explanation blue bibcodes open ADS page with paths to full text
Author name code: altschuler
ADS astronomy entries on 2022-09-14
author:"Altschuler, Martin D."
---------------------------------------------------------
Title: Obituary: Ludwig Friedrich Oster, 1931-2003
Authors: Sofia, Sabatino; Altschuler, Martin D.
2003BAAS...35.1468S Altcode:
Ludwig Friedrich Oster died at the Anchorage Nursing and Rehabilitation
Center in <P />Salisbury, MD on 28 February 2003, of complications
from advanced Alzheimer's <P />disease. He is survived by his wife
Cheryl M. (Oroian) and his two children by a <P />previous marriage,
Ulrika and Mattias Oster. He had a distinguished career both as a <P
/>researcher in solar physics and as a science administrator in the
National Science <P />Foundation. <P />Ludwig was born on 8 March
1931 in Konstanz, Germany and emigrated to the U.S. in <P />1958,
acquiring American citizenship in 1963. His mother and father were
Emma <P />Josefine (Schwarz) and Ludwig Friedrich Oster. He got a
BS degree in physics at the <P />University of Freiburg under the
guidance of Prof. K. O. Kiepenheuer in 1951, and a <P />MS (1954)
and PhD from the University of Kiel in 1956 under the guidance of
Prof. A. <P />Unsold. From 1956 to 1958 he was a Fellow of the German
Science Council at Kiel and, <P />upon his arrival to the US in 1958, he
became a Postdoctoral Research Associate in the <P />Physics Department
of Yale University. He became an Assistant Professor of Physics <P />and
Astrophysics at Yale in 1960 and five years later he was promoted to
Associate <P />Professor. In 1967 he became an Associate Professor
of Physics and Astrophysics at the <P />University of Colorado
and a Fellow of the Joint Institute for Laboratory Astrophysics;
<P />he was promoted to Full Professor in 1970. In 1981 he was a
Visiting Professor at Johns <P />Hopkins University, and shortly
thereafter became a National Research Council Senior <P />Associate at
NASA/Goddard Space Flight Center in Greenbelt, MD, where he worked on
<P />solar variability. He joined the National Science Foundation in
1983, where he became <P />the Program Manager for the National Radio
Astronomy Observatory in the Division of <P />Astronomical Sciences
of the Foundation; he remained there until his retirement in 1996. <P
/>His early work, started in Germany and continued at Yale, concerned
radiation <P />mechanisms related to solar phenomena. His works on
cyclotron radiation, plasma <P />oscillations and bremsstrahlung
radiation have become classic publications in plasma <P />physics
and they continue to be referenced in the current literature. During
this period he <P />started his student mentoring work that led to
the awarding of several PhD degrees. <P />At Boulder, he extended his
work on solar and plasma physics to the newly discovered <P />quasars
and pulsars. He loved to study and understand the mysterious and the
puzzling <P />phenomena, which the Universe so generously provides. <P
/>While at Goddard, he joined the effort to understand the variations
in total solar <P />irradiance then recently discovered by the Nimbus
7 satellite and the ACRIM experiment <P />on the SMM satellite. He made
significant contributions to that problem, particularly <P />regarding
the ultraviolet radiation component, and continued to work on it after
he had <P />joined the NSF as a science administrator. He published
his last scientific paper in 1983, <P />after having joined NSF. <P
/>Ludwig was a great teacher and an even greater friend. He taught
courses including <P />electromagnetic theory, relativistic theory of
radiation, quantum mechanics, solar physics <P />and radio astronomy
among others. He wrote an introductory textbook in astronomy that
<P />was translated into several languages. He directed PhD theses
in a variety of topics. Best <P />of all, he instilled in his
students a sense of curiosity and confidence that lasted for a <P
/>lifetime. He used to say, “if what you think disagrees with the
opinion of well-known <P />astronomers, do not simply assume that
you are wrong and they are right. It may well be <P />that you are
right! Think carefully about it." That advice has served all of us,
his former <P />students, well. We will miss his cheerful disposition,
his friendliness, and his never- <P />ending curiosity.
