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Field observations of the atmospheric boundary layer were made over urban and suburban terrain in the Yangtze River Delta, China. A multiresolution decomposition was applied over three different types of terrain: flat homogeneous terrain, suburban terrain and urban terrain, with results indicating that, (1) the average scale contribution of u, v, w...
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Citations
... We decomposed the time series into low-and high-pass-filtered components as a function of the period τ , and computed the cospectra and variances using the multiresolution technique (e.g., Howell and Mahrt 1997;Vickers and Mahrt 2003;Nilsso et al. 2014;Zhang et al. 2016). Following Howell and Mahrt (1997), compared with Fourier (co)spectra, which measure the eddy sizes based on the period of a sinusoidal wave, the multiresolution (co)spectra, based on the Reynolds averaging time scale, are shifted into somewhat higher frequencies. ...
Above an evaporating heated surface under fair-weather daytime conditions, the cospectra between the vertical velocity component, temperature, and water-vapour mixing ratio should be positive. We have applied a multi-resolution technique to a 3.64-h long, 10-Hz time series centred at midday for 16 fair-weather days at a mid-latitude site during spring to measure the averaging period τc at which the crossover from the domain of the three positive cospectra to a mixed-sign domain occurs. The τc values broadly range from 9 to 42 min, with 13 of the 16 days having values less than 30 min. When mesoscale circulations induced by surface heterogeneity are likely to be present, the vertical heat (or moisture) flux computed with the conventional averaging period of 30 min τ30 is as large (or small) as 1.09 (or 0.78) times that using τc. However, on 14 (or 13) days, the vertical heat (or moisture) fluxes using the period τc are explained by those calculated with the period τ30 within a difference range of ± 1%. The insignificant difference is due to the insensitivity of the fluxes to the averaging period at scales larger than approximately 7 min. Therefore, despite a broad range of τc values, the 30-min-averaged surface fluxes can be treated as the required turbulent fluxes. Although this finding is not robust, given that data were collected at one location over 16 days, it supports the use of 30-min-averaged surfaces fluxes, particularly for the composite midday fluxes on fair-weather days.
... Observational data show that high-frequency losses usually consist of losses of CO 2 and H 2 O fluxes rather than the sensible heat flux, because the poor high-frequency response of measurement system causes the CO 2 or H 2 O cospectrum to roll-off more rapidly than for temperature (Aubinet et al., 2012). Zhang et al. (2016) reported that in urban environment the scale contribution to heat flux at 10 Hz is very close to 0, implying that the smaller-scale (i.e., higher-frequency) contribution can be neglected. Low-frequency losses mainly result from the finite sampling duration, since the averaging period is not always sufficiently long to include all relevant low frequencies (Aubinet et al., 2012). ...
... Low-frequency losses mainly result from the finite sampling duration, since the averaging period is not always sufficiently long to include all relevant low frequencies (Aubinet et al., 2012). However, analyses in Zhang et al. (2016) show that for the lowfrequency components at the time scale larger than 30 min, their contributions to heat flux can be found in suburban environment but not in urban environment. This is because turbulent eddies are reshaped by the urban buildings and the low-frequency motions are not common in urban environment. ...
Eddy-correlation measurements have been carried out at six different heights above the urban canopy in three cities of China, i.e., Nanjing, Changzhou and Suzhou. Observations at these heights are used to evaluate the dependence of normalized standard deviations of velocity components σi/u*l (i = u, v, w) and temperature σTv/Tv*l on local atmospheric stability ζ (=(z − zd)/Λ), where u*l is the local friction velocity, Tv*l is the local temperature scale, zd is the displacement height, and Λ is the local Obukhov length. It is found that the universal functions ai(1 + bi| ζ| )1/3 and bTvζ−1/3, in which ai, bi and bTv are empirical coefficients, are suitable for describing the behaviors of σi/u*l and σTv/Tv*l respectively. Under neutral conditions (|ζ| < 0.05), the value of σi/u*l (approximately equal to ai) decreases with height. On the other hand, bi increases with height under both unstable (ζ < − 0.05) and stable (ζ > 0.05) conditions, suggesting that the thermal effect of stratification on the standard deviations of velocity components increases with height in the urban roughness sublayer. However, the behavior of σTv/Tv*l is different from that of σi/u*l. bTv remains constant with height under unstable conditions but increases with height under stable conditions. Vertical variations of these coefficients in the universal functions are consistent with the concept of local similarity, suggesting that the turbulence behavior in the urban roughness sublayer is different from that over the flat terrain.
... Alfieri and Blanken [57] found that a single point measurement (EC systems) is not sufficient to accurately describe this sand-sagebrush environment where the components of the surface energy budget can differ substantially across short distances. Meanwhile, EC could not capture the large-scale motions, which were beyond its footprint [58]. The difference between LAS and EC might have been caused by the large-scale turbulence at the experimental site. ...
