Труды сотрудников ИВМ СО РАН

/ N.V. Erkaev, V.S. Semenov, H.K. Biernat // Phys. Plasmas. - 2012. - Vol. 19, Is. 6. - Ст. 62905, DOI 10.1063/1.4725506. - Cited References: 22. - This work is supported by RFBR Grants Nos. 12-05-00152-a and 12-05-00918-a, and also by St. Petersburg University grant. V. S. S. and H. K. B. are supported from the FP7 Programme under Grant No. 269198-Geoplasmas (Marie Curie Exchange Scheme). Additional support is due to the Austrian "Fonds zur Forderung der wissenschaftlichen Forschung" under Project I 193-N16 and the "Verwaltungsstelle fur Auslandsbeziehungen" of the Austrian Academy of Sciences. . - ISSN 1070-664XРУБ Physics, Fluids & Plasmas

Аннотация: Magnetic filament approach is applied for modeling of nonlinear "kink"-like flapping oscillations of thin magnetic flux tubes in the Earth's magnetotail current sheet. A discrete approximation for the magnetic flux tube was derived on a basis of the Hamiltonian formulation of the problem. The obtained system of ordinary differential equations was integrated by method of Rosenbrock, which is suitable for stiff equations. The two-dimensional exact Kan's solution of the Vlasov equations was used to set the background equilibrium conditions for magnetic field and plasma. Boundary conditions for the magnetic filament were found to be dependent on the ratio of the ionospheric conductivity and the Alfven conductivity of the magnetic tube. It was shown that an enhancement of this ratio leads to the corresponding increase of the frequency of the flapping oscillations. For some special case of boundary conditions, when the magnetic perturbations vanish at the boundaries, the calculated frequency of the "kink"-like flapping oscillations is rather close to that predicted by the "double gradient" analytical model. For others cases, the obtained frequency of the flapping oscillations is somewhat larger than that from the "double gradient" theory. The frequency of the nonlinear flapping oscillations was found to be a decreasing function of the amplitude. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4725506]


Доп.точки доступа:
Erkaev, N.V.; Еркаев, Николай Васильевич; Semenov, V.S.; Biernat, H.K.

[Text] / N. V. Erkaev, V. S. Semenov, H. K. Biernat // Geophys. Res. Lett. - 2008. - Vol. 35, Is. 2. - Ст. L02111, DOI 10.1029/2007GL032277. - Cited References: 13 . - ISSN 0094-8276РУБ Geosciences, Multidisciplinary

Аннотация: A new kind of magnetohydrodynamic waves are analyzed for a current sheet in a presence of a small normal magnetic field component varying along the sheet. As a background, two simplified models of a current sheet are considered with a uniform and nonuniform current distributions in the current sheet. On a basis of these two models, the flapping-type waves are obtained which are related to a coexistence of two gradients of the tangential and normal magnetic field components along the normal and tangential directions with respect to the current sheet. A stable situation for the current sheet is associated with a positive result of the multiplication of the two magnetic gradients, and unstable ( wave growth) condition corresponds to a negative result of the product. In the stable region, the "kink''-like wave mode is interpreted as so called flapping waves observed in the Earth's magnetotail current sheet.


Доп.точки доступа:
Erkaev, N.V.; Еркаев, Николай Васильевич; Semenov, V.S.; Biernat, H.K.

[Text] / N. V. Erkaev, V. S. Semenov, H. K. Biernat // Phys. Rev. Lett. - 2007. - Vol. 99, Is. 23. - Ст. 235003, DOI 10.1103/PhysRevLett.99.235003. - Cited References: 10 . - ISSN 0031-9007РУБ Physics, Multidisciplinary

Аннотация: A new kind of magnetohydrodynamic instability and waves are analyzed for a current sheet in the presence of a small normal magnetic field component varying along the sheet. These waves and instability are related to the existence of two gradients of the tangential (B(tau)) and normal (B(n)) magnetic field components along the normal (del(n)B(tau)) and tangential (del(tau)B(n)) directions with respect to the current sheet. The current sheet can be stable or unstable if the multiplication of two magnetic gradients is positive or negative. In the stable region, the kinklike wave mode is interpreted as so-called flapping waves observed in Earth's magnetotail current sheet. The kink wave group velocity estimated for the Earth's current sheet is of the order of a few tens of kilometers per second. This is in good agreement with the observations of the flapping motions of the magnetotail current sheet.


