qiáng)輻散區(qū)和強(qiáng)上升運(yùn)動區(qū)不在渦旋的中心,而是位于渦旋的東側(cè),這預(yù)示著未來新的對流有可能在渦旋的東側(cè)發(fā)展,這也許與高低空急流的耦合有密切的關(guān)系。渦度收支分析表明風(fēng)場的低層輻合、高層輻散配置對渦旋的渦度增長起著非常大的作用。在對流層低層,輻合輻散項(xiàng)和傾斜項(xiàng)是正渦度的來源,垂直輸送項(xiàng)和平流項(xiàng)抑制局地渦度的增大。低層初始的輻合和地面擾動,會觸發(fā)對流產(chǎn)生降水,降水釋放的潛熱有利于渦旋的生成。低空急流除了輸送水汽外,還會向中尺度渦旋區(qū)輸送正渦度,而中層的正渦度強(qiáng)迫有利于地面的減壓。因而,渦旋的產(chǎn)生是多個(gè)因子共同作用的結(jié)果。渦旋產(chǎn)生后反過來影響降水,兩者存在正反饋?zhàn)饔谩５蛯虞椇�、高層輻散的配置以及潛熱的釋放使得渦旋得以發(fā)展和維持。
[Abstract]:The mesoscale vortex is one of the main weather systems that cause the warm season rainstorm in the middle and lower reaches of the Yangtze River. It is a cyclonic circulation that appears in the middle and low layers of the troposphere and between the horizontal scale from dozens to hundreds of kilometers, and is often accompanied by the convective activity. In order to deepen the understanding of the mesoscale vortex, this paper uses a horizontal resolution of 0.5 degrees. The data of CFSR (Climate Forecast System Reanalysis) with time resolution of 6h are reanalyzed. The mesoscale vortices of the middle and lower reaches of the middle and lower reaches of the Yangtze River are surveyed by neural network algorithm for a total of 20 years in 1996-2015 years, and a total of 309 mesoscale vortex samples are obtained, from the interannual and monthly variation of the vorticity occurrence frequency to the formation of the source area. The statistical characteristics of the MCS (Mesoscale Convective System) in the warm season of the middle and lower reaches of the Yangtze River in 2015 were investigated, and 5 wet vortices formed in MCS were found, and the synthetic analysis of the 5 vortices was analyzed. The structural characteristics of 1 cases with the longest duration were analyzed, the evolution process of the vortex and the mechanism of its development were demonstrated in detail. The results showed that the frequency of mesoscale vortices in the middle and lower reaches of the Yangtze River was basically the same in 5,6,7 months, but in August, most of the vortices were local freshmen. The vortex, 02:00 in the morning (Beijing time, the same below) is the high onset period of the vortex. At 14:00 in the afternoon, it is the second peak of the vortex. Most of the vortices have shorter maintenance time (less than 30h), the radius is around 100km, the vertical thickness is less than 250hPa, the most obvious height of the closed circulation is 850hPa., and the middle ruler of the warm season in the middle and lower reaches of the Yangtze River The vortex is a shallow system at a lower level. The moving path of the vortex is mainly North, South, eastward and quasi-static four, of which the northward path is the most. According to the dry and wet properties of the vortex, the vortex, dry vortex and MCV (Mesoscale Convective Vortex, MCV can be considered as a special case of wet Eddy). The number of spin is far more than that of the dry vortex. It shows that most of the mesoscale vortices are inseparable from the water vapor, the phase change and the latent heat release dominate the formation of the vortex, and the horizontal scale and duration of the dry vortex are smaller, and the formation of the vortex is mainly the result of the dynamic action. In 2015, 5 wet systems formed in the organized convection system are wet. It is found that these vortices are the structure distribution of the upper and lower cooling structures. They are different from the cold heart structure of the temperate cyclone in the mature period, and different from the strong warm heart structure of the tropical cyclone, but a kind of weak warm heart structure, which may belong to the characteristics of the mesoscale eddy thermal structure in the East Asian monsoon region and the sub heat zone; The strong convergence zone, the strong divergence area and the strong ascending motion area are not at the center of the vortex, but on the east side of the vortex, which indicates that the future new convection may develop in the east of the vortex, which may be closely related to the coupling of the high and low altitude jet. The growth of swirl vorticity plays a very important role. In the lower troposphere, the convergence and divergence term and the tilting term are the source of the positive vorticity. The vertical transport term and the flow term inhibit the increase of the local vorticity. The initial convergence and the ground disturbance in the lower layer will trigger the convection to produce precipitation, and the latent heat released by the precipitation is beneficial to the formation of the vortex. In addition, the positive vorticity is transported to the mesoscale vortex region, and the positive vorticity of the middle layer is forced to facilitate the decompression of the ground. Therefore, the vortex is produced by the joint action of several factors. The vortex is produced in turn to affect the precipitation, and there is a positive feedback effect. The low layer convergence, the configuration of the high rise divergence and the release of latent heat make the vortex. To develop and maintain.

【學(xué)位授予單位】：南京大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：P458.1

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