Countergradient heat transfer in the atmospheric boundary layer over a rough surface

The nonlocality of the mechanism of turbulent heat transfer in the atmospheric boundary layer over a rough surface manifests itself in the form of bounded areas of countergradient heat transfer, which are diagnosed from analysis of balance items in the transport equation for the variance of temperature fluctuations and from calculation of the coefficients of turbulent momentum and heat transfer invoking the model of “gradient diffusion.” It is shown that countergradient heat transfer in local regions is caused by turbulent diffusion or by the term of the divergence of triple correlation in the balance equation for the temperature variance.     

Fine structure of the turbulent atmospheric boundary layer over the water surface

In this paper, the results of a laboratory experiment on investigating the wind-velocity field over a water surface using the PIV method are described. The use of a rapid CCD-camera made it possible to perform a detailed study of the eddy structure of airflow. We have measured the velocity fields over a flat plate by wind waves and waves induced by a wave generator. The model of a turbulent boundary layer over a rough surface was directly verified. It has been shown that the wind-velocity profiles over waves obtained by averaging the instantaneous fields over the ensemble of samples and horizontal coordinate are satisfactorily consistent with the profiles calculated within the frameworks of the model of wind flow over rough water surface.     

Three-parameter model of turbulence for the atmospheric boundary layer over an urbanized surface

A modified three-parameter model of turbulence for a thermally stratified atmospheric boundary layer (ABL) is presented. The model is based on tensor-invariant parametrizations for the pressure-strain and pressure-temperature correlations that are more complete than the parametrizations used in the Mellor-Yamada model of level 3.0. The turbulent momentum and heat fluxes are calculated with explicit algebraic models obtained with the aid of symbol algebra from the transport equations for momentum and heat fluxes in the approximation of weakly equilibrium turbulence. The turbulent transport of heat and momentum fluxes is assumed to be negligibly small in this approximation. The three-parameter E ? ε ? 2> model of thermally stratified turbulence is employed to obtain closed-form algebraic expressions for the fluxes. A computational test of a 24-h ABL evolution is implemented for an idealized two-dimensional region. Comparison of the computed results with the available observational data and other numerical models shows that the proposed model is able to reproduce both the most important structural features of the turbulence in an urban canopy layer near the urbanized ABL surface and the effect of urban roughness on a global structure of the fields of wind and temperature over a city. The results of the computational test for the new model indicate that the motion of air in the urban canopy layer is strongly influenced by mechanical factors (buildings) and thermal stratification.     

The wind-field structure in a stably stratified atmospheric boundary layer over a rough surface

Both wind turning with height and ageostrophic flow in a stably stratified atmospheric boundary layer are analyzed using a three-parameter turbulence model. For a quasi-steady state of the boundary layer, the cross-isobaric flow is determined only by turbulent stress at the surface in the direction of geostrophic wind. The “operative” prediction models, in which the first-order turbulence closure schemes are used, tend to overestimate the boundary-layer depth and underestimate the angle between the surface and geostrophic winds when compared to “research” models (schemes of high-level turbulence closure). The true value of the angle between the surface and geostrophic winds is significant for the presentation of a large-scale flow. A nocturnal low-level jet is a mesoscale phenomenon reflected in data obtained from measurements in a stably stratified atmospheric boundary layer. It is found that such jets are of great importance in transporting humidity, momentum, and air pollution. In this study, the difference between jet flows over a homogeneous underlying surface and over a spatially localized large-scale aerodynamic roughness is shown.     

Wind wave breaking under the conditions of inhomogeneous currents and of the atmospheric boundary layer

As known fromin situ observations, inhomogeneities of flows and of the atmospheric boundary layer produce variations of the intensity of wind wave breaking. A relevant phenomenological model is suggested here, describingin situ data on the breaking of waves in the presence of internal waves. The response of the wave breaking to the flow's inhomogeneity enhances with the growth of its spatial or temporal scale. For the mesoscale (10–100 km) inhomogeneities, the model is essentially simplified—wave breakings depict the local energy inputs to wind waves. The model allows us to compute currents of various type in the wave breaking intensity field. The results may have practical implications, in terms of remote sensing of the ocean. Translated by Vladimir A. Puchkin.     

