Author name code: withbroe
ADS astronomy entries on 2022-09-14
author:"Withbroe, George"
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Title: Sources of Solar Total Irradiance Variations
Authors: Withbroe, George L.
Bibcode: 2009SoPh..257...71W
Altcode:
The daily images and magnetograms acquired by MDI are a rich source of
information about the contributions of different types of solar regions
to variations in the total solar irradiance (TSI). These data have
been used to determine the temporal variation of the MDI irradiance,
the mean intensity of the solar disk in the continuum at 676.8 nm. The
short-term (days to weeks) variations of the MDI irradiance and TSI are
in excellent agreement with rms differences of 0.011%. This indicates
that MDI irradiance is an excellent proxy for short-term variations
of TSI from the competing irradiance contributions of regions
causing irradiance increases, such as plages and bright network,
and regions causing irradiance decreases, such as sunspots. However,
the long-term or solar cycle variation of the MDI proxy and TSI differ
over the 11-year period studied. The results indicate that the primary
sources of the long-term (several months or more) variations in TSI are
regions with magnetic fields between about 80 and 600 G. The results
also suggest that the difference in the long-term variations of the MDI
proxy and TSI is due to a component of TSI associated with sectors of
the solar spectrum where the contrast in intensity between plages and
the quiet Sun is enhanced (e.g., the UV) compared to the MDI proxy. This
is evidence that the long-term variation of TSI is due primarily to
solar cycle variations of the irradiance from these portions of solar
spectrum, a finding consistent with modeling calculations indicating
that approximately 60% of the change in TSI between solar minimum and
maximum is produced by the UV part of the spectrum shortward of 400 nm
(Solanki and Krivova, Space Sci. Rev. 125, 53, 2006).
Title: Quiet Sun Contribution to Variations in the Total Solar
Irradiance
Authors: Withbroe, George L.
Bibcode: 2006SoPh..235..369W
Altcode:
An analysis of spatially-resolved measurements of the intensity of
the photospheric continuum by the Michelson Doppler Imager (MDI)
on the SOHO spacecraft indicates that these data can be used to
study variations of the Total Solar Irradiance (TSI). Since the
techniques employed depend upon ratios of intensities measured by MDI,
they are independent of the absolute photometric calibration of the
instrument. The results suggest that, while it is possible to account
for short-term (weeks to months) variation in TSI by variations in
the irradiance contributions of regions with enhanced magnetic fields
(larger than ten G as measured by MDI), the longer-term variations are
influenced significantly by variations in the brightness of the quiet
Sun, defined here as regions with magnetic field magnitudes smaller
than ten G. The latter regions cover a substantial fraction of the
solar surface, ranging from approximately 90% of the Sun near solar
minimum to 70% near solar maximum. The results provide evidence that
a substantial fraction, 50% or more, of the longer term (≥one year)
variation in TSI is due to changes in the brightness of the quiet Sun.
Title: Origins of the International Living With a Star program
Authors: Withbroe, G. L.; Guhathakurta, M.; Hoeksema, J. T.
Bibcode: 2005AdSpR..35...40W
Altcode:
This paper briefly summarizes the origins, objectives, and
organizational structure for a new international cooperative program
in solar-terrestrial physics, International Living With a Star.
Title: Living With a Star: New Opportunities in Sun-Climate Research
Authors: Eddy, John A.; Bond, Gerard C.; Bradley, Raymond S.; Broecker,
Wallace S.; Fisk, Lennard; Garcia, Rolando; Jackman, Charles H.;
Lean, Judith L.; Prather, Michael J.; Reid, George C.; Rind, David;
Schlesinger, Michael E.; Withbroe, George; Anderson, Donald; Fisher,
Richard R.; Guhathakurta, Lika; St. Cyr, O. C.
Bibcode: 2003lws..book.....E
Altcode:
No abstract at ADS
Title: Origins of the International Living With a Star program
Authors: Withbroe, G.
Bibcode: 2002cosp...34E1079W
Altcode: 2002cosp.meetE1079W
In the year 2000 NASA established a new research program called
Living With a Star (LWS). The objective of this program is to "develop
the scientific understanding necessary to effectively address those
aspects of the Connected Sun- Earth system that directly affect life
and society." This program is now broadening into a coordinated
international space science research effort involving multiple
international agencies, the International LWS program. This paper
discusses the origins, goals and status of this new international
program in solar-terrestrial physics.
