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1.
Eddy-correlation measurements of the vertical fluxes of ozone, carbon dioxide, fine particles with diameter near 0.1 m, and particulate sulfur, as well as of momentum, heat and water vapor, have been taken above a tall leafless deciduous forest in wintertime. During the experimental period of one week, ozone deposition velocities varied from about 0.1 cm s–1 at night to more than 0.4 cm s-1 during the daytime, with the largest variations associated primarily with changes in solar irradiation. Most of the ozone removal took place in the upper canopy. Carbon dioxide fluxes were directed upward due to respiration and exhibited a strong dependence on air temperature and solar heating. The fluxes were approximately zero at air temperatures less than 5 °C and approached 0.8 mg m–2 s–1 when temperatures exceeded 15 °C during the daytime. Fine-particle deposition rates were large at times, with deposition velocities near 0.8 cm s–1 when turbulence levels were high, but fluxes directed upward were found above the canopy when the surface beneath was covered with snow. Diffusional processes seemed to dominate fine-particle transfer across quasilaminar layers and subsequent deposition to the upper canopy. Deposition velocities for particulate sulfur were highly variable and averaged to a value small in magnitude as compared to similar measurements taken previously over a pine forest in summer. 相似文献
2.
Abstract Dry deposition velocity measurements of SO2 and NO2 over a deciduous forest, a carrot field and a snow surface are compared with estimates obtained from the dry deposition module in the regional Eulerian Acid Deposition and Oxidant Model (ADOM). The comparison with measurements taken in the fall and winter shows large model overestimates, sometimes as large as a factor of 5. The NO2 estimates are particularly poor and support existing evidence that models that employ the constant flux assumption for NO2 are inadequate. The canopy and the snow surface resistances are the largest contributors to the total resistances for SO2 and NO2, except for situations in which some of the snow turns into liquid water, when the aerodynamic resistance becomes important. Increasing the magnitudes, taken from measurements, of the ADOM original values for the stomatal, cuticle, ground and snow resistances and decreasing the NO2 mesophyll resistance and the Leaf Area Index (LAI) yield improved model results, particularly for SO2, reducing the error by almost a factor of 5 at times. The new estimates compare favourably with those from a model that includes Wesely's canopy resistance parametrization. Over snow the NO2 estimates are improved by as much as a factor of 6. Observed deposition velocities for SO2 vary from 0 to 0.65 cm s?2 over a deciduous forest, 0 to 0.60 cm s?2 over a carrot field and are generally less than 0.05 cm s?2 over snow. 相似文献
3.
James M. Godowitch 《Boundary-Layer Meteorology》1990,50(1-4):375-404
The spatial variability and temporal behavior of the vertical flux of ozone have been investigated from turbulence measurements collected on aircraft flight legs in the daytime period during two consecutive summer experimental field programs. The data were obtained during horizontal flight legs conducted over agricultural crops and forested land in three different regions of the eastern United States.Results from individual experimental cases and statistics derived from all cases in each region are presented. Ozone flux generally exhibited a significant height dependency. The strongest negative (downward) fluxes in the lowest-level flight legs were primarily attributed to the uptake of ozone by the surface and vegetative cover. Fluxes were near-zero in the middle of the convective boundary layer (CBL) in the afternoon period. As ozone flux was proportional to concentration, slightly stronger fluxes were found in low-level urban plume segments where ozone concentrations were 10–20 ppb higher than in the surrounding area. The derived deposition velocity showed no such bias as a function of position across the urban plume. Ozone flux differences were not apparent between the more heavily forested sections and the primarily agricultural cropland areas in these regions. During the afternoon period when no clear temporal trend was evident, means from values obtained below 0.15Z
i
(Z
i
being the CBL height) were -0.421 and -0.431 ppb m-2 s-1 for ozone flux and 0.81 and 0.82 cm s-1 for the derived mean deposition velocity in the southeastern Pennsylvania and central Ohio areas, respectively. These experimental results for ozone provide support to a dry deposition parameterization module which computes grid-area averaged deposition velocities for use in regional-scale models.On assignment from the National Oceanic and Atmospheric Administration, U.S. Department of Commerce. 相似文献
4.
