Results from Measurements of Large Aperture Scintillometer over Different Surfaces

Lu Li; Liu Shaomin; Xu Ziwei; Wang Jiemin; Li Xiaowen

Vol.20, NO.2, 2009

Article Contents

Article Navigation > Journal of Applied Meteorological Science > 2009 > 20(2): 171-178

Lu Li, Liu Shaomin, Xu Ziwei, et al. Results from measurements of large aperture scintillometer over different surfaces. J Appl Meteor Sci, 2009, 20(2): 171-178.

Citation:

Lu Li, Liu Shaomin, Xu Ziwei, et al. Results from measurements of large aperture scintillometer over different surfaces. J Appl Meteor Sci, 2009, 20(2): 171-178.

Lu Li, Liu Shaomin, Xu Ziwei, et al. Results from measurements of large aperture scintillometer over different surfaces. J Appl Meteor Sci, 2009, 20(2): 171-178.

Citation:

Lu Li, Liu Shaomin, Xu Ziwei, et al. Results from measurements of large aperture scintillometer over different surfaces. J Appl Meteor Sci, 2009, 20(2): 171-178.

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Results from Measurements of Large Aperture Scintillometer over Different Surfaces

1.
State Key Laboratory of Remote Sensing Science, School of Geography, Beijing Normal University, Beijing 100875
2.
Meteorological Information Center of Beijng, Beijng Meteorological Bureau, Beijing 100089
3.
Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000

Received Date: 2008-06-03
Rev Recd Date: 2009-02-05
Publish Date: 2009-04-30

Abstract

Abstract

For surface flux measurements, large aperture scintillometer (LAS) has become more and more popular in recent years. Compared with traditional observation techniques, it can measure surface fluxes on a larger scale (500 m-10 km). At present, LAS observation is not common in China. Beijing Normal University, associated with other institutes, has carried out several short term measurements of LAS at Xiao tangshan (Beijing, 2002, 2004). A long-term LAS site has also been constructed at Miyun (Beijing) in June, 2006. Sensible heat flux (H) calculation with the LAS data of above measurements shows that the beam height of LAS and wind speed are sensitive factors for sensible heat flux measurement (H_LAs), zeroplane displacement height is crucial unless the beam height is much lager than it, and Bowen ratio needs to be determined accurately over wet surface, while air temperature, air pressure and aerodynamic roughness length are not sensitive for H_LAs. There are two key points of H_LAS calculation under stable condition. First, there is much less agreement on the form which universal stability function f_T should take. In this study, the f_T function proposed by Andreas (as in the LAS manual) is used. Further more, since the iteration process of H_LAS can not be convergence when low wind speed and very stable conditions appearing at night, ψ_m≥-5 is specified. Second, the scintillometer is unable to determine the sign of the heat flux. Richardson Number R_i can be used to determine atmospheric stability and fix the sign of H_LAS. Besides, the sunrise-sunset time and net radiation could be used for this purpose if there is no wind and air temperature profiles. Therefore, a calculation scheme of 24-hour sensible heat flux observed by LAS is obtained after settling the above two key points. According to the observations mentioned above, LAS can measure surface fluxes both over homogeneous and heterogeneous surfaces. The daily and monthly variation of H_LAs is analyzed. And the observation differences between eddy covariance system and LAS, need to be studied further combined with footprint model and energy unbalance of eddy covariance system observation.
- large aperture scintillometer;
- sensible heat flux;
- different surfaces

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References(26)

Figures and Tables

图 1 利用H_EC(H_LAS1)、梯度理查孙数R_i(H_LAS2)、日出日落时间 (H_LAS3) 和净辐射 (H_LAS4) 确定H_LAS符号得到的H_LAS与H_EC以及净辐射R_n的比较

Fig. 1 Daily variation of H_LAS, H_EC and R_n with the sign of H_LAS determined by the measured H_EC(H_LAS1), Richardson number (H_LAS2), sunrise-sunset time (H_LAS3) and net radiation (H_LAS4)

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图 2 均匀、非均匀地表上H_LAS, H_EC与净辐射R_n在白天的变化

Fig. 2 Daily variation of H_LAS, H_EC and R_n over homogeneous, heterogeneous surfaces

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图 3 2007年密云站H_LAS与H_EC的月变化

Fig. 3 Monthly variation of H_LAS and H_EC in 2007 of Miyun

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表 1 波文比不同取值条件下得到的显热通量H_LAS与参考值的比较

Table 1 Statistics of H_LAS flux estimated with different β against the reference value

表 2 风速u和空气温度T不同取值条件下得到的显热通量H_LAS与参考值的比较

Table 2 Statistics of H_LAS estimated under different conditions of u and T against the reference value

表 3 d, z_0m和z_LAS不同取值条件下得到的显热通量H_LAS与参考值的比较

Table 3 Statistics of H_LAS estimated under different conditions of d, z_0m and z_LAS against the reference value

表 4 稳定条件下不同普适函数与f_T_Andreas函数得到的H_LAS值之间的比较

Table 4 Statistics of H_LAS estimated with different f_T_functions against the one with f_T_Andreas under stable condition

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