The scavenging of nitrate by clouds and precipitation     

S. Wurzler  A. I. Flossmann  H. R. Pruppacher  S. E. Schwartz 《Journal of Atmospheric Chemistry》1995,20(3):259-280

A model with spectral microphysics was developed to describe the scavenging of nitrate aerosol particles and HNO₃ gas. This model was incorporated into the dynamic framework of an entraining air parcel model with which we computed the uptake of nitrate by cloud drops whose size distribution changes with time because of condensation, collision-coalescence and break-up. Significant differences were found between the scavenging behavior of nitrate and our former results on the scavenging behavior of sulfate. These reflect the following chemical and microphysical differences between the two systems:

1. nitrate particles occur in a larger size range than sulfate particles.
2. HNO₃ has a much greater solubility than SO₂ and is taken up irreversibly inside the drops in contrast to SO₂.
3. nitric acid in the cloud water is formed directly on uptake of HNO₃ gas whereas on uptake of SO₂ sulfuric acid is formed only after the reaction with oxidizing agents such as e.g., H₂O₂ or O₃.
4. nitrate resulting from uptake of HNO₃ is confined mainly to small drops, whereas sulfate resulting from uptake of SO₂ is most concentrated in the largest, oldest drops, which have had the greatest time for reaction.

Sensitivity studies showed that the nitrate concentration of small drops is significantly affected by the mass accommodation coefficient.  相似文献   

Tropospheric ozone chemistry. The impact of cloud chemistry     

Jan E. Jonson  Ivar S. A. Isaksen 《Journal of Atmospheric Chemistry》1993,16(2):99-122

The effect of clouds and cloud chemistry on tropospheric ozone chemistry is tested out in a two-dimensional channel model covering a latitudinal band from 30 to 60° N. Three different methods describing how clouds affect gaseous species are applied, and the results are compared. The three methods are:

?A first order parameterization scheme for the removal of sulphur and other soluble gases by liquid droplets.

?A parameterization scheme for SO₂, O₃, and H₂O₂ removal is constructed. The scheme is based on the solubility of gases in liquid droplets, cycling times of air masses between clouds and cloud free areas and on the chemical interaction of SO₂ with H₂O₂ and O₃ in the liquid phase.

?Gas-aqueous-phase interactions and aqueous-phase chemical reactions are included in the reaction scheme for a number of components in areas where clouds are present.

In all three methods, a full gas-phase chemistry scheme is used. Particular emphasis is given to the study of how the ozone and hydrogen peroxide levels are affected. Significant changes in the distributions are found when aqueous-phase chemical reactions are included. The result is loss of ozone in the aqueous phase, with pronounced reductions in ozone levels in the middle and lower troposphere. Ozone levels are reduced by 10 to 30% with the largest reductions in the remote middle troposphere, bringing the values in better agreement with observations. Changes in H₂O₂ are harder to predict. Although, in one case study, hydrogen peroxide is produced within the aqueous phase, concentrations are mostly comparable or even lower than in the other cases. Hydrogen peroxide levels are, however, shown to be very pH sensitive. pH values around 5 seem to favour high H₂O₂ levels. High H₂O₂ concentrations may be found particularly in the upper part of the clouds under favourable conditions.  相似文献   

Wind profiles at the Boulder Tower     

Ann Korrell  H. A. Panosky  R. J. Rossi 《Boundary-Layer Meteorology》1982,22(3):295-312

Analysis of wind profiles at the Boulder Tower (BAO) leads to these conclusions:

1. The variation of roughness with wind direction found earlier is confirmed. Roughness lengths measured on the tower are larger than those measured close to the surface.
2. The profiles and measurements of Reynolds stress are consistent with a von-Karman constant of 0.35.
3. The form φ_m=(1?15z/L)^-1/3 fits best in the range -0.6 < z/L < 0. In the range 0 < z/L < 0.5, θ _m ～ 1 + 4.7z/L provides a good fit to the observations. For z/L < 0.1, φ _m also depends on h, the thickness of the PBL. For z/L < -0.6, Φ _m approaches the constant 0.5, in contrast to all previous suggestions. For larger stabilities, the upper level is usually not in the surface layer, and wind ratios become independent of z/L.
4. With snow cover, the effective roughness diminishes to about 1 cm, even for directions for which the roughness length without snow is large.
5. Estimation of winds at 100 or 150 m from information near the surface is best for similarity theory provided that the ratio of height to Monin-Obukhov L is less than 0.1. For larger z/L, simple power laws seem more appropriate.

