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1.
The carbon isotopic ratio of atmospheric carbon dioxide at Tsukuba,Japan   总被引：1，自引：0，他引：1  
To find out the secular and seasonal trends of the 13C value and CO2 concentration in the surface air and the determination of the 13C in the atmospheric CO2 collected at Tsukuba Science City was carried out during the period from July 1981 to October 1983. The monthly average of the 13C value of CO2 in the surface air collected at 1400 LMT ranged from -7.52 to \s-8.45 with an average of -7.96±0.25 and the CO2 concentration in the air varied from 334.5 l 1-1 to 359 l 1-1 with an average of 347.2±6.3 l 1-1. The 13C value is high in summer and low in winter and is negatively correlated with the CO2 concentration. In general, the relationship between the 13C and the CO2 concentration is explainable by a simple mixing model of two different constant carbon isotopic species but the relationship does not always follow the model. The correlation between the 13C value and the CO2 concentration is low during the plant growth season and high at other times. The observed negative deviation of the 13C value from the simple mixing model in the plant growth season is partly due to the isotopic fractionation process which takes place in the land biota.  相似文献   

2.
A numerical case study with a second-order turbulence closure model is proposed to study the role of urban canopy layer (UCL) for the formation of the nocturnal urban boundary layer (UBL). The turbulent diffusion coefficient was determined from an algebraic stress model. The concept of urban building surface area density is proposed to represent the UCL. Calculated results were also compared with field observation data. The height of the elevated inversion above an urban center was simulated and found to be approximately twice the average building height. The turbulent kinetic energy k, energy dissipation rate , and turbulence intensities u 2 and w 2 increase rapidly at the upwind edge of the urban area. The Reynolds stress uw displayed a nearly uniform profile inside the UBL, and the vertical sensible heat flux w had a negative value at the inversion base height. This indicates that the downward transport of sensible heat from the inversion base may play an important role in the formation of the nocturnal UBL.  相似文献   

3.
The relation between the turbulence Reynolds numberR and a Reynolds numberz* based on the friction velocity and height from the ground is established using direct measurements of the r.m.s. longitudinal velocity and turbulent energy dissipation in the atmospheric surface layer. Measurements of the relative magnitude of components of the turbulent kinetic energy budget in the stability range 0 >z/L 0.4 indicate that local balance between production and dissipation is maintained. Approximate expressions, in terms of readily measured micrometeorological quantities, are proposed for the Taylor microscale and the Kolmogorov length scale .  相似文献   

4.
Summary The effect of the Alpine orography on prototype cold fronts approaching from the west is investigated by three-dimensional numerical model simulations. The numerical experiments cover a range of parameter constellations which govern the prefrontal environment of the front. Especially, the appearance and intensity of prefrontal northern Alpine foehn varies from case to case.The behaviour of a cold front north of the Alps depends much on the prefrontal condition it encounters. It is found that prefrontal foehn can either accelerate or retard the approaching front.An important feature is the pressure depression along the northern Alpine rim that results from the southerly foehn flow. In cases where this depression compensates the eastward directed pressure gradient associated with the largescale flow, the front tends to accelerate and the foehn breaks down as soon as the front passes. In contrast, the foehn prevents the front from a rapid eastward propagation if it is connected with a strong southerly wind component.No-foehn experiments are performed for comparison, where either the mountains are removed, or the static stability is set to neutral. Also shown are effects of different crossfrontal temperature contrasts.List of Symbols c F propagation speed of a front - x, y horizontal grid spacing (cartesian system) - , horizontal grid spacing (geographic system) - t time step - z vertical grid spacing (cartesian system) - cross-frontal potential temperature difference - i potential temperature step at an inversion - E turbulent kinetic energy - f Coriolis parameter - FGP frontogenesis parameter (see section 2.2) - g gravity acceleration (g=9.81 m s–2) - vertical gradient of potential temperature - h terrain elevation (above MSL) - h i height of an inversion (h i =1000 m MSL) - H height of model lid (H=9000 m MSL) - K M exchange coefficient of momentum - K H exchange coefficient of heat and moisture - longitude - N Brunt-Väisäla-frequency - p pressure - Exner function (=T/) - latitude - q v specific humidity - R d gas constant of dry air (R d =287.06 J kg–1 K–1) - density of dry air - t time - T temperature - potential temperature - TFP thermal front parameter (see section 2.2) - u, v, w cartesian wind components - u g ,v g geostrophic wind components - horizontal wind vector - x, y, z cartesian coordinates Abbreviations GND (above) ground level - MSL (above) mean sea level - UTC universal time coordinated With 20 Figures  相似文献   

