Remote determination of momentum-flux profiles in the lower atmospheric boundary layer

An acoustic locator—a sodar—is a unique instrument for getting the objective characteristics of the current state of the atmospheric boundary layer (ABL) owing to a combination of such properties as remoteness, mobility, resolution, and information content. This study demonstrates the capabilities of a sodar to obtain data on the second moments of the field of wind-velocity fluctuations, in particular, the profiles of momentum flux in the lower ABL, which are very important in practical applications. A corresponding method is described, and the results of its experimental verification and some examples of its application under the conditions of different ABL stratification are presented.     

On the Development of Models for Height Profiles of the Wind Speed in the Atmospheric Surface Layer

The reliability of the known models of a height profile of the wind speed V(h) in the atmospheric boundary layer (ABL) and near-surface layer (NSL) is analyzed using the data of long-term ABL measurements accumulated in Russia in the state network of meteorological and aerological stations and the data of multilevel measurements at mast wind-measuring complexes. A new multilayer semiempirical model of V(h) is proposed which is based on aerodynamic and physical representations of the ABL vertical structure and relies on the hypothesis that wind-speed profiles providing the minimum wind friction on the ground and satisfying the conditions of profile smoothness are feasible in the ABL. This model ensures the best agreement with the data of meteorological, aerological, and mast wind measurements.     

Anomalous Decimeter Radio Noise from the Region of the Atmospheric Front: I. Characteristics of the Detected Radio Noise and Meteorological Parameters of the Frontal Cloudiness

An extraordinary experimental fact is presented and analyzed, namely, a rather intense broadband radio noise detected during the passage of an atmospheric front through the field of view of UHF antennas. Local atmospheric properties and possible sources of the extraordinary noise, including the thermal noise from cloudiness and extra-atmospheric sources, are considered. A conclusion is made about the presence of an additional nonthermal source of radio noise in the frontal cloudiness. According to the proposed hypothesis, these are multiple electric microdicharges on hydrometeors in the convective cloud.     

Simulation of the diurnal evolution of the atmospheric boundary layer

Results of simulating the diurnal evolution of the atmospheric boundary layer (ABL) with a second-order closure model are presented. The model includes new algebraic expressions for triple correlations to describe their behavior over the entire height of the mixed layer adequately to measurements. The model also takes into account the influence of long-wave radiation on the heat balance, which becomes important in the nocturnal ABL. The modeling results are compared with 24-h ABL evolution simulations by the third-order closure model and available in situ and laboratory measurements.     

Quantitative estimates of disturbances contributed by a megalopolis to the temperature field of the atmospheric boundary layer

Seasonal and diurnal variations in the temperature of the atmospheric boundary layer (ABL) are analyzed, and the features of spatial and temporal variations in ABL temperature that are caused by the influence of a megalopolis are revealed. The gradients of air temperature for the megalopolis, its vicinity, and background conditions are compared. A multiplicative model of the seasonal diurnal variability of ABL temperature is constructed, and the relative frequencies of unstable ABL-temperature stratification are studied.     

On Algebraic Perturbations in the Atmospheric Boundary Layer

Izvestiya, Atmospheric and Oceanic Physics - A simple model for the development of submesoscale perturbations in the atmospheric boundary layer (ABL) is proposed. The growth of perturbations is...     

Generating electric-discharge layers in mesoscale convective systems

A system of quasi-hydrodynamic equations for the electric field, charges, and concentrations of cloud particles and light aeroions in stratified regions of mesoscale convective systems is proposed and analyzed numerically in a one-dimensional approximation. The important role of Debye-charge layers, which are caused by light ions, is established. It is shown that, under certain aerodynamic conditions, both noninductive and inductive melting-related charging of particles may cause a narrow intense positive-charge layer to form near the zero-temperature isotherm; the altitude at which the vertical velocity component changes sign with respect to the height of the zero-temperature isotherm is of particular importance. When consideration is taken for an inductive charging mechanism and the real structure of the rising flow’s velocity, the distributions of charges and field strength (with a peak of about 100 kV/m), which describe the profiles observed in experiments, form in about 30 min. Taking into account the polarization of melting aggregates and water drops in an electric field when aeroions attach to them causes the rate of generating electric-charge layers to reduce. Thus, the solutions obtained in this study describe the structure and dynamics of spatially separated regions of electric charges in the stratified region and offer a satisfactory explanation for the experimental data. The results are important for explaining the abnormally high lightning activity of mesoscale convective systems, their role in initiating charges in the middle atmosphere, and maintaining the quasi-stationary state of the global electric circuit.     

