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The purpose of the paper is a research of a 2nd order finite difference scheme based on the Z-scheme. This research is the numerical solution of several two-dimensional differential equations simulated the incompressible medium convection.

One of real tasks for similar equations solution is the numerical simulating of strongly non-stationary midscale processes in the Earth ionosphere. Because convection processes in ionospheric plasma are controlled by magnetic field, the plasma incompressibility condition is supposed across the magnetic field. For the same reason, there can be rather high velocities of heat and mass convection along the magnetic field.

Ionospheric simulation relevant task is the research of plasma instability of various scales which started in polar and equatorial regions first of all. At the same time the mid-scale irregularities having characteristic sizes 1–50 km create conditions for development of the small-scale instabilities. The last lead to the F-spread phenomenon which significantly influences the accuracy of positioning satellite systems work and also other space and ground-based radio-electronic systems.

The difference schemes used for simultaneous simulating of such multi-scale processes must to have high resolution. Besides, these difference schemes must to be high resolution on the one hand and monotonic on the other hand. The fact that instabilities strengthen errors of difference schemes, especially they strengthen errors of dispersion type is the reason of such contradictory requirements. The similar swing of errors usually results to nonphysical results at the numerical solution.

At the numerical solution of three-dimensional mathematical models of ionospheric plasma are used the following scheme of splitting on physical processes: the first step of splitting carries out convection along, the second step of splitting carries out convection across. The 2nd order finite difference scheme investigated in the paper solves approximately convection across equations. This scheme is constructed by a monotonized nonlinear procedure on base of the Z-scheme which is one of 2nd order schemes. At this monotonized procedure a nonlinear correction with so-called “oblique differences” is used. “Oblique differences” contain the grid nodes relating to different layers of time.

The researches were conducted for two cases. In the simulating field components of the convection vector had: 1) the constant sign; 2) the variable sign. Dissipative and dispersive characteristics of the scheme for different types of the limiting functions are in number received.

The results of the numerical experiments allow to draw the following conclusions.

1. For the discontinuous initial profile the best properties were shown by the SuperBee limiter.

2. For the continuous initial profile with the big spatial steps the SuperBee limiter is better, and at the small steps the Koren limiter is better.

3. For the smooth initial profile the best results were shown by the Koren limiter.

4. The smooth F limiter showed the results similar to Koren limiter.

5. Limiters of different type leave dispersive errors, at the same time dependences of dispersive errors on the scheme parameters have big variability and depend on the scheme parameters difficulty.

6. The monotony of the considered differential scheme is in number confirmed in all calculations. The property of variation non-increase for all specified functions limiters is in number confirmed for the onedimensional equation.

7. The constructed differential scheme at the steps on time which are not exceeding the Courant's step is monotonous and shows good exactness characteristics for different types solutions. At excess of the Courant's step the scheme remains steady, but becomes unsuitable for instability problems as monotony conditions not satisfied in this case.

WENO schemes (weighted, essentially non oscillating) are currently having a wide range of applications as approximate high order schemes for discontinuous solutions of partial differential equations. These schemes are used for direct numerical simulation (DNS) and large eddy simmulation in the gas dynamic problems, problems for DNS in MHD and even neutron kinetics. This work is dedicated to clarify some characteristics of WENO schemes and numerical simulation of specific tasks. Results of the simulations can be used to clarify the field of application of these schemes. The first part of the work contained proofs of the approximation properties, stability and convergence of WENO5, WENO7, WENO9, WENO11 and WENO13 schemes. In the second part of the work the modified wave number analysis is conducted that allows to conclude the dispersion and dissipative properties of schemes. Further, a numerical simulation of a number of specific problems for hyperbolic equations is conducted, namely for advection equations (one-dimensional and two-dimensional), Hopf equation, Burgers equation (with low dissipation) and equations of non viscous gas dynamics (onedimensional and two-dimensional). For each problem that is implying a smooth solution, the practical calculation of the order of approximation via Runge method is performed. The influence of a time step on nonlinear properties of the schemes is analyzed experimentally in all problems and cross checked with the first part of the paper. In particular, the advection equations of a discontinuous function and Hopf equations show that the failure of the recommendations from the first part of the paper leads first to an increase in total variation of the solution and then the approximation is decreased by the non-linear dissipative mechanics of the schemes. Dissipation of randomly distributed initial conditions in a periodic domain for one-dimensional Burgers equation is conducted and a comparison with the spectral method is performed. It is concluded that the WENO7–WENO13 schemes are suitable for direct numerical simulation of turbulence. At the end we demonstrate the possibility of the schemes to be used in solution of initial-boundary value problems for equations of non viscous gas dynamics: Rayleigh–Taylor instability and the reflection of the shock wave from a wedge with the formation a complex configuration of shock waves and discontinuities.

