The influence of thermochemical convection on the fixity of mantle plumes

A general feature of both isochemical and thermochemical studies of mantle convection is that horizontal plume velocities tend to be smaller than typical convective velocities, however, it is not clear which system leads to a greater fixity of mantle plumes. We perform two- and three-dimensional numerical calculations and compare both thermochemical and isochemical cases with similar convective vigor to determine whether presence of a dense component in the mantle can lead to smaller ratios of horizontal plume velocity to surface velocity. We investigate different viscosity and density contrasts between chemical components in the thermochemical calculations, and we perform isochemical calculations with both free-slip and no-slip bottom boundary conditions. We then compare both visually and quantitatively the results of the thermochemical and isochemical calculations to determine which leads to greater plume fixity. We find that horizontal plume velocities for thermochemical calculations are similar to those from isochemical calculations with no-slip bottom boundary conditions. In addition, we find that plumes tend to be more fixed for isochemical cases with free-slip bottom boundary conditions for two-dimensional calculations, however, in three dimensions, we find that plume fixity is similar to that observed in thermochemical calculations.     

Use of the ACDEP trajectory model in the Danish nation-wide Background Monitoring Programme

The frequently observed eutrophication problems in Danish marine waters are associated with high nutrient loads. This paper outlines how the atmospheric part of the load is determined within the framework of the Danish Background Monitoring Programme. The analyses within the programme are carried out by use of both measurements and model calculations, where the modelling part receives the main focus in this paper. The performed calculations indicate that the atmospheric nitrogen deposition to the Danish marine waters is of comparable size to the river run-off, and in some periods even the dominating contribution to the overall nitrogen input. The model results are shown to be sensitive to the resolution of the meteorological input data for the calculations. Strong improvement of the model performance is the result when meteorological data with much higher temporal and spatial resolution are applied.     

Geomagnetic cutoff rigidities of cosmic rays in a model of the bounded magnetosphere with the ring current

The cosmic ray geomagnetic cutoff rigidities are obtained by analytical calculations within an axisymmetric model of bounded magnetosphere, the magnetic field of which is created by the dipole field of the Earth and by two spheres located beyond the Earth with the currents that flow along the parallels and have a value proportional to the cosine of latitude. The inner sphere models the ring current flowing in the westerly direction; the outer sphere simulates the currents over the magnetopause, which flow in the easterly direction. The analytical results of calculations of variations in the geomagnetic cutoff rigidity for different levels of geomagnetic disturbances are given. The results are compared with the results of analytical calculations within the model of unbounded magnetosphere (when the outer sphere is absent).     

Modelling of the lower ionosphere

The model of calculations of electron density profiles in D-region is suggested. The model includes four positive ions, four negative ions and electrons. The effective rate coefficients were received from detailed models of ionization-recombination cycle. The calculations, which were made, and the comparisons with experimental data (Ne-profiles and their variations, absorption of radiowaves) have showed, that in general the model described the basic features of D-region parameters.     

Response using the Rayleigh-Ritz method

As an example of the extension of the Rayleigh-Ritz method to response calculations, analysis is outlined for a damped rectangular plate. For harmonic excitation amplitudes of displacement and bending moment are compared with values from a modal solution from the plate equation. In general, the Rayleigh-Ritz method predicts displacements of acceptable accuracy, but for a given number of terms accuracy is less for response calculations than for the determination of comparable eigenvalues. Bending moments may converge slowly to the true values, as the number of terms in the assumed series is increased.     

Modeling of nonstationary electron precipitation by the whistler cyclotron instability

We study a simple self-consistent model of a whistler cyclotron maser derived from the full set of quasi-linear equations. We employ numerical calculations to demonstrate dependencies of pulsation regimes of whistler-mode wave interactions with energetic electrons on plasma parameters. Possible temporal evolution of those regimes in real conditions is discussed; calculations are compared with case-study experimental data on energetic electron precipitation pulsations. A reasonable agreement of the model results and the observations has been found.     

Simulation of the Hydroecological Regime of the Nizhnekamskoe Reservoir

Water Resources - The hydroecological simulation model GMV-MGU is applied to the Nizhnekamskoe Reservoir. The results of a series of diagnostic model calculations, which characterize the ecological...     

