江淮下游地区强对流发生条件的实况分析与模拟

发布时间：2019-05-18 07:41

【摘要】：我国强对流天气多发,江淮下游地区强对流灾害频繁,给我国造成了巨大的经济损失和人员伤亡。当前对强对流天气的预报依然困难,预报强对流发生的具体位置和时间是强对流预报中最具挑战性的问题之一。本文从个例分析的角度出发,通过多个个例的实况和模拟分析,重点研究了江淮下游地区强对流天气的触发机制。通过对2009年6月5日强对流天气过程的详细分析,发现安徽北部低层大气的西南流场中存在中尺度扰动辐合中心,扰动触发了安徽北部最初对流云的生成。安徽北部存在一条西南气流与偏西气流汇合形成的辐合线,提供了有利于对流生成的位置。辐合线的东端出现风场扰动后对流产生,证明对流的生成与地面风场扰动有关。WRF模式模拟出了安徽北部辐合线、辐合线东端的风场扰动和对流触发的过程。模式结果显示,辐合线引起的上升气流局限在3km高度以下。辐合线东端的风场扰动由高层重力波引起,重力波为沿海对流激发出的n = 1模态的重力波。当n = 1重力波的上升气流与安徽北部的辐合线相交时,交点处的低层上升气流增强,触发了强对流的产生。结合不同个例分析了 n = 1重力波的结构特征和触发作用。n = 1重力波由一对下沉-上升气流构成,深度约12km,贯穿整个对流层,下沉-上升气流的垂直速度中心位于6km处。下沉(上升)气流的上半部分对应水平辐合(辐散)区,下半部分对应水平辐散(辐合)区。n = 1重力波在地面上形成一个低压扰动,低压扰动的气压下降(上升)阶段由下沉增温(上升冷却)造成,传播速度约为30m/s。飑线前部的低压部分由n = 1重力波的下沉气流造成。n = 1重力波的上升气流强于下沉气流时对触发对流有正贡献,地面风场会出现向着重力波传播方向的风分量增量的扰动。2009年6月14日强对流天气过程中飑线激发出了 n = 1重力波,并与飑线前的浅云带相交,触发了强对流生成。本文个例中出现于江淮下游地区部分典型地面辐合线类型有,1)气流绕过大别山、黄山、天目山在山地背风侧形成的辐合线,2)前期对流的出流形成的辐合线(包括阵风锋),3)内陆气流与来自海上的气流形成的沿海附近的辐合线。这些辐合线提供了有利于对流发生的位置,当辐合线与辐合线相交或辐合线与其他系统(如浅云带,对流系统,重力波等)相交时,相交处容易形成深对流。
[Abstract]:There are many severe convective weather in China, and the severe convective disasters in the lower reaches of Jianghuai River and Huaihe River are frequent, which has caused huge economic losses and casualties to our country. At present, the prediction of severe convective weather is still difficult, and the specific position and time of predicting the occurrence of severe convective is one of the most challenging problems in the prediction of severe convective weather. From the point of view of case analysis, this paper focuses on the trigger mechanism of severe convective weather in the lower reaches of Jianghuai River and Huai River through the actual situation and simulation analysis of several cases. Based on the detailed analysis of the severe convective weather process on June 5, 2009, it is found that there is a meso-scale disturbance convergence center in the southwest flow field of the lower atmosphere in northern Anhui, which triggers the formation of the initial convective clouds in northern Anhui. There is a convergence line formed by the confluence of southwest air flow and westward air flow in northern Anhui Province, which provides a favorable position for convective formation. After the wind field disturbance occurs at the eastern end of the convergence line, it is proved that the convective generation is related to the surface wind field disturbance. The WRF model simulates the process of wind field disturbance and convective trigger in the northern Anhui convergence line and the eastern end of the convergence line. The model results show that the updraft caused by the convergence line is limited to the 3km height. The wind field disturbance at the eastern end of the convergence line is caused by the high-level gravity wave, which is a n = 1 mode gravity wave excited by coastal convection. When the updraft of n = 1 gravity wave intersects the convergence line of northern Anhui, the lower updraft at the intersection increases, which triggers the generation of strong convolution. Combined with different examples, the structural characteristics and trigger effect of n = 1 gravity wave are analyzed. N = 1 gravity wave is composed of a pair of sinking-updraft airflow with a depth of about 12km, which runs through the whole tropospheric layer, and the vertical velocity center of subsidence-updraft flow is located at 6km. The upper part of the sinking (ascending) airflow corresponds to the horizontal convergence (divergence) region, and the lower part corresponds to the horizontal divergence (convergence) region. N = 1 the gravity wave forms a low pressure disturbance on the ground. The pressure drop (rise) stage of low pressure disturbance is caused by subsidence and heating (rising cooling), and the propagation speed is about 30 m / s. The low pressure part of the front of the squall line is caused by the downdraft of the n = 1 gravity wave. The updraft of the n = 1 gravity wave is stronger than the downdraft. There will be an incremental disturbance of wind component in the direction of gravity wave propagation in the surface wind field. During the severe convective weather on June 14, 2009, the squall line excited the n = 1 gravity wave and intersected with the shallow cloud belt in front of the squall line, which triggered the strong convective generation. In this paper, some typical ground convergence lines in the lower reaches of Jianghuai River and Huaihe River are as follows: 1) the convergence lines formed by airflow around Dabie Mountain, Huangshan Mountain and Tianmu Mountain on the leeward side of the mountain area. 2) the convergence line (including the wind front) formed by the outflow of the convolution in the early stage, and 3) the convergence line near the coast formed by the inland air flow and the air flow from the sea. These convergence lines provide a position conducive to the occurrence of convolution. When the convergence line intersects the convergence line or the convergence line intersects with other systems (such as shallow cloud belt, convective system, gravity wave, etc.), it is easy to form deep convection at the intersection.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P458.1

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