Author name code: zhugzdha
ADS astronomy entries on 2022-09-14
author:"Zhugzhda, Yuzef D."
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Title: Properties of Local Oscillations in the Lower Sunspot
Atmosphere
Authors: Sych, Robert; Zhugzhda, Yuzef; Yan, Xiaoli
Bibcode: 2020ApJ...888...84S
Altcode: 2019arXiv191007754S
We present a study of wave processes in the sunspot region NOAA 12670
on 2017 August 10 observed by the Goode Solar Telescope in the TiO
7057 Å and Hα 6563 Å spectral lines. To study the distribution
of power oscillations and their dynamics, we applied the pixelized
wavelet filtering technique. For the first time, we obtained the
spatial structure of oscillation sources as the footpoints of fine
magnetic tubes, anchored in the sunspot umbra. We found that at
the chromosphere level, the variation of emission is a combination
of numerous independent oscillations located in the sources with
small angular size. Their spatial shape varies from dots and cells
in the umbra to filaments in the penumbra. Each narrow spectral
harmonic corresponds to its source, without global correlation among
themselves. There is a weak background as low-frequency oscillations
distributed over the whole umbra. At the photosphere level we found
regions with co-phased broadband oscillations of the whole umbra. Their
spectrum includes the ∼3 minutes harmonic, whose maximal value is
localized in umbral dots, and the low-frequency part near a period of
∼5 minutes. It is shown that the oscillation sources are displaced
at different heights with increasing angular size. We assume that the
observed spatial distribution of wave sources indicates the existence
of a slow subphotospheric resonator with a vertical magnetic field
in the umbra and a wave cutoff frequency due to inclination of the
magnetic field line in the penumbra.
Title: Local sunspot oscillations and umbral dots
Authors: Zhugzhda, Yuzef; Sych, Robert
Bibcode: 2018RAA....18..105Z
Altcode: 2018arXiv180403874Z
Data analysis of sunspot oscillations based on a 6-hr SDO run
of an observation showed that low frequency (0.2< ω < 1
{mHz}) oscillations are locally similar to three and five minute
oscillations. The oscillations in the sunspot are concentrated
in cells of a few arcsec, each of which has its own oscillation
spectrum. The analysis of two scenarios for sunspot oscillations
leads to a conclusion that local sunspot oscillations occur due to
a subphotospheric resonator for slow MHD waves. Empirical models of
a sunspot atmosphere and the theory of slow waves in thin magnetic
flux tubes are applied to modeling the subphotospheric resonator. The
spectrum of local oscillations consists of a great number of lines. This
kind of spectrum can occur only if the subphotospheric resonator is
a magnetic tube with a rather weak magnetic field. Magnetic tubes of
this sort are umbral dots that appear due to the convective tongues
in monolithic sunspots. The interrelation of local oscillations with
umbral dots and wavefronts of traveling waves in sunspots is discussed.
Title: Brightness fluctuations of the Sun and p-mode oscillations:
The inverse problem and nonadiabatic waves in the photosphere
Authors: Prokhorov, A.; Zhugzhda, Y. D.; Berdyugina, S.
Bibcode: 2014AN....335..150P
Altcode:
Using photometric observations of the Sun as a star (DIFOS, SoHO) we
were able to solve the inverse heloiseismic problem and determine the
global time-dependent relative temperature fluctuations as functions of
the geometric height. This was done under the adiabatic assumption. A
mathematical tool was developed to solve the inverse problem, which
is ill-posed. The calculations were done using the numerical software
Matlab 7. The adiabatic solution shows signs of temperature waves
in the lower photosphere, which agrees with calculations done by
\citet{Hidalgo} and Stodilka (2011).
Title: Another view on sunspot oscillations
Authors: Sych, Robert; Zhugzhda, Y.
Bibcode: 2014cosp...40E3252S
Altcode:
Analysis of sunspot oscillations is presented. The observations of
sunspot in active region NOAA 11131, 08 December 2010 by SDO/AIA is
analyzed. High space and spectral resolution make possible to explore
basic properties of oscillations which impose restrictions on the
model of sunspot oscillations. The spectrum of 3 min oscillations
consists of numerous number of narrow spectral lines which correspond
to resonances of quality about 200. There is no dominant peak for
period of three minute. Oscillations are local oscillations of
characteristic size about 1500 km. Thus, sunspot oscillations are
cluster of small-scale oscillations of near frequencies. There is no
global oscillations of sunspot. Some regularity of peak frequencies
in spectrum is revealed. This kind of regularity appears if spectral
peaks are high-order modes of low-frequency resonator. Frequency step
of resonance networks in the spectrum of three minute oscillations
is about 0.06mHz and 0.4mHz. Spectral networks manifest itself
by appearance of high-amplitude impulses which consists of few
oscillation of period about 2.5minute. This kind of impulses are known
as umbral flashes. Low-frequency local oscillations of frequencies
about 0.06mHz and 0.4mHz are present in sunspot as well. The model
of sunspot oscillations needs occurrence of local low-frequency
resonator, high-order modes of which provides spectrum of three-minute
oscillations. This kind of resonator occurs only if oscillation in
sunspot do not convert in p-modes under photosphere. They have to be a
slow mode through all sunspot atmosphere from subphotopheric layers to
chromosphere and corona. Local kind of oscillations is manifestation
of Parker model of subphotospheric magnetic field of sunspot. This
model of sunspot oscillations provides new approach to seismology of
subphotospheric layers of sunspots.
Title: The non-adiabatic high-degree f-mode
Authors: Zhugzhda, Y. D.; Roth, M.
Bibcode: 2012AN....333..931Z
Altcode:
The current theory of the high-degree solar f-mode based on an
adiabatic approximation is in contradiction with observations,
since the f-mode is visible in intensity oscillations of the Sun. As
a possible solution we present an universal analytical treatment
for a non-adiabatic f-mode. This non-adiabatic theory provides the
explanation of brightness oscillations due to the f-mode. We find that
the non-adiabatic effects do not lead to a damping of the f-mode since
the dispersion relation is the same as in the adiabatic approximation.
Title: Kappa-effect and brightness oscillations of stars
Authors: Zhugzhda, Y. D.; Roth, M.; Herzberg, W.
