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Author name code: chiuderi
ADS astronomy entries on 2022-09-14
author:"Chiuderi, Claudio"
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Title: Basics of Plasma Astrophysics
Authors: Chiuderi, C.; Velli, M.
2015bps..book.....C Altcode:
No abstract at ADS
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Title: A new fluid scheme for weakly collisional plasmas: 2. The
case of solar wind
Authors: Pietrini, P.; Torricelli-Ciamponi, G.; Chiuderi, C.
2012JGRA..11712105P Altcode:
Chiuderi et al. (2011) (paper 1) investigated the possibility of
extending to weakly collisional plasmas the new fluid scheme recently
developed by Chen et al. (2000) for neutral gases. Paper 1 established
the conditions under which such an extension is feasible and identified
the solar wind as a good candidate to test the new theory. Such a test
is performed in the present paper, where we actually build a model for
the fast solar wind and compare it with the available data. We define
the basic assumptions adopted: steadiness, spherical symmetry, and
neglect of magnetic field and of minor ions. We limit our treatment to
the range 2-215 R<SUB>⊙</SUB>to cover the details of the transition
from collisional to collisionless regimes, excluding the low corona
and the chromosphere that appear to be far too complex to be described
by our simple model. We present a detailed discussion concerning
the choice of the parameters and boundary conditions entering the
model. We then proceed to the actual construction of the model, whose
main merit lies in its simplicity: it is a two-fluid model capable
of accounting for both viscosity and thermal conduction, in spite of
the very limited number of equations to be solved. We then critically
compare our results with the observations and with other recent solar
wind models. The level of agreement with the data is quite satisfactory
and is comparable with that obtained by more sophisticated models.
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Title: A new fluid scheme for weakly collisional plasmas: 1. General
theory
Authors: Chiuderi, C.; Pietrini, P.; Torricelli-Ciamponi, G.
2011JGRA..116.4107C Altcode:
We present a new approach to the study of two-fluid hydrodynamics of
weakly collisional plasma systems, such as those frequently encountered
in the astrophysical context. Our starting point is the novel procedure
developed in past years by Chen, Rao, and Spiegel (CRS) for the
fluid description of semicollisional neutral monoatomic gases. The
new system of fluid equations that include viscous and conductive
effects has been successfully tested. However, the extension of such
a procedure to plasmas is not a straightforward one. We have to deal
with (at least) two components, with vastly different values of the
masses, and the nature of collisions between charged particles is
substantially different from the neutral particle case. We perform a
preliminary careful examination of the basic requirements of the CRS
method and identify the conditions under which an extension of such
method is indeed possible. We then derive the system of fluid equations
appropriate to the description of a weakly collisional two-component
plasma in the new scheme and discuss the differences with respect to
the more familiar Navier-Stokes approach. This paper is therefore of
a general theoretical nature. However, we also point out that solar
wind is a good testing ground for the newly derived system of fluid
equations. This application will be the subject of a subsequent paper.
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Title: Solar MHD: An Introduction
Authors: Chiuderi, C.; Velli, M.
2009LNP...778...45C Altcode:
The Universe is filled by plasmas. In fact, it can be reasonably
estimated that more than 95% of (standard) cosmic matter is found in the
plasma state. Given this basic fact, it is apparent that plasma physics
is the basic tool to understand the mechanisms that are at work in
the astrophysical context and to interpret the observations. The Earth
represents a notable exception as far as the presence of natural plasmas
is concerned, a lucky circumstance for living beings. In practice,
terrestrial plasmas are almost exclusively produced during electrical
discharges, such as lightning. If plasmas are almost absent on Earth
and in the low-altitude atmosphere, they start to be the dominant
state of matter immediately beyond the ionosphere, the magnetosphere,
and the whole heliosphere that includes the entire solar system made
up of plasmas. The Sun, like the other stars, is made up of ionized
gas almost everywhere.
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Title: Effect of suprathermal particles on the quiet Sun radio
emission
Authors: Chiuderi, C.; Chiuderi Drago, F.
2004A&A...422..331C Altcode:
The bremsstrahlung emissivity and absorption coefficient in the
radiofrequency range are derived under the assumption that the electron
population is not purely thermal, but presents a tail of high energy
particles. This population is approximated by a two-component Maxwellian
distribution and by the kappa-functions of different (integer) index. It
is shown that, if the temperature ratio of the two Maxwellians is larger
than 10, the absorption coefficient and the effective temperature
(the quantities entering the radio transfer equation) depend only on
the fraction R of particles in the highest temperature Maxwellian. In
the case of kappa-functions the above quantities depend on the index
n of the functions. <P />The microwave radio spectrum is computed
for different values of R and for 3 ≤ n ≤ 6, finding, in all
cases, brightness temperatures lower than those computed with a pure
thermal distribution. This could explain some inconsistencies found
between radio and EUV observations. <P />Appendix is only available
in electronic form at http://www.edpsciences.org
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Title: Effect of suprathermal particles on the quiet sun radio
emission
Authors: Chiuderi, C.; Chiuderi Drago, F.
2004cosp...35..289C Altcode: 2004cosp.meet..289C
The bremsstrahlung emissivity and absorption coefficient in the
radiofrequencies range are derived in the assumption that the
electron population is not purely thermal, but presents a tail of high
energy particles. This population is approximated by a bi-Maxwellian
distribution and by kappa-functions of different (integer) index. It is
shown that, if the temperature ratio of the two Maxwellians is larger
than 10, the absorption coefficient and the effective temperature
(the quantities entering the radio transfer equation) depend only on
the fraction R of particles in the highest temperature maxwellian. In
case of kappa-functions the above qunatities depend on the index
n of the functions. The microwave radio spectrum is computed for
different values of R and for 3 ≤ n ≤ 6, finding, in all cases,
brightness temperatures lower than those computed with a pure thermal
distribution. This fact could explain some inconsistencies found
between radio and EUV observations.
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Title: Effect of Superthermal Particles in the Quiet Sun Radio
Emission
Authors: Chiuderi, C.; Chiuderi Drago, F.
2003MmSAI..74..695C Altcode:
The bremsstrahlung emissivity and absorption coefficient, in the
radiofrequencies range, are derived in the assumption that the
electron population is not purely thermal, but presents a tail of high
energy particles. This population is approximated by a bi-Maxwellian
distribution. It is shown that, if the temperature ratio of the two
Maxwellians is larger than 10, the absorption coefficient and the
effective temperature depend only on the fraction R of particles in
the highest temperature Maxwellian. The microwave radio spectrum is
computed for some values of R, finding brightness temperatures lower
than those computed with a pure thermal distribution. This fact could
explain some inconsistencies found between radio and EUV observations.
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Title: The World Space Observatory Project WSO/UV
Authors: Pagano, I.; Rodonò, M.; Bonanno, G.; Buson, L.; Cassatella,
A.; De Martino, D.; Wamsteker, W.; Shustov, B.; Barstow, M.; Brosch,
N.; Fu-Zhen, Cheng; Dennefeld, M.; Gomez de Castro, A. I.; Kappelmann,
N.; Sahade, J.; Van der Hucht, K.; Solheim, J. -E.; Haubold, H.;
Altamore, A.; Andretta, V.; Badiali, M.; Becciani, U.; Busà, I.;
Cappellaro, E.; Cardini, D.; Catalano, S.; Castellani, V.; Chiaberge,
M.; Chieffi, A; Chiuderi, C.; Cosentino, R.; Cremonese, G.; Cutispoto,
G.; Falomo, R.; Ferrini, F.; Franchini, M.; Frasca, A.; Giovannelli,
F.; Gori, L.; Gomez, M.; Hack, M.; Lanza, A. F.; Lanzafame, A.;
Malagnini, M. L.; Marilli, E.; Marziani, P.; Matteucci, F.; Morossi,
C.; Munari, U.; Pace, E.; Panagia, N.; Pasinetti, L.; Piotto, G.;
Polcaro, F.; Radovich, M.; Ragaini, S.; Rifatto, A.; Rossi, C.;
Scuderi, S.; Selvelli, P.; Silvotti, R. L. Terranegra5, M. Turatto3,
M. Uslenghi22, R. Viotti4
2003MSAIS...3..327P Altcode: 2003astro.ph..6554P
The World Space Observatory Project is a new space mission concept,
grown out the needs of the Astronomical community to have access to
the part of the electromagnetic spectrum where all known physics can be
studied on all possible time scales: the Ultraviolet range. The physical
diagnostics in this domain supply a richness of new experimental
data unmatched by any other wavelength range, for the studies of the
Universe. As WSO/UV has been driven by the needs of scientists from
many different countries, a new implementation model was needed to
bring the World Space Observatory to reality. The WSO/UV consists of a
single Ultraviolet Telescope in orbit, incorporating a primary mirror
of 1.7 m diameter feeding a UV spectrograph and UV Imagers.