---------------------------------------------------------
Title: A Fast Technique for Improved 3-DIMENSIONAL Mapping of the
Solar Corona
Authors: Perry, R. Michael; Altschuler, Martin D.
1989SoPh..119..301P Altcode:
To obtain improved maps of the coronal electron density distribution we
have devised an iterative technique in which an approximation of the
unknown distribution is successively modified to reduce discrepancies
with the original data. With this technique we can now map the corona
to a much finer resolution than shown in our previous papers, without
greatly increasing the computational cost. The series representation
of density may now contain more than 23 000 terms compared with
previous limit of 128. This results in a fourfold increase in linear
resolution, so that features about a tenth of a solar radius in width
are now separated. The iteration algorithm can be adjusted to apply a
mathematically `optimal' correction to a given approximation of the
density. Although this correction minimizes noise levels, a cheaper
version of the algorithm yields a better result.
---------------------------------------------------------
Title: Solar physics applications of computer graphics and image
processing.
Authors: Altschuler, M. D.
1985NASCP2374..441A Altcode:
Contents: Introduction. Overview of computer graphics and image
processing. Computer graphics as a tool for solar physicists. Setting
up a graphics and image-processing facility.
---------------------------------------------------------
Title: Search for optimal three-dimensional mapping of the solar
corona from K-coronameter data
Authors: Perry, R. M.; Altschuler, M. D.
1981STIN...8212017P Altcode:
An iterative technique was devised in which an approximation of the
unknown solar electron density distribution is successively modified
to reduce discrepancies with the original data. With the technique the
corona can be mapped to a much finer resolution than shown in their
previous papers without greatly increasing the computational cost. The
series representation of density may now contain more than 23,000 terms
compared with the previous limit of 128. This results in a fourfold
increase in linear resolution, so that features about a tenth of a
solar radius in width are now separate. The iteration algorithm can
be adjusted to apply a mathematically optimal correction to a given
approximation of the density. Although this correction minimizes noise
levels, a cheaper version of the algorithm yields a better result.
---------------------------------------------------------
Title: Reconstruction of the global-scale three-dimensional solar
corona
Authors: Altschuler, M. D.
1979irp..book..105A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Open magnetic structures on the sun.
Authors: Levine, R. H.; Altschuler, M. D.; Harvey, J. W.; Jackson,
B. V.
1977ApJ...215..636L Altcode:
High-resolution harmonic analysis of the solar magnetic field has
been used succesfully to calculate the geometry of open magnetic field
lines in the solar corona. Comparison of the loci of open-field-line
footpoints with solar X-ray photographs shows that all the coronal
holes during two solar rotations are successfully represented, including
details of their evolution. Some open magnetic configurations derived in
the calculations precede by up to one solar rotation the manifestation
of coincident dark areas on the X-ray photographs. The only other
areas that contribute open field lines to the corona are separations
between active-region loop systems. By varying the radius at which
field lines are forced to be open in the calculation, it is possible to
reproduce more closely the surface configuration of particular coronal
holes. Comparison of the size of X-ray holes with the fraction of the
solar surface covered by open field lines leads to the conclusion
that a significant part of the area of coronal holes must contain
closed magnetic fields. Comparison of open field lines which lie in
the equatorial plane of the sun with solar-wind data indicates that
eventual high-speed solar-wind streams are associated with those parts
of open magnetic structures that diverge the least.
---------------------------------------------------------
Title: High resolution mapping of the magnetic field of the solar
corona.
Authors: Altschuler, M. D.; Levine, R. H.; Stix, M.; Harvey, J.
