首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
Mean atmospheric circulation, moisture budget and net heat exchange were studied during a pre-monsoon period (18th March to 3rd May, 1988), making use of the data collected on board Akademik Korolev in the central equatorial and southern Arabian Sea region. The net heat exchange (R n ) is found to be about 20 W m–2 for a small area (0–4° N; 55–60° E), 50% less than the dimatological value. The mean value of net radiation (140 W m–2) is less than the climatological value, which was due to higher cloud amount. The higher SST enhanced both the latent and sensible heat fluxes.The mean atmospheric circulation obtained from the upper air data is quite convincing. The mean exchange coefficient (C e ) estimated from the moisture budget is about 1.0 × 10–3 for a wind speed of 4 m s–1. This value is slightly lower than that obtained by the usual methods.National Institute of Oceanography, RC, 52-Kirlampudi layout, Visakhapatnam — 530 023.India Meteorological Department, Gauhati.  相似文献   

2.
Using data collected during 1975–1976 from a meteorological network operating in the vicinity of the Columbia Generating Site approximately 8 km south of Portage, Wis., the influence of the Baraboo Hills on the surface wind field is determined. Half-hour means of wind speed and direction measured at 9 m at three sites were used to compute divergence and vorticity using Bellamy's method. The data were grouped into 18 sectors each 20 deg wide and averages computed for each quantity. Results indicate that for wind directions perpendicular to the eastern edge of the Baraboo Hills, the surface (9m) wind field is significantly perturbed up to 4 km from the bluffs. The largest convergence of 2.1 × 10–4 s–1 occurs with 160 deg wind direction and the largest divergence of 1.2 × 10–4 s–1 with 290 deg wind direction. The maximum anticyclonic vorticity was 1.6 × 10–4 s–1 at 210 deg and the maximum cyclonic vorticity was 1.6 × 10–4 s–1 at 330 deg.  相似文献   

3.
Eddy correlation equipment was used to measure mass and energy fluxes over a soybean crop. A rapid response CO2 sensor, a drag anemometer, a Lyman-alpha hygrometer and a fine wire thermocouple were used to sense the fluctuating quantities.Diurnal fluxes of sensible heat, latent heat and CO2 were calculated from these data. Energy budget closure was obtained by summing the sensible and latent heat fluxes determined by eddy correlation which balanced the sum of net radiation and soil heat flux. Peak daytime CO2 fluxes were near 1.0 mg m–2 (ground area) s–1.The eddy correlation technique was also employed in this study to measure nocturnal CO2 fluxes caused by respiration from plants, soil, and roots. These CO2 fluxes ranged from - 0.1 to - 0.25 mg m–2s–1.From the data collected over mature soybeans, a relationship between CO2 flux and photosynthetically active radiation (PAR) was developed. The crop did not appear to be light-saturated at PAR flux densities < 1800 Ei m–2 s–1. The light compensation point was found to be about 160 Ei m–2 s–1.Published as Paper No. 7402, Journal Series, Nebraska Agricultural Experiment Station. The work reported here was conducted under Nebraska Agricultural Experiment Station Project 27-003 and Regional Research Project 11–33.Post-doctoral Research Associate, Professor and Professor, respectively. Center for Agricultural Meteorology and Climatology, Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, NE 68583-0728.  相似文献   