Bibcode: 2012AN....333..926Z
Altcode:
In this paper the theory of visibility and darkening functions for the
brightness oscillations of stars is outlined. For this the non-grey
approximation is used and the effect of opacity disturbances on
stellar brightness oscillations is explored for different types of
stars. An explanation of the Procyon paradox is proposed. Special
features of the brightness oscillations are discussed. The effect
of opacity fluctuations on the damping of p-mode oscillations is
considered. Furthermore, the photospheric kappa-mechanism is discussed.
Title: Chromospheric Resonances above Sunspot Umbrae
Authors: Botha, G. J. J.; Arber, T. D.; Nakariakov, V. M.; Zhugzhda,
Y. D.
Bibcode: 2011ApJ...728...84B
Altcode:
Three-minute oscillations are observed in the chromosphere above
sunspot umbrae. One of the models used to explain these oscillations
is that of a chromospheric acoustic resonator, where the cavity
between the photosphere and transition region partially reflects
slow magnetoacoustic waves to form resonances in the lower sunspot
atmosphere. We present a phenomenological study that compares simulation
results with observations. The ideal magnetohydrodynamic equations
are used with a uniform vertical magnetic field and a temperature
profile that models sunspot atmospheres above umbrae. The simulations
are initialized with a single broadband pulse in the vertical
velocity inside the convection zone underneath the photosphere. The
frequencies in the spectrum of the broadband pulse that lie below
the acoustic cutoff frequency are filtered out so that frequencies
equal and above the acoustic cutoff frequency resonate inside
the chromospheric cavity. The chromospheric cavity resonates with
approximately three-minute oscillations and is a leaky resonator, so
that these oscillations generate traveling waves that propagate upward
into the corona. Thus, there is no requirement that a narrowband
three-minute signal is present in the photosphere to explain the
narrowband three-minute oscillations in the chromosphere and corona. The
oscillations in the chromospheric cavity have larger relative amplitudes
(normalized to the local sound speed) than those in the corona and
reproduce the intensity fluctuations of observations. Different umbral
temperature profiles lead to different peaks in the spectrum of the
resonating chromospheric cavity, which can explain the frequency shift
in sunspot oscillations over the solar cycle.
Title: Calculation of Spectral Darkening and Visibility Functions
for Solar Oscillations
Authors: Nutto, C.; Roth, M.; Zhugzhda, Y.; Bruls, J.; von der
Lühe, O.
Bibcode: 2008SoPh..251..179N
Altcode: 2008SoPh..tmp...63N; 2008arXiv0803.1228N
Calculations of spectral darkening and visibility functions for
the brightness oscillations of the Sun resulting from global solar
oscillations are presented. This has been done for a broad range of
the visible and infrared continuum spectrum. The procedure for the
calculations of these functions includes the numerical computation of
depth-dependent derivatives of the opacity caused by p modes in the
photosphere. A radiative-transport code was used for this purpose to
get the disturbances of the opacities from temperature and density
fluctuations. The visibility and darkening functions are obtained
for adiabatic oscillations under the assumption that the temperature
disturbances are proportional to the undisturbed temperature of the
photosphere. The latter assumption is the only way to explore any
opacity effects since the eigenfunctions of p-mode oscillations have not
been obtained so far. This investigation reveals that opacity effects
have to be taken into account because they dominate the violet and
infrared part of the spectrum. Because of this dominance, the visibility
functions are negative for those parts of the spectrum. Furthermore,
the darkening functions show a wavelength-dependent change of sign
for some wavelengths owing to these opacity effects. However, the
visibility and darkening functions under the assumptions used contradict
the observations of global p-mode oscillations, but it is beyond doubt
that the opacity effects influence the brightness fluctuations of the
Sun resulting from global oscillations.
Title: Seismology of a Sunspot Atmosphere
Authors: Zhugzhda, Y. D.
Bibcode: 2008SoPh..251..501Z
Altcode: 2008SoPh..tmp..151Z
Two competing theories of sunspot oscillations are discussed. It is
pointed out that the normal mode (eigenoscillations) theory is in
contradiction with a number of observations. The reasons for this
are discussed. The revised filter theory of the three-minute sunspot
oscillations is outlined. It is shown that the reason for the occurrence
of the multipassband filter for the slow waves is the interference that
appears from the multilayer structure of the sunspot atmosphere. In
contrast with Zhugzhda and Locans (Sov. Astron. Lett. 7, 25 - 27, 1981)
it is shown that along with the Fabry - Perot chromospheric passband the
cutoff frequency passband and a number of the high-frequency passbands
occur. The effect of the nonlinearity of the sunspot oscillations in the
upper chromosphere and the transition region is taken into account. The
spectra of the distinct empirical models of the sunspot atmosphere are
explored. An example of the interpretation of the sunspot oscillations
based on the revised filter theory is presented. Only the filter theory
can explain the complicated behavior of the oscillations across the
sunspot. The observations provide evidence of the nonuniformity of
the sunspot atmosphere.
Title: Seismology of sunspot atmosphere: from chromospheric resonance
to nonlinear antireflection
Authors: Zhugzhda, Y. D.
Bibcode: 2007msfa.conf..351Z
Altcode:
The theory of 3-min oscillations in sunspot chromospheres is
revised. Linear and nonlinear effects are taken into account. It is
revealed that not only the chromospheric resonance is responsible or
the 3-min oscillations in sunspots. The spectrum of oscillations in
chromosphere and transition region appears due to the combined effects
of chromospheric resonance, cut-off frequency of temperature minimum
and nonlinear antireflection of the sunspot atmosphere.
Title: On the effect of convection on solar p modes
Authors: Stix, M.; Zhugzhda, Y. D.
Bibcode: 2004A&A...418..305S
Altcode:
We investigate the modulation of acoustic wave modes by convection. We
consider a cavity that encloses a layer of convection rolls. The
stratification due to gravity is taken into account. For the acoustic
oscillation we use a harmonic expansion for the horizontal dependence,
while a finite-difference scheme is employed in the vertical
direction. We calculate the eigenfrequencies of the acoustic modes
under adiabatic conditions, as functions of the velocity amplitude of
the convection. The results confirm the frequency decreases found in
earlier non-stratified models with only a vertical component of the
convective velocity.
Title: Waves and instabilities of periodical shear flows
Authors: Zhugzhda, Y.