1977SoPh...51..345A Altcode:
High resolution KPNO magnetograph measurements of the line-of-sight
component of the photospheric magnetic field over the entire dynamic
range from 0 to 4000 gauss are used as the basic data for a new analysis
of the photospheric and coronal magnetic field distributions. The daily
magnetograph measurements collected over a solar rotation are averaged
onto a 180 × 360 synoptic grid of equal-area elements. With the
assumption that there are no electric currents above the photospheric
level of measurement, a unique solution is determined for the
global solar magnetic field. Because the solution is in terms of an
expansion in spherical harmonics to principal index n = 90, the global
photospheric magnetic energy distribution can be analyzed in terms
of contributions of different scale-size and geometric pattern. This
latter procedure is of value (1) in guiding solar dynamo theories, (2)
in monitoring the persistence of the photospheric field pattern and
its components, (3) in comparing synoptic magnetic data of different
observatories, and (4) in estimating data quality. Different types of
maps for the coronal magnetic field are constructed (1) to show the
strong field at different resolutions, (2) to trace the field lines
which open into interplanetary space and to locate their photospheric
origins, and (3) to map in detail coronal regions above (specified)
limited photospheric areas.
---------------------------------------------------------
Title: Solar sources of the interplanetary magnetic field and
solar wind
Authors: Levine, R. H.; Altschuler, M. D.; Harvey, J. W.
1977JGR....82.1061L Altcode:
Open magnetic field lines, those which extend from the solar photosphere
to interplanetary space, are traced in the current-free (potential
field) approximation using measured photospheric fields as a boundary
condition. It is found that (1) only a relatively small fraction of the
photospheric area connects via open field lines to the interplanetary
magnetic field; (2) those photospheric areas which do contribute open
field lines lie beneath coronal holes and within the boundaries of the
holes as projected onto the photosphere or else between loop systems
of an active region; (3) the interplanetary magnetic field in the plane
of the sun's equator, essentially the field in the ecliptic plane, may
connect to photospheric regions of high latitude; and (4) the fastest
solar wind streams are correlated with those magnetic flux tubes which
expand least in cross-sectional area over the distance between the
photosphere and the coronal height where the solar wind begins.
---------------------------------------------------------
Title: Open Magnetic Structures on the Sun
Authors: Levine, R. H.; Altschuler, M. D.; Harvey, J. W.
1976BAAS....8..326L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Source of the solar flare energy.
Authors: Altschuler, M. D.
1976SoPh...47..183A Altcode:
Recent Skylab and magnetograph observations indicate that strong
photospheric electric currents underlie small flare events such as X-ray
loops and surges. What is not yet certain, because of the non-local
dynamics of a fluid with embedded magnetic field, is whether flare
emission derives from the energy of on-site electric currents or from
energy which is propagated to the flare site through an intermediary,
such as a stream of fast electrons or a group of waves. Nevertheless,
occurrences of: (1) strong photospheric electric currents beneath small
flares; (2) similar magnetic fine structure inside and outside active
regions; (3) eruptive prominences and coronal white light transients
in association with big flares; and, (4) active boundaries of large
unipolar regions suggest the possibility that all phenomena of solar
activity are manifestations of the rapid ejection and/or gradual
removal of electric currents of various sizes from the photosphere. The
challenge is to trace the precise magnetofluid dynamics of each active
phenomenon, particularly the role of electric current build-up and
dissipation in the low corona.
---------------------------------------------------------
Title: Tabulation of the Harmonic Coefficients of the Solar Magnetic
Fields
Authors: Altschuler, Martin D.; Trotter, Dorothy E.; Newkirk, Gordon,
Jr.; Howard, Robert
1975SoPh...41..225A Altcode:
Tables of spherical harmonic coefficients for the global
photospheric magnetic field between 1959 and 1974 are now available
on microfilm. (These are the same coefficients which were used to
construct the maps of the coronal magnetic atlas.)
---------------------------------------------------------
Title: Magnetic fields and solar flares
Authors: Altschuler, M. D.
1975iafe.rept...25A Altcode:
It is proposed that the nonpotential magnetic fields (or electric
currents) responsible for solar flares are generated in the photosphere
itself with little or no magnetic flux contributed from deeper
layers. The solar photosphere and earth's troposphere are compared to
show that pressure differences, magnetic fields, and velocity fields in
the former constitute a strongly interacting system, or 'meteorology',
for the partially ionized visible solar layer. The possibility is
considered that magnetic fields are generated in the photosphere at the
boundaries of convective cells by either large nonparallel gradients in
electron pressure and density or turbulent flows acting on preexisting
magnetic fields. It is also suggested that the photosphere rids itself
of a magnetic field as fast as it is generated, that magnetic fields
are generated continuously in certain photospheric regions, and that
solar activity occurs when too much magnetic flux is produced in a
given region. Observational evidence is examined which indicates that
flare loops, surges, erupting prominences, and other manifestations
of solar activity are associated with the ejection of chromospheric
or photospheric electric currents into the corona.
