634 research outputs found
The Sun's Preferred Longitudes and the Coupling of Magnetic Dynamo Modes
Observations show that solar activity is distributed non-axisymmetrically,
concentrating at "preferred longitudes". This indicates the important role of
non-axisymmetric magnetic fields in the origin of solar activity. We
investigate the generation of the non-axisymmetric fields and their coupling
with axisymmetric solar magnetic field. Our kinematic generation (dynamo) model
operating in a sphere includes solar differential rotation, which approximates
the differential rotation obtained by inversion of helioseismic data, modelled
distributions of the turbulent resistivity, non-axisymmetric mean helicity, and
meridional circulation in the convection zone. We find that (1) the
non-axisymmetric modes are localised near the base of the convection zone,
where the formation of active regions starts, and at latitudes around
; (2) the coupling of non-axisymmetric and axisymmetric modes
causes the non-axisymmetric mode to follow the solar cycle; the phase relations
between the modes are found. (3) The rate of rotation of the first
non-axisymmetric mode is close to that determined in the interplanetary space.Comment: 22 pages, 18 figures. Accepted for publication in the Astrophysical
Journa
Relativistic Landau damping of longitudinal waves in isotropic pair plasmas
Landau damping is described in relativistic electron-positron
plasmas. Relativistic electron-positron plasma theory contains
important new effects when compared with classical plasmas. For
example, there are undamped superluminal wave modes arising from
both a continuous and discrete mode structure, the former even in
the classical limit. We present here a comprehensive analytical
treatment of the general case resulting in a compact and useful
form for the dispersion relation. The classical pair-plasma case
is addressed, for completeness, in an appendix
Quantum key distribution with higher-order alphabets using spatially-encoded qudits
We propose and demonstrate a quantum key distribution scheme in higher-order
-dimensional alphabets using spatial degrees of freedom of photons. Our
implementation allows for the transmission of 4.56 bits per sifted photon,
while providing improved security: an intercept-resend attack on all photons
would induce an error rate of 0.47. Using our system, it should be possible to
send more than a byte of information per sifted photon.Comment: 4 pages, 5 figures. Replaced with published versio
Meridional Circulation and Global Solar Oscillations
We investigate the influence of large-scale meridional circulation on solar
p-modes by quasi-degenerate perturbation theory, as proposed by
\cite{lavely92}. As an input flow we use various models of stationary
meridional circulation obeying the continuity equation. This flow perturbs the
eigenmodes of an equilibrium model of the Sun. We derive the signatures of the
meridional circulation in the frequency multiplets of solar p-modes. In most
cases the meridional circulation leads to negative average frequency shifts of
the multiplets. Further possible observable effects are briefly discussed.Comment: 14 pages, 5 figures, submittted to Solar Physics Topical Issue
"HELAS
Vlasov equation and collisionless hydrodynamics adapted to curved spacetime
The modification of the Vlasov equation, in its standard form describing a
charged particle distribution in the six-dimensional phase space, is derived
explicitly within a formal Hamiltonian approach for arbitrarily curved
spacetime. The equation accounts simultaneously for the Lorentz force and the
effects of general relativity, with the latter appearing as the gravity force
and an additional force due to the extrinsic curvature of spatial
hypersurfaces. For an arbitrary spatial metric, the equations of collisionless
hydrodynamics are also obtained in the usual three-vector form
Theoretical and numerical studies of wave-packet propagation in tokamak plasmas
Theoretical and numerical studies of wave-packet propagation are presented to
analyze the time varying 2D mode structures of electrostatic fluctuations in
tokamak plasmas, using general flux coordinates. Instead of solving the 2D wave
equations directly, the solution of the initial value problem is used to obtain
the 2D mode structure, following the propagation of wave-packets generated by a
source and reconstructing the time varying field. As application, the 2D WKB
method is applied to investigate the shaping effects (elongation and
triangularity) of tokamak geometry on the lower hybrid wave propagation and
absorbtion. Meanwhile, the Mode Structure Decomposition (MSD) method is used to
handle the boundary conditions and simplify the 2D problem to two nested 1D
problems. The MSD method is related to that discussed earlier by Zonca and Chen
[Phys. Fluids B 5, 3668 (1993)], and reduces to the well-known "ballooning
formalism" [J. W. Connor, R. J. Hastie, and J. B. Taylor, Phys. Rev. Lett. 40,
396 (1978)], when spatial scale separation applies. This method is used to
investigate the time varying 2D electrostatic ITG mode structure with a mixed
WKB-full-wave technique. The time varying field pattern is reconstructed and
the time asymptotic structure of the wave-packet propagation gives the 2D
eigenmode and the corresponding eigenvalue. As a general approach to
investigate 2D mode structures in tokamak plasmas, our method also applies for
electromagnetic waves with general source/sink terms, either by an
internal/external antenna or nonlinear wave interaction with zonal structures.Comment: 24 pages, 14 figure
Kinematic dynamo wave in the vicinity of the solar poles
We consider a dynamo wave in the solar convective shell for the kinematic
-dynamo model. The spectrum and eigenfunctions of the
corresponding equations are derived analytically with the aid of the WKB
method. Our main aim here is to investigate the dynamo wave behavior in the
vicinity of the solar poles. Explicit expressions for the incident and
reflected waves are obtained. The reflected wave is shown to be relatively weak
in comparison to the incident wave. The phase shifts and the ratio of
amplitudes of the two waves are found.Comment: 20 pages, 2 EPS figure
Towards A Mean-Field Formulation Of The Babcock-Leighton Type Solar Dynamo. I. Alpha Coefficient Versus Durney's Double Ring Approach
We develop a model of the solar dynamo in which, on the one hand, we follow
the Babcock-Leighton approach to include surface processes like the production
of poloidal field from the decay of active regions, and, on the other hand, we
attempt to develop a mean field theory that can be studied in quantitative
detail. One of the main challenges in developing such models is to treat the
buoyant rise of toroidal field and the production of poloidal field from it
near the surface. We build up a dynamo model with two contrasting methods of
treating buoyancy. In one method, we incorporate the generation of the poloidal
field near the solar surface by Durney's procedure of double ring eruption. In
the second method, the poloidal field generation is treated by a positive
alpha-effect concentrated near the solar surface, coupled with an algorithm for
handling buoyancy. The two methods are found to give qualitatively similar
results.Comment: 32 pages, 27 figures, uses aastex.cls and epsfig.st
Self consistent radio-frequency wave propagation and peripheral direct current plasma biasing: Simplified three dimensional non-linear treatment in the 'wide sheath' asymptotic regime
The chromosphere: gateway to the corona, or the purgatory of solar physics?
I argue that one should attempt to understand the solar chromosphere not only
for its own sake, but also if one is interested in the physics of: the corona;
astrophysical dynamos; space weather; partially ionized plasmas; heliospheric
UV radiation; the transition region. I outline curious observations which I
personally find puzzling and deserving of attention.Comment: To appear in the proceedings of the 25th NSO Workshop "Chromospheric
Structure and Dynamics. From Old Wisdom to New Insights", Memorie della
Societa' Astronomica Italiana, Eds. Tritschler et a
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