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Title: Nonlinear processes in heliospheric plasma: models and
observations
Authors: Velli, M.; Einaudi, G.; Chiuderi, C.; Veltri, P. L.;
MM02242342 project Team; Betta, R.; Londrillo, P.; Rappazzo, F.;
Del Zanna, L.; Landi, S.; Malara, F.; Carbone, V.; Zimbardo, G.;
Primavera, L.; Greco, A.; Sorriso-Valvo, L.; Pommois, P.; Lepreti, F.
2003MmSAI..74..425V Altcode:
We present the scientific objectives of the research project `Nonlinear
processes in heliospheric plasma: models and observations', co-financed
by the Italian Ministry for Universities and Scientific Research, as
well as a summary of some of the results obtained. The objective of the
proposal was a detailed study of the nonlinear and dissipation-scale
dynamics of heliospheric plasmas. The project focused on the study of
wave propagation and properties of turbulence at the various scales,
from the macroscopic scales of the solar wind, down to the microscopic
scales of magnetic reconnection and turbulence dissipation, in its
two aspects of evolutionary internal dynamics, and its effects on the
transport of energetic particles of both heliospheric and extra-solar
origins (cosmic rays, interstellar neutrals ionized in the solar wind
as pickup ions).
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Title: Resistivity Independent Alfven Waves Dissipation
Authors: Chiuderi, C.; Califano, F.
1999ESASP.446..235C Altcode: 1999soho....8..235C
The heating of high temperature plasmas by MHD waves is one of the
most interesting and challenging problems of plasma physics especially
when the energy is injected into the system at length scales much
larger than the dissipative ones. It has been conjectured that in
2-D MHD systems the possibility exist of establishing a state in
which energy is dissipated at a rate that is independent of the ohmic
resistivity and that the time needed to reach such a state is finite and
independent of resistivity as well. We study the nonlinear interaction
of long-wavelength, small amplitude perturbations with an inhomogeneous
magnetic field showing that energy is transferred to the fluctuations
from the background equilibrium. In the case of an isolated system,
the free energy initially stored in the equilibrium would decrease
and the field would tend to become homogeneous. To model the process
of energy injection into the system, we force the large scale field to
maintain its initial profile. In these circumstances, we prove that it
is actually possible after a finite time, independent of the dissipative
mechanism, to generate a well developed 2-D MHD turbulent state where
the dissipation rate does not depend on the Lundquist number, at least
for values of the order of a few thousands. To our knowledge, this is
the first time in which the existence of the conjectured resistivity
independent dissipation has been explicitly demonstrated.
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Title: Resistivity-independent dissipation of magnetohydrodynamic
waves in an inhomogeneous plasma
Authors: Califano, F.; Chiuderi, C.
1999PhRvE..60.4701C Altcode:
The heating of high temperature plasmas by magnetohydrodynamic
(MHD) waves is one of the most interesting and challenging problems
of plasma physics especially when the energy is injected into the
system at length scales much larger than the dissipative ones. It has
been conjectured that in two-dimensional MHD systems the possibility
exists of establishing a state in which energy is dissipated at a
rate that is independent of the Ohmic resistivity and that the time
needed to reach such a state is finite and independent of resistivity
as well. In this paper we prove that this is actually possible as
a result of the nonlinear interaction of long-wavelength, “small”
amplitude perturbations with a constant, inhomogeneous magnetic field,
at least in the relatively moderate Lundquist number (magnetic Reynolds)
range 100<=S<=3200.
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Title: A New Model for Gas Excitation in the Beam of Stellar Jets
Authors: Bacciotti, F.; Pouquet, A.; Chiuderi, C.
1998ajop.conf..239B Altcode:
No abstract at ADS
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Title: Optical Emission in the Beam of Stellar Jets: A Possible
Mechanism
Authors: Bacciotti, F.; Chiuderi, C.; Pouquet, A.
1997ApJ...478..594B Altcode:
We propose a mechanism for the optical emission observed in the
beam section of stellar jets based on the stability properties
of circularly polarized Alfvén waves propagating in the partially
ionized medium filling the jet's channel. We first derive the relevant
magnetohydrodynamic equations, which include the Hall term for such
a partially ionized medium, a term which give rise to dispersive
effects. Quasi-equipartition of thermal and magnetic energies
is assumed, and the model is developed in the one-dimensional
approximation but keeping the three components of the vectorial
fields. Mild compressions or very weak shocks occur in the flow when
instabilities develop, depending on the relative sign of the angular
momentum of the underlying accretion disk and the external magnetic
field. Simulations performed under quite general conditions show that
the temperature/density perturbations associated with the instability
are consistent with the average luminosity contrast observed in the
jet's beam between bright knots and interknot regions.
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Title: Concluding remarks: solar physics and the advancement of
physics
Authors: Chiuderi, C.
1997MmSAI..68..449C Altcode:
No abstract at ADS
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Title: A mechanism for the optical emission of stellar jets
Authors: Chiuderi, Claudio; Bacciotti, Francesca; Pouquet, Annick
1997IAUS..182P..79C Altcode:
A mechanism for the optical emission of stellar jets is proposed,
based on the stability properties of circularly polarized Alfven waves
propagating in the partially ionized medium filling the jet channel. We
adopt a MHD description including the Hall term, as appropriate for
such a medium. Quasi-equipartition of thermal and magnetic energies
is assumed. Shock-like features appear in the flow when instabilities
develop, depending on the alignment of the angular momentum vector of
the accretion disk along or against the background magnetic field. We
show that the proposed mechanism is capable of reproducing the observed
luminosity contrast between bright knots and interknot regions.
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Title: Induced Deposition of Magnetic Energy in the Solar Corona
Authors: Einaudi, Giorgio; Califano, Francesco; Chiuderi, Claudio
1996ApJ...472..853E Altcode:
In this paper a numerical study of the propagation and dissipation
properties of magnetohydrodynamic waves in an incompressible magnetized
plasma is presented. The magnetic field is assumed to be unidirectional,
but its magnitude varies in a direction perpendicular to the field. The
analysis concerns both linear and nonlinear waves. The main findings are
the following. <P />Among the waves whose amplitude never exceeds the
linear limit, short-wavelength waves dissipate more efficiently than
those of long wavelength. The dissipated energy is at most the energy
initially injected into the system in the form of waves, the background
magnetic field remaining unaltered. When the initial amplitude is
significantly increased from very small values, but remains still
substantially lower than the background field, a nonlinear cascade is
excited and dissipation is greatly enhanced in the long- wavelength
limit. The dissipated energy in this case exceeds that contained in
the waves initially injected into the system, which shows that also
part of the unperturbed field is actually dissipated. <P />A second
important point concerns the formation of localized current sheets
in a finite time as a result of the propagation of the waves. Such
current sheets are formed in a nonlinear process triggered by the
same mechanism responsible for the formation of linear resonant normal
modes. The dissipation rate of such modes is known to be independent
of the Reynolds number. By analogy, it is conjectured that the time of
formation of current sheets might not depend on the magnetic Reynolds
number.
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Title: Exact solutions for symmetric magnetohydrodynamic equilibria
with mass flow.
Authors: Del Zanna, L.; Chiuderi, C.
1996A&A...310..341D Altcode:
In this paper the problem of ideal magnetohydrodynamic equilibria with
mass flow is treated. Under the assumption of general symmetry (i.e. one
ignorable spatial coordinate) we derive a generalized Grad-Shafranov
equation in an unspecified curvilinear coordinate system. If
incompressibility is assumed an elliptical equation is derived and a
new, totally analytical method of solution is proposed. This is based
on a particular self-similar separation of the variables in the unknown
flux function and leads to an ordinary, non-linear differential equation
for the profile of the magnetic and flow surfaces. Three novel classes
of solutions are derived in different geometries, all being flexible
(they contain a minimum of three free functions) and regular, which
makes them suitable for astrophysical applications. These are flows
in magnetic flux tubes with non-circular section, flows in magnetic
arcades above the solar surface and collimated, axisymmetric outflows.