Model description of electron concentration in the middle ionosphere

The results of comparison of model calculations of the electron concentration N at ionospheric heights of 120–200 km to the experimental data obtained at a series of geographic points at various levels of solar activity in various seasons of the year in quiet and disturbed conditions are presented and discussed. The calculations are performed using the semiempirical model (SEM) developed by the authors and giving in a general form the relation of N to characteristics of the thermospheric neutral gas and the solar activity index. The data presented in the paper show that the calculations with the SEM in question in the majority of cases agree well with experiment (the difference between them is 10–20%). The authors believe that the results of the comparative analysis presented in the paper manifest a high degree of universality of the discussed SEM.     

Wave effects in the field of a high-frequency horizontal electric dipole

A normal electromagnetic field of the high-frequency horizontal electric dipole is analyzed with allowance for the displacement currents in the earth and air. The components of the field are calculated by the method of partial integration for nonsmooth behavior of the integrand. The boundary between the quasistationary and wave zone of the source is established according to the results of calculations. The effects arising in the wave zone due to the displacement currents in the air are considered. The results of the calculations are confirmed by field experiments.     

Exhalation of radon and thoron: the question of the effect of thermal gradients in soil

Experimental measurements show no evidence for diurnal variation in exhalation of radon and thoron from soil due to convection induced by thermal gradients in the top few decimeters of soil as suggested by several authors. Estimates based on convective calculations indicate that even in the unlikely event of either vertical temperature gradients large enough to cause vertical instability, or horizontal gradients sufficient to cause significant convection, any effect would be too small to be detected. These same calculations suggest that it is difficult to conceive of cases involving typical thermal gradients in unfractured porous media such as soil where thermally induced convection would play an important role in transport of radon or thoron.     

Hydraulic calculations for the transport of a steam-water heat carrier at hydrothermal fields

This paper deals with special features that are peculiar to the hydraulic calculations of pipeworks for the transport of a steam-water mixture at geothermal fields. The special features stem from the need to match input data and borehole parameters. Methods for this matching, viz., successive approximations, the graphic method, and the method of generalized characteristic, are discussed. We examine the past calculations and production work with pipeworks at the Mutnovskii and Pauzhetka fields in Kamchatka.     

Numerical Analysis of the Velocities of Currents Forming in the Kerch Strait at the Motion of Domains of Higher Atmospheric Pressure

Water Resources - A three-dimensional ocean general circulation model (Princeton Ocean Model) along with hydraulic calculations were used to evaluate the velocity of currents from the Sea of Azov...     

Manifestations in the Solar Corona of the Process of Magnetic-Field Generation

Geomagnetism and Aeronomy - The situation with the reliability of calculations of the magnetic field of the solar corona remains a topic of discussion. There is, in particular, the problem of...     

A three-dimensional finite-element model of wind effects upon higher harmonics of the internal tide

A non-linear three-dimensional unstructured grid model of the M₂ tide in the shelf edge area off the west coast of Scotland is used to examine the spatial distribution of the M₂ internal tide and its higher harmonics in the region. In addition, the spatial variability of the tidally induced turbulent kinetic energy and associated mixing in the area are considered. Initial calculations involve only tidal forcing, although subsequent calculations are performed with up-welling and down-welling favourable winds to examine how these influence the tidal distribution (particularly the higher harmonics) and mixing in the region. Both short- and long-duration winds are used in these calculations. Tidal calculations show that there is significant small-scale spatial variability particularly in the higher harmonics of the internal tide in the region. In addition, turbulence energy and mixing exhibit appreciable spatial variability in regions of rapidly changing topography, with increased mixing occurring above seamounts. Wind effects significantly change the distribution of the M₂ internal tide and its higher harmonics, with appreciable differences found between up- and down-welling winds and long- and short-duration winds because of differences in mixing and the presence of wind-induced flows. The implications for model validation, particularly in terms of energy transfer to higher harmonics, and mixing are briefly discussed.     