Доп.точки доступа:
Erkaev, N.V.; Еркаев, Николай Васильевич; Semenov, V.S.; Biernat, H.K.

[Text] / N. V. Erkaev [et al.] // J. Geophys. Res-Space Phys. - 2009. - Vol. 114. - Ст. A03206, DOI 10.1029/2008JA013728. - Cited References: 24. - We thank V. Sergeev for fruitful discussions and help in the preparation of the manuscript. This work is supported by RFBR grants N 07-05-00776-a, N 07-05-00135, by programs 2.16 and 16.3 of RAS, and by project P20341-N16 from the Austrian "Fonds zur Forderung der wissenschaftlichen Forschung,'' and also by project I.2/04 from "Osterreichischer Austauschdienst.'' . - ISSN 0148-0227РУБ Astronomy & Astrophysics

Аннотация: A new kind of magnetohydrodynamic waves is analyzed for a current sheet in the presence of a small normal magnetic field component (B-z) varying along the sheet. For the initial undisturbed state, a simplified model of the current sheet is considered with a Harris-like current density distribution across the sheet. Within the framework of this model, an analytical solution is obtained for the flapping-type wave oscillations and instability, related to the gradient of the normal magnetic field component along the current sheet. The flapping wave frequency is found to be a function of the wave number, which has an asymptotic saturation for large wave numbers. This frequency is pure real in a stable situation for the magnetotail current sheet, when the Bz component increases toward Earth. The current sheet becomes unstable in some regions, where the Bz component decreases locally toward Earth. In the stable region, the "kink''-like wave oscillations are calculated for an initial Gaussian perturbation localized to the center of the current sheet. The flapping wave propagations are analyzed for two cases: (1) the initial perturbation is fixed, and (2) the source is moving toward Earth. In the last case, the Mach cone is obtained for the propagating flapping waves. The source for the flapping waves is associated with the fast plasma flow originated from the reconnection region.


Доп.точки доступа:
Erkaev, N.V.; Еркаев, Николай Васильевич; Semenov, V.S.; Kubyshkin, I.V.; Kubyshkina, M.V.; Biernat, H.K.; RFBR [N 07-05-00776-a, N 07-05-00135]; Austrian "Fonds zur Forderung der wissenschaftlichen Forschung,'' [P20341-N16]

[Text] / N. V. Erkaev [et al.] // Ann. Geophys. - 2009. - Vol. 27, Is. 1. - P417-425. - Cited References: 24. - We thank V. Sergeev for fruitful discussions and help in preparation of the manuscript. This work is supported by RFBR grants N07-05-00776-a, N 07-05-00135, by SFU grant N 10, by Programs 2.16 and 16.3 of RAS, and by project P20341-N16 from the Austrian " Fonds zur Forderung der wissenschaftlichen Forschung", and also by project I.2/04 from "Osterreichischer Austauschdienst". . - ISSN 0992-7689РУБ Astronomy & Astrophysics + Geosciences, Multidisciplinary + Meteorology & Atmospheric Sciences

Аннотация: One-fluid ideal MHD model is applied for description of current sheet flapping disturbances appearing due to a gradient of the normal magnetic field component. The wave modes are studied which are associated to the flapping waves observed in the Earth's magnetotail current sheet. In a linear approximation, solutions are obtained for model profiles of the electric current and plasma densities across the current sheet, which are described by hyperbolic functions. The flapping eigenfrequency is found as a function of wave number. For the Earth's magnetotail conditions, the estimated wave group speed is of the order of a few tens kilometers per second. The current sheet can be stable or unstable in dependence on the direction of the gradient of the normal magnetic field component. The obtained dispersion function is used for calculation of the flapping wave disturbances, which are produced by the given initial Gaussian perturbation at the center of the current sheet and propagating towards the flanks. The propagating flapping pulse has a smooth leading front, and a small scale oscillating trailing front, because the short wave oscillations propagate much slower than the long wave ones.