Title: Living With a Star
Authors: Withbroe, G. L.
Bibcode: 2000SPD....31.0701W
Altcode: 2000BAAS...32..839W
NASA has proposed a new initiative, Living With a Star (LWS), a
research and development program involving studying solar variability
as it affects human technology, humans in space, and terrestrial
climate. The goal of the initiative is to develop a capability to
observe, understand, and predict the aspects of the connected Sun-Earth
system that affect life and society. The initiative includes the
following elements, (a) expanded utilization of the Solar Terrestrial
Probe missions, (b) establishing a Space Weather Research Network with
solar and geospace missions designed to address scientific research
problems relevant to the above goal (c) data analysis/modeling targeted
on scientific problems relevant to the goal of the program (d) Orbiting
Environmental Testbeds for testing rad-hard and rad-tolerant systems,
and (e) partnering with other agencies and industry.
Title: NASA's Space Astronomy for the Next Millennium: The Office
of Space Sciences's New Strategic Plan
Authors: Huntress, W. T.; Weiler, E. J.; Bunner, A.; Withbroe, G.;
Pilcher, C.; Thronson, H. A., Jr.
Bibcode: 1997AAS...191.3001H
Altcode: 1997BAAS...29.1256H
Approximately every four years, NASA's Office of Space Science
(OSS) develops a long-range Strategic Plan, which summarizes the
mission priorities which OSS intends to pursue, the programmatic and
budgetary environment within which therities were determined, and
related issues, such as technology development and education/public
outreach. The new Strategic Plan, which emphasizes the period 2000 -
2004, will be described and discussed in this panel presentation by
the Associate Administrator for Space Science and the four Directors of
the new science themes. This Strategic Plan is especially significant,
as it is the first produced within the new organizational structure
of OSS and covers a significant time period to be considered by the
National Academy of Science's next Decadal Review. The session will
have significant time for questions from the audience.
Title: Overview of the Sun-Earth Connections Program
Authors: Withbroe, G.
Bibcode: 1997SPD....28.1101W
Altcode: 1997BAAS...29..914W
No abstract at ADS
Title: Solar Variability and its Terrestrial Effects
Authors: Withbroe, G. L.; Kalkofen, W.
Bibcode: 1994svsp.coll...11W
Altcode: 1994IAUCo.143P..11W
No abstract at ADS
Title: A Doppler Dimming Determination of Coronal Outflow Velocity
Authors: Strachan, Leonard; Kohl, John L.; Weiser, Heinz; Withbroe,
George L.; Munro, Richard H.
Bibcode: 1993ApJ...412..410S
Altcode:
Outflow velocities in a polar coronal hole are derived from observations
made during a 1982 sounding rocket flight. The velocity results are
derived from a Doppler dimming analysis of resonantly scattered H I
Ly-alpha. This analysis indicates radial outflow velocities of 217
km/s at 2 solar radii from sun-center with an uncertainty range of
153 to 251 km/s at a confidence level of 67 percent. These results are
best characterized as strong evidence for supersonic outflow within 2
solar radii of sun-center in a polar coronal hole. Several means for
obtaining improved accuracy in future observations are discussed.
Title: Invited Talk: (Future Direction of the Space Physics Program)
Authors: Withbroe, G.
Bibcode: 1993SPD....24.0201W
Altcode: 1993BAAS...25.1180W
No abstract at ADS
Title: Guest editorial
Authors: Withbroe, George L.
Bibcode: 1992JGR....9719111W
Altcode:
No abstract at ADS
Title: Report of the solar physics panel
Authors: Withbroe, George L.; Fisher, Richard R.; Antiochos, Spiro;
Brueckner, Guenter; Hoeksema, J. Todd; Hudson, Hugh; Moore, Ronald;
Radick, Richard R.; Rottman, Gary; Scherrer, Philip
Bibcode: 1991spsi....1...67W
Altcode:
Recent accomplishments in solar physics can be grouped by the
three regions of the Sun: the solar interior, the surface, and the
exterior. The future scientific problems and areas of interest involve:
generation of magnetic activity cycle, energy storage and release,
solar activity, solar wind and solar interaction. Finally, the report
discusses a number of future space mission concepts including: High
Energy Solar Physics Mission, Global Solar Mission, Space Exploration
Initiative, Solar Probe Mission, Solar Variability Explorer, Janus,
as well as solar physics on Space Station Freedom.
