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51.
UV attenuation in the cloudy atmosphere 总被引:1,自引:0,他引:1
Jianhui Bai 《Journal of Atmospheric Chemistry》2009,62(3):211-228
Ultraviolet (UV) energy absorption plays a very important role in the Earth–atmosphere system. Based on observational data
for Beijing, we suggest that some atmospheric constituents utilize or transfer UV energy in chemical and photochemical (C&P) reactions, in addition to those which absorb UV energy directly. These constituents are primarily volatile organic compounds
(VOCs) emitted from both vegetative and anthropogenic sources. The total UV energy loss in the cloudy atmosphere for Beijing
in 1990 was 78.9 Wm−2. This attenuation was caused by ozone (48.3 Wm−2), other compounds in the atmosphere (26.6 Wm−2) and a scattering factor (4.0 Wm−2). Our results for a cloudy atmosphere in the Beijing area show that the absorption due to these other compounds occurs largely
through the mediation of water vapor. This fraction of energy loss has not been fully accounted for in previous models. Observations
and previous models results suggest that 1) a cloudy atmosphere absorbs 25∼30 Wm−2 more solar shortwave radiation than models predict; and 2) aerosols can significantly decrease the downward mean UV-visible
radiation and the absorbed solar radiation at the surface by up to 28 and 23 Wm−2, respectively. Thus, quantitative study of UV and visible absorption by atmospheric constituents involved in homogeneous
and heterogeneous C&P reactions is important for atmospheric models. 相似文献
52.
José Luís Argaín Miguel A. C. Teixeira Pedro M. A. Miranda 《Boundary-Layer Meteorology》2017,165(1):145-160
A method is proposed for estimating the surface-layer depth \((z_s)\) and the friction velocity \((u_*)\) as a function of stability (here quantified by the Obukhov length, L) over the complete range of unstable flow regimes. This method extends that developed previously for stable conditions by Argaín et al. (Boundary-Layer Meteorol 130:15–28, 2009), but uses a qualitatively different approach. The method is specifically used to calculate the fractional speed-up \((\varDelta S)\) in flow over a ridge, although it is suitable for more general boundary-layer applications. The behaviour of \(z_s \left( L\right) \) and \(u_*\left( L\right) \) as a function of L is indirectly assessed via calculation of \(\varDelta S\left( L\right) \) using the linear model of Hunt et al. (Q J R Meteorol Soc 29:16–26, 1988) and its comparison with the field measurements reported in Coppin et al. (Boundary-Layer Meteorol 69:173–199, 1994) and with numerical simulations carried out using a non-linear numerical model, FLEX. The behaviour of \(\varDelta S\) estimated from the linear model is clearly improved when \(u_*\) is calculated using the method proposed here, confirming the importance of accounting for the dependences of \(z_s\left( L \right) \) and \(u_*\left( L \right) \) on L to better represent processes in the unstable boundary layer. 相似文献
53.
Juan Huang Yanli Feng Jian Li Bin Xiong Jialiang Feng Sheng Wen Guoying Sheng Jiamo Fu Minghong Wu 《Journal of Atmospheric Chemistry》2008,61(1):1-20
The levels of carbonyl compounds in Shanghai ambient air were measured in five periods from January 2007 to October 2007 (covering
winter, high-air-pollution days, spring, summer and autumn). A total of 114 samples were collected and eighteen carbonyls
were identified. Formaldehyde, acetaldehyde and acetone were the most abundant carbonyls and their mean concentrations of
19.40 ± 12.00, 15.92 ± 12.07 and 11.86 ± 7.04 μg m−3 respectively, in the daytime for five sampling periods. Formaldehyde and acetaldehyde showed similar diurnal profiles with
peak mixing ratios in the morning and early afternoon during the daytime. Their mean concentrations were highest in summer
and lowest in winter. Acetone showed reversed seasonal variation. The high molecular weight (HMW, ≥C5) carbonyls also showed
obvious diurnal variations with higher concentrations in the daytime in summer and autumn, while they were all not detected
in winter. Formaldehyde and acetaldehyde played an important role in removing OH radicals in the atmosphere, but the contribution
of acetone was below 1%. The carbonyls levels in high-air-pollution days were reported. More carbonyl species with higher
concentrations were found in high-air-pollution days than in spring. These carbonyls were transported with other pollutants
from north and northwest in March 27 to April 2, 2007 and then mixed with local sources. Comparing with Beijing and Guangzhou,
the concentrations of formaldehyde and acetaldehyde in Shanghai were the highest, which indicated that the air pollution in
Shanghai was even worse than expected. 相似文献
54.