  相似文献   

Aircraft measurements of oxides of nitrogen along the eastern rim of the Asian continent: Winter observations     

Y. Kondo  W. A. Matthews  A. Iwata  Y. Morita  M. Takagi 《Journal of Atmospheric Chemistry》1987,5(1):37-58

Aircraft observations of oxides of nitrogen (NO _y ), measured with a ferrous sulfate converter, over the sea surrounding the Japanese islands (30–43° N, 131–141° E) were carried out in the winter of 1983 and 1984 at altitudes mostly between 3 and 8 km. NO _y defined here is the sum of NO, NO₂, and other unstable oxides of nitrogen that are converted to NO by ferrous sulfate. The main observations were:

1. Over the Pacific Ocean between the latitudes of 30–35° N, the observed NO _y mixing ratio between 3 and 8 km was a fairly constant 200 pptv. The NO mixing ratio increased with altitude from 15 pptv at 3 km to 35 pptv at 7 km.
2. Over the Sea of Japan, tropospheric NO _y mesured between 1 and 6 km started increasing with latitude North of 35° N and reached about 1000 pptv at 40° N.
3. NO _y was measured in an air mass transported from the stratosphere near a tropopause fold region. When the ozone mixing ratio was between 80 and 140 ppbv, the NO _y mixing ratio was about 200 pptv.

  相似文献   

Atmospheric boundary layer research at Cabauw   总被引：1，自引：1，他引：0  

A. P. Van Ulden  J. Wieringa 《Boundary-Layer Meteorology》1996,78(1-2):39-69

At Cabauw, The Netherlands, a 213 m high mast specifically built for meteorological research has been operational since 1973. Its site, construction, instrumentation and observation programs are reviewed. Regarding analysis of the boundary layer at Cabauw, the following subjects are discussed:

- terrain roughness;

- Monin-Obukhov theory in practice;

- the structure of stable boundary layers;

- observed evolution of fog layers;

- inversion rise and early morning entrainment;

- use of the geostrophic wind as a predictor for wind profiles;

- height variation of wind climate statistics;

- air pollution applications: long range transport and short range dispersion;

- dependence of sound wave propagation on boundary-layer structure;

- testing of weather and climate models.

  相似文献   

Bulk characteristics of heat transfer in the unstable,baroclinic atmospheric boundary layer     

J. R. Garratt  R. J. Francey 《Boundary-Layer Meteorology》1978,15(4):399-421

Field data for the unstable, baroclinic, atmospheric boundary layer over land and over the sea are considered in the context of a general similarity theory of vertical heat transfer. The dependence of δθ/θ_* upon logarithmic functions of h _c z _T and stability (through the similarity function C) is clearly demonstrated in the data. The combined data support the conventional formulation for the heat transfer coefficient δθ/θ_* when,

1. the surface scaling length is z _T (« z ₀), the height at which the surface temperature over land is obtained by extrapolation of the temperature profile
2. the height scale is taken as the depth of convective mixing h _c
3. the temperature profile equivalent of the von Karman constant is taken as 0.41
4. areal average, rather than single point, values of δθ are employed in strongly baroclinic conditions. No significant effect of baroclinity or the height scale ratio as proposed in the general theory is found. Variations in C about a linear regression relation against stability are most probably due to uncertainties in the areal surface temperature and to experimental errors in general temperature measurements.

  相似文献   

Numerical study on the bulk heat transfer coefficient for a variety of vegetation types and densities     

Junsei Kondo  Atsuko Kawanaka 《Boundary-Layer Meteorology》1986,37(3):285-296

The relationship between the geometrical structure of a canopy layer and the bulk transfer coefficient was investigated using a numerical canopy model. The following results were obtained:

1. The bulk transfer coefficients for momentum and heat, C _M and C _H , change with non-dimensional canopy density C _* each has a maximum.
2. The value of C _M is always larger than the value of C _H for a canopy with c _m > c _h , c _m and c _h being the drag coefficient and the heat transfer coefficient of an individual canopy element, respectively.
3. The value of C _* at which C _H has its maximum value is larger than the value of C _* at which C _M has its maximum. Therefore, the reciprocal of the sublayer Stanton number b _h ^?1 ranges between 50 and 65 for C _* around 0.1 while it ranges between 0 and 30 for C _* < 10^?2 and C _* > 2 (when c _m = 0.5).
4. The value of B _H ^?1 in the present study is consistent with most available observations, except for canopies of medium density (when C _* is around 0.1) for which no observational value has been obtained.

