| 1. |
- Korovinskiy, D. B., et al.
(författare)
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The double-gradient magnetic instability : Stabilizing effect of the guide field
- 2015
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 22:1
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Tidskriftsartikel (refereegranskat)abstract
- The role of the dawn-dusk magnetic field component in stabilizing of the magnetotail flapping oscillations is investigated in the double-gradient model framework (Erkaev et al., Phys. Rev. Lett. 99, 235003 (2007)), extended for the magnetotail-like configurations with non-zero guide field By. Contribution of the guide field is examined both analytically and by means of linearized 2-dimensional (2D) and non-linear 3-dimensional (3D) MHD modeling. All three approaches demonstrate the same properties of the instability: stabilization of current sheet oscillations for short wavelength modes, appearing of the typical (fastest growing) wavelength lambda(peak) of the order of the current sheet width, decrease of the peak growth rate with increasing B-y value, and total decay of the mode for B-y similar to 0: 5 in the lobe magnetic field units. Analytical solution and 2D numerical simulations claim also the shift of lambda(peak) toward the longer wavelengths with increasing guide field. This result is barely visible in 3D simulations. It may be accounted for the specific background magnetic configuration, the pattern of tail-like equilibrium provided by approximated solution of the conventional Grad-Shafranov equation. The configuration demonstrates drastically changing radius of curvature of magnetic field lines, R-c. This, in turn, favors the "double-gradient" mode (lambda > R-c) in one part of the sheet and classical "ballooning" instability (lambda < R-c) in another part, which may result in generation of a "combined" unstable mode. (C) 2015 AIP Publishing LLC.
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| 2. |
- Korovinskiy, D. B., et al.
(författare)
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MHD modeling of the double-gradient (kink) magnetic instability
- 2013
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Ingår i: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202 .- 2169-9380. ; 118:3, s. 1146-1158
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents the detailed numerical investigation of the "double-gradient mode," which is believed to be responsible for the magnetotail flapping oscillations-the fast vertical (normal to the layer) oscillations of the Earth's magnetotail plasma sheet with a quasiperiod similar to 100-200 s. The instability is studied using the magnetotail near-equilibrium configuration. For the first time, linear three-dimensional numerical analysis is complemented with full 3-D MHD simulations. It is known that the "double-gradient mode" has unstable solutions in the region of the tailward growth of the magnetic field component, normal to the current sheet. The unstable kink branch of the mode is the focus of our study. Linear MHD code results agree with the theory, and the growth rate is found to be close to the peak value, provided by the analytical estimates. Full 3-D simulations are initialized with the numerically relaxed magnetotail equilibrium, similar to the linear code initial condition. The calculations show that current layer with tailward gradient of the normal component of the magnetic field is unstable to wavelengths longer than the curvature radius of the field line. The segment of the current sheet with the earthward gradient of the normal component makes some stabilizing effect (the same effect is registered in the linearized MHD simulations) due to the minimum of the total pressure localized in the center of the sheet. The overall growth rate is close to the theoretical double-gradient estimate averaged over the computational domain.
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| 3. |
- Korovinskiy, D. B., et al.
(författare)
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The transition from "double-gradient" to ballooning unstable mode in bent magnetotail-like current sheet
- 2019
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Ingår i: Physics of Plasmas. - : AMER INST PHYSICS. - 1070-664X .- 1089-7674. ; 26:10
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Tidskriftsartikel (refereegranskat)abstract
- The magnetotail-like magnetoplasma configuration is examined for the stability to the transversal mode by means of linear 2.5- and nonlinear 3-dimensional MHD simulations. The exact two-dimensional Kan-like solution of the Vlasov-Maxwell equations is utilized for background equilibrium bent current sheets. Both linear and nonlinear simulations reveal the same features: the bent current sheet is unstable to perturbations with the wave vector pointing in the out-of-plane direction; the unstable mode is localized in the summer hemisphere; in-plane plasma flow is rotating from the earthward/tailward direction in the near-Earth region to the vertical direction in the tail. Rotation of the plasma velocity and variation of the background plasma parameters in longitudinal (Earth-Sun) direction allow considering the observed plasma motions as a transient mode from the so-called double-gradient (in distant tail) to the conventional ballooning (close to the Earth) instability. It is found that the mode localization is controlled by second derivatives of the total pressure in longitudinal and normal (north-south) directions. This feature is rendered by a newly developed quasi-two-dimensional analytical model of the transversal mode in the bent current sheet. Published under license by AIP Publishing.
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| 4. |
- Divin, A., et al.