J. Padro W. J. Massman R. H. Shaw A. Delany S. P. Oncley 《Boundary-Layer Meteorology》1994,71(4):327-339
Measurements of dry, deposition velocities (V
d
) of O3 (using the eddy correlation technique) made over a cotton field and senescent grass near Fresno California during July and August 1991 were used to test some dry deposition velocity models. Over the cotton field, the observed maximum daytimeV
d
was about 0.8 cm s–1 and the average nighttime value was about 0.2 cm s–1. Over the grass, daytime values averaged about 0.2 cm s–1 and nighttime values about 0.05 cm s–1. Application of a site-specific model known as ADOM (Acid Deposition and Oxidant Model) over the cotton field generally overestimated the observations except for a few hours in the afternoon when the observations were underestimated The overestimation was attributed to inadequacies in the surface resistance formulation and the underestimation to uncertainties in the aerodynamic formulation. Unlike previous studies which focused on the role of surface resistance, we perform additional tests using a large variety of aerodynamic resistance formulae, in addition to those in ADOM, to determine their influence on the modelledV
d
of O3 over, cotton. Over grass, ADOM considerably overestimated the observations but showed improvement when other surface resistance formulations were applied. 相似文献
5.
The horizontal and vertical wind velocity fluctuations were measured using two sonic anemometers at a height of 135 cm above
a snow surface under a transverse snow wave-forming condition. A snow-wave was formed when the wind at a height of 1 m blew
at a speed of more than 7 m s−1 after an approximate accumulation of from 10 to 20 cm of new snow on a snowfield. For example, when a snow-wave had a wavelength
of 10 m and a wave height of 15 to 20 cm, the measured horizontal and vertical velocity components showed that they had a
frequency peak of 0.7 Hz in coherence and co-spectrum corresponding to this wavelength. The results suggest that wind turbulence
and snow-wave formation interact with each other. 相似文献
6.
The horizontal and vertical wind velocity fluctuations were measured using two sonic anemometers at a height of 135 cm above a snow surface under a transverse snow wave-forming condition. A snow-wave was formed when the wind at a height of 1 m blew at a speed of more than 7 m s–1 after an approximate accumulation of from 10 to 20 cm of new snow on a snowfield. For example, when a snow-wave had a wavelength of 10 m and a wave height of 15 to 20 cm, the measured horizontal and vertical velocity components showed that they had a frequency peak of 0.7 Hz in coherence and co-spectrum corresponding to this wavelength. The results suggest that wind turbulence and snow-wave formation interact with each other. 相似文献
7.
Measurements of ozone concentrations, and meteorological and surface parameters were carried out over a flat green grassland in northwest Spain, in July 1995. Turbulent parameters and sensible and latent heat fluxes were calculated using the gradient technique. Fluxes and deposition velocity and resistances were evaluated assuming that the diffusivity for heat fluxes was equal to pollutant diffusivity. The daily average value of dry deposition velocity was 6 mm s-1 but it was influenced by wind velocity and atmospheric stability. Resistances have been calculated according to a simple resistance model and a comparison between theoretical and measured values has been made. 相似文献
8.
北京延庆山区降雪云物理特征的垂直观测和数值模拟研究 总被引：1，自引：0，他引：1
基于风廓线雷达、云雷达、粒子谱仪、微波辐射计和自动站等垂直观测设备,结合中尺度数值模式WRF对2017年3月23~24日北京延庆海坨山地区的一次降雪过程进行了观测和数值模拟研究。研究结果表明:垂直探测仪器结合中尺度数值模式可以获得降雪的宏观结构和微物理信息,有助于对降雪的深入研究。此次降雪过程由中高层西南及偏南暖湿气流与低层东南偏冷空气交汇造成动力和水汽辐合抬升形成,4~5 km高度处的风切变有利于降雪的增强。上升气流有助于水汽的输送、冰雪转化以及雪晶凝华、聚合,冰晶数浓度中心对应着上升运动顶部。然而此次降雪云系低层过冷云水含量不足,降雪回波<20 dBZ,回波顶高<7 km,雪花垂直下落速度<2 m s-1,地面降水量大值与低层强回波区对应。降雪粒子谱分布范围较窄,以直径1 mm左右的小粒子为主,相态主要为干雪,基本不存在混合相态。 相似文献
9.
Carbon dioxide exchange in a temperate grassland ecosystem 总被引：18，自引：0，他引：18
Carbon dioxide exchange was measured, using the eddy correlation technique, over a tallgrass prairie in northeastern Kansas, U.S.A., during a six-month period in 1987. The diurnal patterns of daytime and nocturnal CO2 fluxes are presented on eight selected days. These days were distributed throughout most of the growing season and covered a wide range of meteorological and soil water conditions. The midday CO2 flux reached a maximum of 1.3 mg m-2 (ground area) s-1 during early July and was near zero during the dry period in late July. The dependence of the daytime carbon dioxide exchange on pertinent controlling variables, particularly photosynthetically active radiation, vapor pressure deficit and soil water content is discussed. The nocturnal CO2 flux (soil plus plant respiration) averaged -0.4 mg m-2 (ground area) s-1 during early July and was about -0.2 mg m-2 s-1 during the dry period.Published as Paper No. 9061, Journal Series, Agricultural Research Division, University of Nebraska-Lincoln, U.S.A.Research Associate and Professor, respectively. 相似文献
10.