Title: The solar wind and its coronal origins.
Authors: Withbroe, George L.; Feldman, William C.; Ahluwalia, Harjit S.
Bibcode: 1991sia..book.1087W
Altcode:
Coronal holes are the most well-established coronal source of
steady-state solar wind, the high-speed solar wind streams which
typically have asymptotic flow speeds of 700 km s-1. Coronal
mass ejections associated with flares and/or eruptive prominences
are another clearly identified source of solar wind, a transient
component that accounts for approximately 5% of the total solar-wind
mass loss. The role of other coronal structures in the generation of
the solar wind is less clear. Streamers and the interfaces between
streamers and other coronal regions are likely sources of low-speed
wind. Small-scale dynamical phenomena observed at the base of the corona
(spicules, macrospicules and high-speed jets) and small-scale structures
observed in polar coronal holes (polar plumes) may or may not play a
significant role in supplying mass, momentum and energy to the solar
wind. Improved measurements are required to determine the role, if any,
of these small-scale structures in the generation of the solar wind.
Title: UV observations of the extended corona
Authors: Withbroe, G.
Bibcode: 1991AdSpR..11a...5W
Altcode: 1991AdSpR..11....5W
Measurements of the intensities and profiles of the resonantly scattered
hydrogen Lyman-alpha line at 1216 Å have provided important insights
on the physical conditions in the extended corona where the solar
wind originates. Comparisons of measured kinetic temperatures with
predictions of models suggest that there is proton heating and/or a
nonthermal contribution to the motions of coronal protons between 1.5
and 4 solar radii. Comparisons of measured Lyman-alpha intensities with
predictions of models provide evidence for subsonic flow for r < 4
Rsolar in a quiet region of the corona and two polar coronal
holes observed near solar maximum. There is evidence for supersonic
flow (~200 km s-1) at r ~ 2 Rsolar
in a large polar coronal hole observed in 1982. Future measurements of
HI Lyman alpha and other coronal lines will greatly expand the quality
and quantity of UV spectroscopic measurements of the extended corona.
Title: Polar Plumes and the Solar Wind
Authors: Withbroe, G. L.; Habbal, S. R.
Bibcode: 1990BAAS...22..851W
Altcode:
No abstract at ADS
Title: A Comparison between Bright Points in a Coronal Hole and a
Quiet-Sun Region
Authors: Habbal, Shadia Rifai; Dowdy, James F., Jr.; Withbroe,
George L.
Bibcode: 1990ApJ...352..333H
Altcode:
A comparison is made of the morphological structure and temporal
behavior of the emission from coronal bright points in a coronal hole
and a quiet region, using data from the Harvard EUV experiment on
Skylab. It is found that, in both regions, coronal bright points are
located at network boundaries and cover a range of sizes from 10 to
40 in in linear extent. In a given bright pint, the peaks of emission
in the six different lines, measured simultaneously through the same
instrument slit, are not always cospatial, implying that bright points
consist of a complex of small-scale loops at different temperatures. The
intensity of bright points in both regions is also characterized by a
significant temporal variability in all the wavelengths measured. This
variability exhibits no regular periodicity. Yet the ratio of the
varying (ac) to the constant (dc) components of the emission, in all
the bright points studied, has a local maximum at 1-2 x 10 to the 5th
k which coincides with the peak of the radiative loss function, and
another local maximum at Mg x (1.4 x 10 to the 6th K). It is found
that coronal bright points in a coronal hole or a quiet region are
indistinguishable structures, and, therefore, conclude that they are
independent of the overlying background corona.
Title: Expectations for solar activity in the 1990s
Authors: Withbroe, George L.
Bibcode: 1990asdy.conf..727W
Altcode:
The solar output of short-wavelength radiation, solar wind, and
energetic particles depends strongly on the solar cycle. These energy
outputs control conditions in the interplanetary medium, and the
terrestrial magnetosphere and upper atmosphere. The current solar
cycle is approaching the time of maximum activity when it appears that
activity will be at high, perhaps record high, levels. As a result,
satellites in low-earth orbit will encounter attitude control problems
at higher altitudes than normal and they will reenter sooner. In this
paper, the present behavior of the current solar cycle is compared with
that of previous cycles, and expectations for its future behavior in
the 1990s is discussed.
