Author name code: durrant
ADS astronomy entries on 2022-09-14
author:"Durrant, Christopher John"
------------------------------------------------------------------------
Title: The Solar Granulation
Authors: Bray, R. J.; Loughhead, R. E.; Durrant, C. J.
Bibcode: 2009sogr.book.....B
Altcode:
Preface; Acknowledgements; 1. Historical introduction; 2. The
morphology, evolution and dynamics of the granulation and
supergranulation; 3. An introduction to the theory of convection;
4. The theory of astrophysical convection; Interpretation of the
granulation and spuergranulation; References; Name index; Subject index.
Title: Plasma Loops in the Solar Corona
Authors: Bray, R. J.; Cram, L. E.; Durrant, C.; Loughhead, R. E.
Bibcode: 2006plsc.book.....B
Altcode:
1. Historical introduction; 2. Cool loops: observed properties; 3. Hot
loops: observed properties; 4. Flare loops: observed properties;
5. Structure, dynamics and heating of loops; 6. The plasma loop model
of the coronae of the sun and stars.
Title: The Mechanism involved in the Reversals of the Sun's Polar
Magnetic Fields
Authors: Durrant, C. J.; Turner, J. P. R.; Wilson, P. R.
Bibcode: 2004SoPh..222..345D
Altcode:
Models of the polarity reversals of the Sun's polar magnetic fields
based on the surface transport of flux are discussed and are tested
using observations of the polar fields during Cycle 23 obtained by
the National Solar Observatory at Kitt Peak. We have extended earlier
measurements of the net radial flux polewards of ±60° and confirm
that, despite fluctuations of ∼20%, there is a steady decline in
the old polarity polar flux which begins shortly after sunspot minimum
(although not at the same time in each hemisphere), crosses the zero
level near sunspot maximum, and increases, with reversed polarity
during the remainder of the cycle. We have also measured the net
transport of the radial field by both meridional flow and diffusion
across several latitude zones at various phases of the Cycle. We can
confirm that there was a net transport of leader flux across the solar
equator during Cycle 23 and have used statistical tests to show that it
began during the rising phase of this cycle rather than after sunspot
maximum. This may explain the early decrease of the mean polar flux
after sunspot minimum. We also found an outward flow of net flux across
latitudes ±60° which is consistent with the onset of the decline of
the old polarity flux. Thus the polar polarity reversals during Cycle
23 are not inconsistent with the surface flux-transport models but the
large empirical values required for the magnetic diffusivity require
further investigation.
Title: A method of evolving synoptic maps of the solar magnetic field,
II. Comparison with observations of the polar fields
Authors: Durrant, C. J.; Mccloughan, J.
Bibcode: 2004SoPh..219...55D
Altcode:
We describe the application of the synoptic transport equation
to simulate the temporal evolution of the magnetic flux over the
solar surface. This provides a means of predicting each day both the
synoptic maps for the Carrington rotation starting the next day and
the instantaneous map of the solar flux over the whole solar surface
for the next day. The reliability of the predicted synoptic maps is
tested by comparing the locations of the zero-flux contour with those
of the observed maps produced by the National Solar Observatory, Kitt
Peak and with the locations of Hα filaments measured on filtergrams
obtained by the Big Bear Solar Observatory. We conclude that the best
match at high latitudes is obtained by long-term simulations (over 20
rotations) with flux updates each rotation between latitudes ± 60°. We
illustrate the use of the simulations to describe the evolution of the
polar fields at the time of the polarity reversals in Cycle 23. The
reconstruction of the instantaneous maps is tested by comparison with
full-disk magnetograms. The method provides a simple means of estimating
the large-scale flux distribution over the whole surface. It does not
take account of flux emerging after the central meridian passage each
rotation so it is only approximate in the activity belts but provides
a reliable map beyond those latitudes.
Title: Observations and Simulations of the Polar Field Reversals in
Cycle 23
Authors: Durrant, C. J.; Wilson, P. R.
Bibcode: 2003SoPh..214...23D
Altcode:
We have used observations obtained by the National Solar Observatory
at Kitt Peak to study the reversals of the polar magnetic fields in
Cycle 23. We have compared them with corresponding data obtained by the
Mt. Wilson Observatory, when these are available, testing both data sets
against the locations of Hα filaments. Because of the unreliability
of the data at extreme latitudes and because the apparent time of
reversal varies with the degree of smoothing applied to the data, it
is difficult to determine precise reversal time in each hemisphere
from direct observations. However, we show that it is possible to
obtain a better-defined and more precise reversal time using polar
maps derived from simulations of the synoptic fields. These indirect
values, however, depend critically on the diffusivity used in the
simulations. We applied various tests to confirm an empirical value for
the diffusivity parameter of about 600 km2 s−1
and hence determined empirical reversal times of CR 1976 in the northern
hemisphere and CR 1981 in the south.
Title: Polar magnetic fields - Filaments and the zero-flux contour
Authors: Durrant, C. J.
Bibcode: 2002SoPh..211...83D
Altcode:
We investigate the reliability with which magnetograph observations
of the large-scale polar fields establish the zero-flux contour by
comparing magnetic maps from various sources with one another and
with the locations of filament structures seen on the disk in Hα
filtergrams. The daily MWO and NSOKP magnetograms smoothed over 120
arc sec provide consistent large-scale zero-flux contours which align
with the filaments out to heliocentric angles of about 75°. Synoptic
maps match in regions where the locations of the zero-flux contour and
of the filaments are maintained for several days. Attention is drawn
to regions at the tips of unipolar `plumes' and the polar crown gap
where the contours are variable from day to day; these are tentatively
identified as regions of active reorganization of large-scale flux.
Title: Bipolar Magnetic Fields Emerging at High Latitudes
Authors: Durrant, C. J.; Turner, J.; Wilson, P. R.