An experimental study of sulfur and NOx fluxes over grassland 总被引：1，自引：0，他引：1
B. B. Hicks M. L. Wesely R. L. Coulter R. L. Hart J. L. Durham R. Speer D. H. Stedman 《Boundary-Layer Meteorology》1986,34(1-2):103-121
Three independent sulfur sensors were used in a study of sulfur eddy fluxes to a field of wheat stubble and mixed grasses, conducted in Southern Ohio in September, 1979. Two of these sensors were modified commercial instruments; one operated with a prefilter to measure gaseous sulfur compounds and the other with a denuder system to provide submicron particulate sulfur data. The third sensor was a prototype system, used to measure total sulfur fluxes. The data obtained indicated that the deposition velocity for gaseous sulfur almost always exceeded that for particulate sulfur; average surface conductances were about 1.0 cm s–1 for gaseous sulfur in the daytime and about 0.4 cm s–1 for particulate sulfur. The data indicate that nighttime values were probably much lower. The total sulfur sensor provided support for these conclusions. The boundary-layer quantity ln(z
0
/z
H
)was found to be 2.75 ± 0.55, in close agreement with expectations and thus providing some assurance that the site was adequate for eddy flux studies. However, fluxes derived using a prototype NOx sensor were widely scattered, partially as a consequence of sensor noise but also possibly because of the effects of nearby sources of natural nitrogen compounds.Formerly with Argonne National Laboratory. 相似文献
11.
The surface energy balance of a snow cover: comparing measurements to two differentsimulation models 总被引：1，自引：0，他引：1
Summary We compared two one-dimensional simulation models for heat and water fluxes in the soil-snow-atmosphere system with respect
to their mathematical formulations of the surface heat exchange and the snow pack evolution. They were chosen as examples
of a simple one-layer snow model and a more detailed multiple-layer snow model (SNTHERM). The snow models were combined with
the same one-dimensional model for the heat and water balance of the underlying soil (CoupModel). Data from an arable field
in central Sweden (Marsta), covering two years (1997–1999) of soil temperature, snow depth and eddy-correlation measurements
were successfully compared with the models. Conditions with a snow pack deeper or shallower than 10 cm and bare soil resulted
in similar discrepancies. The simulated net radiation and sensible heat flux were in good agreement with that measured during
snow-covered periods, except for situations with snowmelt when the downward sensible heat flux was overestimated by 10–20 Wm−2. The results showed that the uncertainties in parameter values were more important than the model formulation and that both
models were useful in evaluating the limitations and uncertainties of the measurements.
Received November 1, 1999 Revised April 20, 2000 相似文献
12.
The surface albedo and the surface roughness for forested areas with snow on the ground are expressed in terms of the tree silhouette parameter s, the projection on the vertical plane of trees per unit area. The absorption of insolation (direct solar beam) is quantitatively described for a horizontal snow surface with vertical tree trunks, stressing the role of the bark at snow level as triggering the snow melt.Measurement of s by field sampling in two forested sites in central Switzerland yielded values ranging from 1.8 to 2.1.Currently at Code 623 NASA/GSFC, Greenbelt, MD U.S.A. 相似文献
13.
Delany A. C. Fitzjarrald D. R. Lenschow D. H. Pearson R. Wendel G. J. Woodrufl B. 《Journal of Atmospheric Chemistry》1986,4(4):429-444
Using the eddy correlation method, fluxes of nitric oxide, nitrogen dioxide, ozone, water, and sensible heat were measured at a site 20 km north of Denver, Colorado over mature crested wheat grass, 0.75 m high in late June and early July. During this period the weather was fair with no synoptic disturbances. In the early morning a well-mixed diluted urban pollution plume traversed the site, by late morning aged pollution had mixed downward into the local boundary layer, and by afternoon the air came from a relatively unpolluted area of the high plains. The mean trace gas concentrations reflect this repeated pattern of local air flow. The fluxes of the trace gases were influenced both by the variation of the means and by other factors including temperature and biological activity. Ozone fluxes were found to be always negative and proportional to the mean, with an average deposition velocity for this case of about 0.006 m s-1. For the oxides of nitrogen this simple treatment was not appropriate. Both deposition and emission were observed, generally deposition predominated in the morning and emission in the afternoon with observed variations in the fluxes of NOx=NO+NO2 from –0.3 to +0.2 ppbv m s-1.The National Center for Atmospheric Research is sponsored by the National Science Foundation 相似文献
14.