Control of the current state of geomagnetic activity based on the satellite magnetic measurements in the magnetosphere

The method for controlling the state of the geomagnetic field in real time, based on comparing the up-to-date models of the magnetospheric magnetic field (the Tsyganenko model, the NIIYaF MGU paraboloid model) with this field measured onboard a spacecraft along its trajectory, is presented. The method is based on the possibility of characterizing the state of the geomagnetic field in the near-Earth space in the scope of such models. The specific state is determined, based on the best correspondence of the measurements to one of these three model calculations, by comparing the model calculations of the geomagnetic field along the satellite trajectory, belonging to different classes of the field state (quiet, disturbed, strongly disturbed), with the current experimental magnetic data. The method was tested using the CHAMP satellite data.     

Physical processes in the middle ionosphere accompanying the solar eclipse of January 4, 2011, in Kharkov

Aperiodic and quasi-periodic variations in the critical frequency of the F2 layer and Doppler frequency shift of radiowaves at vertical paths on the day of a partial (the magnitude was ～0.78) solar eclipse and on background days are analyzed. According to the experiment, the relative decrease in the electron concentration was 0.41 (0.46 according to calculations) and 0.50 (0.53 according to calculations) in the E region and in the lower part of the F region of the ionosphere. At a height of the main maximum of the electron concentration, the relative decrease in the electron concentration was 0.52 (0.51 according to calculations). It is shown that on the day of the eclipse and on the background day, the characteristics of wave disturbances within the height range 160–240 km were substantially different. Changes in the spectral composition began 30 min after the eclipse occurrence and, depending on the period, lasted from 2 to 4 h. The calculation results of the main parameters of the medium and signal correspond to the observational results.     

Modeling Water Flow in the Presence of Higher Vegetation

The notions of hydromechanics of continuum with a complicated structure are used to formulate a closed spatially homogeneous mathematical model of water flow within higher aquatic vegetation (HAV) canopy. Model equations are applied to the analysis of the vertical structure of a turbulent flow in a vegetated open channel. Test calculations are made. The results of calculations and experimental studies of water flow characteristics within vegetation communities in some water bodies [1, 6–8, 10, 14] are shown. The difficulties in implementing such experiments require improving the methods of mathematical simulation of water flows through HAV.     

拉分盆地与海原断裂带新生代水平位移规模

沿海原断裂带发育3个级别的拉分盆地,其中,发育于中新世的老龙湾盆地是规模最大的拉分盆地,长度超过50km。为了估计盆地拉分量,本文建立了数学模型,相关参数包括盆地沉积厚度、盆地长度、滑脱面深度等。计算得到老龙湾盆地的拉分量为30km。对于另外两个较小规模的拉分盆地,本文利用前人资料和平均走滑速率方法得到盆地拉分量分别为22km和8km。这样,沿海原断裂带新生代以来的拉分总量约60km。该数值与景泰至靖远的黄河位错量接近。     

Assessment of the Accuracy of Calculations Using the International Reference Ionosphere Model IRI-2016: I. Electron Densities

Geomagnetism and Aeronomy - The paper quantitatively compares the results of calculations of the electron density Ne by the International Reference Ionosphere model IRI-2016 with experimental data...     

Hydrocarbons in the White Sea: Their inflow and transformation in the marine environment in different regions

Literary data have been used to assess the inflow of petroleum hydrocarbons (with river runoff, precipitation, wastewaters, sea transport, and at ice thawing) into different regions of the White Sea. The hydroecological CNPSi-model was used as an instrument to reproduce the annual dynamics of hydrocarbon concentrations at their parallel inflow and subsequent transformation in the waters of the nine White Sea regions (the bays of Kandalaksha, Onega, Dvina, and Mezen; the Solovetskie Islands; the deep-water part: Bassein, Gorlo, Voronka, and Chupa Bay). The calculations were based on normal annual values of monthly variations of water temperature, light intensity, and transparency, the morphometric parameters of the regions (water areas, mean depths, and water volumes) and water exchange between the regions and with the Barents Sea (calculated by a hydrodynamic model). The calculated concentrations of hydrocarbons, the biomasses and activity characteristics of hydrocarbon-oxidizing bacteria have been analyzed (their values were estimated for the 2-m surface water layer). The results of calculations were used to evaluate hydrocarbon balances for regions and the sea as a whole. The calculations demonstrate the balanced character of hydrocarbon fluxes, the balance discrepancy for the regions being <0.1–16.1%.