4.
A two-dimensional mesoscale model has been developed to simulate the air flow over the Gulf Stream area where typically large gradients in surface temperature exist in the winter. Numerical simulations show that the magnitude and the maximum height of the mesoscale circulation that develops downwind of the Gulf Stream depends on both the initial geostrophic wind and the large-scale moisture. As expected, a highly convective Planetary Boundary Layer (PBL) develops over this area and it was found that the Gulf Stream plays an important role in generating the strong upward heat fluxes causing a farther seaward penetration as cold air advection takes place. Numerical results agree well with the observed surface fluxes of momentum and heat and the mesoscale variation of vertical velocities obtained using Doppler Radars for a typical cold air outbreak. Precipitation pattern predicted by the numerical model is also in agreement with the observations during the Genesis of Atlantic Lows Experiment (GALE).List of Symbols u east-west velocity [m s–1] - v north-south velocity [m s–1] - vertical velocity in coordinate [m s–1] - w vertical velocity inz coordinate [m s–1] - gq potential temperature [K] - q moisture [kg kg–1] - scaled pressure [J kg–1 K–1] - U g the east-south component of geostrophic wind [m s–1] - V g the north-south component of geostrophic wind [m s–1] - vertical coordinate following terrain - x east-west spatial coordinate [m] - y north-south spatial coordinate [m] - z vertical spatial coordinate [m] - t time coordinate [s] - g gravity [m2 s–1] - E terrain height [m] - H total height considered in the model [m] - q s saturated moisture [kg kg–1] - p pressure [mb] - p 00 reference pressure [mb] - P precipitation [kg m–2] - vertical lapse rate for potential temperature [K km–1] - L latent heat of condensation [J kg–1] - C p specific heat at constant pressure [J kg–1 K–1] - R gas constant for dry air [J kg–1 K–1] - R v gas constant for water vapor [J kg–1 K–1] - f Coriolis parameter (2 sin ) [s–1] - angular velocity of the earth [s–1] - latitude [o] - K H horizontal eddy exchange coefficient [m2 s–1] - t integration time interval [s] - x grid interval distance inx coordinate [m] - y grid interval distance iny coordinate [m] - adjustable coefficient inK H - subgrid momentum flux [m2 s–2] - subgrid potential temperature flux [m K s–1] - subgrid moisture flux [m kg kg–1 s–1] - u * friction velocity [m s–1] - * subgrid flux temperature [K] - q * subgrid flux moisture [kg kg–1] - w * subgrid convective velocity [m s–1] - z 0 surface roughness [m] - L Monin stability length [m] - s surface potential temperature [K] - k von Karman's constant (0.4) - v air kinematic viscosity coefficient [m2 s–1] - K M subgrid vertical eddy exchange coefficient for momentum [m2 s–1] - K subgrid vertical eddy exchange coefficient for heat [m2 s–1] - K q subgrid vertical eddy exchange coefficient for moisture [m2 s–1] - z i the height of PBL [m] - h s the height of surface layer [m]  相似文献   

5.
Turbulent dispersion of spores was studied near a source located inside a wheat canopy. Two colors of Lycopodium spores were released simultaneously at a steady rate from line sources at two heights (0.4–0.5 m and 0.7–0.8 m) in a 0.8 to 1.0 m tall crop. The number of spores of each color released was estimated by weighing the sources before and after each release. Aerial spore concentrations were measured at 2 and 4 m downwind of the sources using rotorods placed at four heights above the canopy and small suction traps at two heights inside the canopy. Concentrations near the ground were estimated from deposits on sticky glass microscope slides placed on the ground. Experiments were conducted on six different days. Friction velocities ranged from about 0.3 to 0.5 m s–1. The average horizontal fluxes of spores were calculated as the product of the observed concentrations and average wind speeds. At a distance of 2 m downwind from the sources, more than 16 to 44% of the flux of spores released from the lower source and more than 41 to 50% of the flux of spores released from the upper source were estimated to be above the canopy. These fluxes were compared with fluxes calculated using both a K-theory model and a random-flight-fluid-parcel-trajectory simulation model. The fluxes predicted by the models were generally considerably less than the values determined experimentally.  相似文献   

6.
Heat transfer was studied between intact leaves of various sizes and shapes in vivo under free and forced air conditions. Use of a wind tunnel and a microwave transmitter to heat the leaves facilitated measurements of convective, along with radiative and evaporative, heat losses from plant leaves. Knowledge of input energy, analysis of cooling curves, and established formulae, respectively, formed the basis of the steady-state, unsteady-state, and analytical methods for the determination of heat transfer coefficients.Typical values of steady-state free convection coefficients for Peperomia obtusifolia varied from 1.5 × 10–4 to 1.9 × 10–4 cal cm–2 s–1 C–1 as the temperature difference was increased from 5.9 to 9.6°C, whereas the forced convection coefficient was found to be 4.2 × 10–4 cal cm–2 s–1 C–1 at 122 cm s–1 wind velocity. For egg-plant, this value was about 9 × 10–4 cal cm–2 s–1 C–1 at 488 cm s–1 wind velocity. Convection coefficients as determined under steady-state conditions are compared with those of the unsteady-state and with analytical values for a single leaf and leaves of three different plants. In general, experimental values were found to be higher than the analytical ones.  相似文献   