Bibcode: 2003PADEU..13...27Z
Altcode:
The exact analytical solution of the extended Rayleigh (ER) equation
for the case of the periodical compressible shear flow is found. The
dispersion relation of the problem is the infinite Hill determinant. It
is found that sound waves in a shear flow have a dispersion and its
velocity field contains a solenoidal part. Besides sound waves, new wave
modes such as phonon, waveguide and vortex wave modes are revealed. The
vortex mode is a singular solenoidal mode. Such modes are negative
energy waves for which a dissipative instability is possible. The
absolute phonon-vortex instability appears for Mach number Magtrsim 0.4.
Title: Waves and shear flows
Authors: Zhugzhda, Y. D.
Bibcode: 2003A&AT...22..593Z
Altcode:
No abstract at ADS
Title: Nonlinear Waves in Magnetic Flux Tubes
Authors: Zhugzhda, Y. D.
Bibcode: 2003ASPC..286..397Z
Altcode: 2003ctmf.conf..397Z
No abstract at ADS
Title: High-frequency waves and granulation
Authors: Zhugzhda, Y. D.
Bibcode: 2003AN....324..406Z
Altcode:
The theory of periodical shear flow is applied for the exploration of
the effect of solar granulation on high-frequency waves in the solar
photosphere. It is shown that upgoing and downgoing waves are trapped
in intergranular spaces and granules, respectively. Upgoing waves in
fast downflows are unstable. The theory is in a good agreement with
observations.
Title: Nonlinear waves in magnetic flux tubes: two-mode approximation
Authors: Zhugzhda, Y. D.
Bibcode: 2002ESASP.505..627Z
Altcode: 2002solm.conf..627Z; 2002IAUCo.188..627Z
Two-mode approximation for magnetic flux tubes of arbitrary diameter
is described. The comparison of the approximation with the exact
solution for linear waves reveals that the approximation obtained is not
restricted to thin flux tubes, contrary to what one would expect. The
approximation includes slow and fast body waves for tubes in magnetic
environment. The theory of the weakly nonlinear slow waves in flux
tubes is outlined.
Title: Theory of chromospheric oscillations and umbral flashes
Authors: Zhugzhda, Y. D.
Bibcode: 2002ESASP.505..175Z
Altcode: 2002IAUCo.188..175Z; 2002solm.conf..175Z
The advanced filter theory of 3 min oscillations in the sunspot
atmosphere is presented. The double coupled resonance of sunspot
chromosphere, temperature minimum and upper photosphere is explored. The
effect of amplitude modulation of sunspot oscillations is revealed. The
nonlinear effects are included in the consideration. The local 3 min
oscillations and umbral flashes are discussed. The comparison of the
theory and observations is carried out.
Title: On nonadiabatic waves in the photospheres of cool stars
Authors: Pregla, A. V.; Zhugzhda, Y. D.; Staude, J.
Bibcode: 2002AN....323..465P
Altcode:
The coupled set of equations of hydrodynamics and radiative transfer
is derived for small disturbances in a plane, grey atmosphere. Only
radiative transfer is taken into account in the energy equation;
dynamical effects of radiation are ignored. A mean stationary radiative
flux through the photosphere is taken into account. The radiative
transfer equation is used by assuming the Eddington approximation,
moreover, an exponential height profile of the temperature and an
analytical opacity formula are supposed. For this model we obtained an
asymptotic solution for plane nonadiabatic acoustic waves and radiation
waves. The approach provides a detailed discussion of the interaction
of nonadiabatic p-modes and radiation waves in a realistic model of
the photosphere of a solar-like star.
Title: Hidden problems of thin-flux-tube approximation
Authors: Zhugzhda, Y. D.; Goossens, M.
Bibcode: 2001A&A...377..330Z
Altcode:
This paper scrutinizes the validity of the thin-flux-tube approximation
for magnetic flux tubes embedded in a surrounding magnetic plasma. It
is shown that the thin-flux-tube approximation gives an accurate
description of surface waves for CT2>
CAe2, body waves for C_Te2>
CT2 and surface leaky waves for
CTe2< CT2 <
CAe2. The Leibovich-Roberts equation for
nonlinear surface waves in a flux tube embedded in a field free plasma
is generalized to a flux tube immersed in a magnetic plasma. The
generalized Leibovich-Roberts (GLR) equation describes the propagation
of nonlinear slow surface, body and surface leaky waves in tubes. The
shortcomings of the GLR equation are discussed. The Korteweg-de Vries
equation (KdV) is generalized for surface waves. The advantage of the
second order thin-flux-tube approximation is shown. Two scenarios for
the heating of coronal loops are discussed. It is emphasized, that
the application of the thin-flux-tube approximation to thin tubes of
non-zero diameter has to take into account possible wave emission by
the tube and shock front formation for amplitudes in excess of some
critical value.
Title: Waves in Sunspots: Resonant Transmission and the Adiabatic
Coefficient
Authors: Settele, A.; Staude, J.; Zhugzhda, Y. D.
Bibcode: 2001SoPh..202..281S
Altcode:
We investigate linear acoustic-gravity waves in three different
semi-empirical model atmospheres of large sunspot umbrae. The sunspot
filter theory is applied, that is, the resonant transmission of
vertically propagating waves is modelled. The results are compared
with observed linear sunspot oscillations. For three umbral models we
present the transmission coefficients and the energy density of the
oscillations with the maxima of transmission. The height dependence of
the adiabatic coefficient (the ratio of specific heats) γ strongly
influences the calculated resonance frequencies. The variable γ can
explain the observed closely spaced resonance period peaks. The first
resonance in the 3 min range is interpreted as a resonance of the upper
chromosphere only, while the higher order peaks are resonances of the
whole chromosphere.
Title: Problems in the interpretation of sunspot oscillation
measurements
Authors: Settele, A.; Staude, J.; Zhugzhda, Y. D.
Bibcode: 2001ESASP.464..247S
Altcode: 2001soho...10..247S
Sunspot oscillations are observed in spectral lines formed at different
depths in the sunspot atmosphere. The interpretation of measurements in
chromospheric lines is problematic as the lines are formed in NLTE. So
the measured power spectra do not originate from one specific depth in
the atmosphere but are smoothed out over a larger region. This will also
influence the phase shifts of the waves measured in different spectral
lines and might cause some misinterpretation. These complications
are illustrated by our model calculations: Modelling the transmission
of magneto-atmospheric waves through the sunspot atmosphere by means
of the sunspot filter approach, we show the "real" power spectra at
different atmospheric depths. These results are compared with Ca II-H/K
power spectra gained from the NLTE calculations of the Ca II-H/K lines
in an atmosphere perturbed by our waves. All results are preliminary.