  相似文献   

Limitations of an eddy-correlation technique for the determination of the carbon dioxide and sensible heat fluxes     

R. L. Desjardins  E. R. Lemon 《Boundary-Layer Meteorology》1974,5(4):475-488

A modified infrared CO₂ gas analyzer, a small thermocouple assembly, a heated-thermocouple anemometer for horizontal wind, and a propeller-type vertical wind sensor were used to measure the eddy fluxes of heat and CO₂ above a corn crop. Experimental results of these fluxes are discussed. The main sources of errors of the eddy fluxes using these instruments were estimated:

1. Sensors with a time constant of 0.5 s appear to be fast enough to detect most of the vertical CO₂ transfer as long as the sensors are located at least one meter above the crop surface.
2. The deviation from steady-state conditions for 10-min periods was found to have a significant effect on the eddy flux estimates.
3. Temperature fluctuations of the air sample passing through the CO₂ infrared gas analyzer were found to be non-negligible but could be easily corrected.
4. A 1° misalignment of the vertical anemometer affected these eddy fluxes by less than 10% under all circumstances studied.

  相似文献   

Assessing the Consequences of Climate Change for Food and forest Resources: A View from the IPCC   总被引：1，自引：0，他引：1  

William Easterling  Michael Apps 《Climatic change》2005,70(1-2):165-189

Important findings on the consequences of climate change for agriculture and forestry from the recently completed Third Assessment Report (TAR) of the Intergovernmental Panel on Climate Change (IPCC) are reviewed, with emphasis on new knowledge that emerged since the Second Assessment Report (SAR). The State-Pressure-Response-Adaptation model is used to organize the review. The major findings are:

• Constant or declining food prices are expected for at least the next 25 yr, although food security problems will persist in many developing countries as those countries deal with population increases, political crisis, poor resource endowments, and steady environmental degradation. Most economic model projections suggest that low relative food prices will extend beyond the next 25 yr, although our confidence in these projections erodes farther out into the 21st century.
• Although deforestation rates may have decreased since the early 1990s, degradation with a loss of forest productivity and biomass has occurred at large spatial scales as a result of fragmentation, non-sustainable practices and infrastructure development.
• According to United Nations estimates, approximately 23% of all forest and agricultural lands were classified as degraded over the period since World War II.
• At a worldwide scale, global change pressures (climate change, land-use practices and changes in atmospheric chemistry) are increasingly affecting the supply of goods and services from forests.
• The most realistic experiments to date – free air experiments in an irrigated environment – indicate that C₃ agricultural crops in particular respond favorably to gradually increasing atmospheric CO₂ concentrations (e.g., wheat yield increases by an average of 28%), although extrapolation of experimental results to real world production where several factors (e.g., nutrients, temperature, precipitation, and others) are likely to be limiting at one time or another remains problematic. Moreover, little is known of crop response to elevated CO₂ in the tropics, as most of the research has been conducted in the mid-latitudes.
• Research suggests that for some crops, for example rice, CO₂ benefits may decline quickly as temperatures warm beyond optimum photosynthetic levels. However, crop plant growth may benefit relatively more from CO₂ enrichment in drought conditions than in wet conditions.
• The unambiguous separation of the relative influences of elevated ambient CO₂ levels, climate change responses, and direct human influences (such as present and historical land-use change) on trees at the global and regional scales is still problematic. In some regions such as the temperate and boreal forests, climate change impacts, direct human interventions (including nitrogen-bearing pollution), and the legacy of past human activities (land-use change) appear to be more significant than CO₂ fertilization effects. This subject is, however an area of continuing scientific debate, although there does appear to be consensus that any CO₂ fertilization effect will saturate (disappear) in the coming century.
• Modeling studies suggest that any warming above current temperatures will diminish crop yields in the tropics while up to 2–3 ^°C of warming in the mid-latitudes may be tolerated by crops, especially if accompanied by increasing precipitation. The preponderance of developing countries lies in or near the tropics; this finding does not bode well for food production in those countries.
• Where direct human pressures do not mask them, there is increasing evidence of the impacts of climate change on forests associated with changes in natural disturbance regimes, growing season length, and local climatic extremes.
• Recent advances in modeling of vegetation response suggest that transient effects associated with dynamically responding ecosystems to climate change will increasingly dominate over the next century and that during these changes the global forest resource is likely to be adversely affected.
• The ability of livestock producers to adapt their herds to the physiological stress of climate change appears encouraging due to a variety of techniques for dealing with climate stress, but this issue is not well constrained, in part because of the general lack of experimentation and simulations of livestock adaptation to climate change.
• Crop and livestock farmers who have sufficient access to capital and technologies should be able to adapt their farming systems to climate change. Substantial changes in their mix of crops and livestock production may be necessary, however, as considerable costs could be involved in this process because investments in learning and gaining experience with different crops or irrigation.
• Impacts of climate change on agriculture after adaptation are estimated to result in small percentage changes in overall global income. Nations with large resource endowments (i.e., developed countries) will fare better in adapting to climate change than those with poor resource endowments (i.e., developing countries and countries in transition, especially in the tropics and subtropics) which will fare worse. This, in turn, could worsen income disparities between developed and developing countries.
• Although local forest ecosystems will be highly affected, with potentially significant local economic impacts, it is believed that, at regional and global scales, the global supply of timber and non-wood goods and services will adapt through changes in the global market place. However, there will be regional shifts in market share associated with changes in forest productivity with climate change: in contrast to the findings of the SAR, recent studies suggest that the changes will favor producers in developing countries, possibly at the expense of temperate and boreal suppliers.
• Global agricultural vulnerability is assessed by the anticipated effects of climate change on food prices. Based on the accumulated evidence of modeling studies, a global temperature rise of greater than 2.5 ^°C is likely to reverse the trend of falling real food prices. This would greatly stress food security in many developing countries.