Bibcode: 2002SoPh..211..103D
Altcode:
Three examples of the unusual development of high-latitude large-scale
features during cycle 23 are described. These features are found in
synoptic plots constructed using data obtained at both the NSOKP and
the MWO Observatories. Several properties of these features cannot
be reproduced in direct simulations using a modified form of the
flux-transport equation appropriate for synoptic fields and it is
inferred that their evolution is not due solely to the advection
and diffusion of decaying active region fields. The analysis shows
that one feature may be related to a high-latitude bipolar region
which emerged in an earlier rotation. By imposing the locations
of Hα filaments on enlargements of the NSOKP daily magnetograms,
we can identify the location of the other features and study their
structure at high resolution. This suggests that they are related to
the emergence of small magnetic knots at high latitudes. By repeating
the simulations including overlays of non-random patterns of bipoles
emerging at appropriate times during the simulations, it is possible
to study the effects of different patterns and to reproduce some
of the qualitative properties of these features not present in the
direct simulations. These results support Stenflo's contention that
`quite minute deviations from a random distribution (in the emergence
of small-scale fields) would suffice for these fields to have global
effects'.
Title: A method of evolving synoptic maps of the solar magnetic field
Authors: McCloughan, J.; Durrant, C. J.
Bibcode: 2002SoPh..211...53M
Altcode:
The evolution of magnetic flux at the solar surface is widely modeled by
the flux transport equation. This describes the distribution of flux
from instant to instant over the whole surface but does not describe
how the synoptic map for one Carrington rotation evolves into the
synoptic map for the next rotation. We derive the correct synoptic
evolution equation, show that a simple version yields extremely accurate
predictions of synoptic maps and discuss the implications for previous
studies of the evolution of surface magnetic structures. We also note
that the procedure yields a method of reconstructing an approximate
map of the flux over the whole surface at any instant.
Title: High-resolution Studies of the Polar Magnetic Fields during
Cycle 23
Authors: Varsik, J.; Durrant, C. J.; Turner, J.; Wilson, P. R.
Bibcode: 2002SoPh..205..231V
Altcode:
High-resolution mosaics of the solar polar magnetic fields have been
constructed using individual magnetograms obtained with the video
magnetograph of the Big Bear Solar Observatory, and the properties
of these mosaics are demonstrated in this paper. The mosaics show
selected regions of the polar fields on several days during the rising
phase of Cycle 23, and are related to the global polar fields (i)
by superposing the mosaic for a given day on to a full-disk SOHO-MDI
magnetogram obtained on the same day, (ii) by plotting the mosaics in
polar projection and using these to identify the approximate regions
reported by the mosaics on the NSOKP polar synoptic plots, and (iii)
by imposing the locations of the Hα filaments on to the mosaics in
order to infer the neutral lines of the large-scale fields. We have
studied the fine structure of the large-scale unipolar fields near the
poles and, in particular, have constructed histograms of the magnetic
field intensities within particular regions of the mosaics and, in
this way, have estimated the ratios of the number of magnetic knots of
opposite polarities within the unipolar plumes. We have also generated
enlargements of the polar regions of the NSOKP daily magnetograms. These
and statistical studies have shown that on days for which the BBSO
mosaics are not available, the NSOKP enlargements may be used to study
the high-resolution polar fields. Time-series of mosaics obtained over
four-hour periods on September 6 and November 18 show that considerable
evolution in the structure of existing flux knots and the formation
of several new knots has taken place during these periods.
Title: The Evolution of Trailing Plumes from Active Regions
Authors: Durrant, C. J.; Kress, J. M.; Wilson, P. R.
Bibcode: 2001SoPh..201...57D
Altcode:
We have studied the evolution of several high-latitude flux `plumes',
i.e., unipolar regions, trailing from active regions which emerged
near sunspot maximum in cycle 23. The observed patterns are compared
with simulations using a simple flux transport equation based on the
observed flux for an earlier Carrington rotation. In addition to the
long recognized poleward migration and diffusion of flux from active
regions, it is found that the evolution of the trailing plumes may
be influenced by flux which emerges above latitude 35° over areas of
all scales. We describe two cases in which the emerging flux appears
in the form of bipolar flux patterns which are not obviously related
to sunspots. Further, we find instances in which the observed surface
flux decreases or spreads at rates which cannot be explained solely in
terms of diffusion using the normally accepted rates. Thus in several
cases the poleward migration of flux cannot be described in terms
of passive transport by advection and diffusion as considered here,
and further investigation of the processes that contribute to the
evolution of the polar fields is required.
Title: Coronal Loops
Authors: Durrant, C.
Bibcode: 2000eaa..bookE2270D
Altcode:
Large volumes of the solar CORONA are seen to contain long curved
features stretching upwards from the CHROMOSPHERE. Many arch back
to the chromosphere, forming a closed loop within the corona. These
structures, whether closed or not, are known as coronal loops. The
geometry of these loops is determined by that of the solar magnetic
field which pervades the corona. Nearly all coronal loops contai...
Title: Landolt-Börnstein: Numerical Data and Functional Relationships
in Science and Technology - New Series " Gruppe/Group 6 Astronomy and
Astrophysics " Volume 3 Voigt: Astronomy and Astrophysics. Extension
and Supplement to Volume 2 " Instruments, Methods, Solar System
Authors: Baars, J. W.; Beer, H.; Durrant, C. J.; Graser, U.; Guinot,
B.; Hoffmann, M.; Hopp, U.; Ip, W. -H.; Jessberger, E. K.; Klecker, B.;
Lemke, D.; Meisenheimer, K.; Möbius, E.; Palme, H.; Rahe, J.; Röser,
H. J.; Schubart, J.; Schwenn, R.; Solf, J.; Soltau, G.; Staubert,
R.; Stewart, R.; Trümper, J.; Vanysek, V.; Weigelt, G.; Wolf, R.
Bibcode: 1993lbor.book.....B
Altcode:
No abstract at ADS
Title: Book-Review - Plasma Loops in the Solar Corona
Authors: Bray, B. J.; Cram, L. E.; Durrant, C. J.; Loughhead, R. E.;
Cheng, C. C.