Title: Solar activity cycle - History and predictions
Authors: Withbroe, George L.
Bibcode: 1989JSpRo..26..394W
Altcode:
The solar output of short-wavelength radiation, solar wind, and
energetic particles depends strongly on the solar cycle. These energy
outputs from the sun control conditions in the interplanetary medium and
in the terrestrial magnetosphere and upper atmosphere. Consequently,
there is substantial interest in the behavior of the solar cycle and
its effects. This review briefly discusses historical data on the solar
cycle and methods for predicting its further behavior, particularly
for the current cycle, which shows signs that it will have moderate
to exceptionally high levels of activity. During the next few years,
the solar flux of short-wavelength radiation and particles will be more
intense than normal, and spacecraft in low earth orbit will reenter
earlier than usual.
Title: Line-of-sight effects on spectroscopic measurements in the
inner solar wind region
Authors: Esser, Ruth; Withbroe, George L.
Bibcode: 1989JGR....94.6886E
Altcode:
The effect of the integration along the line of sight on the spectral
line profiles of the resonantly scattered Lyman alpha radiation emitted
by low-density coronal holes at heights above 1.5 Rs from
Sun center is investigated. It is shown how the spectral lines from
this region are influenced by the Lymm alpha emission from surrounding
regions with higher densities. The coronal hole and the surrounding
areas are described by a two-fluid solar wind model. It is shown that
the line-of-sight effects can be important for the interpretation of
the Lyman alpha spectral line measurements in the outer corona and
iner solar wind.
Title: Comparison between Bright Points in a Coronal Hole and the
Quiet Sun
Authors: Habbal, S. R.; Withbroe, G. L.; Dowdy, J., Jr.
Bibcode: 1989BAAS...21R.840H
Altcode:
No abstract at ADS
Title: The Coming Solar Maximum: How Large?
Authors: Withbroe, G. L.
Bibcode: 1989BAAS...21R.827W
Altcode:
No abstract at ADS
Title: Doppler Dimming Measurement of Solar Wind Outflow
Authors: Strachan, L.; Kohl, J. L.; Munro, R. H.; Withbroe, G. L.
Bibcode: 1989BAAS...21..840S
Altcode:
No abstract at ADS
Title: The Solar Wind Mass Flux
Authors: Withbroe, George L.
Bibcode: 1989ApJ...337L..49W
Altcode:
One of the unexplained observations of the solar wind at 1 AU is the
relative constancy of the solar wind mass flux. Calculations using a
radiative energy balance model with a thermally driven wind suggest that
this near constancy of the mass (particle) flux is due to two factors:
(1) the role of inward conduction and radiation in cooling the corona,
and (2) the finding that the particle flux is proportional to the gas
pressure in the outer corona and beyond, where the solar wind flow
becomes radial.
Title: UVCS: An Ultraviolet Coronagraph Spectrometer for SOHO
Authors: Kohl, J. L.; Hartmann, L. W.; van Ballegooijen, A. A.;
Withbroe, G. L.; Rayomnd, J. C.; Weiser, H.; Noci, G.; Antonucci,
E.; Geiss, J.; Gloeckler, G.
Bibcode: 1989ESASP1104...49K
Altcode:
The UltraViolet Coronagraph Spectrometer (UVCS) of SOHO (solar
and heliospheric observatory) provides ultraviolet spectroscopic
observations of the solar corona out to ten solar radii from
suncenter. This capability is expected to greatly expand the
number of plasma parameters that can be specified by remote sensing
techniques. Plasma diagnostic techniques are expected to provide a
sufficient number of empirically derived parameters to significantly
constrain theories of solar wind acceleration, coronal heating, and
solar wind composition. The spectral line profiles and intensities
are sensitive to random velocity distributions and to the effective
temperatures of protons, minor ions, and electrons. Ion densities,
chemical abundances, and outflow velocities of coronal protons and
ions into the solar wind are also taken into consideration.
Title: Solar and stellar winds
Authors: Withbroe, G. L.