  相似文献   

Vertical cross-spectra of horizontal velocity components at the Boulder observatory     

Rick Soucy  Robert Woodward  H. A. Panofsky 《Boundary-Layer Meteorology》1982,24(1):57-66

Cross-spectra between horizontal wind components at different levels of the Boulder Atmospheric Observatory (BAO) tower lead to the following conclusions:

1. Davenport's hypothesis is satisfied that coherence decays exponentially with the ratio of vertical separation to horizontal wave length, at least to very small values of coherence.
2. The decay coefficients increase with z/L for z/L < 0.5. For larger stabilities, irregular fluctuations with periods of order 10–20 min have considerable vertical coherence. Results at BAO are quite consistent with those elsewhere.
3. Eddy slopes in vertical planes increase with wind shear up to a point where the slope (horizontal delay over vertical separation) is just above 2. Beyond that point, the systematic increase of slopes with shear ceases. Since wind shear decreases upward, slopes tend to decrease upward. Slopes for lateral components are significantly larger than those for u-components.

  相似文献   

Bare-ground surface heat and water exchanges under dry conditions: Observations and parameterization     

I. Braud  J. Noilhan  P. Bessemoulin  P. Mascart  R. Haverkamp  M. Vauclin 《Boundary-Layer Meteorology》1993,66(1-2):173-200

A simplified land-surface parameterization is tested against bare-soil data collected during the EFEDA experiment conducted in Spain in June 1991. A complete data set, made up of soil properties as well as hydrological and atmospheric measurements, is described and discussed. The 11-day data set is characterized by very dry conditions and high surface temperatures during the day. Large values of sensible and soil heat fluxes and small values of surface evaporation (≈1 mm/day) were observed. This data set was modelled, leading to the following conclusions:

1. In the model, the parameterization provides values of the soil thermal properties and subsequently of the predicted soil heat fluxes which are overestimated when compared with the observations.
2. Following the literature, a value of the ratio between the roughness lengths for momentumZ _oand heatZ _ohof close to 10 for fairly homogeneous areas of bare soil and vegetation is used. This value leads to a fair prediction of the surface temperature. If the roughness lengths were taken to be equal, as is often assumed in atmospheric modelling, a poorer prediction results.
3. Finally, the vapor phase transfer mode is found dominant close to the surface and a modified parameterization including this effect is proposed. It allows a fair prediction of both surface evaporation and near-surface water content.