Bibcode: 1993SSRv...65..185B
Altcode:
No abstract at ADS
Title: Book-Review - Plasma Loops in the Solar Corona
Authors: Bray, R. J.; Cram, L. E.; Durrant, C. J.; Loughhead, R. E.;
Kleczek, J.
Bibcode: 1992SoPh..138..423B
Altcode:
No abstract at ADS
Title: Plasma Loops in the Solar Corona
Authors: Bray, R. J.; Cram, L. E.; Durrant, C.; Loughhead, R. E.
Bibcode: 1991plsc.book.....B
Altcode: 1991QB529.P57......
A comprehensive account of the properties of plasma loops, the
fundamental structural elements of the solar corona. Plasma loops
cover a wide range of sizes and range in temperature from tens of
thousands to millions of degrees. They not only define the structure of
individual active regions but connect different active regions--even
across the solar equator. Loops also play an integral and decisive
role in the enormous solar explosions called flares. Over recent
years a wealth of space and ground-based observations of loops has
been obtained in various widely-spaced regions of the electromagnetic
spectrum. In this book the authors have selected the best observational
material from the literature on which to base a detailed account of
the properties of flare and non-flare loops. The book also explores
the larger implications of the loop structures for our understanding
of solar and stellar coronae. The text is enhanced by a large number
of illustrations and unique and beautiful photographs obtained from
the ground and from space.
Title: Book-Review - the Atmosphere of the Sun
Authors: Durrant, C. J.; Valnicek, B.
Bibcode: 1991SSRv...56..419D
Altcode:
No abstract at ADS
Title: Plasma loops in the solar corona.
Authors: Bray, R. J.; Cram, L. E.; Durrant, C. J.; Loughhead, R. E.
Bibcode: 1991CAS....18.....B
Altcode:
This book presents the first comprehensive account of the properties
of plasma loops, the fundamental structural elements of the solar
corona. Plasma loops not only define the structure of individual
active regions but connect different active regions. Loops also play an
integral and decisive role in solar flares. The authors have selected
the best observational material from the literature on which to base a
detailed account of the properties of flare and non-flare loops. The
book also explores the larger implications of the loop structures in
our understanding of solar and stellar coronae. The text is enhanced
by a large number of illustrations and photographs obtained from the
ground and from space.
Title: Modelling Coronal Active Region Emission Patterns (With
1 Figure)
Authors: Brown, S. F.; Durrant, C. J.
Bibcode: 1991mcch.conf..132B
Altcode:
No abstract at ADS
Title: Outstanding Theoretical Problems
Authors: Durrant, C. J.
Bibcode: 1990IAUS..138..489D
Altcode:
No abstract at ADS
Title: Corrigenda - Linear Force-Free Magnetic Fields and Coronal
Models
Authors: Durrant, C. J.
Bibcode: 1990AuJPh..43..813D
Altcode:
No abstract at ADS
Title: Book-Review - the Atmosphere of the Sun
Authors: Durrant, C. J.; Jordan, C.
Bibcode: 1989Obs...109..122D
Altcode:
No abstract at ADS
Title: Book-Review - the Atmosphere of the Sun
Authors: Durrant, C. J.
Bibcode: 1989S&T....77..619D
Altcode:
No abstract at ADS
Title: Stokes Profile Analysis and Vector Magnetic Fields. II. Formal
Numerical Solutions of the Stokes Transfer Equations
Authors: Rees, D. E.; Murphy, G. A.; Durrant, C. J.
Bibcode: 1989ApJ...339.1093R
Altcode:
Two numerical methods for formal integration of the Stokes transfer
equations for line formation in a strong magnetic field were tested by
computing Stokes profiles for a Zeeman triplet in a Milne-Eddington
model atmosphere, and for the anomalously split Ca II K line in a
realistic solar model. The first method is a Feautrier (1964) type
method, in which the equations are written in second-order form and
solved by finite-differences. The second method is a new solution
called DELO, in which an integral equation for the Stokes vector is
formulated in terms of the lambda operator (LO) associated with the
diagonal elements (DE) of the absorption matrix. It is shown that the
DELO method is faster and more accurate than the Feautrier method, and
that both methods are more efficient than the Runge-Kutta integration
method.
Title: Book-Review - the Atmosphere of the Sun
Authors: Durrant, C. J.; Brown, J. C.
Bibcode: 1989Natur.338..179D
Altcode:
No abstract at ADS
Title: Book-Review - the Atmosphere of the Sun
Authors: Durrant, C. J.; Bachmann, G.
Bibcode: 1989AN....310..357D
Altcode:
No abstract at ADS
Title: Linear force-free magnetic fields and coronal models
Authors: Durrant, C. J.
Bibcode: 1989AuJPh..42..317D
Altcode:
The mathematical properties of linear force-free fields generated
by the Helmholtz equation are reviewed, and the solutions in terms
of spherical, Cartesian and cylindrical coordinate systems are
discussed. When only the normal component of the field on a single
(photospheric) surface is available as a boundary condition, the
solutions are not uniquely determined. If further conditions are
imposed, solutions may be unique or multiple or may not exist. The
limitations of various methods of modeling the coronal magnetic field
of the sun using linear force-free fields are exposed. A new upper
boundary condition is proposed that guarantees a unique solution,
and takes account of the solar wind effects in a manner as closely
analogous as possible to that used in potential field modeling.
Title: Coronal loops in solar active regions
Authors: Durrant, C. J.; Brown, S. F.