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Title: Theories of Coronal Heating (Invited)
Authors: Chiuderi, Claudio
1996ASPC..111...69C Altcode: 1997ASPC..111...69C
This paper reviews the most recent trends in the theory of coronal
heating. It is argued that the corona does most likely find itself
in a fully developed turbulent state. The turbulence is the direct
consequence of the random photospheric motions that stress the
footpoints of magnetic field lines. Although the details of the
propagation of energy from the photosphere to the corona could depend
on the frequency of the driving motions, in all cases the key feature
to explain coronal heating seems to be the formation and disruption of
localized current sheets. This suggests a statistical approach to the
theory of coronal heating as well as a possible link between heating
and flares.
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Title: Stellar Jets: Spectral Diagnostics and Fluidodynamic Models
Authors: Bacciotti, F.; Chiuderi, C.; Hirth, G.; Natta, A.; Oliva, E.
1996LNP...465..329B Altcode: 1996doay.conf..329B
We present a non-standard, straightforward procedure for a
model-independent determination of crucial physical parameters of the
linear section of stellar jets, such as the hydrogen ionization fraction
x and the temperature T <SUB> e </SUB> of the emitting gas. The method
can be easily applied to every Herbig-Haro jet for which the brightest
red lines have been measured, even if the lines are not calibrated and
the ratios are not corrected for reddening. In the cases of HH 34 and
HH 111 we find x∼0.1 and T <SUB>e</SUB>∼6000. The momentum rates
evaluated with the derived total number densities (N∼10<SUP>4</SUP>
cm<SUP>-3</SUP>) give strong support to the picture in which the
luminous jet is only the fastest and most ionized component of a
wider neutral flow that, in turn, has the capability of accelerating
a molecular outflow. The ionization fraction cannot be explained in
terms of equilibrium processes reflecting the local physical conditions
of the medium, however the recombination length scales turn out to be
comparable to the linear extension of the most luminous part of the
jets: the observed degree of ionization is most likely the remnant of
the heating and the excitation occurred in the initial accelerating
region. This picture is supported by our diagnostics of RW Aur's
optical jet, for which spatially resolved spectra have been taken:
in this case the ionization fraction (around 10% again) is found to
decrease slowly with distance from the star.
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Title: Plasma Astrophysics
Authors: Chiuderi, Claudio; Einaudi, Giorgio
1996LNP...468.....C Altcode: 1996plas.conf.....C
The book contains the notes of the lectures presented by outstanding
experts at the 7th EADN School on plasma astrophysics. It is an
up-to-date review of a number of basic topics in the physics of cosmic
plasmas. The subject is treated both from a theoretical point of view
and from that of the observational and diagnostic tools that provide
us with the physically relevant data. The reader will have at hands a
comprehensive and rather complete presentation of the subject, thanks
also to the parallel development of the theoretical and experimental
aspects. The book addresses graduate students and researchers in
different areas who want to have a rapid and up-to-date introduction
to this subject.
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Title: Stellar Jets: Spectral Diagnostics and Fluidodynamic Models
Authors: Bacciotti, F.; Chiuderi, C.; Hirth, G.; Natta, A.; Oliva, E.
1996LNP...465E.781B Altcode:
No abstract at ADS
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Title: The structure of optical stellar jets: a phenomenological
analysis.
Authors: Bacciotti, F.; Chiuderi, C.; Oliva, E.
1995A&A...296..185B Altcode:
In this paper we discuss the possible mechanisms of formation ot
the nodular structure of Herbig-Haro jets. The available spectral
observations of the linear jet section in the HH 34 and the HH 111
complexes are reviewed, in order to diagnostic the temperature and
ionization state of the emitting material in a way as model-independent
as possible. The values we find by means of an original although
straightforward diagnostic procedure (T~6000K, x=n_H^+^_/n_H_~0.1, in
both cases), are similar to those empirically determined by Bruegel
et al. (1981) and Boehm & Solf (1990) for the compact object HH
7. Our results lead to a value of the momentum rate in these flows
comparable to the rates observed in high-speed neutral winds (Lizano
et al. 1988), giving support to the view according to which the bright
optical jet actually identifies the axial portion of the neutral flow,
and marks the location where the matter attains its maximum velocity
and an observable amount of ionization. The ionization derived from
the observations is likely to be a remnant of the heating and the
excitation occurred in the accelerating region, where the wind is
probably focused by the passage through a nozzle. The recombination
time scale appropriate for the rather low electron densities in the
jet is found to be close to the crossing time of the visible portion
of the jet. Combining kinematical and energetic considerations we show
that physical conditions consistent with the observed jet's emission
can be obtained through "soft" compressions of the central portion of
the flow, caused by 'damped' Kelvin-Helmoltz instabilities generated at
the jet-ambient contact discontinuity. These compressions concentrate
in smaller volumes the already available internal energy that is
eventually radiated in optical and IR lines, unlike the weak shocks
that actually increase the internal energy content by transforming the
bulk kinetic energy into thermal random motions. A picture of this kind
seems capable of resolving the long-standing problem of conciling the
high supersonic velocity of the ionized material and the low excitation
nature of the emission, and, at the same time, provides a very natural
explanation for a number of observational constraints, among which the
increase of the [SII]/Hα ratio along the jet and the disappearance
of the optical emission after a characteristic scale length.
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Title: Normal modes of a resistive nonuniform plasma
Authors: Chiuderi, C.; Califano, F.
1994R&QE...37..355C Altcode:
The propagation and dissipation properties of magnetohydrodynamic
waves in a nonuniform, highlyconducting plasma, is investigated with a
normal mode approach. The interaction between the perturbation and the
non-uniform supporting medium is analyzed as the main mechanism able
to produce the small scale spatial structure necessary to dissipate
efficiently the wave energy. Two fundamental classes of modes are
found, characterized by their resistive or ideal asymptotic behavior;
the damping rates are shown to be orders of magnitude larger than those
obtained when the plasma is perfectly homogeneous, and an application
to the problem of solar coronal heating is discussed.
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Title: Coronal heating and solar activity: The role of waves
Authors: Einaudi, G.; Chiuderi, C.; Califano, F.
1993AdSpR..13i..85E Altcode: 1993AdSpR..13...85E
Coronal heating and solar activity are manifestations of the complex
interaction between the magnetic field and the photospheric plasma
motions. As a result of such an interaction magnetohydrodynamic
waves are generated: their dissipation may provide the basic physical
mechanism to heat the corona. This paper describes the present status of
knowledge of the physics underlying the dissipation of MHD waves. After
having stressed the importance of the formation of small spatial scales
for achieving an efficient dissipation, we review the theory of linear
MHD waves in nonuniform media based on a normal mode approach. We then
present the results of some recent numerical experiments and interpret
them in the framework of the theory of MHD turbulence. A plan of future
work will also be presented.
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Title: Keys to understanding the corona.
Authors: Chiuderi, C.
1993ESASP1157...25C Altcode: 1993srfs.book...25C
The theoretical understanding of the solar corona involves such
different phenomena as the coronal heating and the occurrence of
flares. It is argued that all of these phenomena could be seen as
a manifestation of the same basic physics, the differences being a
question of coherence. The theoretical work needed to support this view
and its possible impact on future observational strategies are outlined.
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Title: LY-A-CO-PO (LY α coronograph/polarimeter): an instrument to
measure coronal magnetic fields
Authors: Fineschi, S.; Chiuderi, C.; Poletto, G.; Hoover, R. B.;
Walker, A. B. C., Jr.
1993MmSAI..64..441F Altcode:
No abstract at ADS
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Title: New Exact Solutions for Magneto-Hydrodynamic Flows and Their
Application to Stellar Jets
Authors: Bacciotti, F.; Chiuderi, C.
1993ASSL..186..357B Altcode: 1993sjbo.conf..357B
No abstract at ADS
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Title: Incompressible Disturbances in Nonuniform Media: Formation
of Small Scales
Authors: Malara, Francesco; Veltri, Pierluigi; Chiuderi, Claudio;
Einaudi, Giorgio
1992ApJ...396..297M Altcode:
The study proposes a phenomenological interpretation of the mechanism
of the formation of small scales during the propagation of an MHD
wave where only z(+) fluctuations are excited. The nonlinear effects
are shown to be negligible when the initial disturbance travels in
the direction of the background magnetic field and its wavelength is
comparable to the nonuniformity scale length. It is shown that the
interaction between the perturbation and the inhomogeneous background
has two effects: the oscillations of neighboring field lines become
rapidly out of phase, producing small scales in the direction of
nonuniformity, and the pressure gradients caused by the perturbation
have the tendency to concentrate energy in the neighborhood of the point
where the wave frequency resonates with the local Alfven frequency,
with a subsequent local creation of small scales.