---------------------------------------------------------
Title: The Large-Scale Solar Magnetic Field
Authors: Altschuler, M. D.; Trotter, D. E.; Newkirk, G., Jr.;
Howard, R.
1974SoPh...39....3A Altcode:
The large-scale photospheric magnetic field, measured by
the Mt. Wilson magnetograph, has been analyzed in terms of
surface harmonics (P<SUB>n</SUB><SUP>m</SUP>)(θ)cosmφ and
P<SUB>n</SUB><SUP>m</SUP>(θ)sinmφ) for the years 1959 through
1972. Our results are as follows. The single harmonic which most
often characterized the general solar magnetic field throughout the
period of observation corresponds to a dipole lying in the plane
of the equator (2 sectors, n = m = 1). This 2-sector harmonic was
particularly dominant during the active years of solar cycles 19
and 20. The north-south dipole harmonic (n = 1, m = 0) was prominent
only during quiet years and was relatively insignificant during the
active years. (The derived north-south dipole includes magnetic fields
from the entire solar surface and does not necessarily correlate with
either the dipole-like appearance of the polar regions of the Sun or
with the weak polar magnetic fields.) The 4-sector structure (n = m =
2) was prominent, and often dominant, at various times throughout the
cycle. A 6-sector structure (n = m = 3) occasionally became dominant
for very brief periods during the active years. Contributions to the
general solar magnetic field from harmonics of principal index 4 ⩽
n ⩽ 9 were generally relatively small throughout this entire solar
cycle with one outstanding exception. For a period of several months
prior to the large August 1972 flares, the global photospheric field
was dominated by an n = 5 harmonic; this harmonic returned to a low
value shortly after the August 1972 flare events. Rapid changes in
the global harmonics, in particular, relative and absolute changes in
the contributions of harmonics of different principal index n to the
global field, imply that the global solar field is not very deep or
that very strong fluid flows connect the photosphere with deeper layers.
---------------------------------------------------------
Title: Representations of coronal magnetic fields including currents
Authors: Levine, Randolph H.; Altschuler, Martin D.
1974SoPh...36..345L Altcode:
Coronal electric currents are superposed on the calculated large-scale
current-free (potential) magnetic field of the solar corona and
the new magnetic configurations are mapped. The results indicate
that relatively large coronal electric currents are required before
significant topological deviations from the potential magnetic field
configuration can be noticed. Thus any agreement between coronal
observations and calculated potential magnetic field configurations
should not be interpreted to mean that coronal electric currents are
necessarily absent or insignificant.
---------------------------------------------------------
Title: Magnetic Structure Responsible for Coronal Disturbances:
Observations
Authors: Altschuler, M. D.
1974IAUS...57....3A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Nonlinear Acceleration of a Magnetic Disturbance in the
Solar Corona
Authors: Altschuler, Martin D.; Smith, Dean F.; Swarztrauber, Paul N.;
Priest, Eric R.
1973SoPh...32..153A Altcode:
The simple form of Ohm's law (SI units)J = σ(E+ v × B)is valid for
high density magnetofluids (where the mean free path for collisions
is less than the Larmor radius) but is not strictly valid for the
tenuous solar corona. We examine the nonlinear evolution of a magnetic
disturbance using a more general form of Ohm's law which includes
the Hall term. The Hall term dominates MHD development in the corona
when the product of the magnetic scale length and the square root
of the density is small enough; in particular when (1) the electron
density is less than about 10<SUP>13</SUP> m<SUP>-3</SUP> and (2) the
scale length is less than a few hundred meters. For these parameters,
a magnetic disturbance may carry electrons at a drift speed in excess of
the Alfvén speed. We believe this nonlinear phenomenon may be important
for the impulsive acceleration of charged particles in the solar corona.