Title: Alternating current generation in flux tubes by pressure
fluctuations
Authors: Zhugzhda, Yuzef; Goossens, Marcel
Bibcode: 2000AIPC..537..317Z
Altcode: 2000wdss.conf..317Z
Alternating current in flux tubes is one of the possible contributors
to the heating of the solar corona. The mechanism of the generation of
alternating currents in flux tubes by turbulent pressure fluctuations
in convective zone is proposed. The thin-flux-tube approximation shows,
that the linear and weakly nonlinear torsional waves in twisted flux
tube, are accompanied by tube cross section fluctuations. Consequently,
external pressure fluctuations generate not only slow MHD waves but
torsional waves as well. The torsional waves are nothing else than
alternating current. .
Title: Multi-mode oscillations of sunspots
Authors: Zhugzhda, Y. D.; Balthasar, H.; Staude, J.
Bibcode: 2000A&A...355..347Z
Altcode:
Oscillations of the magnetic field in the sunspot photosphere have been
detected by recent high-resolution, two-dimensional observations. Their
power is concentrated in isolated small flux bundles (pores) outside of
larger umbrae and at the boundary between umbra and penumbra of larger
spots. The slow body mode provides an explanation of the appearance
of magnetic oscillations in small sunspots if the azimuth number m=0,
but also of the small features piling up in rings in large sunspots. In
the latter model the magnetic oscillations are the signature of the
slow body mode with m>> 1, which bears a resemblance to the
well-known whispering gallery mode in acoustics. The slow surface
modes and fast body modes are also discussed.
Title: Multi-mode Magnetic Oscillations in Sunspots
Authors: Zhugzhda, Y.; Balthasar, H.; Staude, J.
Bibcode: 1999ESASP.448..417Z
Altcode: 1999mfsp.conf..417Z; 1999ESPM....9..417Z
No abstract at ADS
Title: The Influence of the Adiabatic Coefficient and the Magnetic
Field on Sunspot Oscillations
Authors: Settele, A.; Zhugzhda, Y. D.; Staude, J.
Bibcode: 1999ESASP.448..367S
Altcode: 1999ESPM....9..367S; 1999mfsp.conf..367S
No abstract at ADS
Title: Oscillations in Sunspots: Observations and Modelling
Authors: Staude, J.; Rendtel, J.; Balthasar, H.; Zhugzhda, Y.
Bibcode: 1999ESASP.448..373S
Altcode: 1999ESPM....9..373S; 1999mfsp.conf..373S
No abstract at ADS
Title: Nonlinear Waves in Thin Flux Tubes
Authors: Zhugzhda, Y.
Bibcode: 1999ASPC..184..238Z
Altcode:
The nonlinear dynamics of magnetic flux tubes in the solar atmosphere is
discussed. It is shown that the zero-order thin flux tube approximation,
which is a major tool for both numerical and analytical treatment
of nonlinear flux tube dynamics, neglects geometrical dispersion as
well as leakage of waves due to wave radiation by the tube. Both
effects depend on whether the tube is embedded in plasma with or
without magnetic field. A plausible explanation of the origin of the
chromospheric fine structure is proposed.
Title: Magnetic field oscillations in sunspots - - a `whispering
gallery' mode?
Authors: Staude, J.; Balthasar, H.; Zhugzhda, Y. D.
Bibcode: 1999AGAb...15....9S
Altcode: 1999AGM....15..A08S
Oscillations of the magnetic field in the sunspot photosphere have been
detected by recent high-resolution, two-dimensional, spectro-poarimetric
observations at Tenerife and aboard the SOHO satellite. Their power is
concentrated in isolated small flux bundles (pores) outside of larger
umbrae and in patches at the boundary between umbra and penumbra of
larger spots. The slow body mode of magneto-acoustic waves in an intense
magnetic fluxtube provides an explanation of the strange appearance
of such magnetic oscillations. This applies to small sunspots if the
azimuth number m=0, but also to the small features piling up in rings
at the border of the umbrae of larger sunspots. In the latter model
the magnetic oscillations are the signature of the slow body mode with
m >> 1, which bears a resemblance to the well-known whispering
gallery mode in acoustics. The slow surface modes and fast body modes
are also discussed.
Title: A new method to calculate the resonant response of a sunspot
model atmosphere to magneto-atmospheric waves
Authors: Settele, A.; Zhugzhda, Y. D.; Staude, J.
Bibcode: 1999AN....320..147S
Altcode:
In order to understand the observed oscillations in sunspots we
present a new method for calculating the resonant response of a
realistic semi-empirical model of the sunspot umbral atmosphere and
subphotosphere to magneto-atmospheric waves in a vertical magnetic
field. The depth dependence of both the adiabatic coefficient and the
turbulent pressure is taken into account. This requires an extension
of the wave equations by Ferraro & Plumpton (1958). We compare
the coefficients of wave transmission, reflection, and conversion
between fast mode and slow mode waves for different assumptions,
compare the results with those from earlier modelling efforts, and
point out possible sources of mistakes. The depth dependence of the
adiabatic coefficient strongly influences the resulting spectrum of
resonance frequencies. The condition of a conservation of wave flux
is violated if the depth dependence of the turbulent pressure is not
properly considered.
Title: Magnetic Field Oscillations in Sunspots?
Authors: Staude, Juergen; Balthasar, Horst; Zhugzhda, Yuzef
Bibcode: 1999soho....9E..25S
Altcode:
Oscillations of velocity and intensity are known for more than 2
decades; they are observed in spectral lines formed at different height
levels of the sunspot atmosphere. The interpretation of measurements
of magnetic field oscillations, however, is still contradictory. We
give evidence of the presence of such oscillations and describe the
observed properties. The basic features of their spatial structure
can be explained by slow body waves in intense magnetic flux tubes. In
particular, a `whispering gallery'-like mode could be an appropriate
model.
Title: Waves in structured media: non-radial solar P modes
Authors: Stix, M.; Zhugzhda, Y. D.
