【作者】 吴学珂；

【导师】 郄秀书； 袁铁；

【作者基本信息】 兰州大学 ， 大气物理学与大气环境， 2014， 博士

【摘要】 深对流系统能够快速地把边界层的水汽及污染物等垂直输送到对流层上层,有些甚至能突破对流层顶直接进入平流层,从而在全球能量交换、水物质的重新分配以及对流层和平流层之间的物质交换中起着至关重要的作用。对流强烈的深对流系统还伴随着强降水、大风、冰雹和闪电等灾害性天气现象,对人们的生活造成严重影响。青藏高原与亚洲夏季风的相互作用使得亚洲季风区成为对流层物质进入平流层的重要通道。TRMM卫星因其多传感器的同步观测,为我们研究热带、副热带地区深对流系统的三维结构及强度特征提供了宝贵资料。本论文主要基于TRMM卫星观测资料,系统分析了全球尤其是亚洲季风区内20dBZ回波顶高大于14km的深对流系统的时空分布、对流属性和对流结构等特征,结合NCEP再分析资料,进一步对喜马拉雅山脉南麓附近区域内深对流系统形成的动力条件及水汽输送过程进行了研究。主要得到以下结论：1)深对流系统与闪电密度的分布基本一致,主要发生在热带地区的陆地上,并集中分布在非洲中部、南美洲北部以及亚洲南部至大洋洲北部之间的海洋性大陆区域。深对流系统对流深度(用云顶高度与20dBZ回波顶高来反映)和对流强度(用40dBZ强回波顶高、闪电频数以及极化修正温度来反映)的分布存在明显的区域差异。对流强度较大的深对流系统除非洲中部外,主要分布在副热带地区,例如：北美洲南部、南美洲南部以及亚洲季风区；而云顶较高的深对流系统主要分布在非洲中部、北印度洋—海洋性大陆—赤道西太平洋区域,其次是南美洲,与对流有效位能的分布一致。2)亚洲季风区内深对流系统的分布与夏季风活动密切相关且存在显著的区域性特征。夏季风爆发前(3-5月)深对流系统主要分布在20°N以南,集中在印度半岛东海岸附近；夏季风期间(6-9月),深对流系统的分布向中纬度移动并在青藏高原南麓地区最活跃。青藏高原上的深对流系统的对流强度较弱,水平尺度小,但发生频数较中国中东部高；而中国中东部的深对流系统虽然频数低但对流强度大。洋面上的深对流系统云顶高度最高(红外亮温最低)、40dBZ回波水平尺度比陆地上大,但40dBZ回波顶高较低且闪电频数较少。亚洲季风区陆地上的深对流系统存在明显的日变化特征,主要集中发生在午后至午夜,青藏高原上的深对流更集中地发生在午后至傍晚；而洋面上的深对流系统没有明显的日变化,热带海洋性大陆区域深对流系统的日变化与大陆上类似。3)深对流系统和40dBZ回波顶高超过10km的强深对流系统主要发生在陆地上。喜马拉雅山脉南麓的深对流系统约23.0%能够发展成为强深对流系统,其次是青藏高原上(20.8%)以及南亚季风区陆地上(15.3%),洋面上的最少(2.2%)。强深对流系统平均20dBZ回波顶高超过16km,其中有9%能超过了18km。深对流系统和强深对流系统主要发生在4一10月份,但深对流的峰值出现在8月份而强深对流系统在5月份。从青藏高原到喜马拉雅山脉南麓、南亚季风区陆地及洋面上,深对流系统的云顶高度依次升高；喜马拉雅山脉南麓附近区域内深对流系统的对流强度最强,且水平尺度也比南亚季风区陆地上的大；青藏高原深对流系统频发且更易达到对流层上层,但40dBZ强回波发展与闪电活动较弱且水平尺度较小。4)喜马拉雅山脉南麓区域(SSH)强深对流系统的发生与沿喜马拉雅山脉从孟加拉湾向西北方向绕流的水汽输送通道的建立密切相关。强深对流系统主要发生在湿度适中(6—16g kg-1)且有较强湿度梯度的陆地上,太大或太小均不利于其发生。对流抑制能约为-60J kg-1的环境有利于强深对流系统的形成。南亚夏季风爆发前(3—5月)洋面上风速较小,受洋面上湿空气影响,在孟加拉湾北部陆地上比湿与对流有效位能较大,强深对流系统主要发生在SSH东部；夏季风爆发期间(5、6月)洋面上风速开始增大,水汽输送通道开始形成并延伸到SSH中部,此时的强深对流系统较均匀地分布在整个SSH区域；夏季风爆发后(6—9月),强的西南夏季风将洋面上的水汽向西北一直输送到SSH最西端,而此时强深对流系统集中发生在SSH最西端凹痕区域。更多还原