On the effect that the direction of geostrophic wind has on turbulence and quasiordered large-scale structures in the atmospheric boundary layer

The dependence that the structure and intensity of turbulent and large-scale quasiordered eddies in the atmospheric boundary layer (ABL) have on the direction of geostrophic wind has been studied on the basis of a series of numerical experiments with a three-dimensional nonstationary model of high spatial resolution. The presence of the meridional component of the angular velocity of the Earth’s rotation results in a significant intensification of velocity fluctuations in a neutrally stratified turbulent flow during the easterly and northeasterly winds and in their decay during the westerly and southwesterly winds. This, in turn, results in significant variations in the mean velocity profile. It is shown that these variations are associated with the largest scale fluctuations and are comparable (in scale) to the depth of Ekman’s turbulent layer. It is found that, in the neutrally stratified ABL bounded in height and under stable stratification inside the ABL, the wind-direction dependence significantly decreases. The possibilities of parameterizing these effects in locally one-dimensional ABL models are discussed.     

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.     

On the vertical lifting of dust in a convective unstable atmospheric boundary layer

A model for the density Q of vertical mass flux of sand (dust) in the convective atmospheric boundary layer as a function of the number density N of convective elements (including vortices), friction velocity u _*, and vertical (turbulent) buoyancy flux B is proposed. It is shown that the flux Q is proportional to the product of the square root of B and the sixth power of u _*. This finding is consistent with empirical dependences Q(u _*) reported in the literature. We discuss two methods for experimentally determining density N when the lifting of dust occurs, mainly due to (terrestrial and Martian) dust devils.     

On conditions of initiation of electric discharges in the middle atmosphere

This work is devoted to a study of the conditions of initiation of two types of high-altitude discharges: sprites and halos. A quasi-electrostatic model of generation of the electric field in the middle atmosphere is developed; it takes into account the specific features of charge distribution and charge dynamics in the thundercloud, as well as real profile of the atmospheric conductivity. We take into consideration the nonlinear effects associated with the heating of electrons in the electric field. It is shown that the region where the electric field of the lightning flash exceeds the breakdown field is concentrated around an altitude of about 75 km, which is in agreement with the sprite observations. It is found that the dynamics of the current and discharge of the lightning flash plays a significant role in the initiation of high-altitude discharges in the atmosphere.     

Quantitative Study of Relationships of Hydrogen,Methane, Radon,and the Atmospheric Electric Field

Izvestiya, Atmospheric and Oceanic Physics - In this paper we develop a model representation of the relationships of hydrogen, methane, radon, and the atmospheric electric field based on the...     

Convective cloud fields in the Atlantic sector of the Arctic: Satellite and ground-based observations

Convective cloudiness in the Atlantic sector of the Arctic is considered as an atmospheric spatially self-organized convective field. Convective cloud development is usually studied as a local process reflecting the convective instability of the turbulent planetary boundary layer over a heated surface. The convective cloudiness has a different dynamical structure in high latitudes. Cloud development follows cold-air outbreaks into the areas with a relatively warm surface. As a result, the physical and morphological characteristics of clouds, such as the type of convective cloud, and their geographical localization are interrelated. It has been shown that marginal sea ice and coastal zones are the most frequently occupied by Cu hum, Cu med convective clouds, which are organized in convective rolls. Simultaneously, the open water marine areas are occupied by Cu cong, Cb, which are organized in convective cells. An intercomparison of cloud statistics using satellite data ISCCP and ground-based observations has revealed an inconsistency in the cloudiness trends in these data sources: convective cloudiness decreases in ISCCP data and increases in the groundbased observation data. In general, according to the stated hypothesis, the retreat of the sea-ice boundary may lead to an increase in the amount of convective clouds.     