5.
E- turbulence model predictions of the neutralatmospheric boundary layer (NABL) are reinvestigated to determine thecause for turbulence overpredictions found in previous applications. Analytical solutions to the coupled E and equations for the case of steady balance between transport and dissipation terms, the dominant balance just below the NABL top, are derived. It is found that analytical turbulence profiles laminarizeat a finite height only for values of closure parameter ratio c 2 /e equal toor slightly greater than one, with laminarization as z for greater . The point = 2 is additionally foundthat where analytical turbulent length scale (l) profilesmade a transition from ones ofdecreasing ( < 2) to increasing ( > 2)values with height. Numerically predicted profiles near the NABL topare consistent with analytical findings. The height-increasingvalues of l predicted throughout the NABL with standard values ofclosure parameters thus appear a consequence of 2.5(> 2), implied by these values (c 2 = 1.92, = 1.3, e = 1). Comparison of numericalpredictions with DNS data shows that turbulence overpredictions obtained with standard-valued parameters are rectifiedby resetting and e to 1.1 and 1.6, respectively, giving, with c 2 = 1.92, 1.3, and laminarization of the NABL's cappingtransport-dissipation region at a finite height.  相似文献   

6.
The reactions of alkoxy radicals determine to a large extent the products formed during the atmospheric degradations of emitted organic compounds. Experimental data concerning the decompositions, 1,5-H shift isomerizations and reactions with O2 of several classes of alkoxy radicals are inconsistent with literature estimations of their absolute or relative rate constants. An alternative, although empirical, method for assessing the relative importance under atmospheric conditions of the reactions of alkoxy radicals with O2 versus decomposition was derived. This estimation method utilizes the differences in the heats of reaction, (H)=(Hdecomposition–HO 2 reaction), between these two reactions pathways. For (H)[22–0.5(HO 2 reaction)], alkoxy radical decomposition dominates over the reaction with O2 at room temperature and atmospheric pressure of air, while for (H)[25-0.5(HO 2 reaction)], the O2 reaction dominates over decomposition (where the units of H are in kcal mol–1). The utility and shortcomings of this approach are discussed. It is concluded that further studies concerning the reactions of alkoxy radicals are needed.  相似文献   

7.
Effect of finite sampling on atmospheric spectra   总被引：2，自引：0，他引：2  
The effect of a finite averaging time on variances is well known, but its effect on power spectra is less clearly understood. We present numerical solutions for the spectral distortion arising from sampling over a finite time interval T and show that the commonly used filter function (1 – sinc2f T), valid for variances, is a reasonable approximation for power spectra only when T 10 m , where f is the cyclic frequency, and m is the dominant time scale of the process. Our results exhibit an increasingly steeper low-frequency roll-off as T decreases relative to m , indicating that the measured spectrum is subject to a greater suppression of the lower frequencies (f > 1/T) than predicted by (1 – sinc2f T). This suppression is, in a sense, compensated by an overestimation of spectral estimates in the frequency range f 1/T.  相似文献   

8.
This paper describes the similarity between atmospheric fluctuations of carbon dioxide, water vapor and temperature using data which cover a wide range of instability (0.02 < < 10). The is the Monin-Obukhov stability parameter including the humidity effect.The spectral analysis shows that the coherency between fluctuations of carbon dioxide and water vapor or temperature is very close to unity, and the phase difference is basically out of phase for whole frequency ranges analyzed. The stability dependence of the normalized standard deviation of carbon dioxide is very similar to those of water vapor and temperature. The normalized standard deviation is about 2.5 under near neutral conditions, and it decreases with increasing instability following the -1/3; power law as (-)-1/3. The skewness factors of carbon dioxide, water vapor and temperature show a systematic departure with increasing instabilities for 0.02 < s- < 1, and level off at high instabilities for 1 < -\s < 10. The stability dependence of the flatness factors is not so clear as that noted in the standrard deviation and skewness factors. Dissipation rates of carbon dioxide, water vapor and temperature variance are well related to the spectral peak wavelength. This seems to be real since the local production and local dissipation rates are the main terms, almost balancing one another in the variance budget equations for scalar entities.  相似文献   

