Multi-site observation of large-scale eddies in the surface layer of the Loess Plateau

This article aims to build a theory of atmospheric boundary layer turbulence under complex conditions. To achieve this goal, we constructed a multi-site observation and analysis method of atmospheric turbulence based on related principles.This method first requires verification for the ergodicity of the full-scale observation of surface-layer turbulence, which proves that eddies within a scale of 60 min during a four-site observation can easily meet ergodicity. Meanwhile, by applying the second-order structure function for the horizontal wind speed turbulence of a single site and upstream and downstream points, we verified the ergodicity of the turbulence observation. Comparing the turbulence spectrum to the second-order structure function for the horizontal wind speed from the four-site observation, a relatively high accordance was observed, proving the reasonability of the multi-site observation. Moreover, compared to the single-site observation, the four-site observation can improve the estimation accuracy of the surface-layer turbulence spectrum and vertical turbulent flux. As a result, we can describe the threedimensional structure of turbulence more accurately and comprehensively by combining analytical data from single-site and four-site observations. In summary, the multi-site turbulence observation method shows that the horizontal and vertical wind turbulence of the Baimiao plateau has a typical structure of a turbulence spectrum with clear spectral gaps. The result is in accordance with the scale of the turbulence spectral gaps obtained from the 6 h data. The horizontal wind speed is under the influence of the terrain, so its spectrum of large-scale eddies has higher fluctuations, but its spectral gaps can still be clearly distinguished. Although the spectral gaps of the temperature spectrum are not distinguishable, they still have the same scale as the spectral gap of the vertical and horizontal turbulence spectrum. Moreover, the temperature spectrum possesses typical structure characteristics of the boundary-layer turbulence spectrum.

Effect of traffic restriction on atmospheric particle concentrations and their size distributions in urban Lanzhou, Northwestern China

During the 2012 Lanzhou International Marathon, the local government made a significant effort to improve traffic conditions and air quality by implementing traffic restriction measures. To evaluate the direct effect of these measures on urban air quality, especially particle concentrations and their size distributions, atmospheric particle size distributions （0.5-20μm） obtained using an aerodynamic particle sizer （model 3321, TSI, USA） in June 2012 were analyzed. It was found that the particle number, surface area and volume concentrations for size range 0.5-10 μm were （15.0±2.1） cm-3, （11.8±2.6） μm2/cm3 and （1.9±0.6） μm2/cm3, respectively, on the traffic-restricted day （Sunday）, which is 63.2%, 53.0% and 47.2% lower than those on a normal Sunday. For number and surface area concentrations, the most affected size range was 0.5-0.7 and 0.5-0.8 μm, respectively, while for volume concentration, the most affected size ranges were 0.5-0.8, 1.7-2.0 and 5.0-5.4 μm. Number and volume concentrations of particles in size range 0.5-1.0μm correlated well with the number of non-CNG （Compressed Natural Gas） powered vehicles, while their correlation with the number of CNG-powered vehicles was very low, suggesting that reasonable urban traffic controls along with vehicle technology improvements could play an important role in improving urban air quality.

Ergodicity of turbulence measurements upon complex terrain in Loess Plateau

To display the distribution characteristics of turbulence eddy under condition of complex terrain in Loess Plateau,and to enhance the precision of turbulence measurements,the research of turbulence ergodicity is considered to be the prior section of the experiment.With the statistics of single-site turbulence measurements obtained in Baimiao Tableland,Ping Liang,Gan Su,analysis result shows that not only the turbulence with scale less than 10 min,which can easily satisfy the ergodicity,the tableland terrain can also be a major cause of the coherent structure of periodic,large-scale turbulence;compared to which for the turbulence above the flat underlying surface,the distribution of 10–40 min,large-scale turbulence in the tableland region tends to be more steady and,thus,can also satisfy the ergodicity easily.Under the condition of extremely unstable stratification,the wind is comparatively low in speed and features distinctly large-scale,periodical fluctuation,and with the trend of smooth increase in temperature,large-scale wind turbulence and temperature turbulence both tend to satisfy ergodicity.In comparison,under the condition of extremely stable stratification,the aperiodicity of large-scale wind turbulence and temperature turbulence caused by intermittency is comparatively strong,and the turbulence cannot satisfy ergodicity easily.