Influence of a high aerosol concentration on the thermal structure of the atmospheric boundary layer

The influence of increased concentrations of submicron aerosol produced by forest fires on thermal characteristics of the atmospheric boundary layer (ABL) in Moscow and its remote vicinity (the town of Zvenigorod) are analyzed on the basis of regular remote measurements of the ABL temperature profile with the use of MTP-5 profilers. In the air basin of a large city, additional aerosol and accompanying pollutants in early morning hours (at small heights of the Sun) most frequently did not cause substantial changes in the ABL thermal structure. In the locality remote from the megalopolis (Zvenigorod), the atmospheric pollution by aerosol led to noticeable changes in the ABL thermal characteristics. Especially strong changes were observed in the daytime, during the maximum supply of solar radiation. In morning hours, the heating rate of the lower 100-m layer of the polluted air exceeded the heating rate of a relatively pure air by more than one degree. In higher layers, the differences between the rates of temperature changes in a relatively clean atmosphere and in an atmosphere polluted by aerosol (in the suburb) were insignificant.     

黄东海大气边界层高度时空变化特征

根据2006-2007年大连、青岛和台州逐日高分辨率L波段二次测风雷达探空资料、地面观测资料以及再分析资料,采用干绝热法和位温梯度法分别计算了各个台站的边界层高度,继而分析了黄东海边界层高度多时间尺度变化规律和空间演变特征.结果表明:(1)用清晨探空资料计算每日边界层高度,干绝热法比位温梯度法更为合理可靠;(2)沿海台站边界层高度有显著季节变化,夏季最低,秋季最高,这有别于陆地边界层普遍存在的夏季高、秋冬季节低的季节变化;(3)通过小波分析,发现边界层高度有显著的2～4 d天气尺度振荡和10～20 d准双周振荡;(4)黄东海上空海洋大气边界层在时间尺度上同样存在着明显的春夏季节低、秋冬季节高的季节变化特征,大部分海区空间上呈现西北低、东南高的分布形态.     

Organized Roll Circulation and Transport of Mineral Aerosols in the Atmospheric Boundary Layer

Izvestiya, Atmospheric and Oceanic Physics - An investigation into mesoscale roll circulation and its transport characteristics in the atmospheric boundary layer (ABL) is carried out. The case...     

Experience of Studying the Turbulent Structure of the Atmospheric Boundary Layer Using an Unmanned Aerial Vehicle

Izvestiya, Atmospheric and Oceanic Physics - The growing relevance of the use of unmanned aerial vehicles (UAVs) for studying turbulence in the atmospheric boundary layer (ABL) is associated with...     

Helicity and Turbulence in the Atmospheric Boundary Layer

Izvestiya, Atmospheric and Oceanic Physics - Helicity is inherent in many circulating motions and structures in the atmospheric boundary layer (ABL), where it is continuously reproduced due to the...     

Effect of an artificial cloud on the atmospheric electric field

Preliminary experimental data on the effect of an artificial steam-water cloud (SWC) on the atmospheric electric field are presented. The experiments were conducted on October 12, 2004, on the Kamchatka occurrence of thermal-power waters in the region of the active Mutnov power plant. The electric field strength was measured in the immediate vicinity of deep suspended geothermal wells opened during observations. The phenomenon of decreasing electric field strength during SWC existence is detected. Models are proposed and experimental results are discussed.     

Effects of hydrostatic approximation and resolution on the simulation of convective adjustment

A two-dimensional non-hydrostatic ocean model and a hydrostatic version of the same model are used to simulate convective adjustment, without the use of an instantaneous adjustment parameterization. The model geometry is a domain on the vertical plane of width 40 km and depth 500 m. Model results for four cases are examined: hydrostatic and non-hydrostatic, at 0.1 and 1 km spatial resolution. The convectively adjusted stable state obtained in all four cases are qualitatively similar; thus the hydrostatic approximation does not eliminate convective adjustment. The details of the simulated convective plumes depend on resolution and whether the hydrostatic approximation is made. The adjusted state has significant stratification which cannot be captured by the conventional instantaneous adjustment or diffusion-based parameterizations. We also compare the results to the case when an instantaneous adjustment parameterization is used.