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Vol 54, No 6 (2018)
- Year: 2018
- Articles: 13
- URL: https://journals.rcsi.science/0001-4338/issue/view/8869
Article
Investigation into Variations of Wind Directions Near the Surface
Abstract
The results of a full-scale experiment carried out at the Obukhov Institute of Atmospheric Physics testing ground in Tsimlyansk in 2015 are described. The experiment included multipoint measurements of wind variations using 12 vanes arranged in a line across (and in some cases lengthwise) the wind directions. The correlation functions were used to calculate longitudinal and transversal correlation radii, which characterized, accordingly, the longitudinal and transversal dimensions of vortices in the airflow. The longitudinal radius was 1.8 times the transversal radius. The correlation radius dependence on the scale of Obukhov–Monin surface layer was obtained. The maxima of transversal correlation radius (about 20 m) were observed at daytime with great instability. At night they were a few times lower. Wind pulsation spectra depend on the thermal stratification and the mean wind velocity. The technique proposed in the paper allows studying the spatial structure of the direction field of the surface wind.
515-523
On the Local Structure of Two-Dimensional Turbulence
Abstract
Possible consequences of the application of the Kolmogorov theory of local isotropy to two-dimensional turbulence are discussed. In this regard, the cases of both freely decaying and stationary turbulence are considered. Formulae for the third-order structure functions in the inertial interval are obtained as the solutions of the Karman—Howarth equation with the use of the well-known relation between the velocity and vorticity correlators. These formulae differ from those given by other authors; that is, the variable term linear in space turns out to be negative in the corresponding formula, as in the three-dimensional case. The possible relation of the results to the form of the energy spectrum is briefly mentioned.
524-527
Dynamics of the Convective Rise of Thermals in the Atmosphere
Abstract
Exact and approximate relations have been obtained to describe the evolution of the following parameters of heated air parcels during their convective uplifting in the atmosphere: the altitude and temporal dependences of the speed of the parcel center, the parcel characteristic size (radius), and the excess relative temperature. Cases of moderate and strong heating have been considered. The original equations include relations for the rate of uplifting thermals, the mass of entrained cool air, and the complete integral of thermal buoyancy. It has been shown that during uplifting the radius of the heated air parcel increases, the excess temperature decreases, and the uplift rate varies nonmonotonically: first, it increases from zero and reaches a maximum; then it gradually decreases to zero. Numerical estimates for characteristic situations have been performed.
528-535
Generation of the Vortex Movement in the Atmosphere due to Gravity Inhomogeneities
Abstract
One possible mechanism for the effect of gravity-field inhomogeneities (GFIs) on the atmosphere dynamics has been investigated theoretically. It is shown that the vertical heat exchange in an air layer in an inhomogeneous gravity field can disrupt the state of hydrostatic equilibrium and lead to the generation of vortex flows. Estimates of the amplitude of velocity perturbations are made on the basis of a linear stationary hydrodynamic model that takes planetary rotation into account. The magnitude of the vortex component of the velocity can reach values on the order of the product of the buoyancy frequency and amplitude of the geoid deviations. The amplitude of the emerging vertical motions, in addition to the parameters mentioned, also depends on the intensity of the turbulent exchange and horizontal scales of the inhomogeneities.
536-541
Speed of Tropical Cyclone Motion in Field of Gravity Anomalies
Abstract
The dependence of the speed of tropical-cyclone motion on the values of gravity anomalies in the regions of cyclone action is studied. The regression dependence of the cyclone motion speed on the gravity anomalies is revealed. Calculations are performed for cyclonic zones of the northwestern Pacific and western Atlantic. Fields of vertical components of the gravity anomalies are considered.
542-544
Regional Photochemical Surface-Ozone Sources in Europe and Western Siberia
Abstract
The influence of climatically significant regional sources of NOx (=NO + NO2), CO, and biogenic volatile organic compounds (VOCs) on the photochemical generation of surface ozone (O3) in the lower troposphere over Europe and Siberia is studied. The sensitivity of the O3 field to the total emissions of ozone precursors is calculated using a global 3D chemical transport model (GEOS-Chem) based on the 2007–2012 databases for anthropogenic (EDGAR) and biogenic (MEGAN, GFED) emissions. The amount of photochemical ozone generated during the summer months is in good correlation with the air-mass age determined from the ratio between \({\text{N}}{{{\text{O}}}_{x}}\) and (total reactive nitrogen) \({\text{N}}{{{\text{O}}}_{y}},\) when the mean contribution of regional sources is \({\Delta\text{}}{{{\text{O}}}_{{\text{3}}}}\) ~ 10–15 ppb, which is 20–30% of its background concentration in the middle latitudes (\({{{\text{O}}}_{{\text{3}}}}\) ~ 35–45 ppb). The quantitative estimates of the ozone production efficiency \({{{\Delta\text{}}{{{\text{O}}}_{{\text{3}}}}} \mathord{\left/ {\vphantom {{{\Delta\text{}}{{{\text{O}}}_{{\text{3}}}}} \Delta }} \right. \kern-0em} \Delta }{\text{(N}}{{{\text{O}}}_{y}} - {\text{N}}{{{\text{O}}}_{x}}{\text{)}}\) (\({\text{N}}{{{\text{O}}}_{y}}\) is the total reactive nitrogen) for the summer months of the indicated period (~10–30 mol O3/mol NOx) are in good agreement with the theory of photochemical ozone generation under the conditions of slightly polluted air.