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Title: Nonresonant Resistive Dissipation of Compressible
Magnetohydrodynamic Waves
Authors: Califano, Francesco; Chiuderi, Claudio; Einaudi, Giorgio
1992ApJ...390..560C Altcode:
The effect of compressibility on the propagation and resistive
dissipation properties of magnetohydrodynamic waves in nonuniform media
is studied by using a normal mode analysis. The paper concentrates on
wave models for which the resistivity acts over the entire system,
thus excluding localized resonant absorption. The wave modes in
nonhomogeneous situations are identified in term of their familiar
homogeneous counterparts and it is shown that only the shear Alfven
and slow magnetosonic modes survive in the resistive regime. The most
promising heating agents in the astrophysical context are shown to be
the shear Alfven waves that behave almost incompressibly.
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Title: Energy Balance in the Prominence / Corona Transition Region
Authors: Chiuderi, C.; Chiuderi Drago, F.
1991SoPh..132...81C Altcode:
The prominence-corona transition region can be observed both at UV and
radio wavelengths. The physical parameters needed to explain one set
of observations are, however, in disagreement with those consistent
with the other one. A solution of the problem is proposed, based on
the proper consideration of the dependence of the thermal conduction
on the angle between the magnetic field and the direction of the local
temperature gradient.
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Title: Nonresonant Resistive Dissipation of Incompressible
Magnetohydrodynamic Waves
Authors: Califano, Francesco; Chiuderi, Claudio; Einaudi, Giorgio
1990ApJ...365..757C Altcode:
The influence of departures from homogeneity on the dissipative
properties of incompressible MHD waves are examined within the
framework of an analytically solvable model in plane geometry. Only
resistive dissipation is taken into account. The existence of a new
class of rapidly oscillating solutions is proved for which the role
of resistivity is not restricted to a single narrow layer, as in the
well-known resonating case, but extends to the whole system.
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Title: Energy Balance in Prominence-Corona Transition Regions
Authors: Chiuderi, C.; Chiuderi-Drago, F.
1990IAUS..142..325C Altcode:
No abstract at ADS
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Title: A Case for Alfven Wave Heating
Authors: Califano, F.; Chiuderi, C.; Einaudi, G.
1990IAUS..142..223C Altcode:
The present study examines the resistive dissipation of Alfven waves in
magnetically structured media within the framework of an analytically
solvable model in plane geometry. It is shown that consideration of
nonideal asymptotic boundary conditions gives rise to a new type of
solutions for the resistively damped Alfven waves that are characterized
by the appearance of very small scales in the x-direction. Since
the normal modes can be thought of as the asymptotic state of the
temporal evolution of an initial perturbation of arbitrary scale, the
appearance of the small scales is interpreted as the result of the
bilinear interaction of the initial perturbation and the nonuniform
equilibrium structure. During the transient the spectrum of modes in the
z-direction remains essentially unchanged, showing that the formation
of small scales across the field takes place well before the possible
development of the nonlinear mode-mode coupling along the field.
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Title: MHD instabilities
Authors: Chiuderi, Claudio
1990MmSAI..61..359C Altcode:
Recent theoretical studies of MHD instabilities in plasmas are reviewed,
with an emphasis on those relevant to the solar corona. Consideration
is given to the time evolution equations for a heated magnetized
plasma losing energy via optically thin radiation, with dissipative
effects described in terms of a finite constant isotropic resisitivity
and shear viscosity and finite thermal conductivity channeled along
the magnetic-field lines. Rayleigh-Taylor, Kruskal-Schwarzschild,
and Kelvin-Helmholtz instabilities are characterized for various
combinations of plasma parameters, and the refinements introduced
to provide a greater degree of realism in solar-corona modeling are
discussed. It is concluded that, although numerical simulations can
now reproduce many features of solar plasmas, the study of analytical
solutions must be pursued as a check on modeling accuracy.
---------------------------------------------------------
Title: MHD of Solar Activity
Authors: Chiuderi, C.
1990PDHO....7..146G Altcode: 1990ESPM....6..146G; 1990dysu.conf..146G
No abstract at ADS
---------------------------------------------------------
Title: MHD of solar activity.
Authors: Chiuderi, C.
1990PDHO....7..121C Altcode: 1990dysu.conf..121C
After a short overview of the subject, the general trends of the present
efforts of modelisation of solar activity by means of MHD theory are
discussed. Such trends are illustrated with the help of a few examples.
---------------------------------------------------------
Title: Extragalactic Jets as Current-carrying Systems. I. Equilibrium
and Stability
Authors: Chiuderi, Claudio; Pietrini, Paola; Ciamponi, Guidetta
Torricelli
1989ApJ...339...70C Altcode:
We present a model for extragalactic jets considered as magnetized
current-carrying structures. Unlike previous models the return currents
are assumed to flow within the jet itself. Standard MHD equations
in cylindrical geometry are used to investigate the equilibrium and
stability properties of such a model. Incompressible thermal matter
flows are included in the equilibrium, but not in the stability
analysis. Absolute stability regions are found and their boundaries
are determined. Linear growth rates for the unstable m = 0 and m = 1
modes are computed. The paper is intended as a basis for a subsequent
one where the behavior of distribution of relativistic electrons in
the given field is studied and predictions of observable polarization
characteristics are made.
---------------------------------------------------------
Title: MHD instabilities of a cylindrical plasma with a realistic
energy equation
Authors: Torricelli-Ciamponi, Guidetta; Ciampolini, Vittorio;
Chiuderi, Claudio
1987JPlPh..37..175T Altcode:
The influence of a realistic energy equation on the stability of
a cylindrical magnetized plasma in a force-free magnetic field is
discussed. Thermal conduction, heating and line radiation are included
in the treatment. Explicit growth rates for the m = 0 and m = 1 modes
are derived and compared with the standard adiabatic or incompressible
time-scales. Finally, the relevance of these results for laboratory
and solar plasmas is discussed.
---------------------------------------------------------
Title: Resistive Instabilities in Coronal Conditions
Authors: Batistoni, P.; Einaudi, G.; Chiuderi, C.
1985SoPh...97..309B Altcode:
Resistive instabilities in a context referring to the solar corona
are rigorously investigated. Various equilibrium configurations are
considered, differing, among other things, by their behaviour with
respect to fast, ideal instabilities. The computations presented cover
in a unified scheme all known regimes of resistive modes and allow one
to determine the fastest timescale over which resistivity can play a
role. Comparisons with previous work as well as possible extensions
are presented.
---------------------------------------------------------
Title: Heating in the solar mantle.
Authors: Chiuderi, C.
1985NASCP2358..101C Altcode: 1985onhm.rept..101C
In the case of the solar chromosphere and corona (the solar mantle)
the primary energy source is the mechanical energy from photospheric
motions. Plenty of energy is available; the problem is to transfer
the needed amount of energy to the proper place to account for the
observations. The global problem is reviewed from the point of view of
the generation and transmission of energy, the intermediate storage
of energy, and the release of energy in such a way that the observed
features are generated.
---------------------------------------------------------
Title: Resistive instabilities in astrophysical conditions - A
critical discussion
Authors: Batistoni, P.; Einaudi, G.; Rubini, F.; Chiuderi, C.;
Torricelli, G.
1985IAUS..107..277B Altcode:
The linear development of resistive instabilities in astrophysical
conditions is investigated numerically with allowance for the effects
of gradients of the current density at the singular points that
produce asymmetries in the F-profiles. An analysis is also made of
the resistive behavior of a system with cylindrical symmetry under
modes possessing an m = 1 azimuthal symmetry. The computational method
used in the study is essentially a numerical boundary layer, with the
internal solution computed exactly; a shooting technique is used to
find the eigenvalues. This method is sufficiently fast and accurate for
magnetic Reynolds numbers up to 10 to the 9th. The spatial structure
and the maximum growth rate of the resistive modes are examined.
---------------------------------------------------------
Title: Magnetic Fields and Thermal Structure of Solar Plasmas
Authors: Einaudi, G.; Torricelli-Ciamponi, G.; Chiuderi, C.
1984SoPh...92...99E Altcode:
The connection between the magnetic field geometry and the thermal
properties of solar coronal structures is investigated. Gravitational
effects, that can modify the spatial dependence of the thermodynamical
quantities, but have no influence on the plasma-field interaction,
are omitted to simplify the problem. A series of two-dimensional models
is constructed, in which a strong coupling between the magnetic field
shear and the thermal structure of the loop is clearly pointed out.