7.
Line-averaged measurements of the structure parameter of refractive index (C n 2 ) were made using a semiconductor laser diode scintillometer above two markedly different surfaces during hours of positive net radiation. The underlying vegetation comprised in the first instance a horizontally homogeneous, pasture sward well-supplied with water, and in the second experiment, a sparse thyme canopy in a semi-arid environment. Atmospheric stability ranged between near neutral and strongly unstable (–20). The temperature structure parameterC T 2 computed from the optical measurements over four decades from 0.001 to 2 K2 m–2/3 agreed to within 5% of those determined from temperature spectra in the inertial sub-range of frequencies. Spectra were obtained from a single fine thermocouple sensor positioned near the midway position of the 100m optical path and at the beam propagation height (1.5m).With the inclusion of cup anemometer measurements, rule-of-thumb assumptions about surface roughness, and Monin-Obukhov similarity theory, path-averaged optical scintillations allow calculation of surface fluxes of sensible heat and momentum via a simple iterative procedure. Excellent agreement was obtained between these fluxes and those measured directly by eddy correlation. For sensible heat, agreement was on average close to perfect over a measured range of 0 to 500 W m–2 with a residual standard deviation of 30 W m–2. Friction velocities agreed within 2% over the range 0–0.9 m s–1 (residual standard deviation of 0.06 m s–1). The results markedly increase the range of validation obtained in previous field experiments. The potential of this scintillation technique and its theoretical foundation are briefly discussed.  相似文献   

8.
The kinetics of the aqueous phase reactions of NO3 radicals with HCOOH/HCOO– and CH3COOH/CH3COO– have been investigated using a laser photolysis/long-path laser absorption technique. NO3 was produced via excimer laser photolysis of peroxodisulfate anions (S2O 8 2– ) at 351 nm followed by the reactions of sulfate radicals (SO 4 – ) with excess nitrate. The time-resolved detection of NO3 was achieved by long-path laser absorption at 632.8 nm. For the reactions of NO3 with formic acid (1) and formate (2) rate coefficients ofk 1=(3.3±1.0)×105 l mol–1 s–1 andk 2=(5.0±0.4)×107 l mol–1 s–1 were found atT=298 K andI=0.19 mol/l. The following Arrhenius expressions were derived:k 1(T)=(3.4±0.3)×1010 exp[–(3400±600)/T] l mol–1 s–1 andk 2(T)=(8.2±0.8)×1010 exp[–(2200±700)/T] l mol–1 s–1. The rate coefficients for the reactions of NO3 with acetic acid (3) and acetate (4) atT=298 K andI=0.19 mol/l were determined as:k 3=(1.3±0.3)×104 l mol–1 s–1 andk 4=(2.3±0.4)×106 l mol–1 s–1. The temperature dependences for these reactions are described by:k 3(T)=(4.9±0.5)×109 exp[–(3800±700)/T] l mol–1 s–1 andk 4(T)=(1.0±0.2)×1012 exp[–(3800±1200)/T] l mol–1 s–1. The differences in reactivity of the anions HCOO– and CH3COO– compared to their corresponding acids HCOOH and CH3COOH are explained by the higher reactivity of NO3 in charge transfer processes compared to H atom abstraction. From a comparison of NO3 reactions with various droplets constituents it is concluded that the reaction of NO3 with HCOO– may present a dominant loss reaction of NO3 in atmospheric droplets.  相似文献   

9.
Although the bulk aerodynamic transfer coefficients for sensible (C H ) and latent (C E ) heat over snow and sea ice surfaces are necessary for accurately modeling the surface energy budget, they have been measured rarely. This paper, therefore, presents a theoretical model that predicts neutral-stability values of C H and C E as functions of the wind speed and a surface roughness parameter. The crux of the model is establishing the interfacial sublayer profiles of the scalars, temperature and water vapor, over aerodynamically smooth and rough surfaces on the basis of a surface-renewal model in which turbulent eddies continually scour the surface, transferring scalar contaminants across the interface by molecular diffusion. Matching these interfacial sublayer profiles with the semi-logarithmic inertial sublayer profiles yields the roughness lengths for temperature and water vapor. When coupled with a model for the drag coefficient over snow and sea ice based on actual measurements, these roughness lengths lead to the transfer coefficients. C E is always a few percent larger than CH. Both decrease monotonically with increasing wind speed for speeds above 1 m s–1, and both increase at all wind speeds as the surface gets rougher. Both, nevertheless, are almost always between 1.0 × 10–3 and 1.5 × 10–3.  相似文献   