Bibcode: 1989PASA....8..137D
Altcode: 1989PASAu...8..137D
The appearance of solar active regions as seen in EUV line radiation
is discussed in terms of a system of simple static coronal loop
models. The loop models are based on those of Rosner et al. (1978)
and may be understood in terms of the scaling laws introduced by
these authors. Some generalized scaling laws are presented which
demonstrate that the global properties of loops in fixed length are
insensitive to everything but the overall heating rate or the basal
pressure. The model and scaling laws appear to describe hot loops
well. Empirically determined temperatures and densities in cooler
loops are not in agreement with coronal loop models. A simple model of
an active region is computed using a dipole magnetic structure. The
individual loop structures were calculated on the basis of the two
different assumptions of constant basal pressure and of constant heating
rate. This paper presents a preliminary discussion of the results and
a comparison with observation
Title: Overshoot of horizontal and vertical velocities in the deep
solar photosphere
Authors: Nesis, A.; Mattig, W.; Durrant, C. J.
Bibcode: 1988A&A...201..153N
Altcode:
The authors present the results of a coherence analysis of the
centre-to-limb behaviour of the small-scale intensity and velocity
fluctuations. The vertical velocity is coherent throughout the
low-middle photosphere and is correlated with the continuum intensity
variations. The horizontal velocity variations are not coherent with the
intensity variations, and with the vertical velocity variations. The
horizontal velocity is coherent only in the low atmosphere. Thus the
horizontal motion is independent from the vertical motion and is not
of convective nature.
Title: The atmosphere of the sun
Authors: Durrant, Christopher John
Bibcode: 1988atsu.book.....D
Altcode: 1988QB528.D87......
No abstract at ADS
Title: Book-Review - the Solar Granulation
Authors: Bray, R. J.; Loughhead, R. E.; Durrant, C. J.; Weiss, N. O.
Bibcode: 1985SoPh...96..423B
Altcode:
No abstract at ADS
Title: Book-Review - the Solar Granulation - ED.2
Authors: Bray, R. J.; Loughhead, R. E.; Durrant, C. J.; Waddington,
W. G.
Bibcode: 1985Obs...105...18B
Altcode:
No abstract at ADS
Title: Global oscillations and active regions
Authors: Durrant, C. J.
Bibcode: 1985AuJPh..38..839D
Altcode:
The author presents further estimates of the amplitude of the
modulation of the solar global velocity signal caused by the passage
of active regions across the solar disc. Using measurements of the
profile of the K I λ769.9 nm line in the quiet sun and in plages
he finds a global velocity variation of ≡2 m s-1 during
the transit of a typical active region of area 3300 millionths of the
hemisphere. However, during the period in which a velocity amplitude of
6 m s-1 was reported by Claverie et al. (1982), the sunspot
areas were exceptionally large and the author confirms Schröter's
(1984) result that the combination of spot and plage contributions is
sufficient to account for the observed signal. The velocity modulation
is thus attributable to surface inhomogeneities, not to the structure
of the solar core.
Title: Book-Review - the Solar Granulation
Authors: Bray, R. J.; Loughhead, R. E.; Durrant, C. J.; Kleczek, J.
Bibcode: 1984Ap&SS.103..410B
Altcode:
No abstract at ADS
Title: Book-Review - the Solar Granulation - ED.2
Authors: Bray, R. J.; Loughhead, R. E.; Durrant, C. J.
Bibcode: 1984JBAA...94R.196B
Altcode:
No abstract at ADS
Title: Nonlinear two-dimensional dynamics of stellar atmospheres. I -
A computational code
Authors: Stefanik, R. P.; Ulmschneider, P.; Hammer, R.; Durrant, C. J.
Bibcode: 1984A&A...134...77S
Altcode:
The authors present a computational code that allows the nonlinear
equations of motion for a compressible fluid to be solved. Earlier
work on one-dimensional problems using the method of characteristics
is generalised to two dimensions employing cylindrical geometry. The
scheme is described in detail and its effectiveness is demonstrated
using analytic examples of small-amplitude motion in an isothermal,
stably stratified, atmosphere. The code is designed specifically to
handle the problem of the overshoot and decay of convective motion
in stellar atmospheres and their coupling to acoustic and internal
wave fields.
Title: Geometrical Effects in Weighting Functions
Authors: Kaisig, M.; Durrant, C. J.
Bibcode: 1984ssdp.conf..406K
Altcode:
Weighting functions of the first and second order facilitate the
analysis of solar fine structure observed with high and low spatial
resolution, respectively. The authors generalize these functions
to permit their use near the solar limb away from disk center, and
demonstrate how the varying solar parameters along the line-of-sight
lead to geometrical smearing of the observed fluctuations and to
correlated contributions by the horizontal velocity component.
Title: Studies of Overshoot
Authors: Nesis, A.; Durrant, C. J.; Mattig, W.
Bibcode: 1984ssdp.conf..243N
Altcode:
The authors present the results of a power and coherence analysis
of the centre-to-limb behavior of the small-scale intensity and
velocity fluctuations. The vertical velocity is coherent throughout the
low-middle photosphere and is correlated with the continuum brightness
pattern. The horizontal velocity pattern is not coherent with the
vertical velocity and brightness patterns indicating lack of horizontal
heat transport. The horizontal velocity patterns are coherent only in
the low atmosphere. The mechanism causing the breakdown of coherence
may be a property of the convective flow or the intrusion of a gravity
wave field.
Title: Interpretation of Low Resolution Observations (Keynote)
Authors: Durrant, C. J.
Bibcode: 1984ssdp.conf..345D
Altcode:
The information content of low resolution observations is discussed
mainly in terms of the diagnositic properties of line profiles formed
in atmospheres with small fluctuations about the mean.
Title: Book-Review - the Solar Granulation
Authors: Bray, R. J.; Loughhead, R. E.; Durrant, C. J.; Nordlund, A.
Bibcode: 1984SSRv...39R.222B
Altcode:
No abstract at ADS
Title: Book-Review - the Solar Granulation
Authors: Bray, R. J.; Loughhead, R. E.; Durrant, C. J.
Bibcode: 1984S&T....68T.426B
Altcode:
No abstract at ADS
Title: The Asymmetry of Photospheric Absorption Lines in Quiet and
Active Regions of the Sun
Authors: Kaisig, M.; Durrant, C. J.; Schroter, E. H.