Bibcode: 1989HiA.....8..525W
Altcode:
No abstract at ADS
Title: UVCS: an Ultraviolet Coronagraph Spectrometer for SOHO
Authors: Kohl, J. L.; Hartmann, L. W.; van Ballegooijen, A. A.;
Withbroe, G. L.; Raymond, J. C.; Weiser, H.; Noci, G.; Antonucci,
E.; Geiss, J.; Gloeckler, G.
Bibcode: 1988sohi.rept...49K
Altcode:
The UltraViolet Coronagraph Spectrometer (UVCS) of SOHO (solar
and heliospheric observatory) provides ultraviolet spectroscopic
observations of the solar corona out to ten solar radii from
sun-center. This capability is expected to greatly expand the
number of plasma parameters that can be specified by remote sensing
techniques. Plasma diagnostic techniques are expected to provide a
sufficient number of empirically derived parameters to significantly
constrain theories of solar wind acceleration, coronal heating, and
solar wind composition. The spectral line profiles and intensities
are sensitive to random velocity distributions and to the effective
temperatures of protons, minor ions, and electrons. Ion densities,
chemical abundances, and outflow velocities of coronal protons and
ions into the solar wind are also taken into consideration.
Title: Spatial and Temporal Variations of EUV Coronal Bright Points
Authors: Habbal, S. R.; Dowdy, J. F., Jr.; Withbroe, G. L.
Bibcode: 1988BAAS...20Q.977H
Altcode:
No abstract at ADS
Title: Spatial and Temporal Variations of Coronal Heating in Small
Active Regions
Authors: Withbroe, G. L.; Dowdy, J. F., Jr.; Habbal, S. R.
Bibcode: 1988BAAS...20..977W
Altcode:
No abstract at ADS
Title: How Quiet is Quiet?-Movies of the Quiet Sun in EUV Emission
Lines
Authors: Rabin, D. M.; Dowdy, J. F., Jr.; Withbroe, G. L.
Bibcode: 1988BAAS...20.1009R
Altcode:
No abstract at ADS
Title: The Solar Wind Mass Flux
Authors: Withbroe, G. L.
Bibcode: 1988BAAS...20..704W
Altcode:
No abstract at ADS
Title: The Temperature Structure, Mass, and Energy Flow in the Corona
and Inner Solar Wind
Authors: Withbroe, George L.
Bibcode: 1988ApJ...325..442W
Altcode:
Data from remote-sensing and in situ instruments are used as empirical
constraints on a radiative energy balance model in order to determine
the radial variations of coronal temperatures, densities, and outflow
speeds in several types of coronal holes and a quiet, unstructured
region of the corona. The one-fluid solar wind model used in the
investigation includes the effects of radiative and inward conductive
losses in the low corona and the chromospheric-coronal transition
region. It satisfactorily accounts for a variety of measurements of
coronal and solar wind parameters for an equatorial coronal hole, polar
coronal holes at solar minimum and solar maximum, and an unstructured
quiet region of the corona.
Title: Effect of a dense coronal region on line observations from
coronal holes
Authors: Esser, R.; Withbroe, G. L.
Bibcode: 1988ASSL..143..211E
Altcode: 1988acse.conf..211E
The authors discuss the difficulties involved in obtaining information
about the temperature in coronal holes from observed line profiles.
Title: Physics of the inner heliosphere: Mechanisms, models and
observational signatures
Authors: Withbroe, George L.
Bibcode: 1987sao..reptR....W
Altcode:
Selected problems concerned with the important physical processes that
occur in the corona and solar wind acceleration region, particularly
time dependent phenomena were studied. Both the physics of the phenomena
and the resultant effects on observational signatures, particularly
spectroscopic signatures were also studied. Phenomena under study
include: wave motions, particularly Alfven and fast mode waves; the
formation of standing shocks in the inner heliosphere as a result
of momentum and/or heat addition to the wind; and coronal transient
phenomena where momentum and/or heat are deposited in the corona to
produce transient plasma heating and/or mass ejection. The development
of theoretical models for the inner heliosphere, the theoretical
investigation of spectroscopic plasma diagnostics for this region,
and the analysis of existing skylab and other relevant data are also
included.
Title: Models for the Corona and Inner Solar Wind
Authors: Withbroe, G. L.
Bibcode: 1987BAAS...19..932W
Altcode:
No abstract at ADS
Title: Solar Wind Diagnostics from Doppler-enhanced Scattering
Authors: Noci, Giancarlo; Kohl, John L.; Withbroe, George L.