9.
A review of flux-profile relationships   总被引：33，自引：5，他引：33  
Flux-profile relationships in the constant flux layer are reviewed. The preferred relationships are found to be those of Dyer and Hicks (1970), namely, H = W =(1–16(z/L))–1/2, M =(1–16(z/L))–1/4 for the unstable region, and H = W = M = 1+5(z/L) for the stable region.The carefully determined results of Businger et al. (1971) remain a difficulty which calls for considerable clarification.  相似文献   

10.
The structure of atmospheric turbulence in the surface layer over the open ocean is examined under conditions of local free convection. The raw data consist of profile and fluctuation measurements of wind and temperature as obtained from a meteorological buoy. For near neutral conditions and for waves running approximately along the wind direction, wave-induced wind fluctuations can be described by a simplified linear theory based on Miles (1957). In this case, the spectrum of wind velocity is given as the sum of two parts; for the turbulent part, the parameterization as obtained by Kaimal et al. (1972) applies, while the wave-induced part is parameterized using a simplification of Miles' linear theory. For cases of local free convection, the measurements of the vertical component of the wind velocity are well described by similarity theory; as expected, w /(-uw)1/2 is proportional to (- z/L)1/3. In order to scale the longitudinal wind velocity component, it seems to be reasonable to extend the list of relevant parameters by the height of the mixed layer z i. We obtain u /(- uw)1/2 (z/z i)1/3(- z/L)1/3 with only a poor correlation coefficient of r = 0.6. Overall, the results of local free convection scaling obtained from direct measurements show good agreement with those obtained from profile measurements. A comparison between direct and indirect determination of turbulent fluxes of momentum shows an unexplained difference of about 20%. This discrepancy is mainly due to a gap in the uw-cospectrum at the swell frequency.  相似文献   

11.
A Field Study of the Mean Pressure About a Windbreak   总被引：3，自引：0，他引：3  
To provide additional field data for assessingwindbreak flow models, mean ground-level pressurehas been measured upstream and downstream from along porous fence (height H = 1.25 m, resistancecoefficient k r = 2.4). Measurements were madeduring periods of near-neutral stability and near-normallyincident flow, with the fence standing on bare soil(roughness length, z 0 0.8 cm;H/z 0 160), or within a plant canopy. The mean pressure field,measured far from the ends of the fence, was foundto be quite insensitive to mean wind direction( , zero for perpendicular flow), for| | less than about 25°.In the absence of a canopy, during each measurementperiod the minimum pressure occurred at the closestsampling location to leeward of the windbreak, thepressure-gradient in most cases beingmaximally-adverse in the immediate lee, and decayingwith increasing downwind distance (x). On one day ofmeasurements, however, the pressure gradient over2 x/H 6 (H = windbreak height) resembled theleeward plateau identified by Wang and Taklein their numerical studies. Perhaps thisoccasional feature was only due to instrumenterror. Nevertheless a plateau of sorts wasindicated in similar measurements by Judd andPrendergast (with H = 1.92 m, z 0 1.2 cm;H/z 0 160, k r 3). Therefore,existence of a leeward pressure plateau behind athin fence cannot be definitely ruled out.When the windbreak was placed in a canopy, minimumsurface pressure was displaced downwind. Thisagrees with the wind-tunnel study of Judd, Raupach and Finnigan,and is consistent with a simple simulation reported here.  相似文献   