---------------------------------------------------------
Title: The role of magnetic fields in the heating of stellar
atmospheres - Theory
Authors: Chiuderi, C.
1983IAUS..102..375C Altcode:
The last ten years of observations have shown beyond doubt the
fundamental role played by the magnetic field in the heating of stellar
atmospheres. After the recognition of the extreme inhomogeneity of the
solar corona, two new basic trends have appeared in the theoretical
literature on the coronal-heating problem. One is the adoption of a
global point of view that stresses the connection of the properties of
the upper layers to those of the underlying ones. In this way a general
framework is provided, capable of accommodating many possible heating
mechanisms. The second trend is the explicit inclusion in the theory
of the inhomogeneous nature of the stellar envelopes as a result of
the presence of magnetic fields. The present status of knowledge on
the subject, as determined by the above evolution of the theoretical
approach, is reviewed.
---------------------------------------------------------
Title: Equilibrium and Stability of Magnetized Plasmas
Authors: Chiuderi, C.
1982MmSAI..53..863C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Plasmi: il quarto stato della materia.
Authors: Chiuderi, C.
1982GAst....8..361C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Differential rotation, magnetic activity and X-ray emission
of late type giants
Authors: Belvedere, G.; Chiuderi, C.; Paterno, L.
1982A&A...105..133B Altcode:
The observations of X-ray emission from late type main sequence and
giant stars show that a coronal heating due to acoustic waves is
unlikely. <P />As suggested by Vaiana and Rosner, the conversion of
magnetic into thermal energy may be responsible for the X-ray emission
from such a kind of stars. <P />The proposed ingredients in our analysis
are the differential rotation and dynamo action which are able to
generate a magnetic activity at the star's surface which in turn gives
rise to the observed X-ray emission. We assume that the interaction
of rotation with convection, in stars possessing outer convective
envelopes, is the dominant mechanism for generating differential
rotation and dynamo action, and that the stressing of the coronal
magnetic flux tubes by the surface turbulence, converting magnetic into
thermal energy, determine the level of X-ray emission. <P />Therefore
we compute a series of models of luminosity class III giant stars, and
determine the surface X-ray flux. <P />Comparing these results with
those concerning the late type main sequence star models, previously
computed by the same authors, and with observations, it appears that
the proposed mechanism is plausible.
---------------------------------------------------------
Title: Diagnostic of coronal heating processes based on the emission
measure of UV lines
Authors: Torricelli-Ciamponi, G.; Einaudi, G.; Chiuderi, C.
1982A&A...105L...1T Altcode:
It is shown how data on the emission measure (EM) of solar UV lines can
be used to gather information on the structure and heating processes
of solar coronal loops, where the most important feature that must
be incorporated is the presence of a minimum of the EM as a function
of temperature. By doing this, and observing the requirement that the
values of the observable parameters remain in the proper range, it is
possible to strictly limit the value of the temperature exponent in the
heating function. The loop models proposed present strong variations
of the conductive fluxes, and exhibit a marked increase in the region
where heating and radiation balance.
---------------------------------------------------------
Title: The Formation of Solar Prominences
Authors: Chiuderi, C.
1982ASSL...96..137C Altcode: 1982spls.meet..137C
A discussion of the physical conditions and numerical models describing
the formation of solar prominences is presented. Prominences are noted
to occur when thermal conduction is inhibited, with constraints by
gravity and the strength of the magnetic field, which supports the
filament against gravity. Linear growth has been calculated to take
place where the perturbation energy is perpendicular to the field
lines. The fastest linear stage has served as a starting point for
nonlinear computations, which continue on to a new equilibrium. Location
of the equilibrium has been accomplished with three different sets of
boundary conditions, i.e., a fixed slab with no mass or heat flux from
the boundaries, a fixed slab with no mass flux from the boundaries,
and a fixed mass of plasma free to expand or contract, with boundaries
at constant temperature and pressure. It is concluded that a homogeneous
system linearly unstable to thermal instability evolves toward a stable
inhomogeneous state where thin, cool condensations have formed.
---------------------------------------------------------
Title: Loops, fields and all that
Authors: Chiuderi, C.
1981SSRv...29..349C Altcode:
A greater understanding of solar coronal loops may explain the more
elusive processes that heat the solar corona. Loops are strong emitters
in the EUV, XUV, and X-ray ranges and have been recognized as the seat
of coronal flares. They connect regions of opposite magnetic polarity
and therefore delineate the gross topology of the coronal magnetic
field. Since they result from the interplay of pressure, gravitational
and magnetic forces, a quantitative model of the loops must be devised
which will properly account for these forces. The mathematical problem
to be solved is summarized, and the basic equations are presented. The
solutions are simplified, however, since information is missing for some
terms in the equations. It is concluded that high resolution instruments
are needed to probe the solar atmosphere above the chromosphere for
more information if these models are to be completed.
---------------------------------------------------------
Title: Current Confinement in Solar Coronal Loops
Authors: Chiuderi, C.; Einaudi, G.
1981SoPh...73...89C Altcode:
In this paper solar coronal loops are regarded as regions of localized
current flows. The main purpose is to investigate the consequences
of current confinement rather than to produce a model. The physical
and observational basis for this assumption are presented as well
as the connection with previous studies on loop structure. A proper
choice of the current profile allows us to treat quantitatively the
equilibrium structure of the loops and their MHD and resistive stability
properties. Regions of absolute stability against ideal kink modes
are found. Explicit growth rates for the tearing-mode instability are
computed. The possible relevance of other resistive effects is also
discussed and the crucial importance of the small-scale geometry of
the magnetic field outlined.
---------------------------------------------------------
Title: What can we learn from static models of coronal loops
Authors: Chiuderi, C.; Einaudi, G.; Torricelli-Ciamponi, G.
1981A&A....97...27C Altcode:
The possible use of static coronal loop models to derive information on
coronal heating mechanisms is considered. The conditions for the thermal
stability of coronal loops with different sets of boundary conditions
are investigated, and it is shown that stable configurations exist,
including those with zero heat flux at the base. The use of generalized
scaling laws permits the conclusion that no meaningful inferences on
heating processes can be obtained from static models. A comparison
with the results of other authors is also included.
---------------------------------------------------------
Title: Stellar X-ray emission as a consequence of magnetic activity
Authors: Belvedere, G.; Chiuderi, C.; Paterno, L.
1981A&A....96..369B Altcode:
It is noted that the discovery of stellar coronae for main sequence
stars later than FO through K and M is one of the most important
results of Einstein satellite observations. A theoretical estimate is
given of the surface X-ray fluxes for these stars. It is noted that
at coronal temperatures greater than 2,000,000 K X-ray luminosity is
given by the radiative losses of systems of magnetic loops forming
the active regions on the star's surface, namely by the summation of
the single loop emission over the total number of loops in the active
regions. Passing from luminosities to fluxes, it is shown that the
surface X-ray flux is independent of the dimensions of the active
regions present on the star's surface and depends only on the surface
turbulence and the typical strength of the magnetic field in the active
regions. The field twisted by turbulent motions is identified with
the emerging mean toroidal field as computed by stellar dynamo models.
---------------------------------------------------------
Title: Magnetic heating in the sun.
Authors: Chiuderi, C.
1981ASIC...68..269C Altcode: 1981spss.conf..269C
The observational evidence for magnetic heating in the solar corona
is presented. The possible ways of investigating theoretically the
nature of the heating processes are critically discussed. Merits
and disadvantages of the basic mechanisms so far proposed are
reviewed. Finally, a preliminary application of the magnetic heating
concept to stellar coronae is presented.
---------------------------------------------------------
Title: High energy phenomena in the sun
Authors: Chiuderi, C.
1981IAUS...94..367C Altcode:
Solar flares are considered as a model of a widespread astrophysical
phenomenon: the violent conversion of some form of energy into heat
and the kinetic energy of accelerated particles. Following a brief
description of the observational characteristics of solar flares in
the chromosphere and corona, attention is given to mechanisms for
the accumulation of magnetic energy in the solar atmosphere and its
subsequent release by processes of resistive dissipation and dynamical
reconnection giving rise to a flare. It is noted that measurements
of the coronal magnetic field made by EUV polarimeters of the type
planned for the Solar Maximum Mission and Spacelab are necessary for
the definitive solution of the problem of energy release in flares.
---------------------------------------------------------
Title: The stability properties of cylindrical force-free fields:
effect of an external potential field
Authors: Chiuderi, C.; Einaudi, G.; Ma, S. S.; van Hoven, G.