Доп.точки доступа:
Erkaev, N.V.; Еркаев, Николай Васильевич; Semenov, V.S.; Kubyshkin, I.V.; Kubyshkina, M.V.; Biernat, H.K.; RFBR [N07-05-00776-a, N 07-05-00135]; SFU [N 10]; RAS [2.16, 16.3]; Austrian " Fonds zur Forderung der wissenschaftlichen Forschung" [P20341-N16]; Osterreichischer Austauschdienst [I.2/04]

[Text] / D. B. Korovinskiy [et al.] // J. Geophys. Res-Space Phys. - 2011. - Vol. 116. - Ст. A05219, DOI 10.1029/2010JA015942. - Cited References: 45. - This work is supported by the Austrian Science Fund under projects I193-N16 and P21051-N16, by RFBR grant 09-05-91000-ANF-a, and by SPSU grant 11.38.47.2011. V. S. Semenov also thanks ISSI for hospitality and financial support. . - ISSN 2169-9380РУБ Astronomy & Astrophysics

Аннотация: A 2.5-D analytical electron Hall magnetohydrodynamic model of steady state magnetic reconnection in a collisionless compressible plasma with a constant electron temperature is developed. It is shown that as in the incompressible case, the solution of the Grad-Shafranov equation for the magnetic potential is a basis for the problem analysis. The formation of the double electric layers and layers of low-density plasma, mapping the magnetic separatrices, are investigated. It is found that the formation of depletion layers should not be governed by the out-of-plane magnetic field, but rather, the origin of these layers lies inside the electron diffusion region. The double electric layers are found to be thin separatrices-elongated sheets, whose cross sections are of the order of the electron diffusion region half width. These charged layers provide the presence of the strong electric field orthogonal to the in-plane projection of the magnetic field, which forces electrons to accelerate into the out-of-plane direction. Outside of the double electric layers, the condition of quasi-neutrality of the plasma is found to be fulfilled to high accuracy.


Доп.точки доступа:
Korovinskiy, D.B.; Semenov, V.S.; Erkaev, N.V.; Еркаев, Николай Васильевич; Divin, A.V.; Biernat, H.K.; Mostl, U.V.

[Text] / D. B. Korovinskiy [et al.] // Adv. Space Res. - 2011. - Vol. 48, Is. 9. - P1531-1536, DOI 10.1016/j.asr.2011.07.008. - Cited References: 12. - This work is supported by the Austrian Science Fund under project 1193-N16, by RFBR Grant No. 09-05-91000-ANF-a, by SPSU grant No. 11.38.47.2011, and by the European Union Seventh Framework Programme [FP7/2007-2013] under grant agreement No. 269198 - Geoplasmas (Marie Curie International Research Staff Exchange Scheme). V.S. Semenov thanks also ISSI for hospitality and financial support. . - ISSN 0273-1177РУБ Astronomy & Astrophysics + Geosciences, Multidisciplinary + Meteorology & Atmospheric Sciences

Аннотация: A linear MHD instability of the electric current sheet, characterized by a small normal magnetic field component, varying along the sheet, is investigated. The tangential magnetic field component is modeled by a hyperbolic function, describing Harris-like variations of the field across the sheet. For this problem, which is formulated in a 3D domain, the conventional compressible ideal MHD equations are applied. By assuming Fourier harmonics along the electric current, the linearized 3D equations are reduced to 2D ones. A finite difference numerical scheme is applied to examine the time evolution of small initial perturbations of the plasma parameters. This work is an extended numerical study of the so called "double gradient instability", - a possible candidate for the explanation of flapping oscillations in the magnetotail current sheet, which has been analyzed previously in the framework of a simplified analytical approach for an incompressible plasma. The dispersion curve is obtained for the kink-like mode of the instability. It is shown that this curve demonstrates a quantitative agreement with the previous analytical result. The development of the instability is investigated also for various enhanced values of the normal magnetic field component. It is found that the characteristic values of the growth rate of the instability shows a linear dependence on the square root of the parameter, which scales uniformly the normal component of the magnetic field in the current sheet. (C) 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.


Доп.точки доступа:
Korovinskiy, D.B.; Ivanova, V.V.; Erkaev, N.V.; Еркаев, Николай Васильевич; Semenov, V.S.; Ivanov, I.B.; Biernat, H.K.; Zellinger, M.