Dimethyl sulfide in the atmospheric surface layer of the Equatorial Pacific Ocean

This paper reports a case study of atmospheric stability effect on dimethyl sulfide(DMS) concentration in the air. Investigation includes model simulation and field measurements over the Pacific Ocean. DMS concentration in surface sea water and in the air were measured during a research cruise from Hawaii to Tahiti. The diurnal variation of air temperature over the sea surface differed from the diurnal cycle of sea surface temperature because of the high heat capacity of sea water. The diurnal cycle of average DMS concentration in the air was studied in relation to the atmospheric stability parameter and surface heat flux. All these parameters had minima at noon and maxima in the early morning. The correlation coefficient of the air DMS concentration with wind speed (at 15 m high) was 0. 64. The observed concentrations of DMS in the equatorial marine surface layer and their diurnal variability agree well with model simulations. The simulated results indicate that the amplitude of the cycle and the mean     

Methane, carbon monoxide, and carbon dioxide concentrations measured in the atmospheric surface layer over continental Russia in the TROICA experiments

The principal statistical regularities typical of the behaviors of the CH₄, CO, and CO₂ concentrations in the atmospheric surface layer over the continental Russian territory are revealed from the measurements performed in 1997–2004 along the Trans-Siberian Railroad from Moscow to Khabarovsk with a mobile laboratory. The data obtained under the conditions of the atmosphere free of anthropogenic pollutants are analyzed. For near-background conditions, the typical continental methane, carbon monoxide, and carbon dioxide concentrations and characteristic features of their large-scale spatial distributions and daily variations, including those caused by surface inversions, are determined. Variations in the concentrations of these trace gases over industrial regions are analyzed. Our results are compared to the data obtained at background stations of the world network of atmospheric monitoring and to the data of a numerical simulation.     

On two small-scale circulation mechanisms of fine-aerosol transport in the atmospheric surface layer

Small-scale processes are taken to mean the disturbances of the atmospheric basic background which are caused by the thermal inhomogeneity of the underlying surface and under which one can neglect the effects of both centripetal and Coriolis accelerations. Slight disturbances suggest the use of linearized hydrothermodynamic equations of a weakly compressible atmosphere. Two models are considered. In one of the models, circulation over a weakly sloping barchan is analyzed using a refined model of mountain—valley circulation (the well-known Prandtl model). The other model, which is a model of a thermal spot in a geostrophic flow, can conditionally be called “anticonvective.” This problem is solved using the method of universal functions for parabolic equations with variable coefficients.     

The vertical structure of the atmospheric boundary layer over the central Arctic Ocean

The tropopause height and the atmospheric boundarylayer （PBL） height as well as the variation of inversion layer above the floating ice surface are presented using GPS （global position system ） radiosonde sounding data and relevant data obtained by Chinas fourth arctic scientific expedition team over the central Arctic Ocean （86°-88°N, 144°-170°W） during the summer of 2010. The tropopause height is from 9.8 to 10.5 km, with a temperature range between -52.2 and -54.10C in the central Arctic Ocean. Two zones of maximum wind （over 12 m/s） are found in the wind profile, namely, low- and upper-level jets, located in the middle troposphere and the tropopause, respectively. The wind direction has a marked variation point in the two jets from the southeast to the southwest. The average PBL height determined by two methods is 341 and 453 m respectively. These two methods can both be used when the inversion layer is very low, but the results vary significantly when the inversion layer is very high. A significant logarithmic relationship exists between the PBL height and the inversion intensity, with a correlation coefficient of 0.66, indicating that the more intense the temperature inversion is, the lower the boundary layer will be. The observation results obviously differ from those of the third arctic expedition zone （800-85° N）. The PBL height and the inversion layer thickness are much lower than those at 870-88° N, but the inversion temperature is more intense, meaning a strong ice- atmosphere interaction in the sea near the North Pole. The PBL structure is related to the weather system and the sea ice concentration, which affects the observation station.     

Acoustic plane-wave scattering from a rough interface over an inhomogeneous transition fluid layer

Acoustic scattering of a plane wave incident upon a rough surface over a transition fluid layer within which both the density and sound speed vary with depth is considered. A theory based upon a boundary perturbation method has been applied to a typical seabed environment to study the power spectral density representing the energy distribution of the scattered field over the space. The effects of frequency and roughness properties, including the roughness height, spatial correlation, and power spectrum, on the power spectral density have been investigated. The results demonstrate that the power spectral density of the scattered field depends upon all the aforementioned parameters, particularly the correlation length and the power spectrum of the rough surface, a conclusion in distinct contrast to the results for the coherent field obtained in an earlier study. It was found that the constituents of the rough surface such as the correlation length and wavenumber spectrum dominate the angular distribution of the scattered energy. These results indicate that it is crucial to employ a suitable topological model in the study of rough seabed scattering.     