Daytime variations of ozone eddy fluxes to maize 总被引：1，自引：0，他引：1
The vertical fluxes of ozone, momentum and heat in the atmospheric surface layer have been measured by eddy correlation above
both mature and senescent maize canopies. Aerodynamic formulae are applied to find that the bulk canopy surface resistancer
c
to ozone uptake and destruction varies between 4.0 and 0.5 s cm−1 during the daytime. Apparently, surface properties tend to control the removal of ozone at the surface of the earth. For
a lush canopy, the stomatal diffusion resistance is the most important property, while changes in surface temperature have
little effect. Destruction at the soil and exterior plant surfaces appears to account for 20–50% of the total loss if leaf
mesophyll resistances are assumed to be very small. Free water at leaf surfaces may at times inhibit ozone removal by both
senescent and healthy plants. 相似文献
15.
一种大气污染物干沉积速率的计算方法及其应用 总被引：11，自引：2，他引：11
介绍了一种计算大气污染物干沉积速率的方法。这种方法详细地考虑了植物生理特征和冠层内湍流结构对干沉积的影响，考虑了3层覆盖物对表面阻抗的影响，通过计算7个不同的阻抗因子获得干沉积速率。利用该方法计算了农田下垫面上7种不同大气污染物沉积的表面阻抗和江西(鹰洋)红壤典型地区农田下垫面上的二氧化硫(SO2)和硫酸盐(SO4^2—)的干沉积速率，估算了大气硫输入农田生态系统的干沉积通量，并与其他方法作了定量比较。结果表明：农田下垫面上SO2与SO4^2—的干沉积速率平均值分别为0．31cm／s，0．20cm／s；干沉积速率具有明显的日变化特征，一般白天大于夜间，中午时分出现最大值；月际变化也较明显，在冬季有大值；大气硫输入农田生态系统的全年干沉积通量为7．35g/m^2。 相似文献
16.
Adrie F. G. Jacobs Bert G. Heusinkveld Albert A. M. Holtslag 《Boundary-Layer Meteorology》2008,126(1):125-136
Observations for May and August, 2005, from a long-term grassland meteorological station situated in central Netherlands were
used to evaluate the closure of the surface energy budget. We compute all possible enthalpy changes, such as the grass cover
heat storage, dew water heat storage, air mass heat storage and the photosynthesis energy flux, over an averaging time interval.
In addition, the soil heat flux was estimated using a harmonic analysis technique to obtain a more accurate assessment of
the surface soil heat flux. By doing so, a closure of 96% was obtained. The harmonic analysis technique appears to improve
closure by 9%, the photosynthesis for 3% and the rest of the storage terms for a 3% improvement of the energy budget closure.
For calm nights (friction velocity u
* < 0.1 m s−1) when the eddy covariance technique is unreliable for measurement of the vertical turbulent fluxes, the inclusion of a scheme
that calculates dew fluxes improves the energy budget closure significantly. 相似文献
17.
Investigations about VOSCs (volatile organic sulfur compounds) have been received increasing attention for their significant contribution to the nonvolcanic background sulfate layer in the stratosphere and the earth’s radiation balance and as a potential tool to understand the carbon budget. In this study, COS and CS2 were always recorded throughout the entire rice cultivation season of 2014. COS fluxes appeared as emission in non-planted soil and as uptake in planted soil, the corresponding results were obtained as 2.66 and ?2.35 pmol·m?2·s?1, respectively. For CS2, both planted and non-planted paddy fields acted as sources with an emission rate of 1.02 pmol·m?2·s?1 and 2.40 pmol·m?2·s?1, respectively. COS emission or uptake rates showed a distinct seasonal variation, with the highest fluxes at the jointing-booting stage. COS and CS2 fluxes increased with increasing N fertilizer use because of improved plant and microbial growth and activity. Plots treated with both N and S reduced COS and CS2 fluxes slightly compared with plots with only-N treatment. Light, soil moisture or temperature showed no significant correlation with COS and CS2 fluxes, but revealed the important impacts on the magnitude and direction of gases fluxes. The results also showed that the (available) sulfur contents in soil and roots had a certain effect on VOSCs emission or uptake. Our results highlight the significance of biotic and abiotic production and consumption processes existing in the soil. 相似文献
18.