General purpose Computational Fluid Dynamics (CFD) solvers are frequently used in small-scale urban pollution dispersion simulations
without a large extent of ver- tical flow. Vertical flow, however, plays an important role in the formation of local breezes,
such as urban heat island induced breezes that have great significance in the ventilation of large cities. The effects of
atmospheric stratification, anelasticity and Coriolis force must be taken into account in such simulations. We introduce a
general method for adapting pressure based CFD solvers to atmospheric flow simulations in order to take advantage of their
high flexibility in geometrical modelling and meshing. Compressibility and thermal stratification effects are taken into account
by utilizing a novel system of transformations of the field variables and by adding consequential source terms to the model
equations of incompressible flow. Phenomena involving mesoscale to microscale coupled effects can be analyzed without model
nesting, applying only local grid refinement of an arbitrary level. Elements of the method are validated against an analytical
solution, results of a reference calculation, and a laboratory scale urban heat island circulation experiment. The new approach
can be applied with benefits to several areas of application. Inclusion of the moisture transport phenomena and the surface
energy balance are important further steps towards the practical application of the method. 相似文献
55.
Mark Anglin Harris 《Environmental Geology》2009,56(8):1517-1522
Several years (7) after incidental lithification by added gypsum, the effect of crushing and phyto-organics on some physical
properties of red mud wastes (RMW) was examined under laboratory conditions. It was hypothesized that mechanically breaking
up the hardened masses would increase their permeability. However, on the contrary, crushing these rock-hard masses into <2-mm
particles did not increase permeability. A phyto-organic treatment on the other hand greatly improved permeability of the
crushed entities such that infiltration rates increased from 0 to 10 cm/h. After 24 weeks of incubation, the structure of
the newly formed phyto-organically treated gypsum-hardened RMW aggregates was also substantially improved over that of the
controls, as a >3-fold increase in resistance to disintegration during wet sieving was exhibited by the phyto-organically
treated samples. The increase in water infiltration by combining crushing with phyto-organic applications was ascribed to
a decrease in particle dispersion, creating more stable clay clusters, which in turn stabilized channels and pores. Conversely,
it was concluded that the singular crushing of gypsum-hardened bauxite waste in the waste dumps is potentially wasteful and
ineffective. 相似文献
56.
Characteristics of dry-wet abrupt alternation events in the middle and lower reaches of the Yangtze River Basin and the relationship with ENSO 总被引:1,自引:0,他引:1
During recent decades, more frequent flood-drought alternations have been seen in China as a result of global climate change and intensive human activities, which have significant implications on water and food security. To better identify the characteristics of flood-drought alternations, we proposed a modified dry-wet abrupt alternation index (DWAAI) and applied the new method in the middle and lower reaches of the Yangtze River Basin (YRB-ML) to analyze the long-term spatio-temporal characteristics of dry-wet abrupt alternation (DWAA) events based on the daily precipitation observations at 75 rainfall stations in summer from 1960 to 2015. We found that the DWAA events have been spreading in the study area with higher frequency and intensity since 1960. In particular, the DWAA events mainly occurred in May and June in the northwest of the YRB-ML, including Hanjiang River Basin, the middle reaches of the YRB, north of Dongting Lake and northwest of Poyang Lake. In addition, we also analyzed the impact of El Niño Southern Oscillation (ENSO) on DWAA events in the YRB-ML. The results showed that around 41.04% of DWAA events occurred during the declining stages of La Niña or within the subsequent 8 months after La Niña, which implies that La Niña events could be predictive signals of DWAA events. Besides, significant negative correlations have been found between the modified DWAAI values of all the rainfall stations and the sea surface temperature anomalies in the Nino3.4 region within the 6 months prior to the DWAA events, particularly for the Poyang Lake watershed and the middle reaches of the YRB. This study has significant implications on the flood and drought control and water resources management in the YRB-ML under the challenge of future climate change. 相似文献
57.