Bibcode: 1984ssdp.conf..360K
Altcode:
Photoelectric scans of Fe I lines in quiet and active regions of the
sun yield significant differences of the line asymmetry and wavelength
shifts of the line centers. These differences are interpreted
in terms of a modification of the hydrodynamic structure beneath
Ca+-plage regions. To demonstrate this, the authors used a
second-order perturbation analysis and the classical "two-stream model".
Title: Suggestions for future investigations
Authors: Roberts, B.; Einaudi, G.; Toricelli, G.; Cargill, P.; Durrant,
C. J.
Bibcode: 1984ost1.conf..183R
Altcode:
No abstract at ADS
Title: The solar granulation Durrant.
Authors: Bray, R. J.; Loughhead, R. E.; Durrant, C. J.
Bibcode: 1984cup..book.....B
Altcode:
A comprehensive account of observational and theoretical knowledge
of solar granulation is presented. A historical introduction to
the solar granulation is given, and the morphology, evolution,
and dynamics of granulation and supergranulation are discussed. The
theory of convection is introduced, and the theory of astrophysical
convection is addressed. Finally, the interpretation of granulation
and supergranulation is considered.
Title: The analysis of solar limb observations. III - Geometrical
effects in weighting functions
Authors: Kaisig, M.; Durrant, C. J.
Bibcode: 1984A&A...130..171K
Altcode:
Weighting functions of the first and second order facilitate the
analysis of solar fine structure observed with high and low spatial
resolution, respectively. The authors generalize these functions to
permit their use towards the solar limb and demonstrate how the varying
solar parameters along the line of sight lead to geometrical smearing
of the observed fluctuations and to correlated contributions by the
horizontal velocity component.
Title: Solar active regions: observation and theory.
Authors: Durrant, C. J.
Bibcode: 1984ost1.conf...21D
Altcode:
No abstract at ADS
Title: Book-Review - the Solar Granulation
Authors: Bray, R. J.; Loughhead, R. E.; Durrant, C. J.
Bibcode: 1984AExpr...1S..39B
Altcode:
No abstract at ADS
Title: Balloon-borne imagery of the solar granulation. IV - The
centre-to-limb variation of the intensity fluctuations
Authors: Durrant, C. J.; Mattig, W.; Nesis, A.; Schmidt, W.
Bibcode: 1983A&A...123..319D
Altcode:
A reanalysis of the white-light photographs of the granulation obtained
during the flight of the balloon-borne Spektrostratoskop experiment
is presented. A detailed examination of the power spectra of the
intensity fluctuations at various times during the flight reveals a
steady increase in a straylight and a substantial degree of astigmatism
that changed with the focus setting. Allowing for the latter and
normalizing all measurements to that with the least straylight, the
rms relative intensity fluctuation at the center of the disk at 556 nm
is increased from the previously reported value of 8.6 percent to 11.3
percent. The overall change of rms fluctuation from the center of the
disk to 0.3 micron is remarkably small, dropping some 10 percent. The
results agree quite well with those of the Soviet Solar Stratospheric
Observatory, when corrected roughly for instrumental degradation, and
with a granulation model in which the granular temperature perturbation
cuts off at a height of 35 km in the atmosphere.
Title: Solar global velocity oscillations and active region rotation
Authors: Durrant, C. J.; Schroeter, E. H.
Bibcode: 1983Natur.301..589D
Altcode:
Claverie et al.1 have recently reported the detection
of an approximately 13-day periodicity in measurements of the mean
Doppler velocity shift of the integrated solar disk. They attribute
this signal to the presence of a rapidly rotating core. Here we draw
attention to the close correlation between this periodicity and the
rotation of solar active regions across the disk. The presence of
an active region should modulate the measured velocities due to the
temperature sensitivity of the line measured. It seems likely that
this is the origin of the signal observed by Claverie et al.
Title: Die Mitte-Rand-Variation des granularen Geschwindigkeitsfeldes
Authors: Nesis, A.; Durrant, C. J.; Mattig, W.
Bibcode: 1983MitAG..60..279N
Altcode:
No abstract at ADS
Title: The asymmetry of photospheric absorption lines. I - an analysis
of mean solar line profiles
Authors: Kaisig, M.; Durrant, C. J.
Bibcode: 1982A&A...116..332K
Altcode:
The paper investigates the information content of the shifts and
asymmetries of mean line profiles and analyzes in detail, with the
aid of a perturbation analysis and a two-stream model, that of the
solar spectrum observed at the center of the disk. It is shown that the
characteristic C-shape of the line bisectors depends mainly on the run
of temperature fluctuations, correlated with velocities, in combination
with the temperature-dependent opacities. The degree of asymmetry (and
shift) is not only a function of the one-point correlation between
temperature and velocity - which measures the convective flux but
depends also strongly on two-point correlations. The latter can produce
an asymmetry in the absence of heat transport along the line of sight -
at the limb, for instance. The usefulness of measurements of mean line
profiles as a test of convective models is demonstrated by examining
the general characteristics of the asymmetry of the Fe I 7557.6 nm
line in both the sun and examples of other main-sequence stars.
Title: Spectral line transfer effects in Lambdameter measurements
of solar short-period oscillations
Authors: Deubner, F. -L.; Durrant, C. J.; Kaltenbacher, J.
Bibcode: 1982A&A...114...85D
Altcode:
Lambdameter records with different exit-slit settings yield power
spectra of short period oscillations in the solar atmosphere, observed
in the Na D(1) line and medium strong Fe I line, whose structure
is notably stable with regard to slit geometry changes. By means of
short period wavetrain numerical modeling, it is demonstrated that
while such a structure in the power spectra of photospheric lines
is absent for rms wave amplitudes lower than about 0.1 km/sec, it
emerges with higher amplitudes as a consequence of nonlinearities in
the line transfer process. It is emphasized that the nonlinear effect
presently investigated must also be considered in stronger chromospheric
lines. Linear correction factors cannot be applied to the observed power
in order to deduce the energy flux carried by the acoustic waves if
nonlinear effects are the only source of the observed spectral pattern.