---------------------------------------------------------
Title: Coronal Magnetic Fields and the Variation of Geomagnetic
Activity
Authors: Oster, Ludwig; Altschuler, Martin D.
1973BAAS....5R.278O Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Evolution of a Magnetic Disturbance in the Solar Corona With
a General Ohm's Law
Authors: Altschuler, M. D.; Smith, D. F.; Swarztrauber, P.; Priest,
E. R.
1973BAAS....5S.268A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flare-Produced Coronal MHD-Fast-Mode Wavefronts and Moreton's
Wave Phenomenon
Authors: Uchida, Yutaka; Altschuler, Martin D.; Newkirk, Gordon, Jr.
1973SoPh...28..495U Altcode:
The propagation characteristics of MHD fast-mode disturbances, which
can emanate from flare regions, are computed for realistic conditions
of the solar corona at the times of particular flares. The path of a
fast-mode disturbance is determined by the large-scale (global) coronal
distributions of magnetic field and density, and can be computed by
a general raytracing procedure (eikonal equation) adapted to MHD. We
use the coronal (electron) density distribution calculated from daily
K-coronameter data, and the coronal magnetic field calculated under
the current-free approximation from magnetograph measurements of the
photospheric magnetic field. We compare the path and time-development of
an MHD fast-mode wavefront emitted from the flare region (as calculated
from a realistic model corona for the day of the observed Moreton
wave event) with actual observations of the Moreton wave event, and
find that the Moreton wave can be identified with the rapidly moving
intersection of the coronal fast-mode wavefront and the chromosphere
(as hypothesized in our previous paper); the directivity (anisotropic
propagation), as well as other characteristics of the propagation of
the Moreton wave can be successfully explained.
---------------------------------------------------------
Title: Improved Three-Dimensional Mapping of the Electron Density
Distribution of the Solar Corona
Authors: Perry, R. Michael; Altschuler, Martin D.
1973SoPh...28..435P Altcode:
Three-dimensional maps of the distribution of coronal electron density
can now be computed with two radial functions in the series expansion
for the density (rather than with only one radial function as shown
in our previous paper). With the improved maps we can determine the
topological variation of the electron density with radial distance, and
thus can (1) distinguish coronal condensations from coronal streamers,
(2) trace the structure of a streamer as a function of height, and (3)
determine the non-radial orientation of a streamer. We summarize the
previous work in concise mathematical notation, show examples of the
improved maps derived from two radial functions, and discuss in detail
the expectations and limitations of the method. Of great utility are
computer-simulated pictures showing the solar corona as it would appear
if veiwed from above the north (or south) pole.
---------------------------------------------------------
Title: Coronal Holes
Authors: Altschuler, Martin D.; Trotter, Dorothy E.; Orrall, Frank Q.
1972SoPh...26..354A Altcode:
Coronal holes are extensive regions of extremely low density in the
solar corona within 60° of latitude from the equator. (They are not
to be confused with the well-known coronal cavities which surround
quiescent prominences beneath helmet streamers.) We have superposed
maps of the calculated current-free (potential) coronal magnetic field
with maps of the coronal electron density for the period of November
1966, and find that coronal holes are generally characterized by weak
and diverging magnetic field lines. The chromosphere underlying the
holes is extremely quiet, being free of weak plages and filaments. The
existence of coronal holes clearly has important implications for the
energy balance in the transition region and the solar wind.
---------------------------------------------------------
Title: On Determining the Electron Density Distribution of the Solar
Corona from K-Coronameter Data
Authors: Altschuler, M. D.; Perry, R. M.
1972BAAS....4..377A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Atlas of Magnetic Fields in the Solar Corona
Authors: Newkirk, Gordon; Trotter, Dorothy E.; Altschuler, Martin D.;
Howard, Robert
1972SoPh...24..370N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Activity and the Variation of the Geomagnetic
K<SUB>p</SUB>-Index
Authors: Oster, Ludwig; Mariska, John T.; Altschuler, Martin D.;
Trotter, Dorothy E.
