Sensitivity of Orographic Precipitation to Changing Ambient Conditions and Terrain Geometries: An Idealized Modeling Perspective BRIAN A. COLLE 2004 ,JOURNAL.

Presentation on theme: "Sensitivity of Orographic Precipitation to Changing Ambient Conditions and Terrain Geometries: An Idealized Modeling Perspective BRIAN A. COLLE 2004 ,JOURNAL."— Presentation transcript:

1 Sensitivity of Orographic Precipitation to Changing Ambient Conditions and Terrain Geometries: An Idealized Modeling Perspective BRIAN A. COLLE 2004 ,JOURNAL OF THE ATMOSPHERIC SCIENCES VOLUME 61,588~606

2 Introduction Background Moist precipitation and orographic flow
motivation

3 Outline Model setup Impact of mountain with height
Impact of the magnitude of cross-barrier flow Impact of freezing level Impact of vertical wind shear Precipitation efficiency Summary and discussion

4 Model setup Mesoscale model (MM5) version 3
2-D idealized configuration 500 grid points with 4 km horizontal grid spacing 38 vertical half-sigma levels Constant lateral boundary conditions

5 假設山脈為鐘形 hm=山高度(500~3500)m a=山的半幅寬 x=沿著x軸方向離山頂的距離 h(x)=山的形狀

6 The moist nondimensional mountain height Mm is defined by :
Nm=在飽和情況下的穩定度 Mm=在飽和下的無因次參數

7 實線為750mb freezing level、實虛線為500mb freezing level
灰虛線為 1000mb freezing level，灰實線為750mb Nm=0.005

8

9 Impact of mountain height and width
Effect of mountain height for a wide (a=50km) barrier and Nm=0.01s-1 Effect of decreasing barrier width and stability

10 Effect of mountain height for a wide (a=50km)
barrier and Nm=0.01s-1

11 Dp=降大雨的範圍(峰值到 一半峰值的距離)

12 為WM20在山高分別為1000、2000、3000公尺圖形

13 Effect of decreasing barrier width and stability

14 X軸為山的斜率 Y軸為6-12小時的最大降雨

15 (a)：NW20 run 在斜率為 0.04，山高1000m，垂直速度=0.5(m/s)
(b)：WN20run 在斜率為0.04，山高2000m ，垂直速度=0.5(m/s)

16 Impact of the magnitude of cross-barrier
a : Flow effects on precipitation for a wide mountain b : Flow effects on precipitation for a narrow mountain

17 Flow effects on precipitation for a wide mountain
粗灰箭頭：最大降雨量的連線

18 說明上頁圖形中，風速大小對降水極值分布地點的不同

19 38個網格中地表平均降雨 水平範圍為山後52-山前100 (km)

20 在不同靜力穩定度下的比較

21 b : Flow effects on precipitation for a narrow mountain

22 Impact of freezing level

23

24 Impact of vertical wind shear
300km處為山脊 Y 軸為6-12小時的降水 FSH=forward shear (15 to 25) RSH=reverse shear (15 to 5)

25 垂直風切的改變 a)：保持不變 b)：隨高度遞減 c)：隨高度遞增

26 Precipitation efficient
範圍大小：山脊到上游500km處 時間：在相同範圍中，6-12 hr 的地面降水和水汽(water vapor)

27 Summary 1：在飽和的情況下，氣流滯留情形時的無因次參數Mm比在乾空氣下的滯留大2-3倍
3：對於較寬的敏感度試驗其地形降雨分布受到線性理論的越山重力波的垂直波長影響 4：當亮帶高度升高時表示暖雲的過程比較重要，反之則為冷雲過程主導 5：垂直風切隨高度遞減時，越山波發展較強，所以降水離山頂較遠，反之降水則較靠近山頂 6：降水效率跟亮帶的關係密切，在風速增加時亮帶在500mb雨量增加，在1000mb雨量減少

28 Discussion 本篇文章雲微物理參數法用了Resiner scheme， 因為每種雲微物理參數法的假設不同，降水特徵也會改變