  相似文献   

Problems of atmospheric shear flows and their laboratory simulation     

J. E. Cermak  S. P. S. Arya 《Boundary-Layer Meteorology》1970,1(1):40-60

Shear flows generated by movement of the atmosphere near the earth's surface are accompanied by complexities not ordinarily encountered in the treatment of turbulent boundary layers. Problems arising from the following physical features are considered:

1. thermal stratification;
2. surface roughness in the form of forests and cities;
3. non-uniformity of surface roughness and/or temperature (leading to 3-dimensional turbulent boundary layers);
4. surface irregularities in the form of hilly and mountainous topography.

The complex nature of atmospheric shear flows has stimulated efforts to study their characteristics in the laboratory under controlled conditions. Accordingly, questions of similarity between the laboratory and the atmospheric flows for both mean and turbulent quantities arise. Similarity criteria, or appropriate scaling relationships, are discussed. Wind tunnels designed for investigations related to atmospheric shear flows are described. These facilities are shown to have a capability for simulating such flows for a wide range of the physical features listed above.  相似文献   

The internal boundary layer — A review   总被引：2，自引：2，他引：0  

J. R. Garratt 《Boundary-Layer Meteorology》1990,50(1-4):171-203

A review is given of relevant work on the internal boundary layer (IBL) associated with:

1. Small-scale flow in neutral conditions across an abrupt change in surface roughness,
2. Small-scale flow in non-neutral conditions across an abrupt change in surface roughness, temperature or heat/moisture flux,
3. Mesoscale flow, with emphasis on flow across the coastline for both convective and stably stratified conditions.

The major theme in all cases is on the downstream, modified profile form (wind and temperature), and on the growth relations for IBL depth.  相似文献   

Experiments on scalar dispersion within a model plant canopy,part III: An elevated line source     

B. J. Legg  M. R. Raupach  P. A. Coppin 《Boundary-Layer Meteorology》1986,35(3):277-302

An experiment is reported in which heat was released as a passive tracer from an elevated lateral line source within a model plant canopy, with h _s = 0.85 h _c (h _s and h _c being the source and canopy heights, respectively). A sensor assembly consisting of three coplanar hot wires and one cold wire was used to measure profiles of mean temperature % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaiikamaana% aabaGaeqiUdehaaiaacMcaaaa!390C!\[(\overline \theta )\], temperature variance (Σ_θ ²), vertical and streamwise turbulent heat fluxes, and third moments of wind and temperature fluctuations. Conclusions were:

1. Despite the very heterogeneous flow within the canopy, the observed dispersive heat flux (due to spatial correlation between time-averaged temperature and vertical velocity) was small. However, there is evidence from the plume centroid (which was lower than h _s at the source) of systematic recirculating motions within the canopy.
2. The ratio % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeq4Wdm3aaS% baaSqaaiabeI7aXjaab2gacaqGHbGaaeiEaaqabaGccaGGVaWaa0aa% aeaacqaH4oqCaaWaaSbaaSqaaiaab2gacaqGHbGaaeiEaaqabaaaaa!41DF!\[\sigma _{\theta {\text{max}}} /\overline \theta _{{\text{max}}} \] (of maximum values on vertical profiles) decreased from 1 near the source to an asymptotic value of 0.4 far downstream, in good agreement with previous experimental and theoretical work for concentration fluctuations in the surface layer well above the canopy.
3. The eddy diffusivity for heat from the line source (K _HL ) increased, downstream of the source, to a nearly constant ‘far-field’ vertical profile. Within the canopy, the far-field K _HL was an order of magnitude larger than K _HP , the equivalent diffusivity for a plane source; well above the canopy, the two were equal. The time scale defined by (far-field K _HL )/(vertical velocity variance) was independent of height within the canopy.
4. Budgets for temperature variance, vertical heat flux and streamwise heat flux are remarkably similar to the equivalent budgets for an elevated line source in the surface layer well above the canopy, except in the lower part of the canopy in the far field, where vertical transport is much more important than in the surface layer.
5. A random flight simulation of the mean height and depth of the temperature plume was generally in good agreement with experiment. However, details of the temperature and streamwise turbulent heat flux profiles were not correct, suggesting that the model formulation needs to be improved.