1972BAAS....4R.389O Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On Determining the Electron Density Distribution of the Solar
Corona from K-Coronameter Data
Authors: Altschuler, Martin D.; Perry, R. Michael
1972SoPh...23..410A Altcode:
The electron density distribution of the inner solar corona (r ⩽
2 R<SUB>⊙</SUB>) as a function of latitude, longitude, and radial
distance is determined from K-coronameter polarization-brightness
(pB) data. A Legendre polynomial is assumed for the electron density
distribution, and the coefficients of the polynomial are determined by
a least-mean-square regression analysis of several days of pB-data. The
calculated electron density distribution is then mapped as a function of
latitude and longitude. The method is particularly useful in determining
the longitudinal extent of coronal streamers and enhancements and
in resolving coronal features whose projections on the plane of the
sky overlap.
---------------------------------------------------------
Title: A Moving Type IV Radio Burst and Its Relation to the Coronal
Magnetic Field
Authors: Dulk, George A.; Altschuler, Martin D.
1971SoPh...20..438D Altcode:
A moving Type IV burst, observed with the Culgoora radioheliograph on
1970 April 29, moved out to about 3 R<SUB>⊙</SUB> and attained high
circular polarization before fading. The appearance of the moving Type
IV source suggests an isolated, self-contained, synchrotron emitting
plasmoid. Magnetic field maps of the corona derived from photospheric
observations indicate that the plasmoid moved almost radially outward
from the flare region along open field lines. To explain the observed
source structure and high unipolar polarization, we suggest that a
ring of electric current was ejected from the low corona and guided
by coronal magnetic field lines; the radio emission was synchrotron
radiation generated by mildly-relativistic electrons trapped in the
poloidal magnetic field of the ring current.
---------------------------------------------------------
Title: The Dynamics of a Toroidal Magnetic Ring
Authors: Lilliequist, Carl G.; Altschuler, Martin D.; Nakagawa,
Yoshinari
1971SoPh...20..348L Altcode:
Solving the nonlinear partial differential equations of
magnetohydrodynamics numerically, we examine (1) the time
development of a purely toroidal magnetic field (a magnetic ring)
and (2) the interaction of a magnetic ring with a poloidal magnetic
field. Axisymmetry and incompressibility are assumed. Parameters
are chosen to correspond to photospheric conditions. In case (1),
the magnetic ring contracts to the axis and then splits in two with
one ring travelling up along the axis and the other down. In case
(2), a large toroidal velocity field is generated which has opposite
direction of flow above and below the magnetic ring. The magnetic
and flow patterns of case (2) may persist with little change for a
relatively long time. We conjecture that toroidal magnetic fields may be
involved in the bright rings of sunspots or in the dynamics of spicules.
---------------------------------------------------------
Title: The Dynamics of a Toroidal Magnetic Ring and Their Implications
in Solar Phenomena.
Authors: Lilliequist, C. G.; Altschuler, M. D.; Nakagawa, Y.
1971BAAS....3..442L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Motion of Type II Radio Burst Disturbances in the Coronal
Magnetic Field
Authors: Dulk, G. A.; Altschuler, M. D.; Smerd, S. F.
1971ApL.....8..235D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Geometry of the Coronal Magnetic Field
Authors: Altschuler, Martin D.
1971S&T....41..146A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stimulated comption effect in very compact radio sources
Authors: Oster, Ludwig; Altschuler, Martin D.
1971Ap&SS..10..431O Altcode:
Expressions for the stimulated Compton effect are derived that are
complete to order γ/ge/μ, where ɛ is the photon energy in the
laboratory system, and γμ=γm <SUB>0</SUB> C <SUP>2</SUP> is the
electron energy. Explicit formulas are given for the energy flow between
a relativistic electron and a radiation field that obeys a power law so
that the number of photons is proportional to ɛ<SUP>-m-1</SUP>. The
amount of energy gained by an electron per second is then numerically
calculated for conditions suggested by very compact radio sources as
a function of the width of the spectrum, the spectral index, and the
electron energy.
