The Influences of Thermodynamic Characteristics on Aerodynamic Roughness Length over Land Surface

ZHANG Qiang; YAO Tong; YUE Ping; ZHANGF Liyang; ZENG Jian

doi:10.1007/s13351-013-0209-5

It has previously been shown that aerodynamic roughness length changes significantly along with nearsurface atmospheric thermodynamic state; however, at present, this phenomenon remains poorly understood, and very little research concerning this topic has been conducted. In this paper, by using the data of different underlying surfaces provided by the Experimental Co-observation and Integral Research in Semi-arid and Arid Regions over North China, aerodynamic roughness length (z0) values in stable, neutral, and unstable atmospheric stratifications are compared with one another, and the relationship between z0 and atmospheric thermodynamic stability (ζ) is analyzed. It is found that z0 shows great differences among the stable, neutral, and unstable atmospheric thermodynamic states, with the difference in z0 values between the fully thermodynamic stable condition and the neutral condition reaching 60% of the mean z0. Furthermore, for the wind speed range in which the wind data are less sensitive to z0, the surface z0 changes more significantly with ζ, and is highly correlated with both the Monin-Obukhov stability (ζ0) and the overall Richardson number (Rib), with both of their correlation coefficients greater than 0.71 and 0.47 in the stable and unstable atmospheric stratification, respectively. The empirical relation fitted with the experimental observations is quite consistent with the Zilitinkevich theoretical relation in the stable atmosphere, but the two are quite distinct and even show opposite variation tendencies in the unstable atmosphere. In application, however, verification of the empirical fitted relations by using the experimental data finds that the fitted relation is slightly more applicable than the Zilitinkevich theoretical relation in stable atmospheric stratification, but it is much more suitable than the Zilitinkevich relation in unstable atmospheric stratification.

The Influences of Thermodynamic Characteristics on Aerodynamic Roughness Length over Land Surface

1. Institute of Arid Meteorology of CMA;
Key Laboratory of Arid Climatic Change and Disaster Reduction of Gansu Province;
Key Open Laboratory of Arid Climatic Change and Disaster Reduction of CMA,Lanzhou 730020;
Meteorological Bureau of Gansu,Lanzhou 730020;
College of Atmospheric Sciences,Lanzhou University,Lanzhou 730000Institute of Arid Meteorology of CMA;
Key Laboratory of Arid Climatic Change and Disaster Reduction of Gansu Province;
Key Open Laboratory of Arid Climatic Change and Disaster Reduction of CMA,Lanzhou 730020;
Institute of Arid Meteorology of CMA;
Key Laboratory of Arid Climatic Change and Disaster Reduction of Gansu Province;
Key Open Laboratory of Arid Climatic Change and Disaster Reduction of CMA,Lanzhou 730020;
College of Atmospheric Sciences,Lanzhou University,Lanzhou 730000;
Institute of Arid Meteorology of CMA;
Key Laboratory of Arid Climatic Change and Disaster Reduction of Gansu Province;
Key Open Laboratory of Arid Climatic Change and Disaster Reduction of CMA,Lanzhou 730020

Received: 29 May 2012

Funds: Supported by the National Natural Science Foundation of China (40830957, 41075008, and 41075009), National Basic Research and Development (973) Program of China (2013CB430206), and China Postdoctoral Science Foundation (20110490854).

Abstract: It has previously been shown that aerodynamic roughness length changes significantly along with nearsurface atmospheric thermodynamic state; however, at present, this phenomenon remains poorly understood, and very little research concerning this topic has been conducted. In this paper, by using the data of different underlying surfaces provided by the Experimental Co-observation and Integral Research in Semi-arid and Arid Regions over North China, aerodynamic roughness length (z0) values in stable, neutral, and unstable atmospheric stratifications are compared with one another, and the relationship between z0 and atmospheric thermodynamic stability (ζ) is analyzed. It is found that z0 shows great differences among the stable, neutral, and unstable atmospheric thermodynamic states, with the difference in z0 values between the fully thermodynamic stable condition and the neutral condition reaching 60% of the mean z0. Furthermore, for the wind speed range in which the wind data are less sensitive to z0, the surface z0 changes more significantly with ζ, and is highly correlated with both the Monin-Obukhov stability (ζ0) and the overall Richardson number (Rib), with both of their correlation coefficients greater than 0.71 and 0.47 in the stable and unstable atmospheric stratification, respectively. The empirical relation fitted with the experimental observations is quite consistent with the Zilitinkevich theoretical relation in the stable atmosphere, but the two are quite distinct and even show opposite variation tendencies in the unstable atmosphere. In application, however, verification of the empirical fitted relations by using the experimental data finds that the fitted relation is slightly more applicable than the Zilitinkevich theoretical relation in stable atmospheric stratification, but it is much more suitable than the Zilitinkevich relation in unstable atmospheric stratification.

Key words:

near-surface atmosphere /
thermodynamic characteristics /
aerodynamic roughness length /
Zilitinkevich theoretical relationship /
parametric relations

The Influences of Thermodynamic Characteristics on Aerodynamic Roughness Length over Land Surface

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