The Richtmyer–Meshkov and the Rayleigh–Taylor instabilities of viscoplastic (or the Bingham) fluids are studied in the three–dimensional formulation of the problem. A numerical modeling of the intermixing of two fluids with different rheology, whose densities differ twice, as a result of instabilities development process has been carried out. The development of the Richtmyer–Meshkov and the Rayleigh–Taylor instabilities of the Bingham fluids is analyzed utilizing the MacCormack and the Volume of Fluid (VOF) methods to reconstruct the interface during the process. Both the results of numerical simulation of the named instabilities of the Bingham liquids and their comparison with theory and the results of the Newtonian fluid simulation are presented. Critical amplitude of the initial perturbation of the contact boundary velocity field at which the development of instabilities begins was estimated. This critical amplitude presents because of the yield stress exists in the Bingham fluids. Results of numerical calculations show that the yield stress of viscoplastic fluids essentially affects the nature of the development of both Rayleigh–Taylor and Richtmyer–Meshkov instabilities. If the amplitude of the initial perturbation is less than the critical value, then the perturbation decays relatively quickly, and no instability develops.When the initial perturbation exceeds the critical amplitude, the nature of the instability development resembles that of the Newtonian fluid. In a case of the Richtmyer–Meshkov instability, the critical amplitudes of the initial perturbation of the contact boundary at different values of the yield stress are estimated. There is a distinction in behavior of the non-Newtonian fluid in a plane case: with the same value of the yield stress in three-dimensional geometry, the range of the amplitude values of the initial perturbation, when fluid starts to transit from rest to motion, is significantly narrower. In addition, it is shown that the critical amplitude of the initial perturbation of the contact boundary for the Rayleigh–Taylor instability is lower than for the Richtmyer–Meshkov instability. This is due to the action of gravity, which helps the instability to develop and counteracts the forces of viscous friction.

Experimental, theoretical and numerical investigations of equatorial spread F, equatorial plasma bubbles (EPBs), plasma depletion shells, and plasma clouds are continued at new variety articles. Nonlinear growth, bifurcation, pinching, atomic and molecular ion dynamics are considered at there articles. But the authors of this article believe that not all parameters of EPB development are correct. For example, EPB bifurcation is highly questionable.

A maximum speed inside EPBs and a development time of EPB are defined and studied. EPBs starting from one, two or three zones of the increased density (initial plasma clouds). The development mechanism of EPB is the Rayleigh-Taylor instability (RTI). Time of the initial stage of EPB development went into EPB favorable time interval (in this case the increase linear increment is more than zero) and is 3000–7000 c for the Earth equatorial ionosphere.

Numerous computing experiments were conducted with use of the original two-dimensional mathematical and numerical model MI2, similar USA standard model SAMI2. This model MI2 is described in detail. The received results can be used both in other theoretical works and for planning and carrying out natural experiments for generation of F-spread in Earth ionosphere.

Numerical simulating was carried out for the geophysical conditions favorable for EPBs development. Numerical researches confirmed that development time of EPBs from initial irregularities with the increased density is significantly more than development time from zones of the lowered density. It is shown that developed irregularities interact among themselves strongly and not linearly even then when initial plasma clouds are strongly removed from each other. In addition, this interaction is stronger than interaction of EPBs starting from initial irregularities with the decreased density. The numerical experiments results showed the good consent of developed EPB parameters with experimental data and with theoretical researches of other authors.

The aim of the work is to study a monotone finite-difference scheme of the second order of accuracy, created on the basis of a generalization of the one-dimensional Z-scheme. The study was carried out for model equations of the transfer of an incompressible medium. The paper describes a two-dimensional generalization of the Z-scheme with nonlinear correction, using instead of streams oblique differences containing values from different time layers. The monotonicity of the obtained nonlinear scheme is verified numerically for the limit functions of two types, both for smooth solutions and for nonsmooth solutions, and numerical estimates of the order of accuracy of the constructed scheme are obtained.

The constructed scheme is absolutely stable, but it loses the property of monotony when the Courant step is exceeded. A distinctive feature of the proposed finite-difference scheme is the minimality of its template. The constructed numerical scheme is intended for models of plasma instabilities of various scales in the low-latitude ionospheric plasma of the Earth. One of the real problems in the solution of which such equations arise is the numerical simulation of highly nonstationary medium-scale processes in the earth’s ionosphere under conditions of the appearance of the Rayleigh – Taylor instability and plasma structures with smaller scales, the generation mechanisms of which are instabilities of other types, which leads to the phenomenon F-scattering. Due to the fact that the transfer processes in the ionospheric plasma are controlled by the magnetic field, it is assumed that the plasma incompressibility condition is fulfilled in the direction transverse to the magnetic field.