Variability of trace gases in the atmospheric surface layer from observations in the city of Moscow

The results of continuous minute measurements of the surface concentrations of ozone, nitric oxide, nitrogen dioxide, carbon monoxide, and sulfur dioxide during the 2002–2004 period at the environmental station of the Oboukhov Institute of Atmospheric Physics, Russian Academy of Sciences (IAP), and the Faculty of Geography, Moscow State University (MSU), are discussed. It is shown that the conditions of Moscow’s southwestern region remote from large local pollution sources reflect the general regularities of the variability of trace gases in an urban atmosphere. This is manifested in the mean annual value of the ratio NO/NO₂ (a little less than 1), decreased daylight values of O₃, increased values of the rest of the trace gases as compared to the background region, and the presence of a secondary nocturnal maximum in the diurnal cycle of O₃. The features of the annual and diurnal cycles of the concentrations of the substances under analysis are discussed. In the diurnal cycle of the primary products of combustion (NO and CO), an excess of the morning maximum (over the evening one) is observed during both warm and transition periods and higher values of the night maximum (as compared to the daylight one) are noted for summer. The temperature stratification properties determined from the MSU long-term acoustic sounding data serve as a possible cause for both of the effects revealed. The annual cycle of the concentration of surface ozone is characterized by the highest values for spring and summer. The annual cycles of NO, NO₂, CO, and SO₂ do not demonstrate any obvious seasonal regularities. A significant seasonal variation of the ratio NO/NO₂, which is associated with the oxidizing properties of the urban atmosphere, is revealed. The record high concentrations of trace gases in the atmosphere over Moscow are given, and the meteorological conditions for their accumulation are discussed.     

<Superscript>222</Superscript>Rn concentrations in the atmospheric surface layer over continental Russia from observations in TROICA experiments

Both space and time variations in the ²²²Rn concentration in the atmospheric surface layer over continental Russia were analyzed on the basis of data obtained in the Transcontinental Observations into the Chemistry of the Atmosphere (TROICA) experiments. The measurements were taken from a mobile laboratory which was part of a passenger train moving along the Trans-Siberian Railway from Moscow to Vladivostok. The factors that affect the spatial distribution of both daily and seasonal variations in the concentrations of ²²²Rn in the surface air were determined: atmospheric vertical stability, geological features of the area under study, and atmospheric precipitation. The influence of temperature inversions on the accumulation of ²²²Rn in the atmospheric surface layer was analyzed. The fluxes of ²²²Rn from the soil into the atmosphere were estimated for different regions of Russia.     

Characteristics of radiative heat transfer in the atmospheric surface layer from the results of direct measurements

Results of direct measurements of the long-wavelength (LW) radiative heat influx (RHI) in the atmospheric surface layer (ASL) are presented. These measurements were performed in August 2003 at the IAP RAS base in Tsimlyansk under the conditions of unstable and stable stratification during a weak wind and a cloudless sky and under nonsteady conditions during cumulus cloudiness in the daytime. The underlying surface was dry steppe with spars grass. The in situ RHI measurements were performed with an original optoacoustic receiver having a quasi-spherical angle of view at heights from 0.15 to 4 m. It is shown that the radiative heating in the ASL was many times the actual heating, especially during near-noon hours. In the daytime, the radiative heating attained its maximum at the heights of measurements 0.15–1 m and decreased with height. The radiative heating at these heights in the near-noon hours was on average about 20 K/h, attaining 60 K/h under a cloudless sky and a weak wind. Under inversion stratification, the radiative cooling usually exceeded the actual cooling, amounting on average from 0 to ?8 K/h and changing with height only slightly. Periods with close (in phase) fluctuations of the radiative and actual cooling, sometimes changing to heating, were observed during the night. Regression equations, showing a high correlation between the RHI values at the heights of measurements 0.5 and 1 m and the soil-air temperature differences at the height of measurements, are obtained for different heights. The diurnal mean RHI profiles are characterized by a heating on the order of several K/h in the lower part of the layer of measurements, which decreases with height and changes to cooling at heights of up to 4 m. A change in the effective radiation with height in the layer of measurements, which was obtained through the summation of RHI values at several heights, was significant, attaining on average ?25 W/m² in the near-noon hours and +10 W/m² in the evening hours. The nonradiative (turbulent) heat influx, obtained as the difference between the rates of actual and radiative temperature variations measured in situ, decreased the radiative heating in the daytime many times. The main sources of error in direct RHI measurements are estimated.     