【Abstract】 Deep convective systems (DCSs) transport water vapor and pollutants vertically to upper troposphere, some even penetrate tropopause and transport water vapor and pollutants into stratosphere directly, which are vital in terms of global energy exchange, hydrological cycle and stratosphere-troposphere exchanges. Some intense DCSs associated with heavy rain, strong winds, hails and lightning, resulting in a serious impact on people’s lives. The Asian monsoon region is an important pathway for water vapor and pollutants entering the stratosphere, due to the physical interaction of the Tibetan Plateau and the Asian summer monsoon. TRMM data is valuable for analyzing3-D structure and intensity of DCSs over tropical and sub-tropical regions because of the simultaneous observations of its onboarded multi-sensors. Based on TRMM data and NCEP Climate Forecast System reanalysis data, this thesis studied the spatiotemporal distributions, convective properties and structure features of DCSs with20dBZ echo top height exceeding14km over the world, especially the Asian monsoon region. Finally, a dynamic condition as well as transportation of water vapor and convective available potential energy (CAPE) for the forming of DCSs near southern slope of the Himalayas were investigated. The main conclusions are as follows:1) DCSs and lightning are both mainly distributed over the tropical continental regions, e.g., central Africa, northern South America and maritime continent between the Asia and the Oceania. It was found that the distributions of DCSs are different significantly in terms of convective depth (expressed by cloud top height and20dBZ echo top height) and convective intensity (represented by40-dBZ echo top height, lightning flash rate). DCSs with stronger convective intensity preferred to locate in the mid-latitude regions, e.g., southern North America, southern South America and the Asian monsoon region, except over Central Africa. While, DCSs with higher cloud top are mainly distributed over the northern India Ocean-maritime continent-western equatorial Pacific and central Africa, followed by South America, which is consistent with the distribution of convective available potential energy. Distribution of DCSs over the Tibetan Plateau-Asian monsoon region showed a significant particularity.2) The distribution of DCSs over the Asian monsoon region showed significant regional features and closely related to the Asian summer monsoon. DCSs are mainly distributed in south of20°N and concentrated near the India’s east coast during the pre-monsoon season (March to May), further move markedly to mid-latitude area and most frequent near the Himalayan foothills in monsoon (June to September). DCSs over the Tibetan Plateau is weak in convective intensity and small in horizontal size, but occurred more frequent than over central and eastern China. While, intensity of DCSs over central and eastern China is more intense. Convective intensity of oceanic DCSs is weak, but the cloud top height is tallest and horizontal size is larger than continental DCSs significantly. DCSs over the terrestrial Asian monsoon region showed obvious diurnal variation, mainly appeared in the afternoon until midnight, while DCSs over the Tibetan Plateau are more concentrated in the afternoon until evening, consistent with the solar radiation. There is no obvious diurnal variation over the ocean. The diurnal variation of DCSs over Maritime Continent is similar with that over the mainland.3) DCSs and intense DCSs (IDCSs, with40-dBZ echo tops exceeding10km) occur more frequently over the continental regions than over the ocean. About23.0%of total DCSs develop into IDCSs in the SSH, followed by the TP (20.8%) and the SAMR (15.3%), and the least over the ocean (2.2%). The average20-dBZ echo-top height of IDCSs exceeds16km asl and9%of them even exceeds18km asl. Although most of both DCSs and IDCSs occur between April and October, DCSs have a peak in August, while IDCSs have a peak in May. The cloud top heights of DCSs increase from the Tibetan Plateau, to the Himalayan foothills nearby, the south Asian monsoon region, and to the ocean. Oceanic DCSs is tallest in cloud top but convective intensity is weak. The most intense DCSs are more concentrated near the Himalayan foothills, and the horizontal size is larger than that over the south Asian monsoon region (terrestrial). DCSs over the Tibetan Plateau occur frequently and can grow up to upper troposphere easier than adjacent lower regions due to its higher elevation and strong sensible heat flux in boreal summer, but its convective intensity is weaker.4) The distribution of IDCSs (the1000most intense DCSs) is closely related to the establishment of the water vapor transport passage, which flows from the Bay of Bengal along the Himalayas to northwest and reaches the westernmost in monsoon. IDCSs mainly occur over continental regions with moderate humidity (6-16g kg-1) and accompanied by a strong moisture gradient. Moreover, the environment with convective inhibition about-60J kg-1is conducive to the formation of IDCSs. Wind speed over the ocean is weak before the onset of Indian Summer Monsoon (March to May), impacted by the oceanic moisture, the specific humidity and convective available potential energy (CAPE) over north of the Bay of Bengal is larger than other continental regions, as a result, IDCSs mainly located in eastern SSH. During the onset of Indian Summer Monsoon (May and June), wind speed begin to increase and the water vapor transport passage is formed and extends to the middle of the SSH, then, IDCSs more evenly distributed throughout the Himalayan foothills. During the Indian Summer Monsoon (June to September), strong southwest wind transport water vapor from the Bay of Bengal to the westernmost SSH, which ultimately lead to IDCSs concentrated over the concave indentation region in the westernmost SSH.更多还原