1980JPlPh..24...39C Altcode:
A large-scale potential field with an embedded smaller-scale force-free
structure ( × B = αB) is studied in cylindrical geometry. We consider
cases in which α goes continuously from a constant value α<SUB>0</SUB>
on the axis to zero at large r. Such a choice of α(r) produces fields
which are realistic (few field reversals) but not completely stable. The
MHD-unstable wavenumber regime is found. Since the considered
equilibrium field exhibits a certain amount of magnetic shear,
resistive instabilities can arise. The growth rates of the tearing
mode in the limited MHD-stable region of º space are calculated,
showing time-scales much shorter than the resistive decay time.
---------------------------------------------------------
Title: The solar corona.
Authors: Chiuderi, C.
1980HiA.....5..335C Altcode:
Recent observations from space have shown that the solar corona is
spatially a very structured medium and temporally a very dynamic
one. The consequent changes in the current theoretical ideas about
coronal physics are reviewed. Particular emphasis is placed on the
role of magnetic fields in shaping and heating the coronal structures.
---------------------------------------------------------
Title: The filament instability in a sheared field
Authors: Chiuderi, C.; van Hoven, G.
1980IAUS...91..295C Altcode:
A self-consistent calculation of the thermal instability in a
non-uniform field is performed. It is shown how the dynamic response
of density and temperature to the competing effects of optically-thin
radiation and field-collimated thermal conduction leads to the formation
of characteristic knife-blade filaments. The dynamic calculation
reflects the sheared magnetic field and the finite geometry, as well
as the intimate relation of the sheared magnetic fields to flares.
---------------------------------------------------------
Title: Recent development in coronal structure thermodynamics and
stability.
Authors: Chiuderi, C.
1980AnPh....5..425C Altcode: 1980mhda.conf..425C
No abstract at ADS
---------------------------------------------------------
Title: Wave propagation in a non-isothermal atmosphere and the solar
five-minute oscillations
Authors: Chiuderi, C.; Giovanardi, C.
1979SoPh...64...27C Altcode:
This paper presents a detailed discussion of the properties of
linear, periodic acoustic waves that propagate vertically in a
non-isothermal atmosphere. In order to retain the basic feature of
the solar atmosphere we have chosen a temperature profile presenting
a minimum. An analytical solution of the problem is possible if
T/μ, μ being the mean molecular weight, varies parabolically with
height. The purpose of this study is to point out the qualitative
differences existing between the case treated here and the customary
analysis based on a locally isothermal treatment. The computed velocity
amplitude and the temperature-perturbation as functions of the wave
period exhibit a sharp peak in the region between 180 and 300 s, thus
showing the possibility of interpreting the five-minute oscillations
as a resonant phenomenon. The propagating or stationary nature of
the waves is investigated by a study of the phase of the proposed
analytical solution.
---------------------------------------------------------
Title: The dynamics of filament formation: the thermal instability
in a sheared magnetic field.
Authors: Chiuderi, C.; van Hoven, G.
1979ApJ...232L..69C Altcode:
The dynamics of the thermal plasma instability in a nonuniform magnetic
field, involved in the formation of solar filaments or prominences
in sheared coronal magnetic fields, are examined. An expression is
derived for a perturbation of equilibrium conditions corresponding
to the physical configuration to observed filaments, which allows
the dynamic response of plasma pressure, density and temperature to
optically thin radiation and field-collimated thermal conduction to
be determined. Numerical solutions to the equations demonstrate the
formation of characteristic knife blade condensations and can predict
the initial temporal and spatial scales of coronal filament appearance.
---------------------------------------------------------
Title: High-Energy Phenomena on the Solar Surface
Authors: Chiuderi, C.
1979ASSL...75...33C Altcode: 1979sss..meet...33C
This paper reviews observations of events in the solar atmosphere
that involve the presence of suprathermal particles and the emission
of radiation whose brightness temperature exceeds the kinetic
temperature. Observed characteristics of solar flares are discussed,
emphasizing the buildup of energy prior to a flare and the mechanism
of primary energy release. Magnetic-field reconnection is taken to be
the best candidate for the mechanism of energy conversion required to
fuel a flare. Several phenomenological flare models are considered,
along with shortcomings of these models.
---------------------------------------------------------
Title: Does the structure of the chromosphere-corona arise entirely
from small-scale MHD effects?
Authors: Chiuderi, C.
1979ssms.conf..105C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Polytropic models of radio stars.
Authors: Chiuderi, C.; Torricelli Ciamponi, G.
1978A&A....69..333C Altcode:
Summary. This paper extends our previous work on models for radio
emitting stars undergoing mass loss. The emission is assumed to
be of thermal nature and the dynamics of the envelope is treated
in the polytropic approximation. No limitations on the value of the
polytropic index are introduced. Analytic results are derived whenever
possible. For the other cases, the results of numerical integration of
the model are fitted in a simple mathematical form that allows an easy
application of the model to the observations. Detailed predictions,
in particular for the mass-loss rate, are made for a few selected
stars. A very good agreement is found with the estimates of the same
quantities found by different authors. The possibility of reproducing
the infrared spectrum is also discussed. Key words: radiostars stellar
winds - mass loss
---------------------------------------------------------
Title: The structure of coronal magnetic loops. II: MHD stability
theory.
Authors: Giachetti, R.; van Hoven, G.; Chiuderi, C.
1977SoPh...55..371G Altcode:
We present the second part of a complete theory for the plasma and field
structure of a cool coronal arch, corresponding to those observed in
the EUV from Skylab. The global magneto-hydrodynamic (MHD) stability
of a previously described equilibrium-loop model is evaluated, and
compared with that of an unmodified ambient force-free field. The
influence of the photospheric boundary condition is also evaluated,
producing a specification of stability limits which depend on the
relative field and plasma pressures and scale widths. The resulting
restrictions on the allowable field configuration of a coronal loop are
then compared with observed values. The implications of this general
method for deducing small-scale coronal magnetic-field structure from
the measured plasma profile of an emissive feature are also described.
---------------------------------------------------------
Title: The structure of coronal magnetic loops. I: Equilibrium theory.
Authors: Chiuderi, C.; Giachetti, R.; van Hoven, G.
1977SoPh...54..107C Altcode:
We present here a model, based on observations, for the magnetic-field
equilibrium of a cool coronal loop. The pressure structure, taken
from the Harvard/Skylab EUV data, is used to modify the usual
force-free-field form in quasi-cylindrical symmetry. The resulting
field, which has the same direction but different strength, is
calculated and its variation displayed. Finally, localized interchange
stability is evaluated and discussed, as the first step in a subsequent
complete magnetohydrodynamic-stability analysis.
---------------------------------------------------------
Title: The solar corona and the origin of the solar wind
Authors: Chiuderi, C.
1977MmSAI..48..561C Altcode:
The paper deals with the properties of the solar corona and the
techniques by which they have been observed. The corona is treated,
in general, as a spherically symmetric stationary gas. This model,
although admittedly unrealistic, has a certain right to exist if it is
considered as an average model (corresponding to a lower resolution
or to a greater distance to the sun). Particular attention is given
to the problem of coronal heating and to the solar wind.
---------------------------------------------------------
Title: Radio emission from mass-outflow stars.
Authors: Chiuderi, C.; Torricelli Ciamponi, G.
1977A&A....59..395C Altcode:
The problem of the radio emission from the extended envelopes
surrounding early-type stars undergoing mass loss is considered. The
emission is interpreted as due to thermal bremsstrahlung processes. The
dynamics of the expanding atmosphere is treated in the polytropic
approximation without prescribing the density and temperature profiles,
as done in previous models. For a particular value of the polytropic
index falling in the physically interesting range, analytical
expressions are deduced for the spectral index, the radio flux, and
the angular size of the emitting object, as well as a relationship
between these quantities and the mass-loss rate. The model applied to
P Cyg and MWC 349 gives good agreement with the existing data.
---------------------------------------------------------
Title: Cyclotron instabilities of a magnetized electron plasma with
anisotropic temperatures
Authors: Chiuderi, C.; Einaudi, G.; Giachetti, R.
1977JPlPh..17..453C Altcode:
The dispersion relation for an electron plasma in a magnetic field
is investigated for a bi-Maxwellian distribution function. A new set
of solutions for non-perpendicular propagation is found. The linear
growth rates are computed and the instability regions in the (k, cos
θ) plane are determined. An approximate analytical treatment of the
problem is also given for certain ranges of the parameters.