12.
A numerical model of airflow above changes in surface roughness and thermal conditions is extended to include cases with stable thermal stratification within the internal boundary-layer. The model uses a mixing-length approach with empirical forms for M and H.Results are presented for some basic cases and an attempt is then made to compare results given by the model with the experimental results of Rider, Philip and Bradley. Tolerable agreement is achieved. The importance of roughness change and thermal stability effects in the diffusion of heat and moisture near a leading edge is emphasised.Notation A Refers to Taylor (1970) - B Businger-Dyer constant (= 16.0) in forms for M and H - C Constant in form for in stable case - c p Specific heat at constant pressure - E Scaled absolute humidity - g Acceleration due to gravity - H Upward vertical heat flux - H 0, H 1 Surface heat fluxes for x <0, x0 - H E Upward latent heat flux - k Von Kármán's constant (= 0.4) - K H K W Eddy transfer coefficients for heat and water vapour - L Monin-Obukhov length - L H Latent heat of evaporation for water - m Ratio of roughness lengths ( = z 1/z 0) - RPB Refers to Rider et al. (1964) - RL* Non-dimensional parameter (see Equations (9), (20a), (22a), (24a)) - R* Net radiation less ground heat flux (see Equations (15), (16)) - T Scaled temperature - T 1 Downstream scaled surface temperature - u 0 u 1(x) Surface friction velocities for x <0, x0 - U, W Horizontal and vertical mean velocities - x, z Horizontal and vertical co-ordinates - Z i Local roughness length - z 0, z i Roughness lengths for x < 0, x 0 - Temperature - 0, 1 Surface temperatures for x<0, x0 - E Non-dimensional absolute humidity gradient - H Non-dimensional temperature gradient of heat flux - M Non-dimensional wind shear - = M = H = E an assumption used in stable conditions - Air density - Absolute humidity - w Density of water - Kinematic shear stress - Logarithmic height scale (= ln(z+z 1)/z 1)  相似文献   

13.
In a recent paper, the author introduced a new viscous boundary layer, called the mesolayer, in turbulent shear flow. Its importance stems from its location between the inner and outer regions which are controlled by the law of the wall and Reynolds number similarity, respectively. This intrusion prevents the classical overlap assumption which appears to be fundamental in the derivation of the classical logarithmic behavior. The mesolayer has a thickness proportional to Taylor's microscale . This, and the analogy between the energy equation for the spectrum function of isotropic turbulence and the momentum equation for shear flow, suggest the existence of a similar region in wavenumber space with wavenumber k ~ -1. This mesoregion separates the inner region k ~ k s(where k s-1 and is the Kolmogorov length) and the outer region k k e(where k e -1 and l is the energy-containing eddy size) and again invalidates the overlap assumption which appears to be fundamental in the derivation of the classical k -5/3-behavior of the inertial subrange.Incorporation of the mesoregion into the argument leads to a new theory with k -5/3-behavior in two regions (-1 k k s) and (k e k -1) although with two different coefficients of proportionality (Kolmogorov constants). This leads to a wandering of the spectrum curve about the classical k -5/3 line similar to a wandering in turbulent shear flow about the logarithmic curve. This is clearly indicated by the data for the variation of the Kolmogorov constant.Other data support the new theory. In particular, the location of the point k mwhere the curve of the nonlinear energy-transfer function goes through zero shows agreement with the theory, i.e., k m-1.  相似文献   

14.
We present the first application of a multi-stage impactor to study volcanic particle emissions to the troposphere from Masaya volcano, Nicaragua. Concentrations of soluble SO4 2–,Cl–, F–, NO3 –, K+, Na+,NH4 +, Ca2+ and Mg2+ were determined in 11 size bins from 0.07 m to >25.5 m. The near-source size distributions showed major modes at 0.5m (SO4 2–, H+,NH4 +); 0.2 m and 5.0 m (Cl–) and 2.0–5.0 m(F–). K+ and Na+ mirrored the SO4 2– size-resolvedconcentrations closely, suggesting that these were transported primarily asK2SO4 and Na2SO4 in acidic solution, while Mg2+ andCa2+ presented modes in both <1 m and >1 m particles. Changes in relative humidity were studied by comparing daytime (transparent plume) and night-time (condensed plume) results. Enhanced particle growth rates were observed in the night-time plume as well as preferential scavenging of soluble gases, such as HCl, by condensed water. Neutralisation of the acidic aerosol by background ammonia was observed at the crater rim and to a greater extent approximately 15 km downwind of the active crater. We report measurements of re-suspended near-source volcanic dust, which may form a component of the plume downwind. Elevated levels ofSO4 2–, Cl–, F–,H+, Na+, K+ and Mg2+ were observed around the 10 m particle diameter in this dust. The volcanic SO4 2– flux leaving the craterwas 0.07 kg s–1.  相似文献   