Bibcode: 1998A&A...335..685S
Altcode:
For non-radial solar p modes we calculate corrections to the
eigenfrequencies arising from the sound speed and velocity inhomogeneity
of the convection zone. We use a simple periodic model, and obtain the
frequency corrections by solving a Hill determinant. The frequency
shifts are significant, and in most cases negative; they increase
in magnitude with increasing frequency and harmonic degree l. The
dependence on degree scales with the mode inertia. For large degree
l this trend reverses. For very large degree coupling occurs between
the p modes and ``vibrational'' modes that only exist because of the
horizontal structure in sound speed and velocity.
Title: Waves in a convective atmosphere: 1D periodical model
Authors: Zhugzhda, Y. D.
Bibcode: 1998A&A...332..314Z
Altcode:
This paper treats a one-dimensional model of stationary convection. In
this model I derive the equation governing acoustic waves in
an atmosphere that is structured by hot and cold flows. An exact
solution is obtained in terms of an infinite Hill determinant. The
physics of acoustic waves in a convective atmosphere and in a crystal
lattice are similar, and some of the concepts of solid state physics
are generalized to the current problem. It is shown that there are
three basic wave modes, namely, acoustic waves, vibrational waves
and turbulent sound, which are all different from acoustic waves
in a uniform atmosphere. The vibrational waves could appear due to
local oscillations of the convective elements. The turbulent sound is
driven only by the dynamical pressure. The temperature and velocity
fluctuations in a convective atmosphere are responsible for the
appearance of Brillouin zones. Waves with frequencies within the band
gap of the convective atmosphere undergo reflection at the edge of the
Brillouin zones, where they meet a potential barrier. The application
of the model to a turbulent atmosphere is discussed. Some effects
relevant to helioseismology are outlined.
Title: German-Russian Cooperation in Helioseismology
Authors: Horn, T.; Hasler, K. -H.; Arlt, K.; Staude, J.; Oraevsky,
V. N.; Zhugzhda, Y. D.
Bibcode: 1998ESASP.417..243H
Altcode: 1998cesh.conf..243H
No abstract at ADS
Title: Nonlinear Waves in Force-Free Fibrils
Authors: Zhugzhda, Y. D.; Nakariakov, V. M.
Bibcode: 1998ASPC..150..151Z
Altcode: 1998npsp.conf..151Z; 1998IAUCo.167..151Z
No abstract at ADS
Title: Linear Waves in Force-free Fibrils
Authors: Zhugzhda, Y. D.
Bibcode: 1998ASPC..150..155Z
Altcode: 1998IAUCo.167..155Z; 1998npsp.conf..155Z
No abstract at ADS
Title: Latent Heating of Coronal Loops
Authors: Zhugzhda, Y. D.; Nakariakov, V. M.
Bibcode: 1997SoPh..175..107Z
Altcode:
The theory of weakly nonlinear slow magnetosonic waves in thin flux
tubes is developed. A Korteweg-de Vries equation is derived for
slow body waves. The analysis of solitary and periodic solutions
shows that the nonlinear waves produce running narrowings of the
tube. The similarity of the shallow-water theory and the thin-flux-tube
approximation helps to outline the peaking and breaking of the nonlinear
slow body waves. It appears that the running narrowing of the tube
works as the de Laval nozzle in generating a cool supersonic jet
and a subsequent shock that heats the plasma. The presented theory of
nonlinear slow body waves suggests a mechanism of coronal loop heating,
which meets many of the observational constraints.
Title: Comments on the "analytic theory of P modes" by Dzhalilov
and Staude.
Authors: Zhugzhda, Y.; Stix, M.
Bibcode: 1997A&A...322..982Z
Altcode:
Dzhalilov & Staude (1995A&A...303..561D; hereinafter DS)
have proposed a new "analytic theory" of p modes for the atmospheres
of the Sun and Sun-like stars, which explains the p-mode spectrum in
terms of "resonant transmission" of acoustic waves. It is shown that
this result is mistaken because of an incorrect fit of the piecewise
analytic solutions at the boundaries between the diverse layers of the
atmosphere. Apart from this incorrect treatment of wave propagation,
the interpretation in terms of resonant transmission appears to arise
from a mix-up of resonance and interference phenomena. There is also
some confusion about the concepts of tunnel effect and turning point.
Title: Observation of solar low-l p-modes by the CORONAS-DIFOS
experiment.
Authors: Hasler, K. -H.; Zhugzhda, Y. D.; Lebedev, N. I.; Arlt, R.;
Oraevsky, V. N.
Bibcode: 1997A&A...322L..41H
Altcode:
The CORONAS satellite, launched on 1994 March 2, carried the DIFOS
experiment to observe irradiance fluctuations due to global solar
oscillations. The DIFOS experiment was working for almost 50-days
near solar activity minimum. We present first results of the Fourier
analysis of the full time series. The fine structure of the low-l
p-modes is shown and fitted with Lorentzian line profiles. Results of
the wavelet analysis show strong variations of the p-modes in time.
Title: Wave propagation in inhomogeneous media: shifts of solar
p-mode frequencies.
Authors: Stix, M.; Zhugzhda, Y. D.
Bibcode: 1996AGAb...12..166S
Altcode:
No abstract at ADS
Title: On the interaction of longitudinal and transversal waves in
thin magnetic flux tubes.
Authors: Nakariakov, V. M.; Zhugzhda, Y. D.; Ulmschneider, P.
Bibcode: 1996A&A...312..691N
Altcode:
An analytical investigation of the nonlinear interaction of longitudinal
and transversal waves in thin magnetic flux tubes is presented and
the nonlinear terms which give rise to wave generation of other modes
and to shock formation are isolated. The nonlinear resonant three-wave
interaction of longitudinal and transversal waves is studied together
with the growth and decay behaviour of these waves. This analytical
study clarifies our previous numerical computations of nonlinear wave
generation and of the steepening of longitudinal as well as transversal
wave profiles.
Title: Wave trapping in intergranular lanes
Authors: Stix, M.; Zhugzhda, Y. D.
Bibcode: 1996ASPC..109..163S
Altcode: 1996csss....9..163S
No abstract at ADS
Title: Spectral darkening functions of solar p-modes - an effective
tool for helioseismology.
Authors: Zhugzhda, Y. D.; Staude, J.; Bartling, G.
