scholarly journals Time-Dependent Convective Collapse of Flux Tubes

1983 ◽  
Vol 102 ◽  
pp. 73-77
Author(s):  
S. Sirajul Hasan
Keyword(s):  
Flux Tube ◽  
Convection Zone ◽  
Temporal Evolution ◽  
Dynamic Equilibrium ◽  
Mhd Equations ◽  
Time Dependent ◽  
Initial State ◽  
Flux Tubes ◽  
Initial Epoch ◽  
Flow Variables

The time-dependent collapse of a slender flux tube extending vertically in the convection zone of the Sun is modelled. Starting from an initial state in which the flux tube is in hydrostatic equilibrium, the non-linear MHD equations are used to examine its temporal evolution. A detailed study of the flow variables and magnetic field within the tube is presented. It is seen that asymptotically in time a unique state of dynamic equilibrium is established, irrespective of the value of βo (the ratio of the thermal to magnetic pressure at the initial epoch).

scholarly journals Dynamical Effects in Solar Photospheric Flux Tubes

1996 ◽  
Vol 154 ◽  
pp. 155-158
Author(s):  
S.S. Hasan
Keyword(s):  
Flux Tube ◽  
Ambient Medium ◽  
Resonant Interaction ◽  
Scale Height ◽  
Mhd Equations ◽  
Time Dependent ◽  
Radiative Transport ◽  
Local Pressure ◽  
Flux Tubes ◽  
Pressure Scale

AbstractThe interaction of an intense flux tube, extending vertically through the photosphere, with p-modes in the ambient medium is modelled by solving the time dependent MHD equations in the thin flux tube approximation. It is found that a resonant interaction can occur, which leads to the excitation of flux tube oscillations with large amplitudes. The resonance is not as sharp as in the case of an unstratified atmosphere, but is broadened by a factor proportional to H−2, where H is the local pressure scale height. In addition, the inclusion of radiative transport leads to a decrease in the amplitude of the oscillations, but does not qualitatively change the nature of the interaction.

scholarly journals Linking Thin Flux Tube MHD Models to Apparent Stellar Surface Activity

2004 ◽  
Vol 219 ◽  
pp. 546-551
Author(s):  
T. Granzer ◽  
K. G. Strassmeier
Keyword(s):  
Magnetic Flux ◽  
Surface Activity ◽  
Flux Tube ◽  
Convection Zone ◽  
Active Regions ◽  
Similar Model ◽  
Flux Tubes ◽  
Stellar Convection ◽  
Magnetic Flux Tubes ◽  
Spot Formation

We model thin magnetic flux tubes as they rise from the bottom of a stellar convection zone to the photosphere. On emergence they form active regions, i.e. star spots. This model was very successfully applied to the solar case, where the simulations where in agreement with the butterfly diagram, Joy's law, and Hale's law. We propose the use of a similar model to describe stellar activity in the more extreme form found on active stars. A comparison between Doppler-images of well-observed pre-MS stars and a theoretically derived probability of star-spot formation as a function of latitude is presented.

Photoinduced Charge Transfer Dynamics in Carotenoid-Porphyrin-C60 Triad via the Linearized Semiclassical Nonequilibrium Fermi's Golden Rule

2020 ◽  
Author(s):  
Zhengqing Tong ◽  
Margaret S. Cheung ◽  
Barry D. Dunietz ◽  
Eitan Geva ◽  
Xiang Sun
Keyword(s):  
Charge Transfer ◽  
Golden Rule ◽  
Time Dependent ◽  
Rate Coefficients ◽  
Initial State ◽  
Photoinduced Charge Transfer ◽  
Transfer Rates ◽  
Fermi's Golden Rule ◽  
Photoinduced Charge ◽  
Fermi’S Golden Rule

The nonequilibrium Fermi’s golden rule (NE-FGR) describes the time-dependent rate coefficient for electronic transitions, when the nuclear degrees of freedom start out in a <i>nonequilibrium</i> state. In this letter, the linearized semiclassical (LSC) approximation of the NE-FGR is used to calculate the photoinduced charge transfer rates in the carotenoid-porphyrin-C<sub>60</sub> molecular triad dissolved in explicit tetrahydrofuran. The initial nonequilibrium state corresponds to impulsive photoexcitation from the equilibrated ground-state to the ππ* state, and the porphyrin-to-C<sub>60</sub> and the carotenoid-to-C<sub>60</sub> charge transfer rates are calculated. Our results show that accounting for the nonequilibrium nature of the initial state significantly enhances the transition rate of the porphyrin-to-C<sub>60</sub> CT process. We also derive the instantaneous Marcus theory (IMT) from LSC NE-FGR, which casts the CT rate coefficients in terms of a Marcus-like expression, with explicitly time-dependent reorganization energy and reaction free energy. IMT is found to reproduce the CT rates in the system under consideration remarkably well.

scholarly journals Can short time delays influence the variability of the solar cycle?