Title: Vertical structure of the solar photosphere. II - The
small-scale velocity field
Authors: Durrant, C. J.; Nesis, A.
Bibcode: 1982A&A...111..272D
Altcode:
Measurements of solar line shifts in spectra obtained during the
Spektrostratoskop balloon flight of 1975 are described. By averaging
the shifts of several lines, the noise level that is particularly
apparent in measurements of single weak lines is strongly reduced,
and line shift measurements extremely close to the continuum level are
possible. An account is given of two investigations. In the first,
oscillations are removed by spatial filtering, and the probability
density distribution of the velocity field is then compared with that of
the continuum brightness fluctuations, that is, the granulation. The
histograms for brightness and velocity in the deepest atmospheric
layers are very similar, and they show a consistent departure from a
normal distribution. In the upper atmosphere, the velocity histogram
is more variable, and systematic behavior is not observed. In the
other investigation, the correlation between the velocity fields at
different levels and between the velocity and brightness field at the
base of the atmosphere is studied by means of a coherence analysis.
Title: Vertikale Struktur der solaren Photosphäre II. Das
Geschwindigkeitsfeld kleiner räumlicher Strukturen
Authors: Nesis, A.; Durrant, C. J.
Bibcode: 1982MitAG..55...92N
Altcode:
No abstract at ADS
Title: The analysis of solar limb observations. I - Restoration of
data in a tilted reference frame
Authors: Wiesmeier, A.; Durrant, C. J.
Bibcode: 1981A&A...104..207W
Altcode:
Expressions are derived for the correction of the statistical
properties of two-dimensional fields degraded by arbitrary (without
axial symmetry) point-spread functions. Attention is given to both
oneand two-dimensional sampling. A number of earlier estimates of
corrections to observations of brightness and volocity fluctuations away
from the center of the solar disk are shown to be in error. Corrected
values are reported of the rms granular brightness fluctuations as a
function of heliocentric angle.
Title: The analysis of solar limb observations. II - Geometrical
smearing
Authors: Durrant, C. J.; Kneer, F.; Maluck, G.
Bibcode: 1981A&A...104..211D
Altcode:
Center-of-disk and limb observations of photospheric brightness
fluctuations reveal a systematic suppression of the values at the
limb. This is a geometrical effect arising from the line of sight at the
limb passing through various structures across the surface. This effect
is examined here in the light of recent granular temperature models
using a simple model incorporating the dominant granular scale. The
geometry is found to have little influence on the deep-seated granular
brightness field but to strongly suppress the brightness fluctuations
caused by the upper photospheric temperature field. The significance
of these results for the restoration of limb observations is discussed.
Title: Hope yet for a chromospheric model!
Authors: Durrant, C. J.
Bibcode: 1981SSRv...29..357D
Altcode:
Current chromospheric models are briefly reviewed with particular
emphasis on the inadequacy of the dynamical description. Whilst an
improvement in models of the gross structure seems possible with present
knowledge, a fully self-consistent model, of the upper chromosphere
in particular, requires the better empirical understanding that awaits
a space observing facility.
Title: Konvektion in der Sonnenatmosphäre.
Authors: Durrant, C. J.; Nesis, A.
Bibcode: 1981S&W....20..405D
Altcode:
Convection, in addition to radiation, plays an important role in
the processes involved in the transportation of energy from the solar
interior to the solar surface. The solar convection zone begins directly
below the photosphere and, extending into the solar interior, covers
approximately one-third of the solar radius. An investigation of the
convection zone is only possible for its upper boundary layer. Of
particular interest in this area is the granulation phenomenon. The
dynamics of the solar photosphere are discussed. The velocity field
can be studied with the aid of the Doppler shift. Attention is given to
the extension of the area in which the transport of heat takes place as
consequence of motions in the photosphere. Two spectral areas are used
in an investigation conducted to obtain values regarding the intensity
of large structures. Measurements of the Doppler shift were also
carried out. The obtained results show that the brightness and velocity
variations of the lowest photospheric layers are of convective origin.
Title: Determination of microturbulent velocities in early-type stars
Authors: Dufton, P. L.; Durrant, C. J.; Durrant, A. C.
Bibcode: 1981A&A....97...10D
Altcode:
In the case of B-type stars, microturbulent velocities are often derived
from the requirement that abundances estimated from individual lines
show no systematic variation with line strength. It is demonstrated
that this method results in an overestimate of the microturbulent
velocity. For high-quality equivalent widths, the systematic error is
found to be approximately 2 km/sec; for less accurate observational
data, the error is larger.
Title: Vertical structure of the solar photosphere
Authors: Durrant, C. J.; Nesis, A.
Bibcode: 1981A&A....95..221D
Altcode:
Observations of intensity structures seen in the wings of the Mg b2 line
from both quiet and active regions of the sun are presented. A linear
statistical analysis indicates that at least three distinct intensity
(temperature) components are present: a very low photospheric component
seen at all scales, and two components in the upper atmosphere,
one in the high photosphere at scales smaller than 5 arcsec in the
quiet atmosphere and one in the middle-high photosphere at larger
scales. Only the former is strictly granulation. The physical processes
underlying each component in quiet regions are tentatively identified
as convection, gravity waves and network. Active regions appear to
differ only in the relative contribution of these components.
Title: Landolt-Börnstein. Numerical data and functional
relationships in science and technology. New series. Group VI:
Astronomy, astrophysics and space research. Volume_2. Astronomy and
astrophysics. Extension and supplement to Volume_1. Subvolume a:
methods - constants - solar system.