Bibcode: 1996A&A...305L..33Z
Altcode:
Darkening functions (contrasts) of intensity fluctuations due to waves
in a nongrey LTE model of the solar atmosphere are calculated for
different wavelengths λ in the optical continuum spectrum. Adiabatic
and isothermal acoustic waves as well as temperature waves are
considered. A change of the sign of the darkening function for certain
ranges of λ is revealed for adiabatic waves. This effect makes it
possible to observe modes with l>=3 even in stars. Observations of
the darkening function of p-modes at different λ are proposed as a
new tool, making it possible to check numerical models of p-modes, to
impose restraints to the choice of the boundary conditions, to reduce
the arbitrariness in the calculation of nonadiabatic corrections
to eigenfrequencies, and to improve the accuracy of solar interior
sounding in this way.
Title: On the possibility of detection of p-modes with L> 3 in
the sun-like stars
Authors: Staude, J.; Zhugzhda, Y. D.
Bibcode: 1996ASPC..109..161S
Altcode: 1996csss....9..161S
No abstract at ADS
Title: Dynamics of thin force-Free flux tubes and heating of star
atmospheres
Authors: Zhugzhda, Y. D.
Bibcode: 1996ASPC..109..175Z
Altcode: 1996csss....9..175Z
No abstract at ADS
Title: Propagation of nonlinear longitudinal-transverse waves along
magnetic flux tubes in the solar atmosphere. II. The treatment
of shocks.
Authors: Zhugzhda, Y. D.; Bromm, V.; Ulmschneider, P.
Bibcode: 1995A&A...300..302Z
Altcode:
Equations were derived permitting the treatment of shocks which occur
in longitudinal-transverse waves propagating in thin magnetic flux
tubes. Such waves usually lead to kinks which may grow into oblique
shocks. The kink angles between the shock and the tube directions are
found to be symmetrical with respect to the shock. Purely longitudinal
shocks occur only in special cases of high symmetry or of well defined
propagation conditions. Wave calculations were performed which show
the formation of oblique shocks. We also discuss recent suggestions
that the basic equations for the treatment of longitudinal-transverse
waves are incomplete.
Title: Solar Irradiance Oscillations: Preliminary Results of the
Coronas-Difos Experiment
Authors: Lebedev, N. I.; Oraevsky, V. N.; Zhugzhda, Y. D.; Kopaev,
I. M.; Kostyk, R. I.; Pflug, K.; Rüdiger, G.; Staude, J.; Bettac,
H. -D.
Bibcode: 1995ESASP.376b.353L
Altcode: 1995soho....2..353L; 1995help.confP.353L
No abstract at ADS
Title: Force-Free Thin Flux Tubes: Basic Equations and Stability
Authors: Zhugzhda, Y. D.
Bibcode: 1995ESASP.376b.515Z
Altcode: 1995help.confP.515Z; 1995soho....2..515Z
No abstract at ADS
Title: First results of the CORONAS-DIFOS experiment. Space
observations of solar irradiance oscillations.
Authors: Lebedev, N. I.; Oraevsky, V. N.; Zhugzhda, Y. D.; Kopaev,
I. M.; Kostyk, R. I.; Pflug, K.; Ruediger, G.; Staude, J.; Bettac,
H. -D.
Bibcode: 1995A&A...296L..25L
Altcode:
The DIFOS experiment aboard the satellite CORONAS has been designed to
observe irradiance fluctuations due to global solar oscillations. The
satellite was launched on March 2, 1994. It uses a photometer measuring
fluctuations of the solar flux in three channels: near 550nm, 750nm,
and from 400nm through 1.1μm. After a short description of the
instrumentation and the data analysis we present first, preliminary
results of observations of low-degree p-modes including their variation
in time.
Title: Acoustic Waves in Structured Media and Helioseismology
Authors: Zhugzhda, Y. D.; Stix, M.
Bibcode: 1995ASPC...76..326Z
Altcode: 1995gong.conf..326Z
No abstract at ADS
Title: Visibility Functions of Solar and Stellar Irradiance Variations
Authors: Staude, J.; Bartling, G.; Zhugzhda, Y. D.; Dzhalilov, N. S.
Bibcode: 1995ASPC...83..451S
Altcode: 1995IAUCo.155..451S; 1995aasp.conf..451S
No abstract at ADS
Title: Space Helioseismology Experiment DIFOS
Authors: Zhugzhda, Y. D.; Oraevsky, V. N.; Lebedev, N. I.; Kopaev,
I. M.; Kostyk, R. I.; Keselman, I. G.; Osipov, S. N.
Bibcode: 1995ASPC...76..436Z
Altcode: 1995gong.conf..436Z
No abstract at ADS
Title: Nonadiabatic Magneto-Acoustic Gravity Waves in a Stratified
Atmosphere
Authors: Babaev, E. S.; Dzhalilov, N. S.; Zhugzhda, Y. D.
Bibcode: 1995AZh....72..240B
Altcode:
No abstract at ADS
Title: Effects of Radiative Losses on the Wave Properties in Solar
Active Regions
Authors: Babaev, E. S.; Dzhalilov, N. S.; Zhugzhda, Y. D.
Bibcode: 1995AZh....72..230B
Altcode:
No abstract at ADS
Title: Radiation-Hydrodynamic Waves and Solar P Modes: Visibility
Functions
Authors: Staude, J.; Zhugzhda, Y. D.; Dzhalilov, N. S.
Bibcode: 1995ASPC...76..338S
Altcode: 1995gong.conf..338S
No abstract at ADS
Title: Gapped Time Series Analysis by Time Transformation
Authors: Zhugzhda, Y. D.
Bibcode: 1995ASPC...76..516Z
Altcode: 1995gong.conf..516Z
No abstract at ADS
Title: Acoustic waves in structured media and helioseismology.
Authors: Zhugzhda, Y. D.; Stix, M.
Bibcode: 1994A&A...291..310Z
Altcode:
A simple two-stream model of alternating hot and cool vertical layers,
with uniform upwards and downwards velocities, respectively, was
studied to investigate the influence of convection on solar global
oscillations. The effect on vertically propagating acoustic waves is
small at low frequency, but leads to a significant decrease of the mean
phase velocity of high-frequency modes which are more confined to the
cool layers. As our main result we thus find frequency corrections
for solar p modes of low degree and high order which may reconcile
the calculated with the observed eigenfrequencies. Our model also
yields high-frequency modes with more or less horizontal propagation,
representing the distortion of the wave fronts due to the horizontal
structure, and a "slow mode", a surface wave propagating along the
boundaries between the layers of different vertical velocity.