Observations of a single boundary-layer event — the generation of an atmospheric gravity wave by an unstable shear flow at Haswell, Colorado on November 12, 1971 — are briefly described and discussed. The observations were made using: (a) an acoustic echo sounder, (b) anemometers mounted at two fixed levels on a 150-m tower, (c) an anemometer and a thermometer mounted on a movable carriage on the tower, and (d) a microbarograph array, including one microbarograph mounted atop the tower. The wave phase velocity (–3.5–4.0 m s–1) was found to equal the wind velocity in the middle of the shear flow, as assumed by other authors. The wave-associated vertical fluxes of momentum and energy measured just above the wave critical layer were estimated to be –5 dyn cm–2 and –800 erg cm–2 s–1, respectively. These are large values. The annual average vertical flux of momentum at temperate and high latitudes is –0.25 dyn cm–2, while the average kinetic energy dissipation rate in a unit column of atmosphere is –5 × 103 erg cm–2 s–1. If the region of wave generation was itself propagating horizontally, its propagation velocity was large compared with the horizontal phase speed of the small-scale waves generated. Wave generation appeared to occur over an area large compared with the size of the microbarograph array (i.e., 2 km). 相似文献
19.
Intact soils cores were taken with a stainless steel corer from a sandy podzol and a loamy luvisol, and used to measure the flux (J) of NO between soil and atmosphere and the vertical profile of the NO mixing ratios (m) in the soil atmosphere, both as function of the NO mixing ratio (m
a) in the atmosphere of the headspace. These measurements were repeated after stepwise excavation of the soil column from the top, e.g. by removing the upper 2 cm soil layer. The gaseous diffusion coefficients of NO in the soil cores were either computed from soil porosity or were determined from experiments using SF6. The NO fluxes (J) that were actually measured at the soil surface were compared to the fluxes which were calculated either from the vertical NO profiles (J
c
) or from the NO production and uptake rates (J
m
) determined in the excavated soil samples. In the podzol, the actually measured (J) and the calculated (J
m
, Jm) NO fluxes agreed within a factor of 2. In the luvisol, the measured NO fluxes (J) and those calculated from the vertical NO profiles (J
c
) also agreed well, but in the upper 6 cm soil layer the NO fluxes (J
m
) calculated from NO production and uptake rates were up to 7 times higher than the measured NO fluxes. This poor agreement was probably due to the inhomogeneous distribution of NO production and consumption processes and the change of diffusivities within the top layers of the luvisol. Indeed, the luvisol showed a pronounced maximum of the NO mixing ratios at about 6 cm depth, whereas the podzol column exhibited a steady and exponential decrease of the NO mixing ratios with depth. The inhomogeneities in the luvisol were confirmed by incubation of the soil cores under anoxic conditions. This treatment resulted in production of NO at several depths indicating a zonation of increased potential activities within the luvisol profile which may have biased the modelling of the NO surface flux from turnover measurements in soil samples. Inhomogeneities could be achieved even in homogenized soil by fertilization with nitrate solution. 相似文献
20.
A system capable of measuring the fluxes of trace gases was developed. It is based on a simpler version of the eddy-accumulation technique (EA), known as the relaxed eddy-accumulation technique (REA). It accumulates air samples associated with updrafts and downdrafts at a constant flow rate in two containers for later analysis of the trace gas mean concentration. The flux integration is based on the durations of updraft and downdraft events, rather than on the vertical wind velocity (W) as is the case for EA and eddy-correlation (EC) techniques. The flux, calculated by the REA technique, is equal to the difference in the mean concentration of the trace gas of interest between the upward and downward moving eddies, multiplied by the standard deviation of the vertical wind velocity and an empirical coefficient. CO2 fluxes measured for 162 half-hour periods over a soybean field by both EC and REA techniques showed excellent agreement (coefficient of determination,R
2=0.92). The slope (0.985) and the intercept (–0.042 mg m–2 s–1) were not significantly different from 1 and 0, respectively, at the 5% level; and the standard error of estimate was 0.074 mg m–2 s–1. It is also shown that the empirical coefficient can be calculated from either latent or sensible heat fluxes. A model describing the effect on this empirical coefficient of not sampling aroundW equal to zero is proposed.Centre for Land and Biological Resources Research Contribution No. 92-212. 相似文献