  相似文献   

The ‘MESOGERS 84’ experiment: A report     

A. Weill  C. Mazaudier  F. Baudin  C. Klapisz  F. Leca  M. Masmoudi  D. Vidal Madjar  R. Bernard  O. Taconet  B. S. Gera  A. Sauvaget  A. Druilhet  P. Durand  J. Y. Caneil  P. Mery  G. Dubosclard  A. C. M. Beljaars  W. A. A. Monna  J. G. Van Der Vliet  M. Crochet  D. Thomson  T. Carlson 《Boundary-Layer Meteorology》1988,42(3):251-264

  相似文献   

Multiple windbreaks: An aeolean ensemble   总被引：1，自引：0，他引：1  

K. J. McAneney  M. J. Judd 《Boundary-Layer Meteorology》1991,54(1-2):129-146

Near-neutral measurements of the turbulent wind field within and above a sequence of 15 parallel windbreaks on a flat pastoral site are presented. The windbreak fences each had a porosity of 60% and were equally-spaced at 6 times their height (h = 2 m). The following conclusions seem justified for wind directions within 10 ° of the normal to the array:

1. Above the windbreaks (2h), mean windspeeds first decreased and then increased asymptotically to a value in equilibrium with the new surface roughness. At 0.5h, windspeeds exhibited a slow increase down the entire array.
2. Reflecting differences in approach flows, the drag on the initial fence was almost twice that on barriers farther downstream. This reduction in momentum extraction per windbreak was associated with an elevation in the zero-plane displacement to a level equal to 0.8h.
3. At positions well-removed from the initial fences, mean windspeeds were reduced throughout the entire region below shelter height. In this region, the flow became increasingly dominated by downward moving air with velocities much greater than the local average. The zone of reduced turbulence was small, extending only 2h downstream of a barrier at a height of 0.25h. This corresponded with the region excluded from smoke trails released at the top of windbreaks.
4. An approximate TKE budget mid-way between windbreaks 7 and 8 suggests that shear and wake production peak near z = h and that production is balanced by dissipation and vertical transport components. Advective and inertial interaction terms are negligible at this midway position but are likely to be major sources of TKE closer to the windbreak. Local equilibrium is attained above z = 1.5h implying the existence of a constant-stress layer.

The measurements show the practical difficulty of simultaneously reducing both mean windspeeds and turbulence levels with repeated windbreaks at conventional spacings for horticultural applications.  相似文献   

Experiments on scalar dispersion within a model plant canopy part II: An elevated plane source     

P. A. Coppin  M. R. Raupach  B. J. Legg 《Boundary-Layer Meteorology》1986,35(1-2):167-191

This paper describes a wind-tunnel experiment on the dispersion of trace heat from an effectively planar source within a model plant canopy, the source height being h _s = 0.80 h _c , where h _c is the canopy height. A sensor assembly consisting of three coplanar hot wires and one cold wire was used to make simultaneous measurements of the temperature and the streamwise and vertical velocity components. It was found that:

1. The thermal layer consisted of two parts with different length scales, an inner sublayer (scaling with h _s and h _c ) which quickly reached streamwise equilibrium downstream of the leading edge of the source, and an outer sublayer which was self-preserving with a length scale proportional to the depth of the thermal layer.
2. Below 2h _c , the vertical eddy diffusivity for heat from the plane source (K _HP ) was substantially less than the far-field limit of the corresponding diffusivity for heat from a lateral line source at the same height as the plane source. This shows that dispersion from plane or other distributed sources in canopies is influenced, near the canopy, by turbulence ‘memory’ and must be considered as a superposition of both near-field and far-field processes. Hence, one-dimensional models for scalar transport from distributed sources in canopies are wrong in principle, irrespective of the order of closure.
3. In the budgets for temperature variance, and for the vertical and streamwise components of the turbulent heat flux, turbulent transport was a major loss between h _s and h _c and a principal gain mechanism below h _s , as also observed in the budgets for turbulent energy and shear stress.
4. Quadrant analysis of the vertical heat flux showed that sweeps and ejections contributed about equal amounts to the heat flux between h _s and h _c , though among the more intense events, sweeps were dominant. Below h _s , almost all the heat was transported by sweeps.