Authors: Hellwege, K. -H.; Schaifers, K.; Voigt, H. H.; Wolf, R.;
Durrant, C. J.; Behr, A.; West, R. M.; Solf, J.; Weigelt, G.; Schmahl,
G.; Staubert, R.; Trümper, J.; Lemke, D.; Hachenberg, O.; Enslin, H.;
Fricke, W.; Bruzek, A.; Gondolatsch, F.; Ip, W. -H.; Axford, W. I.;
Schubart, J.; Jessberger, E. K.; Rahe, J.; Fechtig, H.; Leinert, C.;
Grün, E.; Pilipp, W.; Scholer, M.; Palme, H.; Suess, H. E.; Zeh,
H. D.; Kirsten, T.
Bibcode: 1981lndf.book.....H
Altcode:
No abstract at ADS
Title: Small-scale velocity fields and mean line profiles
Authors: Durrant, C. J.
Bibcode: 1980A&A....91..251D
Altcode:
The mean equation of transfer for a line formed in the presence of a
small-scale velocity field is derived. Approximate expressions for
effects arising from fluctuating quantities are illustrated by the
case of short-period waves; correlations between fluctuations are taken
into account. It is shown that mean line profiles are best generated by
averaging the time variation of accurate individual profile sequences.
Title: Some more effects of waves on spectral line analysis
Authors: Durrant, C. J.
Bibcode: 1980A&A....89...80D
Altcode:
The effects on spectral line shifts due to velocity-correlated opacity
and source function fluctuations in waves are discussed in the context
of a simple exponential atmospheric model. These correlations contribute
a steady net line shift and, if the velocity amplitude is small enough,
a small correction to the fluctuating component of the shift. Also
noted are the minor changes in the form of the line shift reflecting
height-dependent velocity amplitudes and nonlinear source functions. The
results and limitations of the model are discussed with reference
to the large-amplitude calculations of Cram et al. (1979) and the
estimates of the high frequency power in the sun made by Deubner (1976).
Title: The effect of waves on spectral line analysis in the Fourier
domain.
Authors: Durrant, C. J.
Bibcode: 1979A&A....76..208D
Altcode:
An attempt is made to discuss an analysis of Fourier transforms of
wave-broadened spectral-line profiles in terms of microturbulence
and total velocity field. Synthetic line profiles are calculated
numerically and analyzed by following the procedures outlined by Gray
(1975, 1976). It is concluded that: (1) the presence of a progressive
wave field cannot be diagnosed directly from a mean line transform; (2)
the microvelocity field derived in the Fourier domain by matching the
position of the first minimum is strongly dependent on line strength;
(3) the Fourier microfield and classical microturbulence are identical
only for very strong lines lying at the upper end of the first portion
of the curve of growth; (4) the residual macrovelocity transform
is not simply describable by commonly used functions; and (5) the
macrovelocity parameters can be overestimated or underestimated unless
caution is exercised.
Title: The effect of waves on spectral line analysis.
Authors: Durrant, C. J.
Bibcode: 1979A&A....73..137D
Altcode:
A simple analytical model is developed for the instantaneous effect
of a wave train on spectral lines of arbitrary strength and shape. The
most important proviso of this model is that the velocity disturbance
must be small in comparison with the thermal Doppler line width. The
model is used to investigate the diagnostic value of various methods
of spectral-line analysis.
Title: Studies of granular velocities. VIII. The height dependence
of the vertical granular velocity component.
Authors: Durrant, C. J.; Mattig, W.; Nesis, A.; Reiss, G.; Schmidt, W.
Bibcode: 1979SoPh...61..251D
Altcode:
Spectral observations of solar velocity fields made during a partial
solar eclipse are described. Continuum intensity measurements at
the lunar limb allow the modulation transfer function to be derived
and the true spatial power spectrum of the velocity field to be
reconstructed. The oscillatory and granular components are separated
by applying spatial filters cutting off at 3″.7. The oscillatory
component values are in good agreement with those of Canfield (1976) but
the granular component has substantially more power and a smaller height
gradient. The discrepancy can be resolved by noting the uncertainties
of the seeing corrections and of the separation into components in
the work of Canfield.
Title: Die Höhenabhängigkeit der vertikalen granularen
Geschwindigkeitskomponente
Authors: Durrant, C. J.; Mattig, W.; Nesis, A.; Reiss, R.; Schmidt, W.
Bibcode: 1979MitAG..45..149D
Altcode:
No abstract at ADS
Title: The Solar Chromosphere - still enigmatic?
Authors: Durrant, C. J.
Bibcode: 1978QJRAS..19..411D
Altcode:
No abstract at ADS
Title: Some comments on Suemoto's paper "An empirical, statistical
model for the formation of the cores of chromospheric Fraunhofer
lines".
Authors: Cram, L. E.; Durrant, C. J.; Grossmann-Doerth, U.
Bibcode: 1978SoPh...58..279C
Altcode:
We discuss a recent model for the solar chromosphere proposed by Suemoto
(Solar Phys.54, 3). We conclude that the model is incompatible with the
basic constraints imposed by high resolution observations and by line
formation theory, and that consequently the model does not adequately
describe the solar chromosphere.
Title: a Model for Diagnosing Stellar Velocity Fields
Authors: Durrant, C. J.
Bibcode: 1978hrs..conf..474D
Altcode:
No abstract at ADS
Title: Illustrated glossary for solar and solar terrestrial physics
Authors: Bruzek, A.; Durrant, C. J.
Bibcode: 1977ASSL...69.....B
Altcode: 1977igss.conf.....B; 1977assl...69.....B
This book collects all terms of relevance to solar and solar-terrestrial
physics that appear in current English-language literature. Each
term or group of related terms is given a concise phenomenological
and quantitative description, including the relationship to other
phenomena and an interpretation in terms of physical processes. The
major topics of the glossary encompass the solar interior, the solar
cycle, solar rotation, large-scale circulation, nonspot magnetic
fields, the quiet photosphere and chromosphere, the transition
region, the solar corona, active regions, spots and faculae, flares
and associated phenomena, prominences, solar radio emission, the
solar wind and interplanetary medium, solar-terrestrial physics,
and general theoretical terms. Specific terms defined include solar
neutrinos, convective theory, the solar activity cycle, dynamos,
the general solar magnetic field, the quiet sun, granulation and
supergranulation, coronal holes, sunspot groups, solar activity
indexes, the Evershed and Wilson effects, X-ray flares, EUV bursts,
particle flares, prominence phenomenology, radio noise storms, solar
radio bursts, macro/microturbulence, solar-wind models, geomagnetic
indexes, geomagnetic storms, radiation belts, and aurorae.
