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地形影响蒙古气旋发展的观测和模拟研究
OBSERVATIONAL AND NUMERICAL STUDY OF TOPOGRAPHY INFLUENCE ON MONGOLIA CYCLOGENESIS
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摘要: 针对2001年4月上旬一次蒙古气旋发展过程中的地形因素进行了观测和模拟研究, 结果表明:依据低层冷空气是否越过阿尔泰—萨彦岭山地产生气旋冷锋, 蒙古气旋的发生发展过程可以划分为触发和发展两个阶段。在气旋的发展阶段, 斜压不稳定是其主要强迫机制。伴随地形对低层冷空气阻滞程度的变化, 蒙古气旋经历了从缓慢发展到剧烈加强的过程。阿尔泰—萨彦岭山地通过对低层冷空气的阻滞使山地上空等熵面更为陡立, 加强了对流层低层的斜压强迫, 从而使斜压强迫的涡度增长向低层聚集, 导致气旋发展强度增强。阿尔泰—萨彦岭山地及其南侧形成的峡谷地形对低空急流的位置、范围、强度及演变过程具有较重要影响。另外, 对流层高层位涡平流也是气旋发展的一个强迫因素, 但其影响较小。Abstract: Observational study and numerical simulation are conducted on the topography influences on the Mongolia cyclogenesis. The results show that the Mongolia cyclogenesis can be divided into two processes, namely triggering process and development process, according to the appearance of surface cyclonic cold front. In the development process, the baroclinicity is the main forcing mechanism causing the development of Mongolia cyclone. The topography influences focus on: 1) The Altai-Sayan complex mountains retarded the cold air in the lower troposphere so that the Mongolia cyclone developed slowly before the cold air completely toughed the lee side and after that it developed explosively. 2) The baroclinicity was enhanced by the complex mountains (steepened the isentropic surface), which made the enhancement of vorticity concentrated downward at the low troposphere and so reinforced the development of surface cyclone. 3) The complex mountains affected the position, range and strength of the lowel level jet. In the upper troposphere the isentropic potential vorticity (IPV) advection contributed to the cyclogenesis and its effect was limited.
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图 1 2001年4月5日20:00(a), 6日08 :00(b), 6日20 :00(c)700 hPa形势图以及相对应的地面形势图 (d)5日20 :00, (e)6日08 :00, (f)6日20 :00
(图中700 hPa实线为高度, 虚线为温度。地面图上标注为气压和3 h变压。阴影区为地形高度)
图 5 对照试验 (a) 和平面地形试验 (b) 模拟6日17 :00穿过气旋中心东西向垂直剖面图
(实线为位温, 单位:K, 间隔:4;虚线为南北风 (南风为正), 单位:m·s-1, 间隔:4。三角表示气旋中心)
图 7 对照试验 (a) 和平面地形试验 (b) 模拟6日14:00 700 hPa全风速 (实线, 单位:m·s -1, 间隔:4) 和温度 (虚线, 单位:K, 间隔:4;阴影区表示地形高度)
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