10.
On the cool skin of the ocean   总被引：1，自引：0，他引：1  
Previous data relating sea-surface temperature to heat flux across the air-sea interface were reanalyzed with a common formula for the wind-stress coefficient. An expression is proposed for the nondimensional thickness of the thermal sublayer: the expression increases with wind velocity at light winds and has a value of 7 when the wind velocity reaches 7 m s–1.  相似文献   

11.
An experimental micrometeorological set-up was established at the CARBOEURO-FLUX site in Tharandt, Germany, to measure all relevant variables for the calculation of the vertical and horizontal advective fluxes of carbon dioxide. The set-up includes two auxiliary towers to measure horizontal and vertical CO2 and H2O gradients through the canopy, and to make ultrasonic wind measurements in the trunk space. In combination with the long-term flux tower an approximately even-sided prism with a typical side-length of 50 m was established. It is shown that under stable (nighttime) conditions the mean advective fluxes have magnitudes on the same order as the daily eddy covariance (EC) flux, which implies that they play a significant, but not yet fully understood, role in the carbon budget equation. The two advective fluxes are opposite and seem to cancel each other at night (at least for these measurements). During the day, vertical advection tends to zero, while horizontal advection is still present implying a flow of CO2 out of the control volume. From our measurements, a mean daily gain of 2.2 gC m–2 d–1 for the horizontal advection and a mean daily loss of 2.5 gC m–2d–1 for the vertical advection is calculated for a period of 20 days. However the large scatter of the advective fluxes has to be further investigated. It is not clear yet whether the large variability is natural or due to measurement errors and conceptual deficiencies of the experiment. Similar results are found in the few comparable studies.  相似文献   

12.
For the first time, the exchange coefficient of heat CH has been estimated from eddy correlation of velocity and virtual temperature fluctuations using sonic anemometer measurements made at low wind speeds over the monsoon land atJodhpur (26°18' N, 73°04' E), a semi arid station. It shows strong dependence on wind speed, increasing rapidly with decreasing wind speed, and scales according to a power law CH = 0.025U10 -0.7 (where U10 is the mean wind speed at 10-m height). A similar but more rapid increase in the drag coefficient CDhas already been reported in an earlier study. Low winds (<4 m s-1) are associated with both near neutral and strong unstable situations. It is noted that CH increases with increasing instability. The present observations best describe a low wind convective regime as revealed in the scaling behaviour of drag, sensible heat flux and the non-dimensional temperature gradient. Neutral drag and heat cofficients,corrected using Monin–Obukhov (M–O) theory, show a more uniform behaviour at low wind speeds in convective conditions, when compared with the observed coefficients discussed in a coming paper.At low wind convective conditions, M-O theory is unable to capture the observed linear dependence of drag on wind speed, unlike during forced convections. The non-dimensional shear inferred from the present data shows noticeable deviations from Businger's formulation, a forced convection similarity. Heat flux is insensitive to drag associated with weak winds superposed on true free convection. With heat flux as the primary variable, definition of new velocity scales leads to a new drag parameterization scheme at low wind speeds during convective conditionsdiscussed in a coming paper.  相似文献   

13.
Air-sea bulk transfer coefficients in diabatic conditions   总被引：13，自引：0，他引：13  
On the basis of recent data for the roughness Reynolds number of the sea surface, and using the Owen-Thomson theory on the transfers of heat and mass between a rough surface and the flow above it, the bulk transfer coefficients of the sea surface have been estimated. For a reference height of 10 m, the neutral-lapse transfer coefficient for water vapor is larger by only a few percent than that for sensible heat. When the wind speed at the 10-m height is u 10>3 m s–1, the coefficient for sensible heat C H is larger by about 10% than that for momentum C D . For u 10<5 m s–1, however, the value of C D exceeds the value of C H , and for u 10=15 m s–1 it is shown that C H 0.8C D . It may be also proposed that 103 C D =1.11 to 1.70, 103 C E =1.18 to 1.30, and 103 C H =1.15 to 1.26 for a range of u 10=4 to 20 m s–1. A plot of diabatic transfer coefficients versus wind speed is obtained by using a parameter of the sea-air temperature difference. For practical purposes, the coefficients are approximated by empirical formulae.  相似文献   

14.
An experimental study of sulfur and NOx fluxes over grassland   总被引：1，自引：0，他引：1  
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   