Bibcode: 1987ApJ...315..706N
Altcode:
Solar wind ions can attain sufficient outflow speed, w, to cause line
excitation by chromospheric or transition region radiation in a nearby
line. It is shown that this extends the diagnostic possibilities of a
coronal EUV line to much larger values of w than would be possible if
pumping were limited to radiation from the same spectral line. For the
1037.6 A coronal line of O VI, the pumping effect of the chromospheric
C II 1037.0 A line is efficient for w between 100 and 250 km/s. An
approximate expression for the line ratio for a doublet of the Li or
Na isoelectronic sequences is derived, and the diagnostic capabilities
of doublet line ratios, either by themselves or combined with the
observation of other quantities, are discussed. In particular, that
the determination of doublet line ratios at several heights can be
sufficient to yield the solar wind velocity at those heights together
with a constraint on other coronal parameters.
Title: Acceleration of the Solar Wind as Inferred from Observations
(R)
Authors: Withbroe, G. L.
Bibcode: 1987sowi.conf...23W
Altcode:
No abstract at ADS
Title: Analysis of Coronal H i Lyman-Alpha Measurements in a Polar
Region of the Sun Observed in 1979
Authors: Withbroe, G. L.; Kohl, J. L.; Weiser, H.
Bibcode: 1986ApJ...307..381W
Altcode:
Measurements of the intensities and spectral line profiles of resonantly
scattered hydrogen Ly-alpha radiation have been used to determine
hydrogen kinetic temperatures and electron densities between r = 1.5
and 2.2 solar radii in a polar region of the corona observed in 1979
near solar maximum. The mean temperature, 1.8 x 10 to the 6th K, in
this region is significantly higher, by about 60 percent, than that
obtained in a similar region observed in a 1980 rocket flight. The
densities in these two polar regions are similar and are a factor
of about 4 larger than in polar coronal holes observed at solar
minimum. The flow velocities in both regions are most likely subsonic
for r less than about 4 solar radii. The results reported here support
the hypothesis that polar coronal holes observed at different times
during the solar cycle can have different temperatures, densities,
and possibly flow velocities.
Title: Solar Coronal Bright Points Observed with the VLA
Authors: Habbal, S. R.; Ronan, R. S.; Withbroe, G. L.; Shevgaonkar,
R. K.; Kundu, M. R.
Bibcode: 1986ApJ...306..740H
Altcode:
The first observations of solar coronal bright points made at 20-cm
wavelength with the VLA are reported. The brightness temperature of
the sources observed varies between 1 and 5 x 10 to the 5th K. The
observations indicate that significant fluctuations in the brightness
temperature as well as in the spatial extent of these sources can occur
over a few minutes. These fluctuations are shown to be due to density
and temperature fluctuations at transition region heights combined
with either plasma motions along magnetic field lines or changes in
magnetic field topology, or both.
Title: Corona and solar wind
Authors: Withbroe, G. L.
Bibcode: 1986sfcp.nasa..221W
Altcode:
The Pinhole/Occulter Facility is a powerful tool for studying
the physics of the extended corona and origins of the solar
wind. Spectroscopic data acquired by the P/OF coronal instruments can
greatly expand empirical information about temperatures, densities,
flow velocities, magnetic fields, and chemical abundances in the
corona out to r or approx. 10 solar radii. Such information is needed
to provide tight empirical constraints on critical physical processes
involved in the transport and dissipation of energy and momentum, the
heating and acceleration of plasma, and the acceleration of energetic
particles. Because of its high sensitivity, high spatial and temporal
resolutions, and powerful capabilities for plasma diagnostics, P/OF can
significantly increase our empirical knowledge about coronal streamers
and transients and thereby advance the understanding of the physics of
these phenomena. P/OF observations can be used to establish the role
in solar wind generation, if any, of small-scale dynamical phenomena,
such as spicules, macrospicules and coronal bullets, and the role of
the fine-scale structures, such as polar plumes. Finally, simultaneous
measurements by the P/OF coronal and hard X-ray instruments can provide
critical empirical information concerning nonthermal energy releases
and acceleration of energetic particles in the corona.
Title: A two-fluid solar wind model with Alfven waves: parameter
study and application to observations
Authors: Esser, Ruth; Leer, Egil; Habbal, Shadia R.; Withbroe,
George L.