Boltzmann-Jaynes variational method and the temperature distribution of thermals in the turbulent convective atmospheric surface layer

A statistical mechanism that explains the formation of probability distribution functions of thermals according to temperature fluctuations is considered. In the proposed approach based on the Boltzmann-Jaynes variational method, a statistical ensemble of convective thermals is characterized by a class of stationary probability densities that depend on temperature fluctuations. It is assumed that the probability density functions of this class may depend on the potential energy, as well as on the available potential energy. For a class of stationary probability density functions, the entropy functional is defined to be an analogue of the Boltzmann H-entropy. The equilibrium distributions of thermals according to temperature fluctuations correspond to the most probable distributions that yield a maximum of the entropy functional. The exponential and normal distributions of thermals according to temperature fluctuation that are constructed using the variational method quite adequately approximate field atmospheric observations, as well as the results of laboratory modeling.     

Eclipse effects in the atmospheric boundary layer

The influence of a solar eclipse on solar-radiation fluxes, meteorological parameters, turbulence characteristics, and vertical temperature profiles in the atmospheric boundary layer is analyzed. Air-temperature variations caused by an eclipse and time delays of these variations with respect to the onset of the total-eclipse phase in the atmospheric surface and boundary layers are determined. The influence of a solar eclipse on the turbulent kinetic energy, turbulent heat flux, and variance and spectral density of the power of air-temperature pulsations are estimated. Variations in aerosol parameters and concentrations of light ions during a total solar eclipse are discussed.     

On the effect of spray on the dynamics of the marine atmospheric surface layer in strong winds

A nonlinear analytical model of the near-water air layer is considered. In the model, the effect of spray droplets on turbulent exchange is taken into account through their effect on density stratification. To close the system of equations, a semiempirical turbulence theory in the Kolmogorov-Monin form is used. Unlike previous publications, we use an alternative closure scheme that seems more appropriate. A version is also proposed for generalizing the model to the case where heavy admixture particles (spray droplets) make a dominant contribution to the average density of a medium. This model allows a general analytical solution that, in principle, describes non-linear effects such as a decrease in the effective friction and “self-closure” of the heavy admixture in the near-surface layer because of turbulence suppression due to the strengthening of stratification stability. As the current data show, however, the intensity of spray production is probably insufficient to explain the recently discovered phenomenon of the aerodynamic-drag decrease (saturation) in storm winds.     

Comparative analysis of pollution of the surface atmospheric layer in such megalopolises as Moscow and Beijing

The results of simultaneous investigations of atmospheric aerosol in two large megalopolises—Moscow and Beijing—are presented. The purpose of these investigations was to compare parameters and reveal common characteristics of urban aerosols. Aerosol parameters were measured in the megalopolises simultaneously from October 23, 2007, through November 2, 2007. The mass concentrations of aerosols were measured continuously with a nephelometer (Mosscow) and discretely with the use of aspiration samplers according to the weight method (Moscow, Beijing). The number concentration and the particle size distribution function were determined with analyzers of the size spectrum in the interval 0.15–15.0 μm and were measured synchronously with sampling for elementary analysis. The elementary compositions of samples were determined by mass spectrometry, which made it possible to identify 60 chemical elements.     

Simulation of additive transport from the land surface on the basis of experimental data on heat transfer in the atmospheric surface layer

A method is proposed to study the transport of a passive additive in the atmospheric surface layer with the use of the atmospheric transfer function. This method makes it possible to estimate the spatial distribution of the concentration of a passive additive in the atmospheric surface layer from the additive’s surface source without experimentally determining the vertical profile of the transport coefficient or without resorting to various hypotheses for the character of its behavior. The transfer function, which contains the information on the wind-field structure, can be obtained from simple one-point measurements of surface-and air-temperature fluctuations and from subsequent spectral processing of the data. The effects of the wind-velocity profile and turbulence on the spatial distribution of additive concentration are assessed. This method allows one to simplify experiments during development and verification of the models of atmospheric diffusion. This method may also be useful in emergency situations to predict the propagation of hazardous additives.     

Boltzmann statistical theory and asymptotics of the temperature distribution of spontaneous jets in the convective atmospheric surface layer

An ensemble of convective thermals is distinguished from the surface layer of penetrative turbulent convection over a heated horizontally uniform surface. A statistical model of the ensemble of convective thermals is developed that uses the idea of entropy in the Boltzmann-Jaynes form. The distribution of thermals by potential energies is shown to display an entropy maximum. On the basis of the Boltzmann distribution by potential energies, the temperature distribution of spontaneous jets is obtained and found to be consistent with known experimental data.