水汽含量对飑线组织结构和强度影响的数值试验

利用2009年6月3～4日一次产生大风、冰雹强对流天气的飑线个例进行数值试验，研究整层水汽含量及其垂直分布对中尺度对流系统的发生发展过程、组织类型和强度等的影响。本文的试验表明环境场中不同的水汽含量和垂直分布，会影响下沉气流和冷池的强度，从而影响对流的组织形态、维持时间和强度。整层水汽试验表明，增加（减少）水汽，对流增强（减弱），冷池和雷暴高压增强（减弱）导致大风增强（减弱）。增加水汽越多发展阶段冷池强度越强，最大风速越强，但成熟阶段后期冷池减弱的越快，层状云区的后部入流减弱，不利于雷暴大风的出现和维持。不同层次水汽试验表明，在保持整层水汽含量不变的情况下，线状对流和雷暴大风易发生在中层干、下层湿的环境中，这种层结条件对雷暴高压的增强有重要作用，但不利于整个对流系统的长时间维持。

Impact of Moisture on the Organizational Mode and Intensity of Squall Lines Determined Through Numerical Experiments

Numerical experiments were conducted on a squall line occurring on June 3-4, 2009, in Henan, Anhui, and Jiangsu provinces, China, that produced high winds and hail. The impact of moisture on the entire air column and that of its vertical distribution on the intensity, development process, and morphology of mesoscale convective systems (MCSs) were investigated. Analysis revealed that the amount of moisture and its vertical distribution had a significant effect on the strength of the downdraft and cold pool, which thus affected the morphology, duration, and strength of convection. The experiments on the entire air column demonstrated that the intensity of MCSs increased with moisture and that the strengths of the cold pool and the thunderstorm high increased, which led to higher winds. Conversely, the intensities of MCSs, cold pool, and surface winds decreased with moisture. Additional moisture led to a stronger cold pool, which caused the maximum winds to strengthen at the developmental stages of the MCSs. However, the cold pool and rear inflow jet weakened more rapidly, which was unfavorable for high wind development and maintenance at mature stages. Precipitable water in entire air column remained unchanged. Linear MCSs and high winds tended to occur in environments of mid-level drier air and low-level moister air that favored the development of stronger thunderstorm highs and discouraged the persistence of MCSs.