Parameterization of Turbulent Orographic Form Drag and Implementation in GRAPES

Xue Haile; Shen Xueshun; Su Yong

Vol.22, NO.2, 2011

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Xue Haile, Shen Xueshun, Su Yong. Parameterization of turbulent orographic form drag and implementation in GRAPES. J Appl Meteor Sci, 2011, 22(2): 169-181.

Citation:

Xue Haile, Shen Xueshun, Su Yong. Parameterization of turbulent orographic form drag and implementation in GRAPES. J Appl Meteor Sci, 2011, 22(2): 169-181.

Xue Haile, Shen Xueshun, Su Yong. Parameterization of turbulent orographic form drag and implementation in GRAPES. J Appl Meteor Sci, 2011, 22(2): 169-181.

Citation:

Xue Haile, Shen Xueshun, Su Yong. Parameterization of turbulent orographic form drag and implementation in GRAPES. J Appl Meteor Sci, 2011, 22(2): 169-181.

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Parameterization of Turbulent Orographic Form Drag and Implementation in GRAPES

Xue Haile¹,
Shen Xueshun^{1,2
,
,},
Su Yong²

1.
State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 100081
2.
Numerical Weather Prediction Center, China Meteorological Administration, Beijing 100081

Received Date: 2010-06-07
Rev Recd Date: 2010-10-18
Publish Date: 2011-04-30

Abstract

Abstract

Due to the limited model resolution, scales of topographies below the model resolution are called sub-grid scale orography. Sub-grid scale orography plays important roles on the atmosphere from the thermal and dynamic aspects, and these effects are fed back to the model atmosphere through parameterization.Generally, the dynamic effects of sub-grid scale orography includes: Sub-grid orographic turbulent form drag caused by turbulent flow over hills; sub grid-scale form drag of orographic flow blocking, separating and lee vortex; buoyancy waves drag caused by breakdown of gravity-waves that excited by flow over mountains and transmitting upward in the upper atmosphere. With resolution raised, turbulent form drag becomes more important which is associated with small-scale orography. Given these facts, the characteristics and effects of the sub-grid orographic turbulent form drag and its parameterization are studied.Usually, effects of the turbulent form drag due to sub-grid scale orography in numerical models are simply considered as enhancing surface roughness, known as the effective roughness method. In recent years, according to asymptotic theory and numerical simulations, a new scheme of sub-grid orographic turbulent form drag is developed. As an independent physical process, the new scheme is of three-dimension features in the model, while the effective roughness method is only considered being on the surface level.It is significant to consider turbulent form drag in NWP model for completing physical processes of model and improving the model prediction of the surface layer. A single-column model is used to simulate the characteristics of turbulent form drag, comparing the advantages and disadvantages between the effective roughness method and direct parameterizing method. Two direct parameterization schemes are also compared, one is developed and applied in NWP model recently, and the other is based on ideal terrain. Finally, the form drag scheme that developed and applied in NWP model is implemented into the GRAPES regional model. Case studies are conducted to investigate the possible influences of form drag on the forecast of near surface wind fields and other variables.
- sub-grid orographic turbulent form drag;
- parameterization;
- GRAPES

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References(33)

Figures and Tables

图 1 有效粗糙度法和直接参数化法 (应用WBH01方案) 对低层气流的作用

(a) 有效粗糙度随坡度和地面粗糙度的变化，(b) 地表总应力 (被摩擦速度的平方标准化) 随坡度的变化，(c) 模式第1层 (5.5 m) 纬向风随坡度变化，(d) 模式第1层 (5.5 m) 经向风随坡度变化

Fig. 1 The influence of effective roughness method and directed method (using WBH01 scheme) on the lower layer

(a) the effective roughness changes with local roughness and slope, (b) the total surface stress (normalized by friction velocity square), (c) the zonal velocity changes of the 1st model level (5.5 m) with slope, (d) the meridional velocity changes of the 1st model level (5.5 m) with slope

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Fig. 2 Momentum flux (a) and velocity (b) profile

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Fig. 3 The influence of form drag on zonal velocity (a), meridional velocity (b) and zonal flux (c), meridional flux (d)

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Fig. 4 The diagnosis of kinetic energy tendency for WBH01 scheme (a) and BBW04 scheme (b)

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Fig. 5 The change of the normalized surface form drag with slope

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Fig. 6 The change of area average velocity tendency caused by form drag with time in case I2B6 (the time interval is 3 hours)

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Fig. 7 30°N zonal section of velocity tendency (shaded area) caused by 24-hour prediction form drag, the 1st level wind speed (green line) and orographic standard deviation (red line) in case I2B6

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Fig. 8 The relative bias of wind speed (unit:m·s^-1)

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Fig. 9 RMS error and bias of 10-meter zonal and meridional winds between cases with and without BBW04 scheme

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Table 1 Cases concise table

试验简称	描述	区域	起报时间
O8B15	外围考虑BBW04方案，0.15°分辨率	15°~65°N，70°~145°E	2008-12-08T00：00
O8N15	外围不考虑拖曳力方案，0.15°分辨率	15°~65°N，70°~145°E	2008-12-08T00：00
O2B15	外围考虑BBW04方案，0.15°分辨率	15°~65°N，70°~145°E	2009-08-02T00：00
O2N15	外围不考虑拖曳力方案，0.15°分辨率	15°~65°N，70°~145°E	2009-08-02T00：00
I8B6	嵌套，考虑BBW04方案，0.06°分辨率	20°~38°N，92°~113°E	2008-12-08T00：00
I8N6	嵌套，不考虑拖曳力方案，0.06°分辨率	20°~38°N，92°~113°E	2008-12-08T00：00
I2B6	嵌套，考虑BBW04方案，0.06°分辨率	20°~38°N，92°~113°E	2009-08-02T00：00
I2N6	嵌套，不考虑拖曳力方案，0.06°分辨率	20°~38°N，92°~113°E	2009-08-02T00：00

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