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1.
The winter-time arctic atmospheric boundary layer was investigated with micrometeorological and SF6 tracer measurements collected in Prudhoe Bay, Alaska. The flat, snow-covered tundra surface at this site generates a very small (0.03 cm) surface roughness. The relatively warm maritime air mass originating over the nearby, partially frozen Beaufort Sea is cooled at the tundra surface resulting in strong (4 to 30 °C · (100 m)-1) temperature inversions with light winds and a persistent weak (1 to 2 °C · (100 m)-1) surface inversion with wind speeds up to 17 m s-1. The absence of any diurnal atmospheric stability pattern during the study was due to the very limited solar insolation. Vertical profiles were measured with a multi-level mast from 1 to 17 m and with a Doppler acoustic sounder from 60 to 450 m. With high wind speeds, stable layers below 17 m and above 300 m were typically separated by a layer of neutral stability. Turbulence statistics and spectra calculated at a height of 33 m are similar to measurements reported for non-arctic, open terrain sites and indicate that the production of turbulence is primarily due to wind shear. The distribution of wind direction recorded at 1 Hz was frequently non-Gaussian for 1-hr periods but was always Gaussian for 5-min periods. We also observed non-Gaussian hourly averaged crosswind concentration profiles and assume that they can be modeled by calculating sequential short-term concentrations, using the 5-min standard deviation of horizontal wind direction fluctuations () to estimate a horizontal dispersion coefficient (
y
), and constructing hourly concentrations by averaging the short-term results. Non-Gaussian hourly crosswind distributions are not unique to the arctic and can be observed at most field sites. A weak correlation between horizontal (
v
) and vertical (
w
) turbulence observed for both 1-hr and 5-min periods indicates that a single stability classification method is not sufficient to determine both vertical and horizontal dispersion at this site. An estimate of the vertical dispersion coefficient,
z
, could be based on or a stability classification parameter which includes vertical thermal and wind shear effects (e.g., Monin-Obukhov length, L). 相似文献
2.
The Langevin equation is used to derive the Markov equation for the vertical velocity of a fluid particle moving in turbulent flow. It is shown that if the Eulerian velocity variance
wE is not constant with height, there is an associated vertical pressure gradient which appears as a force-like term in the Markov equation. The correct form of the Markov equation is: w(t + t) = aw(t) + b
wE + (1 – a)T
L
(
wE
2)/z, where w(t) is the vertical velocity at time t, a random number from a Gaussian distribution with zero mean and unit variance, T
L the Lagrangian integral time scale for vertical velocity, a = exp(–t/T
L), and b = (1 – a
2)1/2. This equation can be used for inhomogeneous turbulence in which the mean wind speed,
wE and T
L vary with height. A two-dimensional numerical simulation shows that when this equation is used, an initially uniform distribution of tracer remains uniform. 相似文献
3.
Calculation of particle trajectories in the presence of a gradient in turbulent-velocity variance 总被引：1，自引：0，他引：1
Recent papers by Wilson et al. (1981b) and Legg and Raupach (1982) give methods for the calculation of particle trajectories in turbulence with a gradient in vertical velocity variance
2
w. However the two methods seem contradictory.This paper demonstrates that in systems in which l(d
w
/dz) (where / is the length scale) varies only slowly with height z, the two methods give similar predictions, and indicates why this is the case. For a particular system in which the restriction on l(d
w
/dz) is not satisfied, it is shown that neither method is correct but that a simple modification of the method of Wilson et al. (1981b) gives reasonable predictions. 相似文献
4.
It is shown that the ratio of standard deviation of lateral velocity to the friction velocity, /u
*, and therefore wind direction fluctuations, are sensitive to mesoscale terrain properties. Under neutral conditions, /u
* is almost 40% larger in rolling terrain than over a horizontal surface. In the lee of a low mountain, the fluctuations may be 2.5 times as strong as over horizontal terrain. In contrast, vertical velocity fluctuations are little influenced by mesoscale terrain features.Now with Air Weather Service, Offutt AFB, Omaha, Nebraska. 相似文献
5.
The characteristics of a Lyman-alpha humidiometer have been carefully examined in an air-conditioned test chamber. The results confirm that when carefully used, this humidiometer is suitable for measurements of turbulent humidity fluctuations. Measurements with a Lyman-alpha humidiometer were carried out in the surface boundary layer over the ocean. The relation between turbulent intensity (
a
= a
ov2) and the friction humidity (a
*) can be expressed as
a
= l.6a
*. The spectrum of turbulent humidity for wind speeds larger than 3 m s –1 conforms to the similarity law in the surface boundary layer. The spectrum has two characteristic normalized frequencies, namely, a higher peak and a secondary peak (or a shoulder). 相似文献
6.