Bibcode: 1986JGR....91.2950E
Altcode:
The effects of Alfven waves from the inner corona on the solar wind
density profile, flow velocity and on the random motion of protons
are studied. Different base densities, temperatures, and wave velocity
amplitudes, as well as different flow geometries, are considered. The
model calculations are compared to simultaneous observations of the
electron density profile and the resonantly scattered Lyman alpha
line. Present observations, out to 4 solar radii, can be used to
place limits on the coronal base density and temperature, and put
an upper limit on the wave amplitude. It is pointed out that future
observations of the electron density and the Lyman alpha line, out
to larger heliocentric distances, and of lines from heavier elements,
should be used to place more stringent constraints on the amplitudes
of MHD waves in the corona.
Title: OVI Diagnostics of Solar Wind Generation
Authors: Noci, G.; Kohl, J. L.; Withbroe, G. L.
Bibcode: 1986ASSL..123...53N
Altcode: 1986shtd.symp...53N
The O VI resonance doublet is partly collisionally and partly
radiatively excited in the solar corona. In the solar wind the O VI
ions can attain sufficient outflow speed to cause excitation of the
2P1/2 level by the chromospheric C II λ1037.0 line. The
authors show that this extends the diagnostic possibilities of the O VI
resonance doublet. In particular, the determination of the intensity
ratio of the doublet lines at several heights can be sufficient to
yield the solar wind velocity at those heights and hence information
on the mechanisms of solar wind acceleration.
Title: Origins of the Solar Wind in the Corona
Authors: Withbroe, G. L.
Bibcode: 1986ASSL..123...19W
Altcode: 1986shtd.symp...19W
The coronal origins of the solar wind are considered. Potential
sources of low-speed wind which are consistent with current data,
including streamers and the interfaces between them and other
coronal regions, await mass flow measurements for confirmation. A
Doppler-dimming technique utilizing a white-light coronagraph and
UV coronal spectrometer is to be employed aboard the Space Shuttle
SPARTAN program, and its usage on Ulysses may provide information on
mass flows in streamers and their surroundings.
Title: Corona and solar wind.
Authors: Withbroe, G. L.
Bibcode: 1986NASCP2421..221W
Altcode:
The purpose of this paper is to briefly discuss the role that the
Pinhole/Occulter Facility (P/OF) can play in addressing a few scientific
problems in the above areas. Spectroscopic plasma diagnostics and
coronal physical processes, the structure and physics of streamers and
coronal holes and coronal transients and mass ejections are considered.
Title: Coronal Spectroscopy and Imaging from Spartan during the
Polar Passage of Ulysses
Authors: Kohl, J. L.; Weiser, H.; Withbroe, G. L.; Noci, G.; Munro,
R. H.
Bibcode: 1986ASSL..123...39K
Altcode: 1986shtd.symp...39K
A joint payload consisting of a UV Coronal Spectrometer and a White
Light Coronagraph is being developed for a series of flights on NASA's
Spartan carrier. Spartan, which is deployed and retrieved by Shuttle,
is intended to provide at least 27 orbits of solar observations per
mission. The first flight of this payload is planned for October 1986,
and it is anticipated that a subsequent flight will occur at each polar
passage of Ulysses. Coordinated measurements of solar wind acceleration
parameters in polar regions of the solar corona with Spartan and
'in situ' measurements of the polar wind from Ulysses will provide a
unique opportunity to establish empirical constraints on polar wind
models. Spectroscopic diagnostics to be provided by Spartan include
determinations of the electron and neutral hydrogen random velocities,
outflow velocities in the 30 to 300 km/s range and electron densities.
Title: Coronal temperatures, heating, and energy flow in a polar
region of the sun at solar maximum
Authors: Withbroe, G. L.; Kohl, J. L.; Weiser, H.; Munro, R. H.