545-557
A Study of the Column Methane Short-Term Variability in the Atmosphere on a Regional Scale
Abstract
The short-term variability of the methane column has been analyzed based on ground-based observations and numerical modeling at the St. Petersburg NDACC station for 2009–2016. The methane variability for different atmospheric altitude layers is presented. Short-term methane variability is found to be significant compared to long-term trends. The results of numerical experiments with the global chemistry-transport model of the troposphere and stratosphere demonstrate that short-term methane variability is basically defined by methane concentration changes between an altitude of 5 km and 20 km.
558-569
Methane Fluxes Into Atmosphere from Fennoskandian Lakes
Abstract
The experimental data on methane fluxes into the atmosphere from Fennoscandian lakes is analyzed. The contribution made by the lake network of this northern region to the atmospheric methane budget is estimated as 320 ± 23 KtCH4 per year. From 16 to 37% of the annual methane emission from Fennoscandian lakes is carried out by methane produced during the ice cover period. The methane fluxe rate from studied lakes is estimated as 2.6 ± 0.2 gCH4m–2 yr–1. Among lakes of the region, small lakes (area <0.1 km2) are the most intensive sources of atmospheric methane per unit area.
570-580
Seasonal Variability and Hydrodynamic Regimes of the Novaya Zemlya Bora
Abstract
The features of bora formation in the region of Novaya Zemlya surrounded by the Barents and Kara seas, differing in hydrometeorological conditions, are considered. The annual course of average magnitude of buoyancy frequency estimation at the points of the Barents and Kara seas has been constructed. The necessary conditions of bora development in the winter and summer periods are considered. The value of Froude number Fr is used as the main criterion. The statistics of bora cases made on the basis of joint distributions of values of buoyancy frequency and wind speed is given. Results of numerical simulations using the WRF-ARW model for three (small, intermediate, and large) values of Froude number Fr are given. The features of the formation of bora hydrodynamic characteristics for cases conventionally referred to shallow and deep bora types are considered. Estimations of orographic drag and its separate components are given.
581-593
Role of Penetrative Convection under the Ice in the Formation of the State of the World Ocean
Abstract
The results of numerical experiments on the sensitivity of the INMCM48 Earth System model (Institute of Numerical Mathematics, Russian Academy of Science (INM RAS)) to the various parameterizations of convection induced by the formation of a new ice are presented and analyzed. It is shown that the response in temperature and salinity is observed not only directly under the ice, but in ocean subpolar regions as well, which is especially pronounced in the North Atlantic. An effective parameterization is proposed which significantly reduces the estimation error of the surface salinity in the AO with no formation of the trends of the near-bottom salinity fields, in contrast with the well-known parameterization (Nguyen, Menemenlis and Kwok, 2009).
594-607
Internal Tide in the Drake Passage
Abstract
Internal tidal waves in the Drake Passage have been studied on the basis of moored measurements, numerical modeling, and dispersion relation calculated from the profiles of temperature and salinity. Two main generation sources of internal tides are found: over a submarine elevation and over the Shackleton Ridge. The wavelength based on different estimates is close to 120 km. The numerical model shows that internal perturbations near submarine slopes are in the form of beams, while at a distance of approximately one wavelength the beams diffuse and the beam structure transforms to lower modes. The amplitude of waves near submarine slopes is close to 100 m and decreases to 30 m in the course of their propagation.
608-615
Wind Pulse Effect on Coastal Current
Abstract
Shallow water equations have been used to analyze the final stage of the response of a semi-infinite rotating basin to the wind impulse effect simulating the passage of a storm in the presence of a coastal current. It has been shown that the most significant effect upon a high storm intensity is that the coastal stream core shifts several kilometers toward the coast or from the coast, depending on the sign of the Ekman transport. The additional currents arising after the storm passage in the presence of an alongshore stream differ only quantitatively from the currents arising in its absence.
616-620
Spatial Structure of the Antarctic Water Flow in the Vema Fracture Zone of the Mid-Atlantic Ridge
Abstract
We study the Antarctic Bottom Water (AABW) flow in the Vema Fracture Zone of the Mid-Atlantic Ridge using the high-resolution Institute of Numerical Mathematics Ocean Model (INMOM) and data from field measurements. The key feature of this numerical modeling is high horizontal and vertical resolution in the bottom layer for the simulation of the flow in the narrow deepwater fracture, as well as the use of high-quality topography based on multibeam echo sounder measurements. Direct CTD and LADCP measurements performed onboard the R/V Akademik Sergey Vavilov in 2006 and 2014–2016 were used to verify the model. In this work, we analyze both the thermohaline structure of the bottom layer in the Vema Fracture Zone and kinematics of the flow over its entire length.
621-625