Gary A. Briggs 《Boundary-Layer Meteorology》1982,23(4):489-502
Past work on analyzing ground-source diffusion data in terms of surface-layer similarity theory is reviewed; these analyses assume that
z
/L orh/L is a function of u
*
x/L (where h = Q/ dy). It is argued that an alternative scaling, h
*/L versus x/L, is nearly as universal in that it is very weakly influenced by surface roughness, except for a modest influence in the free convective case (h
* = Q/u
* dy); the advantage of this scaling is that it eliminates the need to reassess as vertical diffusion progresses. The Prairie Grass data set is adjusted for the difference in source and sampling heights, and is plotted with this scaling. Simple analytic equations are suggested that fit the resultant data plots for stable and unstable conditions, and suggestions are made towards practical application of these results.On assignment from the National Oceanic and Atmospheric Administration, U.S. Department of Commerce. 相似文献
7.
The variations of and in the drainage flow in the Brush Creek valley of western Colorado are investigated using data from Doppler acoustic sodars and instrumented towers. The data were obtained on two experimental nights during the 1984 ASCOT field study. There is good agreement between the variations derived from low-level observations of the sodars and those derived from the towers located throughout the valley. The observed hourly average and in the nocturnal drainage flow are about 20 ° to 25 ° and 5 °, respectively; these values are much larger than those generally observed over flat terrain during nighttime stable conditions. After sunrise (about 0600 MST), as the valley warms and the flow direction changes to up-valley, these parameters increase sharply to their peak values at about 0800 MST and then decrease to their normal daytime values after about two hours.In the drainage flow, the hourly average varies inversely with wind speed according to the relation
u 0.7ms-1. The vertical standard deviation is much less enhanced by complex terrain than the horizontal standard deviation. The observed values are predicted fairly well by the local similarity theory.Oak Ridge Associated Universities (ORAU) Summer Research Participant at ATDD in 1987 andOak Ridge Associated Universities (ORAU) Summer Research Participant at ATDD in 1987 and 相似文献
8.
P. J. Walklate 《Boundary-Layer Meteorology》1987,39(1-2):175-190
A random-walk model is presented for calculating the dispersion of heavy particles in a turbulent air flow when only air turbulence statistics and the drag characteristics of the particle are known. Algebraic expressions for the modification of air velocity variance 2 and Lagrangian autocorrelation tune-scale T
L,due to particle inertia effects, are derived. These expressions introduce only a very small computational overhead on the random-walk models for inertia-less particles of Wilson et al. (1983). Measurements of T
Land by Snyder and Lumley (1971) for four different particles are used to determine constants in the heavy-particle model. It is shown that the agreement between the model, for a single set of constants, and the dispersion measurements is good for the 47 m hollow glass, 87 m glass, and 47 m copper particles. The predictions for the 87 m corn pollen particles show less satisfactory agreement by underestimating dispersion measurements by 15% after 0.4s. Finally, some aspects of the model's application to spray dispersion in and above a crop canopy are considered. 相似文献
9.
Further laboratory studies of emission by O(1
S) and by O2
A
3
u
+
,A3
u
andc
1
u
–
in the oxygen afterglow lead to the conclusion that Barth's mechanism for the excitation of the auroral green line O
2
*
+O(3P=O2+O(1S)–(1) is correct and that levelsv=6 and 7 of O2
A
3
u
+
are Barth precursors. The value ofk
1=7×10–11 cm3 s–1 deduced for these levels is shown to be in fair agreement with atmospheric measurements. 相似文献
10.