15.
Summary The integral aerosol optical depths (k ) at the hour of 08:20 Local Standard Time (LST), are compared with those calculated previously at 11:20 and 14:20 LST, for clear days during summer in Athens over the period 1962–1988. The mean values at 08:20 LST were consistently lower than the values at 11:20 and 14:20 LST. The influence of the vertical wind profile on the values ofk was also investigated. A comparison was made of the wind profiles at 02:00 and 14:00 LST, for days in which the 11:20 and 14:20 LST values ofk were 0.200 andk 0.350, respectively. The corresponding bulk wind shear s was also found for the period 1980–1988. The most significant results occurred with the first category of days. The resultant wind velocities from the surface to the 900 hPa level, in each hour were higher by 2–4 m·s–1 with respect to the corresponding values for the second category. At 02:00 LST the bulk wind shear showed a considerable difference (1.8) between the two categories of days in the surface to 700 hPa layer at 02:00 LST. Finally, the associated weather conditions that appear to initiate a period of low values ofk (k 0.200) at 11:20 and 14:20 LST were examined for the period 1980–1988. Fifteen such cases were identified and it was found that they all occurred after the passage of weak cold fronts.With 6 Figures  相似文献   

16.
The impact of urbanization is assessed by comparing values of the radiation parameters at an urban location with those of a rural site. Urban Delhi was divided according to land-use and the effects of urbanization was studied on incoming short-wave (K), albedo, incoming longwave (L, outgoing longwave (L), and net radiation (Q *), were individually studied at four representative sites (Rural, Commercial, Residential and Industrial). MaximumK was observed in the rural and commercial areas whereas highL was observed in the commercial and industrial locations. High depletion ofK of the order of 13% was observed for the industrial location in the winter season. An increase ofL in, the industrial location is of the same order as that of the commercial location, i.e. 20%. The residential location shows quite moderate (4.6%) depletion ofK in comparison with other sites.Nomenclature U Urban - R Rural - K Incoming Short-wave radiation - L Incoming Long-wave radiation - L Outgoing Long-wave radiation - Q * Net Radiation - Albedo - K * Net Short-wave radiation - L * Net Long-wave radiation  相似文献   

17.
Summary An analysis of the report of the (U.S.) National Academy of Sciences (NAS) on atmospheric effects of a nuclear exchange leads to conclusions that differ from those of the NAS and of the earlier TTAPS and AMBIO studies. Any cooling of the earth's surface is likely to beshort-lived because of rapid removal of the smoke clouds originating from nuclear burst-initiated fires, andminor because of appreciable green-house effects due to several distinct physical causes. (One of these, neglected in prior analyses, is the infrared absorption from cirrus clouds produced directly by the nuclear bursts.) Taken together, these effects may even induce slight surface warming (nuclear summer) instead of cooling (nuclear winter). The consequences to atmospheric ozone are similarly ambiguous; depending on the detailed nuclear scenario, the net ozone content may increase-rather than decrease as argued by TTAPS. Experiments could settle some uncertainties.With 2 Figures  相似文献   

18.
Analytical solutions for the Ekman layer   总被引：1，自引：0，他引：1  
The PBL equation that governs the transition from the constant-stress surface layer to the geostrophic wind in a neutrally stratified atmosphere for which the eddy viscosityK(z) is assumed to vary smoothly from the surface-layer value U *z (0.4,U *=friction velocity,z=elevation) to the geostrophic asymptoteK GU *d forzd is solved through an expansion in fd/U *1 (f=Coriolis parameter). The resulting solution is separated into Ekman's constant-K solution an inner component that reduces to the classical logarithmic form forzd and isO() relative to the Ekman component forzd. The approximationKU *d is supported by the solution of Nee and Kovasznay's phenomenological transport equation forK(z), which yieldsK–U *d exp(–z/d), where is an empirical constant for which observation implies, 1. The parametersA andB in Kazanskii and Monin's similarity relation forG/U * (G=geostrophic velocity) are determined as functions of . The predicted values ofG/U * and the turning angle are in agreement with the observed values for the Leipzig wind profile. The predicted value ofB based on the assumption of asymptotically constantK is 4.5, while that based on the Nee-Kovasznay model is 5.1; these compare with the observed value of 4.7 for the Leipzig profile. A thermal wind correction, an asymptotic solution for arbitraryK(z) and 1, and an exact (unrestricted ) solution forK(z)=U *d[1–exp(–z/d)] are developed in appendices.  相似文献   