15.
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   

16.
A study to explain the emission of nitric oxide from a marsh soil   总被引：1，自引：0，他引：1  
In the period 18–21 September 1989, soil NO emission was studied at Halvergate Marshes, Norfolk (U.K.) within the framework of the BIATEX-LOVENOX joint field experiment. Using a dynamic chamber technique, 186 measurements at four plots were performed showing a net NO flux of 7.2–14.6×10–12 kgN m–2 s–1. Soil samples from a soil profile (1.0 m) at a representative site and from the uppermost layer (0.1 m) of each of the four plots were sent to the laboratory for (a) detailed physical and chemical soil analysis, (b) determination of NO production rates, NO uptake rate constants, and NO compensation mixing ratios, and (c) characterization of the microbial processes involved. A diffusive model (Galbally and Johansson, 1989) was applied to the laboratory results to infer NO fluxes of the individual soil samples. When we compared these fluxes with those measured in the field, we found agreement within a factor 2–4. Furthermore, laboratory studies showed, that NO was produced and consumed only in the upper soil layer (0–0.1 m depth) and that the NO production and consumption activities observed in the Halvergate marsh soil were most probably due to the anaerobic metabolism of denitrifying bacteria operating in anaerobic microniches within the generally aerobic soil.  相似文献   

17.
The purpose of this study was to develop a diffusion model for a continuous point source which takes into account the increase of wind speed with height, and to compare this model with short-range diffusion experiments. The main problem was to find a good expression for the vertical diffusion coefficient. It turned out that good agreement between theory and experiment could only be obtained by introducing a settling speed W for the tracer combined with a conventional expression for the vertical diffusion (K(Z) = K 0Z1−p). An empirical relation was found between K 0 and τ vU and between W and bar σ vU2.  相似文献   

18.
The hydrodynamic equations governing the water-level response of a lake to wind stress are inverted to determine wind stress from water-level fluctuations. In order to obtain a unique solution, the wind-stress field is represented in terms of a finite number of spatially dependent basis functions with time-dependent coefficients. The discretized version of the inverse equation is solved by a least-squares procedure to obtain the coefficients, and thereby the stress. The method is tested for several ideal cases with Lake Erie topography. Real water-level data is then used to determine hourly values of vector wind stress over Lake Erie for the period 5 May–31 October, 1979. Results are compared with measurements of wind speed and direction from buoys deployed in the lake. Calculated stress direction agrees with observed wind direction for wind speeds > 7.5 m s−1. Under neutral conditions, calculated drag coefficients increase with the wind speed from 1.53 × 10−3 for 7.5−10 m s−1 winds to 2.04 × 10−3 for 15−17.5 m s−1 winds. Drag coefficients are lower for stable conditions and higher for unstable conditions.  相似文献   

19.
Surface measurements of cloud condensation nuclei (CCN) number concentration (cm−3) are presented for unmodified marine air and for polluted air at Mace Head, for the years 1994 and 1995. The CCN number concentration active at 0.5% supersaturation is found to be approximately log-normal for marine and polluted air at the site. Values of geometric mean, median and arithmetic mean of CCN number concentration (cm−3) for marine air are in the range 124–135, 140–150 and 130–157 for the two years of data. Analysis of CCN number concentration for high wind speed, U, up to 20 m s−1 show enhanced CCN production for U in excess of about 10–12 m s−1. Approximately 7% increase in CCN per 1 m s−1 increase in wind speed is found, up to 17 m s−1. A relationship of the form log10CCN=a+bU is obtained for the periods March 1994 and January, February 1995 for marine air yielding values a of 1.70; 1.90 and b of 0.035 for both periods.  相似文献   

20.
A resistance model to calculate the deposition of cloud droplets on a coniferous forest and some improved parameterizations of the indispensable input parameters are described. The deposition model is adapted to the coniferous forest at the Kleiner Feldberg site and verified by the data of a drip water monitoring station below the forest canopy. The measurements of liqud water content, wind speed and trace substance compounds in cloud water of the Ground-based Cloud Experiment (GCE) at Kleiner Feldberg in 1990 are used to calculate the cloud water deposition fluxes and the deposition of trace substances via cloud water interception. The calculated deposition of trace substances via cloud water interceptions is three to six times higher than via rain during the experiment. On a long term data basis the yearly amount of cloud water deposition is 180 mm year–1 at Kleiner Feldberg site (840 m a.s.l.) while the precipitation amount is 1030 mm year–1. Due to higher trace substance concentrations in cloud water compared to rain the ionic deposition via cloud water interception and via precipitation were assessed to be of comparable magnitude.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号