---------------------------------------------------------
Title: Time Evolution of the Large-Scale Solar Magnetic Fields
Authors: Altschuler, M. D.; Newkirk, G., Jr.; Trotter, D. E.;
Howard, R.
1971IAUS...43..588A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stimulated Compton Effect in Very Compact Radio Sources
Authors: Altschuler, Martin D.; Oster, Ludwig
1970BAAS....2T.290A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Fields and the Solar Corona. III: The Observed
Connection between Magnetic Fields and the Density Structure of
the Corona
Authors: Newkirk, Gordon; Altschuler, Martin D.
1970SoPh...13..131N Altcode:
Coronal magnetic fields calculated by the methods developed in Paper I
(Altschuler and Newkirk, 1969) and the empirical description of the
solar corona of November 1966 derived in Paper II (Newkirket al.,
1970) are combined in order to investigate what connection exists
between the magnetic fields and the density structure of the corona.
---------------------------------------------------------
Title: Magnetic Fields and the Structure of the Solar Corona. I:
Methods of Calculating Coronal Fields
Authors: Altschuler, Martin D.; Newkirk, Gordon
1969SoPh....9..131A Altcode:
Several different mathematical methods are described which use the
observed line-of-sight component of the photospheric magnetic field to
determine the magnetic field of the solar corona in the current-free
(or potential-field) approximation. Discussed are (1) a monopole
method, (2) a Legendre polynomial expansion assuming knowledge of the
radial photospheric magnetic field, (3) a Legendre polynomial expansion
obtained from the line-of-sight photospheric field by a least-meansquare
technique, (4) solar wind simulation by zero-potential surfaces in
the corona, (5) corrections for the missing flux due to magnetograph
saturation. We conclude (1) that the field obtained from the monopole
method is not consistent with the given magnetic data because of
non-local effects produced by monopoles on a curved surface, (2)
that the field given by a Legendre polynomial (which is fitted to the
measured line-of-sight magnetic field) is a rigorous and self-consistent
solution with respect to the available data, (3) that it is necessary to
correct for the saturation of the magnetograph (at about 80 G) because
fields exceeding 80 G provide significant flux to the coronal field,
and (4) that a zero-potential surface at 2.5 solar radii can simulate
the effect of the solar wind on the coronal magnetic field.
---------------------------------------------------------
Title: Magnetic Fields and the Structure of the Solar Corona
Authors: Newkirk, G.; Altschuler, M.
1969BAAS....1Q.288N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Possible Acceleration Mechanism for a Solar Surge
Authors: Altschuler, Martin D.; Lilliequist, Carl G.; Nakagawa,
Yoshinari
1968SoPh....5..366A Altcode:
We examine a non-linear mechanism for a solar surge in which plasma
regions of high electrical conductivity and macroscopic dimension
can be rapidly accelerated without diffusion of magnetic field. The
mechanism is suggested by Rust's observations, which show that surges
occur near sunspots in regions of reversed magnetic polarity. For the
purposes of numerical calculation, we replace the magnetic field near a
polarity reversal in a sunspot by magnetic fields of current loops. The
relaxation of the magnetic field generated by two antiparallel coaxial
current loops in an incompressible plasma is traced by computer. The
results suggest that plasma in the form of a vortex ring can be expelled
at the Alfvén velocity from active solar regions.
---------------------------------------------------------
Title: Concerning the Origin of Evershed Motion in Sunspots
Authors: Altschuler, Martin D.; Nakagawa, Yoshinari; Lilliequist,
Carl G.
1968SoPh....3..466A Altcode:
The non-linear, partial differential equations of magnetohydrodynamics
are iterated simultaneously by computer to determine the time
development of a single sunspot. Axisymmetry and incompressibility are
assumed. The initial conditions are (1) zero velocity everywhere, and
(2) the magnetic-field distribution of a ring current embedded in the
photosphere. The initial magnetic field is then allowed to relax by
magnetic diffusion and by the creation of a velocity field. It is shown
that (1) Evershed motion outward from the sunspot will develop from a
wide range of reasonable initial parameters, and (2) the growth rate
of the magnetic configuration depends on the strength of the initial
magnetic field.