An equation is derived for the components of the horizontal (turbulent) frictional force in the -coordinate system with special attention to mesometeorological flow models. The starting point is the horizontal equation of motion in its flux-form in the -system in which we replace (following Reynolds' procedure) the velocity components u,v and % MathType!MTEF!2!1!+- % feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGafq4WdmNbai % aaaaa!37B8! \[ \dot \sigma \] aswell as other relevant quantities by terms of the form u = + u,..., = ± + % MathType!MTEF!2!1!+- % feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGafq4WdmNbai % Gbauaaaaa!37C3! \[ \dot \sigma ' \] , etc. ( = time average of u; u = fluctuating part of u.) Next, the equation is averaged with respect to time and terms which we believe are small in mesometeorological flows, are neglected. On expressing by an appropriate expression that involves w, the result shows the appearance of two new terms which, have not been considered previously in the published literature. While the expression earlier used in the literature involved the -derivative of % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG1bGbauaaceWG3bGbauaaaaaaaa!380B!\[\overline {u'w'} \] alone, the new terms add the -derivatives of % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG1bGbauaadaahaaWcbeqaaiaaikdaaaaaaaaa!37EC!\[\overline {u'^2 } \] and % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG1bGbauaaceWG2bGbauaaaaaaaa!380A!\[\overline {u'v'} \] for the x-component of the force, and the -derivatives of % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG2bGbauaadaahaaWcbeqaaiaaikdaaaaaaaaa!37ED!\[\overline {v'^2 } \]} and % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG1bGbauaaceWG2bGbauaaaaaaaa!380A!\[\overline {u'v'} \] for the y-component, where and are the slopes of the -surfaces in the x- and y-directions, respectively. Further, a few numerical simulations of the sea-breeze over topography are carried out with and without the correction terms. It is shown that when corrections terms are not included the effective smoothing is stronger above the sloping regions and may amount to as high as 50 percent of the convergence with slopes of ~.04. The ìnclusìon of the new terms does not lead to any special computational difficulties and for that reason there is no compelling reason to neglect them, all the more so because, as is shown, the addition of the new terms results in a consistent apportioning of the degree of horizontal diffusion.On leave from CIMMS, Norman, OK.Now visiting Dept. of Met., Helsinki, Finland. 相似文献
11.
Lagrangian integral time scales were calculated from crosswind concentration distributions of oil-fog smoke released from a continuous point source over the ocean during stable atmospheric conditions assuming an exponential correlation function. Variance of the lateral velocity fluctuations,
v
2, and the energy dissipation rate, , were obtained from simultaneous Eulerian measurements at the beach. An Eulerian energy dissipation scale defined as
v
2/ was then computed. The ratio of the Lagrangian integral scale to the Eulerian energy dissipation scale was found to be close to 1. This ratio was also estimated to be 1 based on physical and dimensional considerations regarding the cascade of energy. Length scales for longitudinal, lateral and vertical directions were interpreted with a model based on similarity considerations applicable for over-water atmospheric flows.Authored under contract EY-76-C-02-0016 with the U.S. Department of Energy. Accordingly, the U.S. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes. 相似文献
12.
Comparisons between sensible heat flux measured using eddy correlation instrumentation and estimated using the temperature fluctuation method are presented for four types of surface in West Africa. Agreement between measured and estimated values is good. Regression of estimated on measured sensible heat flux gave a mean slope of 0.98 with a mean r
2 of 0.94 for bare soil, mature millet, fallow savannah and tiger bush. Estimates of heat flux from temperature fluctuations measured by an instrument mounted beneath a tethered balloon are also shown to be in close agreement with eddy correlation measurements made at the surface (regression slope = 0.98, r
2 = 0.84). The results provide evidence that the ratio /×is indeed a universal function of z/L for all the surface types considered. 相似文献
13.
The turbulent structure of the lake breeze penetration and subsequent development of the thermal internal boundary layer (TIBL) was observed using a kytoon-mounted ultrasonic anemometer-thermometer. The lake breeze penetrated with an upward rolling motion associated with the upward flow near the lake breeze front. After the lake breeze front passed, the behaviors of the velocity and temperature at the top of the lake breeze layer were similar to those found in convective boundary layers (CBL). Comparing gq/*,
u
/w
* and
w
/w
* between the present observation of TIBL development after the passage of the lake breeze front and CBL data from the literature, the /* values showed reasonable agreement; however,
u
/w
* and
w
/W* had smaller values in the TIBL than in the CBL at higher altitudes. This is due to the differences in the mean velocity profiles. While the CBL has a uniform velocity profile, the TIBL has a peak at lower elevation due to the lake breeze penetration; the velocity then decreases with height.Present address: The Institute of Behavioral Science, 1-35-7 Yoyogi, Tokyo 151, Japan. 相似文献
14.
The paper considers a puff diffusion in its inertial stage when particle separation obeys the laws of the inertial subrange and depends only on eddy energy dissipation rate . The can be determined in the surface layer by the turbulent kinetic energy equation. Similarity equations connect with diffusion measure .A simple analytical model has been deduced to estimate pollutants diffusion during calms. 相似文献
15.