(författare)
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Scaling of the inner electron diffusion region in collisionless magnetic reconnection
- 2012
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117, s. A06217-
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Tidskriftsartikel (refereegranskat)abstract
- The Sweet-Parker analysis of the inner electron diffusion region of collisionless magnetic reconnection is presented. The study includes charged particles motion near the X-line and an appropriate approximation of the off-diagonal term for the electron pressure tensor. The obtained scaling shows that the width of the inner electron diffusion region is equal to the electron inertial length, and that electrons are accelerated up to the electron Alfven velocity in X-line direction. The estimated effective plasma conductivity is based on the electron gyrofrequency rather than the binary collision frequency, and gives the extreme (minimal) value of the plasma conductivity similar to Bohm diffusion. The scaling properties are verified by means of Particle-in-Cell simulations. An ad hoc parameter needs to be introduced to the scaling relations in order to better match the theory and simulations.
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| 5. |
- Korovinskiy, D., et al.
(författare)
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MHD Modeling of the Kink "Double-gradient" Branch of the Ballooning Instability in the Magnetotail
- 2014
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Ingår i: NUMERICAL MODELING OF SPACE PLASMA FLOWS. - : ASTRONOMICAL SOC PACIFIC. - 9781583818602 ; , s. 149-154
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Konferensbidrag (refereegranskat)abstract
- We present a numerical investigation of the double-gradient mode, which is believed to be responsible for the magnetotail flapping oscillations the fast vertical oscillations of the Earth's magnetotail plasma sheet (quasiperiod similar to 100 - 200 s). It is known that this mode has an unstable solution in the region of the tailward-growing normal magnetic field component. The kink branch of the mode is the focus of our study. The instability is studied using the magnetotail near-equilibrium configuration, fixed by the approximate solution of the Grad-Shafranov equation. The linear three-dimensional numerical analysis is complemented with full 3-D MUD simulations. The results of our linearized MHD code agree with the theory, and the growth rate is found to be close to the peak value provided by an analytical estimate. Also, the eigenfunctions, calculated analytically, are very similar to the perturbations obtained numerically. The full 3D MHD simulations are initialized with the numerically relaxed magnetotail equilibrium, similar to the linear code initial condition. The calculations show that the double-gradient mode is excited in a region of small radii of the magnetic field lines curvature, which is in accordance with the analytical predictions. In contrast to the linearized MHD simulations, non-local interactions are involved; hence, the overall growth rate turns out to be close to the theoretical estimate averaged over the computational domain.
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| 6. |
- Lammer, H., et al.
(författare)
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Geophysical and Atmospheric Evolution of Habitable Planets
- 2010
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Ingår i: Astrobiology. - : Mary Ann Liebert Inc. - 1531-1074 .- 1557-8070. ; 10:1, s. 45-68
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of Earth-like habitable planets is a complex process that depends on the geodynamical and geophysical environments. In particular, it is necessary that plate tectonics remain active over billions of years. These geophysically active environments are strongly coupled to a planet's host star parameters, such as mass, luminosity and activity, orbit location of the habitable zone, and the planet's initial water inventory. Depending on the host star's radiation and particle flux evolution, the composition in the thermosphere, and the availability of an active magnetic dynamo, the atmospheres of Earth-like planets within their habitable zones are differently affected due to thermal and nonthermal escape processes. For some planets, strong atmospheric escape could even effect the stability of the atmosphere.
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| 7. |
- Kubyshkina, D., et al.
(författare)
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The Kepler-11 system : Evolution of the stellar high-energy emission and initial planetary atmospheric mass fractions
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 632
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Tidskriftsartikel (refereegranskat)abstract
- The atmospheres of close-in planets are strongly influenced by mass loss driven by the high-energy (X-ray and extreme ultraviolet, EUV) irradiation of the host star, particularly during the early stages of evolution. We recently developed a framework to exploit this connection and enable us to recover the past evolution of the stellar high-energy emission from the present-day properties of its planets, if the latter retain some remnants of their primordial hydrogen-dominated atmospheres. Furthermore, the framework can also provide constraints on planetary initial atmospheric mass fractions. The constraints on the output parameters improve when more planets can be simultaneously analysed. This makes the Kepler-11 system, which hosts six planets with bulk densities between 0.66 and 2.45 g cm-3, an ideal target. Our results indicate that the star has likely evolved as a slow rotator (slower than 85% of the stars with similar masses), corresponding to a high-energy emission at 150 Myr of between 1 and 10 times that of the current Sun. We also constrain the initial atmospheric mass fractions for the planets, obtaining a lower limit of 4.1% for planet c, a range of 3.7-5.3% for planet d, a range of 11.1-14% for planet e, a range of 1-15.6% for planet f, and a range of 4.7-8.7% for planet g assuming a disc dispersal time of 1 Myr. For planet b, the range remains poorly constrained. Our framework also suggests slightly higher masses for planets b, c, and f than have been suggested based on transit timing variation measurements. We coupled our results with published planet atmosphere accretion models to obtain a temperature (at 0.25 AU, the location of planet f) and dispersal time of the protoplanetary disc of 550 K and 1 Myr, although these results may be affected by inconsistencies in the adopted system parameters. This work shows that our framework is capable of constraining important properties of planet formation models.
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