---------------------------------------------------------
Title: Flare mechanisms
Authors: Chiuderi, C.
1977MmSAI..48..321C Altcode:
The paper considers a 'standard' model of a solar flare as defined
by morphology, energetics (thermal, gravitational and magnetic), and
temporal evolution; the quantitative data considered are characteristic
of a large flare (3 plus magnitude). Detailed consideration is given to
the three stages of flare evolution: preparatory, peak, and decay. Flare
evolution is discussed in reference to three determining factors:
(1) the macroscopic instability which leads to intensification of
local currents, (2) plasma turbulence, and (3) particle acceleration
mechanisms.
---------------------------------------------------------
Title: A model for a stable coronal loop.
Authors: van Hoven, G.; Chiuderi, C.; Giachetti, R.
1977ApJ...213..869V Altcode:
A plasma-physics model of a stable active-region arch is presented which
corresponds to the structure observed in the EUV. Pressure gradients
are seen, so that the equilibrium magnetic field must depart from
the force-free form valid in the surrounding corona. The data and the
approximate cylindrical symmetry are exploited to develop a modified
form of the commonly assumed sheared-spiral structure. The dynamic MHD
behavior of this pressure/field model is then evaluated by the Newcomb
criterion (1960) from controlled-fusion physics, and the results
show short-wavelength stability in a specific parameter range. For
pressure profiles with widths of the order of the magnetic-field
scale, the possibility is demonstrated that such arches can persist
for reasonable periods. Finally, the spatial proportions and magnetic
fields of a characteristic stable coronal loop are described.
---------------------------------------------------------
Title: Mechanisms of Heating and Heat Transfer in the Outer Solar
Atmosphere
Authors: Chiuderi, C.; Kuperus, M.
1977ebhs.coll..223C Altcode: 1977IAUCo..36..223C
No abstract at ADS
---------------------------------------------------------
Title: Circular polarization and magnetic fields of white dwarfs.
Authors: Chiuderi, C.; Silvi, M.
1976MmSAI..47...65C Altcode:
A simple method to estimate the strength of the surface magnetic
field of a white dwarf from the degree of circular polarization in
its continuum spectrum is proposed. The method is applied to the
observed spectra of G99-37 and G227-35 giving a fairly good fit in
the optical range.
---------------------------------------------------------
Title: Solar five-minute oscillations as a resonance phenomenon.
Authors: Chiuderi, C.; Giovanardi, C.
1975ApJ...200L.165C Altcode:
The response of a nonisothermal gravitational atmosphere to an
oscillatory perturbation is studied in the case of a parabolic
temperature profile. The exact analytical solution is then applied to a
model solar atmosphere. An interpretation of the 5-minute oscillations
as free oscillations of the atmosphere as a whole is proposed.
---------------------------------------------------------
Title: The LOFER (Landau Orbital Ferromagnetism) Mechanism for the
Generation of Intense Magnetic Fields
Authors: Chiuderi, C.; Lee, H. J.
1975NYASA.257...82C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Acoustic Waves in the Lower Solar Atmosphere
Authors: Chiuderi, C.; Giovanardi, C.
1975SoPh...41...35C Altcode:
The propagation and dissipation of acoustic waves in the lower solar
atmosphere is studied. The level of shock formation is computed for
various initial conditions. It is shown that shocks form rather low
in the atmosphere and that this result does not depend critically on
the assumed initial conditions.
---------------------------------------------------------
Title: Proceedings of the First European Solar Meeting. Florence,
February 25 - 27, 1975.
Authors: Chiuderi, C.; Landini, M.; Righini, A.; Zwaan, C.
1975MmArc.105....1C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: CESRA-5
Authors: Chiuderi, C.; Landini, M.; Righini, A.
1975cesra...5.....C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: European solar meeting : 1 : 1975
Authors: Chiuderi, C.
1975esm..meet.....C Altcode:
The papers in this collection report on current European research in
solar physics, recently developed instruments for solar observations,
and future developments in this field. Specific topics include a
theoretical review of dynamic processes in the solar atmosphere,
magnetic structures in the chromosphere and photosphere, magnetic
structures observed in the corona, and the solar brightness temperature
in the far infrared. Attention is given to future solar-physics programs
in space, current research being conducted in a number of Western
and Eastern European countries, the design of a high-sensitivity
radioheliograph, a proposal for a collecting array of 144 antennas,
and a film of the solar spectrum during an eclipse. Individual items
are announced in this issue.
---------------------------------------------------------
Title: Neutrino Reactions in Strong Magnetic Field
Authors: Canuto, V.; Chiuderi, C.; Chou, C. K.; Fassio-Canuto, L.
1974Ap&SS..28..145C Altcode:
We present the energy losses due to several neutrinos processes: (1)
synchrotron neutrinos, (2) pair annihilation neutrinos, (3) plasmon
neutrinos, and (4) photoneutrinos in the presence of a superstrong
magnetic field. Numerical results are tabulated and illustrated for
several values of densities and temperatures. In the low density regime
(ϱ≲10<SUP>7</SUP> g cm<SUP>-3</SUP>) the presence of a magnetic
field decreases the luminosity, whereas the opposite is true at higher
densities. This last effect is however almost entirely due to the
existence of a new process the synchrotron neutrinos that disappear
whenH→0. Even though the overall effect can only be quantitatively
ascertain after a complete cooling computation is performed, one should
however expect a much lower temperature for neutron star surface than
the one computed in theH=0 case.
---------------------------------------------------------
Title: Spectral and Polarization Properties of Radiation Generated
by Plasma Turbu- lence
Authors: Chiuderi, C.; Veltri, P.
1974A&A....30..265C Altcode:
Summary. We have studied a system which consists of a cold plasma
containing an ultrarelativistic distribution of electrons. The response
of such a system to a periodic electromagnetic disturbance is first
discussed. The problem is then specialized to the case of a longitudinal
stationary plasma wave. The emission and propagation of radiation in
such a system is analysed in detail by a method which is analogous to
the one used in synchro tron radiation theory. Explicit results are
given for a power-law distribution of relativistic electrons, and they
are compared to synchrotron emission under the same conditions. It
is shown that the frequency dependence and polarization are quite
similar in the two cases. Key words: plasma radiation mechanism -
transfer equation - polarized radiation
---------------------------------------------------------
Title: High Resolution Studies of Type III Solar Radio Bursts
(presented by H. Rosenberg)
Authors: Chiuderi, C.; Giachetti, R.; Mercier, C.; Rosenberg, H.;
Slottje, C.
1974IAUS...57..225C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Fine Structure in Type IV Solar Radio Bursts (presented by
H. Rosenberg)
Authors: Caroubalos, C.; Pick, M.; Chiuderi, C.; Giachetti, R.;
Rosenberg, H.; Slottje, C.
1974IAUS...57..291C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Dynamical Model for the Chromosphere-Corona Transition Region
Authors: Chiuderi, Claudio; Riani, Iacopo
1974SoPh...34..113C Altcode:
A dynamical, homogeneous model of the chromosphere-corona
transition region and of the lower corona is presented, based on the
hydrodynamical equations and on a semi-empirical relation deduced
from radio observations. The model is shown to be in agreement with
radio and UV observations and with the particle flux given by solar
wind measurements. A comparison with the analogous static model shows
that dynamical effects are very small.
---------------------------------------------------------
Title: Excitation of Longitudinal Waves in a Magnetized Plasma under
Coronal Conditions
Authors: Chiuderi, C.; Giachetti, R.; Rosenberg, H.
1974cesra...4..155C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: NonLinear Wave Coupling in Type IV Solar Radio Bursts
Authors: Chiuderi, Claudio; Giachetti, Riccardo; Rosenberg, Hans
1973SoPh...33..225C Altcode:
In order to explain a fine structure of parallel ridges in stationary
type IV continua, the emission due to the coupling of electrostatic
upper hybrid waves and Bernstein waves at the sum frequency of the upper
hybrid and harmonics of the gyro frequency has been calculated. If
the energy density of these electrostatic waves is of the order of
10<SUP>-3</SUP> times the thermal energy density, then the observed
zebra pattern can be emitted by a region with a diameter of ∼
10<SUP>3</SUP> km.
---------------------------------------------------------
Title: Nonlinear wave coupling in type IV solar radio bursts.
Authors: Chiuderi, C.; Giachetti, R.; Rosenberg, H.