... Alfieri and Blanken [57] found that a single point measurement (EC systems) is not sufficient to accurately describe this sand-sagebrush environment where the components of the surface energy budget can differ substantially across short distances. Meanwhile, EC could not capture the large-scale motions, which were beyond its footprint [58]. The difference between LAS and EC might have been caused by the largescale turbulence at the experimental site. ...
The sensible heat is an important component in surface energy partitioning over the land surface. This paper compared the sensible heat fluxes measured by a large aperture scintillometer system (LAS) and an eddy covariance system (EC) over a rice paddy with a patch of mulberry seedlings in the east China coastal region during the period from 13 September-11 October 2015. During the observation period, easterlies and northerlies prevailed, and 96%easterlies and northerlies had a speed of 0-6 ms⁻¹. The sensible heat fluxes measured by the two systems reflected that the value of HLAS generally was inclined to be larger than HEC with the average difference of 20.30 W m⁻², and the uncertainty for two instruments was less than 17 W m⁻². Analysis of the average footprint resulted that the mulberry seedling field always had a higher contribution to LAS than that to EC, which could be the reason that HLAS was always larger than HEC. During the days when the contributions of the mulberry seedling field to the two systems were close to each other, the sensible heat flux measurements of the two instruments were similar. The case analysis on typical sunny days showed that there would be larger sensible heat fluxes over the mulberry seedling field than in the rice paddy field especially under larger net radiation conditions.
Based on observation data from urban observation stations in Nanjing and Suzhou at two heights in the roughness sublayer above the canopy and observation data at three heights in the SORPES station at the Xianlin Campus of Nanjing University in a suburban area, the representativeness of land-atmosphere turbulent flux exchange and the energy balance over complex underlying surfaces were analyzed. The results indicated that in the roughness sublayer above the canopy, the near-surface momentum flux, sensible heat flux, and latent heat flux increase with height, and the observation value of the surface albedo increases with height. However, the observation value of the net radiation decreases with height, thus resulting in a change in the urban surface energy budget with height. At the SORPES station in the Xianlin Campus of Nanjing University located in a hilly area, the momentum flux, sensible heat flux, and latent heat flux of the ground observation field significantly differed from those of the two heights on the tower, while the two heights on the tower were extremely close. These results indicate that the flux observation over the complex underlying surface exhibits adequate local representativeness only when it is conducted at a higher altitude above the ground. The turbulent flux observation results at a lower altitude in urban areas are underestimated, while the turbulent flux observation results near the surface produce a large deviation over the underlying hilly complex.
Since the founding of the People’s Republic of China 70 years ago, the subject of atmospheric physics and atmospheric environment has developed rapidly in China, providing important support for the development of atmospheric science and guarantee for the development of national economy. In this paper, the general advancement of atmospheric physics and atmospheric environment in last 70 years was described. The main research progress of atmospheric physics and atmospheric environment in the past 40 years of reform and opening-up was reviewed, the outstanding research achievements since the 21st century were summarized, the major problems and challenges are pointed out, and the key directions and suggestions for future development are put forward.
Knowledge of turbulent exchange in complex environments is relevant to a wide range of hydro-meteorological applications. Observations are required to improve understanding and inform model parameterisations but the very nature of complex environments presents challenges for measurements. Scintillometry offers several advantages as a technique for providing spatially-integrated turbulence data (structure parameters and fluxes), particularly in areas that would be impracticable to monitor using eddy covariance, such as across a valley, above a city or over heterogeneous landscapes. Despite much of scintillometry theory assuming flat, homogeneous surfaces and ideal conditions, over the last 20 years scintillometers have been deployed in increasingly complex locations, including urban and mountainous areas. This review draws together fundamental and applied research in complex environments, to assess what has been learnt, summarise the state-of-the-art and identify key areas for future research. Particular attention is given to evidence, or relative lack thereof, of the impact of complex environments on scintillometer data. Practical and theoretical considerations to account for the effects of complexity are discussed, with the aim of developing measurement capability towards more reliable and accurate observations in future. The usefulness of structure parameter measurements (in addition to fluxes, which must be derived using similarity theory) should not be overlooked, particularly when comparing or combining scintillometry with other measurement techniques and model simulations.
This paper uses an optimal interregional input-output model to focus on how interregional industrial shifts alone might enable China to reduce carbon intensity instead of national shifts. The optimal industry shifts assure integration of all regions by regional products and goods in which carbon emissions are embodied via energy consumption. Generally speaking, high-tech industries concentrate in affluent regions to replace construction. Selected services increase output shares across most of regions. Meanwhile, energy-intensive manufacturing, rather than agriculture, decrease their shares to achieve the national annual growth constrained by nation’s carbon targets. Due to the need to decelerate energy use, carbon intensity goal puts particularly extreme pressure on less-developed regions to shutter heavy industries. Explicit shifts toward cleaner resources and renewable energy appear to be quite important for coal mines in Central China.