Effects of heat and water vapor transport on eddy covariance measurement of CO2 fluxes 总被引：2，自引：0，他引：2
Flux densities of carbon dioxide were measured over an arid, vegetation-free surface by eddy covariance techniques and by a heat budget-profile method, in which CO2 concentration gradients were specified in terms of mixing ratios. This method showed negligible fluxes of CO2, consistent with the bareness of the experimental site, whereas the eddy covariance measurements indicated large downward fluxes of CO2. These apparently conflicting observations are in quantitative agreement with the results of a recent theory which predicts that whenever there are vertical fluxes of sensible or latent heat, a mean vertical velocity is developed. This velocity causes a mean vertical convective mass flux (=
cw for CO2, in standard notation). The eddy covariance technique neglects this mean convective flux and measures only the turbulent flux
c w. Thus, when the net flux of CO2 is zero, the eddy covariance method indicates an apparent flux which is equal and opposite to the mean convective flux, i.e.,
c w = –
c w. Corrections for the mean convective flux are particularly significant for CO2 because
cw and
c w are often of similar magnitude. The correct measurement of the net CO2 flux by eddy covariance techniques requires that the fluxes of sensible and latent heat be measured as well. 相似文献
16.
K. L. Davidson 《Boundary-Layer Meteorology》1974,6(1-2):305-331
Turbulence data obtained over ocean waves during the BOMEX experiment of 1969 are presented. Procedures in measurement and analyses are described which include adjustments for possible platform, R/V FLIP, motion. Momentum transfer is shown to have been influenced by both stability and wind-wave coupling. The wind-wave coupling influence is separated from the stability influence and is described in terms of a linear dependence of the deviation from the logarithmic profile on C/u
*, where C is the phase speed corresponding to the wave spectrum peak. As observed by others, a value of C/u
* near 25 is associated with minimal wind-wave coupling influence. For C/u
* greater than 25, momentum transfer is decreased relative to the neutral profile prediction. Expressions are also presented for the wind-wave coupling influence on relative intensities,
u
/u
*,
u
/u
* and
w/u
*. Values of the relative intensities approximate neutral overland values when the expressions are written such that the wave influence is zero near a C/u
* value of 25. 相似文献
17.
Y. Sadhuram 《Boundary-Layer Meteorology》1986,34(1-2):99-101
For an airport site near Visakhapatnam, India, and based on 10 years of data for the months of January, April, August and October, values of are given as a function of wind speed, wind direction and Pasquill diffusion category. 相似文献
18.
B. B. Hicks 《Boundary-Layer Meteorology》1978,15(2):255-258
Panofsky et al. (1977) have presented an analysis which seems to show a clear dependence of the dimensionless turbulence statistics
u
/u
* and v/u
* on the planetary boundary-layer stability parameter z
i/L. However it is possible that much of the apparent relationship results from artificial correlations introduced by the use of inter-related dimensionless parameters. Apparent dependencies of similar statistical quantities on z/L in the surface boundary layer might also be contaminated.This work was supported by the U.S. Department of Energy, and is a contribution of the Multistate Atmospheric Power Production Pollution Study (MAP3S). 相似文献
19.
Microwave vegetation optical depth and inverse modelling of soil emissivity using Nimbus/SMMR satellite observations 总被引：2，自引：0，他引：2
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
20.
Prof. S. Hastenrath 《Meteorology and Atmospheric Physics》1997,64(1-2):51-59
Summary During an expedition to the high Andes of Southern Peru in June–July 1977, measurements of direct solar radiation in four spectral bands (0.270–0.530–0.630–0.695–2.900 ) were conducted at six sites in elevations ranging from sea level to 5645 m. These measurements were evaluated in Langley plots to determine total optical depths () and irradiances at the top of the atmosphere. In addition, water vapor optical depths (wv) were calculated from the mean radiosounding over Lima during the expedition, and Rayleigh (ray) and ozone (oz) optical depths were obtained from published tabulations. Subtracting ray, oz, and wv from yielded estimates of aerosol optical depth aer. The components ray and oz decrease from the shorter towards the longer wavelength bands and from the lower towards the higher elevation sites; aer also decreases towards the higher elevations. Particularly pronounced is the decrease of aer and from the lowlands of the Pacific coast to the highlands of the interior, reflecting the effect of a persistent lower-tropospheric inversion and the contrast from the marine boundary layer to the clear atmosphere of the high Andes.With 4 Figures 相似文献