  相似文献   

Increases of wet deposition at remote sites in Japan from 1991 to 2009     

Kyo Kitayama  Sinya Seto  Manabu Sato  Hiroshi Hara 《Journal of Atmospheric Chemistry》2012,69(1):33-46

Temporal trends in wet deposition of major ions were explored at nationwide remote sites in Japan from April 1991 to March 2009 by using the seasonal Kendall slope estimator and the nonparametric seasonal Kendall test. For the trend analysis, datasets from eight remote sites (Rishiri, Echizenmisaki, Oki, Ogasawara, Shionomisaki, Goto, Yakushima, and Amami) were selected from the Japanese Acid Deposition Survey (JADS) conducted by the Ministry of the Environment. Deposition of H⁺ has been increasing at remote sites in Japan on a national scale. Significant (p????0.05) increases in H⁺ deposition were detected with changes of +3?C+9?%?year^?1 at seven sites, while insignificant increases were observed at one site. Depositions of non-sea salt (nss)-SO ₄ ^2? and NO ₃ ^? significantly increased at four and six sites, respectively, with changes of +1?C+3?%?year^?1. Significant increases in precipitation at four sites would have contributed to the increase in depositions of H⁺, nss-SO ₄ ^2? , and NO ₃ ^? . The emission trends of SO₂ and NO_x did not corresponded to the deposition trends of nss-SO ₄ ^2? and NO ₃ ^? . The different trends indicated that temporal variation of precipitation amount trend dominated the deposition trends.  相似文献   

Economics of climate policy and collective decision making   总被引：1，自引：0，他引：1  

Beat Bürgenmeier  Andrea Baranzini  Catherine Ferrier  Céline Germond-Duret  Karin Ingold  Sylvain Perret  Peter Rafaj  Socrates Kypreos  Alexander Wokaun 《Climatic change》2006,79(1-2):143-162

This paper explores the reasons why economic instruments of climate change are reluctantly applied and stresses the need for interdisciplinary research linking economic theory and empirical testing to deliberative political procedures. It is divided in three parts. The first one recalls the main issues in implementing Cost-Benefit Analysis such as information problems, uncertainties, discounting the future and irreversibilities. The second part shows how these issues can be treated in integrated assessment and techno-economic models and presents a case study, which shows that

• The chosen scenario tends to stabilize atmospheric CO₂ concentration at around 550 ppm in the long run.
• Exclusion of possibility to trade CO₂ emission permits under a cap regime would increase the cost of emission abatement for OECD countries.
• Combining different flexibility instruments might lead to significant gains in the overall cost of climate policy.

The third part presents results of a survey conducted among the main economic and environmental associations in Switzerland. The survey reveals conflicting views on economic instruments. It shows how the social acceptability of these instruments can be improved in taking explicitly into account these opposing views of special interest groups. Therefore, policy scenarios should be selected in combining techno-economic models with empirical studies about their political and normative context.  相似文献   

A comparison of ABL heights inferred routinely from lidar and radiosondes at noontime     

W. A. J. Van Pul  A. A. M. Holtslag  D. P. J. Swart 《Boundary-Layer Meteorology》1994,68(1-2):173-191

The height of the atmospheric boundary layer (ABL) obtained with lidar and radiosondes is compared for a data set of 43 noon (12.00 GMT) cases in 1984. The data were selected to represent the synoptic circulation types appropriately. Lidar vertical profiles at 1064 nm were used to obtain three estimates for the ABL height (h _lid), based on the first gradient in the back-scatter profile, namely, at the beginning, middle and top of the gradient. The boundary-layer height obtained with the radiosondes (h _s) was determined with the dry-parcel-intersection method in unstable conditions. As a first guess for near-neutral and stable conditions, the height of the first significant level in the potential temperature profile was taken. Overall, the boundary-layer thickness estimates agree surprisingly well (regression lineh _lidb=h_s:cc.=0.93 and the standard error=121 m). However, in 10% of the cases, the lidar estimate was significantly lower (difference>400 m) than the routinely inferredh _s. These outliers are discussed separately. For stable conditions, an estimate of ABL height (h _N) is also made based on the friction velocity and the Brunt-Väisälä frequency. The agreement betweenh _Nandh _lidbis good. Discrepancies between the two methods are caused by:

1. rapid growth of the boundary layer arround the measurement time;
2. the presence of a deep entrainment layer leading to a large zone in which quantities are not well mixed;
3. a large systematic error of 100–200 m in the estimate of boundary-layer height obtained from the radiosonde due to the way that profiles are recorded, as a series of significant points.

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