Title: Radiation-hydrodynamic waves in an optically grey
atmosphere. II. Analysis of wave properties and effects of thermal
conductivity in a homogeneous model.
Authors: Dzhalilov, N. S.; Zhugzhda, Y. D.; Staude, J.
Bibcode: 1994A&A...291.1001D
Altcode:
The properties of radiation-hydrodynamic waves in a radiative,
thermally conducting, uniform atmosphere are investigated, avoiding the
Eddington approximation and considering a temporal as well as a spatial
analysis. The analysis of the dispersion equation shows the existence
of acoustic, radiation, and thermal wave modes and a relaxation mode
as well. The generalized Spiegel formula is discussed and the accuracy
of the Eddington approximation for the radiation-hydrodynamic waves
is considered. The amplitudes and phases of disturbances of gas
and radiation pressure, intensity, and temperature are obtained for
standing and travelling waves and for the relaxation mode too. The
polar angle dependence of the phase shift between velocity and intensity
is investigated. The predictions for full-disk intensity observations
and the deficiencies of earlier, less complete approaches are discussed.
Title: Radiation Hydrodynamic Waves and Global Solar Oscillations
Authors: Staude, J.; Dzhalilov, N. S.; Zhugzhda, Y. D.
Bibcode: 1994SoPh..152..227S
Altcode: 1994IAUCo.143..227S; 1994svs..coll..227S
We investigate nonadiabatic hydrodynamic waves in a nongrey, radiating,
thermally conducting, homogeneous atmosphere in LTE with a finite mean
free path of photons. Avoiding the Eddington approximation the remaining
simplifications in the basic equations are discussed, the generalized
dispersion relation is analysed, and some wave properties in a grey
model are studied. The properties of waves in a stratified atmosphere
are analysed as well. In connection with the predicted properties of
the nonadiabatic waves we discuss observations ofp-modes by measuring
brightness fluctuations.
Title: Oblique shocks in longitudinal-transverse MHD tube waves
Authors: Zhugzhda, Y.; Ulmschneider, P.; Bromm, V.
Bibcode: 1994smf..conf..402Z
Altcode:
No abstract at ADS
Title: Visibility functions of solar and stellar luminosity
oscillations.
Authors: Staude, J.; Bartling, G.; Dzhalilov, N. S.; Zhugzhda, Y. D.
Bibcode: 1994AGAb...10..116S
Altcode:
No abstract at ADS
Title: Radiation-Hydrodynamic Waves in the Solar Atmoshere
Authors: Zhugzhda, Y. D.; Staude, J.; Dzhalilov, N. S.
Bibcode: 1994emsp.conf....9Z
Altcode:
No abstract at ADS
Title: Radiation-hydrodynamic waves in an optically non-grey
atmosphere
Authors: Zhugzhda, Y. D.; Dzhalilov, N. S.; Staude, J.
Bibcode: 1993A&A...278L...9Z
Altcode:
We derive the dispersion equation of radiation-hydrodynamic waves for
a nongrey atmosphere in Local Thermodynamic Equilibrium (LTE) avoiding
the Eddington approximation. It is shown that the Rosseland mean opacity
doesn't describe the relaxation processes in the atmosphere except the
opaque limit. For the transparent limit the relaxation time depends on
the so-called Newton mean opacity. The grey and nongrey approximations
are compared for a model of the solar photosphere.
Title: Radiation-hydrodynamic waves in an optically gray atmosphere. I
- Homogeneous model
Authors: Dzhalilov, N. S.; Zhugzhda, Y. D.; Staude, J.
Bibcode: 1992A&A...257..359D
Altcode:
We consider the coupled set of equations of hydrodynamics and
radiative transfer. Only radiative transfer is taken into account
in the energy equation, while other mechanisms of heat transfer
are ignored. Disturbances of the tensor of radiative pressure are
included in the linearized momentum equation. This term proves to be
of great importance for radiation-acoustic waves. LTE as well as a
gray approximation and homogeneity of the atmosphere are assumed. The
hydrodynamic equations are solved by using an exact solution of the
radiative transfer equation (no Eddington approximation is made). The
dispersion equation for the nonadiabatic oscillations is derived. This
equation is valid for arbitrary optical thickness and generalizes all
hitherto known results.
Title: On Propagation and Absorption of Alfvén Waves in Coronal Loops
Authors: Zhugzhda, Y. D.
Bibcode: 1991mcch.conf..442Z
Altcode:
No abstract at ADS
Title: Waves in sunspots and active regions: theory.
Authors: Zhugzhda, Y. D.
Bibcode: 1990PDHO....7..290Z
Altcode:
No abstract at ADS
Title: Probing of Sunspot Umbral Structure by Oscillations
Authors: Zhugzhda, Y. D.; Staude, J.; Locans, V.
Bibcode: 1989ASIC..263..601Z
Altcode: 1989ssg..conf..601Z
No abstract at ADS
Title: Temperature Waves and Solar Granulation
Authors: Zhugzhda, Y. D.
Bibcode: 1989ASIC..263..219Z
Altcode: 1989ssg..conf..219Z
No abstract at ADS
Title: Oscillations trapped in a chromosphere with a horizontal
magnetic field
Authors: Zhugzhda, Y. D.; Dzhalilov, N. S.
Bibcode: 1985PAZh...11..712Z
Altcode:
The propagation of adiabatic MHD waves in a conductive isothermal
atmosphere in the presence of a horizontal magnetic field and gravity
is considered. It is shown that the oscillations may be trapped in the
middle layer of a three-layer atmosphere with temperatures T1
> T2 > T3 for discrete frequencies. In
the presence of a horizontal magnetic field the solar chromospheric
trapped waves have periods in the range of 250 - 2730 s.
Title: Oscillations Trapped in a Chromosphere with a Horizontal
Magnetic Field
Authors: Zhugzhda, Y. D.; Dzhalilov, N. S.
Bibcode: 1985SvAL...11..300Z
Altcode:
No abstract at ADS
Title: Magneto-acoustic-gravity waves on the Sun. II - Transformation
and Propagation
Authors: Zhugzhda, Y. D.; Dzhalilov, N. S.
Bibcode: 1984A&A...132...52Z
Altcode:
A comprehensive theory of mutual transformation of all types of
magneto-acoustic-gravity waves in an isothermal atmosphere has been
developed. The transformation coefficients strongly depend on the
relative directions of magnetic fields and wave propagation in the
plane containing gravity force, wave vector, and magnetic field. The
slow wave spectrum has been calculated for different magnetic field
inclinations and by a given acoustic noise spectrum in the convective
zone. It is shown that there are neither resonance levels nor valve
effects in an oblique field.
