中小尺度天气动力学课件 第二章

Cap clouds
Cap clouds indicate likely wave activity downstream. They often appear along mountain ridges as air is forced up the windward side. If the flow is sufficiently humid, the moisture will condense into a cloud bank (云堤) that follows mountain contours. Quite often, heavy orographic precipitation occurs on the upwind side of the barrier
一般 2-6m/s
最大 > 15m/s
Trapped Lee Waves and clouds
Lee waves whose energy does not propagate vertically because of strong wind shear or low stability above are said to be "trapped." Trapped lee waves are often found downstream of the rotor zone, although a weak rotor may exist under each lee wave. These waves are typically at an altitude within a few thousand feet of the mountain ridge
operational NWP models to resolve rotors so that they can be identified in the absence of rotor clouds.
2、背风波的特征及大气条件
波长 1.8-70 km 振幅 垂直速度
一般 5-20 km ，
一般 0.3-0.5 km >6.0km(水跃型)
波动气流（背风波,lee wave） 山脉背风面的波动气流，风切变大。
转子气流（rotor streaming） 山脉背风波的一种特殊形式 (闭合涡旋) 风速有极大值。
This figure shows the development of the typical features often associated with a mountain wave system. Notice the wind flow, with a strong component perpendicular to the primary ridge line. This is a typical condition for mountain wave development, as is a stable atmosphere. If air is being forced over the terrain, it will move downward along the lee slopes, then oscillate in a series of waves as it moves downstream. Sometimes these waves can propagate long distances in "lee wave trains."
Rotor location can often be identified if sufficient moisture is available to form an associated rotor cloud. Rotor clouds are found near the top of the rotor circulation and under higher lenticular clouds（荚状云）. Immediately above the rotor cloud, smooth, wavy air is likely. The rotor cloud can look innocuous（无害 的）, but does contain strong turbulence and should be avoided by pilots. Eventually, we can expect
图2.1 Trajectories of free balloon ( Von Ficker，1913）
infrared 红外云图
Water vapor水汽图像
Satellite images observed on March 6,2004,in East side of Rocky Mountain
Mountain wave clouds forming east of the Rockies.
MODIS image of mountain wave clouds over Turkey.
1、地形波的基本类型：
层状气流（山脉波,mountain wave） 山脉上空的平滑浅波 ,风小。
驻涡气流（驻涡,standing eddy） 山脉背风面的半永久性涡旋，山顶以上 风速大。
（N. L. Uhlenbrock , et al, 2006）
图2.2
图2.3
图2.4
(a) 19：40 UTC ,Oct.28,2004
(b) 19：50 UTC, March
6, 2004, bright temperature（K） （N. L. Uhlenbrock , et al, 2006）
下垫面的起伏不平或冷 热不均所引起的
中尺度 大气环 流系统
地Biblioteka Baidu性 环流系统
自由大气 环流系统
热力性强迫运动 （如热岛环流、海 陆风、山谷风等）
非对流性环流（如 移动性重力波、锋急流次级环流等）
对流性环流
深对流
雷暴、超级单体、飑线
浅对流 锋面雨带
2.1 地形波
一般把气流过山所引起的气流波动称为地形波。 观测工具：卫星、雷达、飞机和微压计等。 图2.1、图2.2、图2.3、图2.4
第二章 地形性中尺度环流
§2.1 地形波 §2.2 尾流中的环流 §2.3 热岛环流 §2.4 海陆风和山谷风
本章要求
掌握： 地形波的类型 熟悉： 背风波的形成条件 理解： Scorer背风波理论 了解： 尾流环流；城市热岛环流；海陆
风；山谷风 初步了解：复杂地形的影响
中尺度大气环流系统
机械性强迫运动 （如地形波、下 坡风、尾流等）