---------------------------------------------------------
Title: A Possible Mechanism for A Solar Surge.
Authors: Lilliequist, Carl G.; Altschuler, Martin D.; Nakagawa,
Yoshinari
1968AJS....73R..68L Altcode:
A primary difficulty in our understanding of the acceleration
mechanism of the solar surge is that all reasonable estimates of
electrical conductivity indicate excessively long time scales for
the reconnection (or diffusion) of magnetic field lines (Parker,
Astrophys. J. Suppl. 8,177,1963). We examine a nonlinear mechanism by
which plasma of high electrical conductivity and macroscopic dimension
may be accelerated in short time scales. Electric current loops in
a highly conducting plasma medium accelerate one another by means of
velocity fields created by JXB forces. Computer calculations concerned
with the interaction of two coaxial current loops in an incompressible,
conducting fluid indicate that under suitable conditions plasma in
the form of a vortex ring might be expelled at the Alfven velocity.
---------------------------------------------------------
Title: Influence of Magnetic Fields on the Structure of the Solar
Corona
Authors: Newkirk, G.; Altschuler, M. D.; Harvey, J.
1968IAUS...35..379N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Concerning the Development of the Evershed Motion in Sunspots
Authors: Altschuler, M. D.; Nakagawa, Y.; Lilliequist, C. G.
1968IAUS...35..193A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Electrical Conductivity Gradients in Sunspots
Authors: Altschuler, Martin D.
1967SoPh....1..377A Altcode:
Recently E. H. Schroeter showed that the electrical conductivity of
the sunspot umbra, at least in the upper photospheric layers, is about
ten-thousand times less than the value used by Cowling. This result
implies that electrical conductivity gradients near sunspots may be
relatively large. Upon taking such gradients into consideration, we
find that the photosphere is current free and that current rings might
encircle the sunspot, under suitable conditions, both in the lower
photosphere and in the chromosphere. Plasma motions are neglected in
the calculation.
---------------------------------------------------------
Title: Autocorrelation of Solar Activity
Authors: Altschuler, Martin D.; Sastry, Ch. V.
1965Natur.206.1035A Altcode:
IN this communication we examine the autocorrelation function R of
various indexes of solar activity over time-lags,τ, of 1-200 days. Four
indexes of solar activity were used: the daily relative sunspot number
(Zurich), and the mean daily fluxes from Nagoya at the frequencies 1,000
Mc/s, 3,750 Mc/s and 9,400 Mc/s. The data were analysed for the years
1957-58 (more than 700 days) and for the years 1960-63 (900 days),
thus comparing the highly active years of the solar cycle with the
less-active years. In addition, the relative sunspot numbers for the
years 1947-48 and 1937-38 were analysed for comparison.
---------------------------------------------------------
Title: Electromagnetic Radiation From Plasma Oscillations
Authors: Oster, L.; Altschuler, M.
1964NASSP..50..377O Altcode: 1964psf..conf..377O
No abstract at ADS
---------------------------------------------------------
Title: Theoretical Model for Type III Radio Emission from the Sun.
Authors: Altschuler, Martin D.; Oster, Ludwig
1964AJ.....69R.530A Altcode:
A model is suggested which can explain the excitation of type III radio
bursts from the sun. The physical picture is a stream of fast charged
particles that induce electric fields (polarization) in the surrounding
corona. These electric fields will accelerate the electrons in the
neighboring coronal regions which in turn emit a spectrum that consists
of a weak (bremsstrahlung) continuum and a superimposed resonance line
just above the plasma frequency. The resonance emission is thus able
to propagate out from the corona. Its spectral characteristics depend
crucially on the speed and other physical properties of the exciting
charge cloud. Predicted spectra for various possible physical situations
are shown. This work was supported by the National Aeronautics and
Space Administration.
---------------------------------------------------------
Title: Interaction of Fast Charged Particles with the Coronal Plasma.
Authors: Altschuler, Martin David
1964PhDT........21A Altcode:
No abstract at ADS