Title: Resonance oscillations in sunspots
Authors: Zhugzhda, Y. D.
Bibcode: 1984PAZh...10...51Z
Altcode:
Sunspots are shown to contain three resonant layers, namely the
chromospheric resonator on slow magnetoacoustic waves and two
subphotospheric resonators on slow and fast waves. The resonators
are coupled to each other by the wave transformation level. A
qualitative model for combined oscillatory convection in sunspots
is proposed. The proposed scheme is used to examine the three- and
five-minute oscillations and the bright dots in sunspots.
Title: Resonance Oscillations in Sunspots
Authors: Zhugzhda, Y. D.
Bibcode: 1984SvAL...10...19Z
Altcode:
No abstract at ADS
Title: Nonadiabatic oscillations in an isothermal atmosphere
Authors: Zhugzhda, Y. D.
Bibcode: 1983PAZh....9..631Z
Altcode:
An analytical solution of the equation of small disturbances in an
isothermal atmosphere with stratified heat exchange is found. Reflection
and transmission coefficients of acoustic gravity waves from the zone
of interaction with temperature waves are deduced. Optically thick
and thin disturbances are considered. The effect of heat exchange
stratification on the five-minute oscillations and granulation in the
solar atmosphere is discussed.
Title: Nonadiabatic Oscillations in an Isothermal Atmosphere
Authors: Zhugzhda, Y. D.
Bibcode: 1983SvAL....9..329Z
Altcode:
No abstract at ADS
Title: A Model of the Oscillations in the Chromosphere and Transition
Region Above Sunspot Umbrae
Authors: Zhugzhda, Y. D.; Staude, J.; Locans, V.
Bibcode: 1983PDHO....5..451Z
Altcode: 1984PDHO....5..451Z
In an earlier paper the authors proposed a model for the interpretation
of velocity and intensity oscillations with periods between 2 and 3
minutes observed above umbrae. The oscillations are explained by the
resonant transmission of slow mode magneto-acoustic waves which are
semi-trapped in a chromospheric cavity. The model has now been improved
by more detailed calculations and corroborated by recently published
observations: The calculations are in good agreement with (1) the
height dependence of the observed phase difference between velocity
and intensity oscillations, and with (2) the frequency spectrum of
oscillations in the transition region above sunspots observed on the
SMM spacecraft during the SMY.
Title: The fundamental mode of nonradial, nonadiabatic stellar
oscillation
Authors: Zhugzhda, Y. D.
Bibcode: 1982PAZh....8..562Z
Altcode:
Fundamental-mode nonadiabatic oscillations of a star that
have a large value for the order l of the spherical harmonic are
examined. Oscillations of this type have been observed on the sun as one
branch of the two-dimensional spectrum for the 5-min oscillations. A
system of energy equations for nonadiabatic oscillations is derived
and applied to the fundamental mode of high-1, nonradial, nonadiabatic
oscillation. It is shown that the f-mode of the 5-min oscillation on the
sun can be excited only through interaction with a turbulent convection.
Title: Conversion of Magnetogravitational Waves in the Solar
Atmosphere
Authors: Zhugzhda, Y. D.; Dzhalilov, N. S.
Bibcode: 1981SvA....25..477Z
Altcode:
No abstract at ADS
Title: The transformation of magnetogravity waves in the solar
atmosphere
Authors: Zhugzhda, Y. D.; Dzhalilov, N. S.
Bibcode: 1981AZh....58..838Z
Altcode:
A theory for the mutual transformation of all types of magnetogravity
waves in the isothermal atmosphere is developed. The transformation
coefficients allow a calculation of the spectra of slow waves for
the case where the spectrum of acoustic noise in the convective zone
is given. The transformation leads to an increase in the directivity
of slow waves and to the appearance of reflected slow modes for the
selected value of the horizontal wavelength at which the transformation
coefficient is a maximum.
Title: Resonance oscillations in sunspots
Authors: Zhugzhda, Y. D.; Locans, V.
Bibcode: 1981PAZh....7...44Z
Altcode:
A model for the 180-sec oscillations observed in the chromosphere
above sunspots is developed. In addition, a method is proposed for
determining the temperature gradient in the chromosphere along with
the value of the temperature minimum and its effective thickness on
the basis of the observed oscillation periods.
Title: Resonance Oscillations in Sunspots
Authors: Zhugzhda, Y. D.; Locans, V.
Bibcode: 1981SvAL....7...25Z
Altcode:
No abstract at ADS
Title: Oscillations in the Loop Prominence
Authors: Zhugzhda, Y. D.; Larionov, N. V.; Makhmudov, M. M.
Bibcode: 1979BSolD...7...98Z
Altcode:
No abstract at ADS
Title: An Evaluation of the Temperature and Density in Loop
Prominences
Authors: Zhugzhda, Y. D.; Mahmudov, M. M.
Bibcode: 1979BSolD...6...96Z
Altcode:
No abstract at ADS
Title: Oscillations In The Loop Prominence
Authors: Zhugzhda, Y. D.; Larionov, N. V.; Makhmudov, M. M.
Bibcode: 1979SolD....7...98Z
Altcode:
No abstract at ADS
Title: Tunnel-Effect and Propagation of 5-min Oscillations in the
Solar Atmosphere
Authors: Zhugzhda, Y. D.
Bibcode: 1972SoPh...25..329Z
Altcode:
Tunneling of surface waves (which are also called `non-propagating' or
`evanescent mode') in isothermal atmosphere is considered. Tunneling
of 5-min oscillations in solar atmosphere is discussed. Phase lead of
chromospheric oscillations with respect to photospheric oscillations
(Tanenbaum et al., 1971) can be explained by tunneling only.
Title: Low Frequency Oscillatory Convection in the Strong Magnetic
Field
Authors: Zhugzhda, Y. D.
Bibcode: 1971CoEl....2..267Z
Altcode:
No abstract at ADS
Title: Oscillatory Convection in Strong Magnetic Fields and Origin
of Active Regions
Authors: Syrovatsky, S. I.; Zhugzhda, Y. D.
Bibcode: 1968IAUS...35..127S
Altcode:
No abstract at ADS