中国东部植被NDVI对气温和降水的时空响应(英文) 总被引:4,自引:4,他引:4
Temporal and spatial response characteristics of vegetation NDVI to the variation of temperature and precipitation in the whole year,spring,summer and autumn was analyzed from April 1998 to March 2008 based on the SPOT VGT-NDVI data and daily temperature and precipitation data from 205 meteorological stations in eastern China.The results indicate that as a whole,the response of vegetation NDVI to the variation of temperature is more pronounced than that of precipitation in eastern China.Vegetation NDVI maxi... 相似文献
58.
改进的能量守恒方法及其在CHAMP重力场恢复中的应用 总被引:1,自引:0,他引:1
XU Tianhe HE Kaifei Xi’an Research Institute of Surveying Mapping Middle Yanta Road Xi’an China. 《地球空间信息科学学报》2008,11(3):168-173
An efficient method for gravity field determination from CHAMP orbits and accelerometer data is referred to as the energy balance approach. A new CHAMP gravity field recovery strategy based on the improved energy balance approach IS developed in this paper. The method simultaneously solves the spherical harmonic coefficients, daily Integration constant, scale and bias parameters. Two 60 degree and order gravitational potential models, XISM-CHAMPO1S from the classical energy balance approach, and XISM-CHAMPO2S from the improved energy balance, are determined using about one year's worth of CHAMP kinematic orbits from TUM and accelerometer data from GFZ. Comparisons among XISM-CHAMPO1S, XISM-CHAMPO2S, EIGEN-CGO3C, EIGEN-CHAMPO3S, EIGEN2, ENIGNIS and EGM96 are made. The results show that the XISM-CHAMPO2S model is more accurate than EGM96, EIGENIS, EIGEN2 and XISM-CHAMPO1S at the same degree and order, and has almost the same accuracy as EIGEN-CHAMPO3S. 相似文献
59.
基于交互多模型的水下目标跟踪方法 总被引:1,自引:0,他引:1
According to the requirements of real-time performance and reliability in underwater maneuvering target tracking as well as clarifying motion features of the underwater target, an interacting multiple model algorithm based on fuzzy logic inference (FIMM) is proposed. Maneuvering patterns of the target are represented by model sets, including the constant velocity model (CA), the Singer mode~, and the nearly constant speed horizontal-turn model (HT) in FIMM technology. The simulation results show that compared to conventional IMM, the reliability and real-time performance of underwater target tracking can be improved by FIMM algorithm. 相似文献
60.
Building damage in Dujiangyan during Wenchuan Earthquake 总被引:2,自引:1,他引:1
A field damage survey of 1,005 buildings damaged by the Wenchuan Earthquake in Dujiangyan City was carried out and the resulting data was analyzed using the statistical method. It is shown that buildings that were seismically designed achieved the desired seismic fortification target; they sustained less damage than the non-seismically designed buildings. Among the seismically designed buildings investigated, RC frame buildings performed the best in terms of seismic resistance. Masonry buildings with a ground story of RC frame structure were the second best, and masonry buildings performed the worst. Considering building height, multistory buildings sustained more severe damage than high-rise buildings and 2- and 3-story buildings. Compared to residential buildings, public buildings, such as schools and hospitals, suffered more severe damage. 相似文献