Title: Flows in magnetic flux tubes.
Authors: Durrant, C. J.
Bibcode: 1977IAUS...62..267D
Altcode:
No abstract at ADS
Title: General Theoretical Terms
Authors: Durrant, C. J.
Bibcode: 1977ASSL...69..139D
Altcode: 1977igss.conf..139D
Anomalous Dispersion Contrast Mechanisms Dynamical Stability Hanle
Effect or Level Crossing Interference Lighthill Mechanism Line
Control Macro/Microturbulence Magnetic Buoyancy Non-Thermal Velocities
Overstability Penetrative Convection or Overshoot Rotational Braking
Source Function Thermodynamic Equilibrium Turbulence Waves Wave
Tunnelling
Title: Solar Interior
Authors: Durrant, C. J.; Roxburgh, I. W.
Bibcode: 1977ASSL...69....1D
Altcode: 1977igss.conf....1D
Solar Standard Model Internal Rotation Energy Generation Solar Neutrinos
Convection Zone Convective Theory Boussinesq Assumption
Title: The sun's chromospheric velocity field as inferred from the
Ca II K line.
Authors: Durrant, C. J.; Grossmann-Doerth, U.; Kneer, F. J.
Bibcode: 1976A&A....51...95D
Altcode:
Theory and observation of the solar Ca II K line under high spatial
resolution are briefly reviewed. It is shown that contrary to popular
belief, present theory is not capable of explaining the observed
features of the K line. An attempt is made to develop a schematic model
of the temporal behavior of the spatially resolved K line, based on
Leibacher's (1971) investigation of waves in the solar atmosphere
Title: Solar activity (Activité solaire).
Authors: Newkirk, G.; Dunn, R. B.; Mehltretter, P.; MacQueen, R.;
Bonnet, R. M.; White, O. R.; Fokker, A. D.; Zwaan, C.; Bruzek, A.;
Durrant, C.; Grossmann-Doerth, U.; Mehltretter, J. P.; Svestka, Z.;
de Feiter, L. D.; Tandberg-Hanssen, E.; Howard, R.; Stix, M.; Pneuman,
G. W.; Hundhausen, A. J.; Sawyer, C.; Simon, P.
Bibcode: 1976IAUTA..16b..13N
Altcode:
No abstract at ADS
Title: Spectroscopic Investigation of the Chromosphere. IV: A
Reassessment of the Cloud Model
Authors: Durrant, C. J.
Bibcode: 1975SoPh...44...41D
Altcode:
The cloud model employed in the analysis of chromospheric contrast
profiles is subject to two criticisms. The source function in
the cloud may not be varied independently of the Doppler width in
the case of Hα and the radiative coupling between the cloud and
the underlying atmosphere cannot be ignored. These criticisms are
investigated quantitatively with two simple extreme models. It is
found that by taking account of both effects the cloud model may be
reinstated. Observed chromospheric features may be understood in terms
of clouds of varying parameters embedded in the uppermost regions of
a generally undisturbed homogeneous atmosphere. The variable cloud
parameters are the optical thickness, the Doppler width, the bulk
velocity and the angular size viewed from the line forming regions of
the underlying atmosphere.
Title: The Appearance of Chromospheric Structures in Hα
Authors: Durrant, C. J.
Bibcode: 1975MitAG..36..139D
Altcode:
No abstract at ADS
Title: Book Review: The Quiet Sun
Authors: Durrant, C. J.
Bibcode: 1974JATP...36..909D
Altcode:
No abstract at ADS
Title: Shock Wave Dissipation in Magnetically Active Regions
Authors: Durrant, C. J.; Michalitsanos, Andrew G.
Bibcode: 1971SoPh...18...60D
Altcode:
No abstract at ADS
Title: Magnetographic and Spectrographic Observations of Weakly
Active Regions
Authors: Durrant, C. J.
Bibcode: 1971IAUS...43..268D
Altcode:
No abstract at ADS
Title: Rotation and chemical abundances in the peculiar A stars - I.
Authors: Durrant, C. J.
Bibcode: 1970MNRAS.147...59D
Altcode:
The classifications and atmospheric structures displayed by early type
peculiar stellar spectra are compared empirically with those of normal
stars. It is concluded that the structures of the metal line forming
regions of the atmospheres of the peculiar A and B stars are identical
with those of the normal stars of the same hydrogen type. A consistent
temperature sequence can be established for both types later than
spectral type B . The differences in metal line strengths in stars
of similar hydrogen type can be interpreted only as differences of
abundance in the atmospheres.
Title: Rotation and chemical abundances in the peculiar A stars - II.
Authors: Durrant, C. J.
Bibcode: 1970MNRAS.147...75D
Altcode:
New measurements of the distribution of silicon line strengths amongst
early type stars having similar atmospheric structures do not allow
a clear-cut separation into normal and anomalous types. It is shown
that those stars having line strengths much larger than the mean
tend to have rotational velocities less than 200 km -1 It is likely
that in many, if not most, strong-line stars no single temperature
and pressure parameters will suffice to describe the atmosphere, and
the assumption of a mean temperature can lead to large errors in the
derived abundances of all but a few elements. The production of stars
described by the oblique rotator model is discussed briefly.
Title: Rotation and chemical abundances in the peculiar A stars
Authors: Durrant, Christopher John
Bibcode: 1968PhDT........80D
Altcode:
No abstract at ADS