19.
A previously published technique for using tethered spherical balloons as anemometers for measuring light low-level winds has been further developed. Earlier data on the relationship between the aerodynamic drag coefficient and the Reynolds number of spherical rubber balloons were combined with a large number of new data and re-analysed; and the errors in the relationship were estimated. The results allowed a more accurate calculation of wind speed from the deflection of a tethered balloon from the vertical. When combined with a new technique for calculating the effects of the tether, this enabled light to moderate low-level winds at fixed heights up to 600 m or more to be measured with simple, cheap, and readily mobile equipment; and a slight modification of the technique allowed measurement of winds in and above fog. Wind speeds measured by the ballon technique showed reasonably good agreement with measurements by an anemometer carried beneath the balloon.Glossary of Symbols a, b, c Coefficients in the relationship between lnC d and lnR - A Quantity under square root in solution for lnV whena0 - C d Wind drag coefficient for balloon - C dc Value ofC d given by calibration curve of Table I - D Dynamic wind pressure force on balloon - F Buoyant free lift of balloon with load - Re Reynold's number of balloon (sphere) - R = Re/105 - r Radius of sphere - T Tension in tether - V Wind speed - 83() =(lnC dc -lnC d ) when 83° , or 0 for other - Error in lnC d - Elevation of tether where attached to balloon - Elevation of balloon from ground tether point - Molecular viscosity of air - Ratio of circumference to diameter of circle - Density of air  相似文献   

20.
Summary A radiative transfer model has been used to determine the large scale effective 6.6 GHz and 37 GHz optical depths of the vegetation cover. Knowledge of the vegetation optical depth is important for satellite-based large scale soil moisture monitoring using microwave radiometry. The study is based on actual observed large scale surface soil moisture data and observed dual polarization 6.6 and 37 GHz Nimbus/SMMR brightness temperatures over a 3-year period. The derived optical depths have been compared with microwave polarization differences and polarization ratios in both frequencies and with Normalized Difference Vegetation Index (NDVI) values from NOAA/AVHRR. A synergistic approach to derive surface soil emissivity from satellite observed brightness temperatures by inverse modelling is described. This approach improves the relationship between satellite derived surface emissivity and large scale top soil moisture fromR 2=0.45 (no correction for vegetation) toR 2=0.72 (after correction for vegetation). This study also confirms the relationship between the microwave-based MPDI and NDVI earlier described and explained in the literature.List of Symbols f frequency [Hz] - f i(p) fractional absorption at polarizationp - h surface roughness - h h cos2 - H horizontal polarization - n i complex index of refraction - p polarization (H orV) - R s microwave surface reflectivity - T B(p) brightness temperature at polarizationp - T * normalized brightness temperature - T polarization difference (T v-T H) - T s temperature of soil surface - T c temperature of canopy - T max daily maximum air temperature - T min daily minimum air temperature - V vertical polarization - soil moisture distribution factor; also used for the constant to partition the influence of bound and free water components to the dielectric constant of the mixture - empirical complex constant related to soil texture - microwave transmissivity of vegetation (=e –) - * effective transmissivity of vegetation (assuming =0) - microwave emissivity - s emissivity of smooth soil surface - rs emissivity of rough soil surface - vs emissivity of vegetated surface - soil moisture content (% vol.) - K dielectric constant [F·m–1] - K fw dielectric constant of free water [F·m–1] - K ss dielectric constant of soil solids [F·m–1] - K m dielectric constant of mixture [F·m–1] - K o permittivity of free space [8.854·10–12 F·m–1] - high frequency limit ofK wf [F·m–1] - wavelength [m] - incidence angle [degrees from nadir] - polarization ratio (T H/T V) - b soil bulk density [gr·cm–3] - s soil particle density [gr·cm–3] - R surface reflectivity in red portion of spectrum - NIR surface reflectivity in near infrared portion of spectrum - eff effective conductivity of soil extract [mS·cm–1] - vegetation optical depth - 6.6 vegetation optical depth at 6.6 GHz - 37 vegetation optical depth at 37 GHz - * effective vegetation optical depth (assuming =0) - single scattering albedo of vegetation With 12 Figures  相似文献   

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