2010 ◽  
Vol 6 (S271) ◽  
pp. 288-296
Author(s):  
Laurène Jouve ◽  
Michael R. E. Proctor ◽  
Geoffroy Lesur
Keyword(s):  
Solar Cycle ◽  
Convection Zone ◽  
Mean Field ◽  
Period Doubling ◽  
Temporal Modulation ◽  
Solar Convection Zone ◽  
Flux Tubes ◽  
Solar Convection ◽  
Short Time ◽  
Period Doubling Bifurcations

AbstractWe present the effects of introducing results of 3D MHD simulations of buoyant magnetic fields in the solar convection zone in 2D mean-field Babcock-Leighton models. In particular, we take into account the time delay introduced by the rise time of the toroidal structures from the base of the convection zone to the solar surface. We find that the delays produce large temporal modulation of the cycle amplitude even when strong and thus rapidly rising flux tubes are considered. The study of a reduced model reveals that aperiodic modulations of the solar cycle appear after a sequence of period doubling bifurcations typical of non-linear systems. We also discuss the memory of such systems and the conclusions which may be drawn concerning the actual solar cycle variability.

scholarly journals Modelling Time-Dependent Diffusion in Am Star Envelopes

1993 ◽  
Vol 137 ◽  
pp. 272-274 ◽  
Author(s):  
G. Alecian
Keyword(s):  
Diffusion Process ◽  
Mass Loss ◽  
Main Sequence ◽  
Convection Zone ◽  
Time Dependent ◽  
Radiative Zone

AbstractWe study the diffusion process occurring just below the superficial convection zone of Am stars, improving the methods used sofar. We are now able to compute, in a more realistic way, the evolution of the concentrations during the stay of the stars on the main sequence for a large number of elements. This allows to better constrain the different properties (mass loss, depth of the superficial convection zone, transition between convection and radiative zone) entering the modelling of Am stars in the framework of a diffusion-dominant description.

scholarly journals Ion velocity distributions within the LLBL and their possible implication to multiple reconnections

2004 ◽  
Vol 22 (1) ◽  
pp. 213-236 ◽  
Author(s):  
O. L. Vaisberg ◽  
L. A. Avanov ◽  
T. E. Moore ◽  
V. N. Smirnov
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Flux Tube ◽  
Magnetic Flux Tube ◽  
Flux Tubes ◽  
Different Types ◽  
Subsolar Point ◽  
Magnetic Flux Tubes ◽  
Ion Velocity ◽  
Field Lines

Abstract. We analyze two LLBL crossings made by the Interball-Tail satellite under a southward or variable magnetosheath magnetic field: one crossing on the flank of the magnetosphere, and another one closer to the subsolar point. Three different types of ion velocity distributions within the LLBL are observed: (a) D-shaped distributions, (b) ion velocity distributions consisting of two counter-streaming components of magnetosheath-type, and (c) distributions with three components, one of which has nearly zero parallel velocity and two counter-streaming components. Only the (a) type fits to the single magnetic flux tube formed by reconnection between the magnetospheric and magnetosheath magnetic fields. We argue that two counter-streaming magnetosheath-like ion components observed by Interball within the LLBL cannot be explained by the reflection of the ions from the magnetic mirror deeper within the magnetosphere. Types (b) and (c) ion velocity distributions would form within spiral magnetic flux tubes consisting of a mixture of alternating segments originating from the magnetosheath and from magnetospheric plasma. The shapes of ion velocity distributions and their evolution with decreasing number density in the LLBL indicate that a significant part of the LLBL is located on magnetic field lines of long spiral flux tube islands at the magnetopause, as has been proposed and found to occur in magnetopause simulations. We consider these observations as evidence for multiple reconnection Χ-lines between magnetosheath and magnetospheric flux tubes. Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; solar wind-magnetosphere interactions)

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