1973UtrOv.237.....C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal Abundance of Elements and a Model of the Quiet Sun
from Radio Observations
Authors: Chiuderi, Claudio; Chiuderi Drago, Franca; Noci, Giancarlo
1972SoPh...26..343C Altcode:
It is shown that the combined use of radio observations of the quiet Sun
and UV line intensities allows to compute the absolute coronal abundance
of the elements. The abundances found by this method agree very well
with the most recent determinations. A model of the transition region
and corona in hydrostatic equilibrium is also presented. Similarities
and differences with models based on UV observations are discussed.
---------------------------------------------------------
Title: Coronal Abundances and a Model of the Quiet Sun from Radio
Observations
Authors: Chiuderi, C.; Chiuderi Drago, F.; Noci, G.
1972BAAS....4T.379C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Evidence for non linear effects in solar metric radiation
Authors: Chiuderi, C.
1972ppsr.conf..288C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Radio Model of the Transition Layer in Solar Active Regions
Authors: Chiuderi, Claudio; Drago, Franca Chiuderi; Noci, Giancarlo
1971SoPh...17..369C Altcode:
A model of the transition layer of an active region of the Sun
is presented based on radio observations. The model is deduced by
using the Laplace transform of the brightness temperature and the
hydrostatic equilibrium equation. A rational function, well-behaved in
the coronal region, has been used to represent the observed brightness
temperature. The model indicates the existence of a very steep
temperature gradient and suggests the presence of a constant conductive
flux from the corona into the chromosphere. Both these conclusions are
quantitatively in a very good agreement with those deduced from the
UV emission lines observations, thus removing a previous discrepancy
between radio and optical based models. It is also shown that the
presence of a weak magnetic field does not alter the above conclusions.
---------------------------------------------------------
Title: Model of the quiet sun and coronal abundance of elements from
radio observations
Authors: Chiuderi, C.; Chiuderi-Drago, F.; Noci, G.
1971cesra...2...55C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Plasmon Neutrinos Emission in a Strong Magnetic Field. II:
Longitudinal Plasmons
Authors: Canuto, V.; Chiuderi, C.; Chou, C. K.
1970Ap&SS...9..453C Altcode:
The decay of a longitudinal plasmon into two neutrinos is studied
in the presence of a strong magnetic field. Contrary to the
transverse case, for longitudinal plasmons the existence of a new
mode, entirely dependent on the magnetic field, greatly enhances
the energy loss at high densities. Denoting byQ <SUB>H</SUB>andQ
<SUB>0</SUB>the neutrino energy losses with and without magnetic field
respectively, the situation is as follows: atH≃10<SUP>11</SUP>
G andT≥10<SUP>9</SUP>K,Q <SUB>0</SUB>≫10<SUP>5</SUP> Q
<SUB>H</SUB>for ϱ<10<SUP>11</SUP>g cm<SUP>-3</SUP>, WhileQ
<SUB>H</SUB>≫10<SUP>10</SUP> Q <SUB>0</SUB>for ϱ>10<SUP>11</SUP>g
cm<SUP>-3</SUP>. A second physically interesting feature is the
anisotropic character of the energy loss which is highly peaked along
the field lines, giving rise to a shorter cooling time in that direction
than in any other.
---------------------------------------------------------
Title: Plasmon Neutrinos Emission in a Strong Magnetic Field. I:
Transverse Plasmons
Authors: Canuto, V.; Chiuderi, C.; Chou, C. K.
1970Ap&SS...7..407C Altcode:
In this paper we generalize the Adams, Ruderman, Woo and Zaidi plasmon
decay process to include the presence of a strong magnetic field. Two
cases are studied; propagation parallel and perpendicular to the
magnetic field. In either case we found that relevant changes only
show forH≌10<SUP>12</SUP> 10<SUP>13</SUP>G.
---------------------------------------------------------
Title: Shape of the Crab Pulsar and its Period Fluctuations
Authors: Chiuderi, Claudio; Occhionero, Franco
1970Natur.226..337C Altcode:
RICHARDS et al.<SUP>1</SUP> have recently recorded sinusoidal
variations in the arrival times of radio pulses from NP 0532 with
a period of about three months and an amplitude Δ<SUB>τ</SUB>=
6 × 10<SUP>-4</SUP> s. This effect can be interpreted in terms
of genuine sinusoidal variations of the circular frequency of the
Crab pulsar where Ω ~= 200 s<SUP>-1</SUP>, ω ~= 10<SUP>-6</SUP>
s<SUP>-1</SUP>, A ~= 10<SUP>-10</SUP>. Equation (1) can be explained
by the widely accepted oblique rotator model<SUP>2-4</SUP> simply by
investigating an interesting consequence of the possible ellipticity of
the neutron star. To account for the history and energy balance of the
Crab Nebula<SUP>3</SUP>, an upper limit must be placed<SUP>4,5</SUP>
to this ellipticity, such that the gravitational quadrupole radiation
dominates the magnetic dipole radiation only in the early life of the
pulsar. It turns out that the explanation given here for the anomalies
in the pulse arrival times provides in the end an even stronger limit
to the deviations from spherical symmetry allowed in a neutron star.
---------------------------------------------------------
Title: Transverse Electrical Conductivity of a Relativistic Gas in
an Intense Magnetic Field
Authors: Canuto, V.; Chiuderi, C.
1970PhRvD...1.2219C Altcode:
The transverse electrical conductivity is computed for a system
of degenerate relativistic electrons in a strong magnetic field
H~10<SUP>10</SUP>-10<SUP>13</SUP> G. As suggested by pulsar models,
such fields exist in nature in collapsed bodies, like neutron
stars. The present computation is valid in the outer regions of the
star where the scatterers are not degenerate, while the electrons
are taken to be at zero temperature. The scattering mechanism
is assumed to be the electron-ion Coulomb scattering. Numerical
values of the transverse conductivity are given in the range
10<SUP>9</SUP><=H<=10<SUP>13</SUP> G, and a comparison is made
with the longitudinal and zero-field conductivities. It is found that
for densities 10<SUP>7</SUP><=ρ<=5×10<SUP>7</SUP>,
σ<SUB>II</SUB>~20σ<SUB>0</SUB> and
σ<SUB>0</SUB>~3σ<SUB>⊥</SUB>. As the density increases, both
σ<SUB>⊥</SUB> and σ<SUB>II</SUB> tend to σ<SUB>0</SUB>.
---------------------------------------------------------
Title: Physical Sciences: New Source of Intense Magnetic Fields in
Neutron Stars
Authors: Canuto, V.; Chiu, H. Y.; Chiuderi, C.
1970Natur.225...47C Altcode:
RECENTLY there has been interest in the problem of intense magnetic
fields (IMF) in gravitationally collapsed bodies<SUP>1-6</SUP>. In
particular, the radio emission from neutron stars (pulsars) suggests
strong magnetic fields of the order of 10<SUP>12</SUP> G (refs. 5
and 7). According to the law of flux conservation, in a collapse
process the magnetic fields strength increases as the square of the
contracting factor a (> 1). If the initial magnetic field is of the
order of 10<SUP>3</SUP> G (the field in sunspots) before collapse, then
assuming contraction from a star of one solar radius ~10<SUP>11</SUP>
cm to that of a neutron star of 10<SUP>6</SUP> cm, a field strength
of 10<SUP>13</SUP> G may be achieved. Magnetic fields in ordinary
stars are usually attributed to non-equilibrium processes such as the
existence of currents in the form of drifting charges, but we have
recently shown that a new kind of quasi -equilibrium state exists,
which possesses a uniform self-consistent magnetization<SUP>8</SUP>.
---------------------------------------------------------
Title: New State of Ferromagnetism in Degenerate Electron Gas and
Magnetic Fields in Collapsed Bodies
Authors: Lee, Hyung Joon; Canuto, Vittorio; Chiu, Hong-Yee; Chiuderi,
Claudio
1969PhRvL..23..390L Altcode:
A new state of "ferro" magnetism in a degenerate electron gas is found
and shown to be stable. This magnetism is the sum of all microscopic
magnetic moments associated with electrons in their respective Landau
levels while the Landau levels of the system are in turn maintained
by this macroscopic magnetization. The maximum field in the Landau
orbital ferromagnetism state is 10<SUP>7</SUP> G for white-dwarf
densities and 10<SUP>12</SUP> G for neutron-star densities.
---------------------------------------------------------
Title: Solution of the Dirac equation in orthogonal electric and
magnetic fields.
Authors: Canuto, V.; Chiuderi, C.
1969NCimL...2..223C Altcode:
No abstract at ADS