Bibcode: 1985ApJ...297..324W
Altcode:
The profiles of resonantly scattered Lyman-alpha coronal radiation have
been used to determine the hydrogen kinetic temperature from 1.5 to 4
solar radius from the center of the polar region of the corona observed
in 1980 at solar maximum. Hydrogen temperatures derived from the line
profiles were found to decrease with height from 1.2 million K at r =
1.5 solar radii to 600,000 K at r = 4 solar radius. Comparison of the
measured kinetic temperatures with predictions from a semiempirical
two-fluid model showed evidence of a small amount of heating or a
nonthermal contribution to the motions of coronal protons between
1.5 and 4 solar radius. The widths of the profiles confirmed an upper
limit of 110 + or - 15 km/s on the rms magnitude of the line-of-sight
component of velocities between 1.5 and 4 solar radius. Density
measurements obtained in situ in the solar wind in the ecliptic were
used to locate the sources of low speed and high-speed winds in the
polar region. An eclipse photograph of the corona at solar maximum
is provided.
Title: Extreme Ulraviolet Observations of Subflares and Surges
Authors: Withbroe, G. L.
Bibcode: 1985SoPh...99..145W
Altcode:
EUV observations of two subflares and associated surges have been
analyzed. At maximum brightness the emission measures and radiative
outputs of the subflares were approximately 20% of the corresponding
values for the active region. Multiple EUV surges were observed
during and following each subflare, with surge material being ejected
in a variety of directions, including toward a coronal bright point
located outside of the active region. The total energy of the surges
appears to be comparable to that radiated by the subflares, a few times
1028 erg. As reported in previous studies of surges, we find
that there was no significant emission from these features in spectral
lines formed at temperatures T>106K. The ejection of
surges in several different directions and nearly simultaneous flaring
of various areas of the active region suggest that the primary site
of the subflares was magnetically connected to a variety of different
areas in the active region and the surrounding quiet region.
Title: Spatial and Temporal Variations of Solar Coronal Loops
Authors: Habbal, S. R.; Ronan, R.; Withbroe, G. L.
Bibcode: 1985SoPh...98..323H
Altcode:
Skylab EUV observations of an active region near the solar limb
were analyzed. Both cool (T < 106 K) and hot (T >
106 K) loops were observed in this region. For the hot loops
the observed intensity variations were small, typically a few percent
over a period of 30 min. The cool loops exhibited stronger variations,
sometimes appearing and disappearing in 5 to 10 min. Most of the cool
material observed in the loops appeared to be caused by the downward
flow of coronal rain and by the upward ejection of chromospheric
material in surges. The frequent EUV brightenings observed near the loop
footpoints appear to have been produced by both in situ transient energy
releases (e.g. subflares) and the infall/impact of coronal rain. The
physical conditions in the loops (temperatures, densities, radiative
and conducting cooling rates, cooling times) were determined. The mean
energy required to balance the radiative and conductive cooling of the
hot loops is approximately 3 × 10−3 erg cm−3
s−1. One coronal heating mechanism that can account for
the observed behavior of the EUV emission from McMath region 12634 is
heating by the dissipation of fast mode MHD waves.
Title: Effects of coronal disturbances on the ionization state of
the solar wind
Authors: Withbroe, G. L.
Bibcode: 1985sao..reptS....W
Altcode:
A theoretical investigation of the relationship between physical
conditions in coronal disturbances and the ionization states of the
resulting perturbed solar wind was conducted. Available measurements
of active solar wind associated with solar flares often show an
enhanced degree of ionization (e.g., Fe(+17)), implying that the
measured solar wind material is flare-heated at its coronal source. In
contrast, other active solar wind flows sometimes show anomalously
low degrees of ionization (e.g., He(+)), implying that some solar
material is expelled from the corona without ever reaching coronal
temperatures. The effects of impulsive heat and/or momentum addition
in the corona on the hydrodynamics and ionization state of the corona
and solar wind were studied. One of the primary objectives of the
current grant was the development of a software package suitable for:
(1) generating models for the effects of impulsive heat and/or momentum
deposition on plasma temperatures, densities and flow velocities; and
(2) calculating the ionization state of the solar wind as a function of
the location, duration and magnitude of heat and/or momentum deposition.
Title: Physics of the inner heliosphere: Mechanisms, models and
observational signatures
Authors: Withbroe, G. L.
Bibcode: 1985sao..reptQ....W
Altcode:
The physics of the solar wind acceleration phenomena (e.g. effect of
transient momentum deposition on the temporal and spatial variation of
the temperature, density and flow speed of the solar wind, formation
of shocks, etc.) and the resultant effects on observational signatures,
particularly spectroscopic signature are studied. Phenomena under study
include: (1) wave motions, particularly spectroscopic signatures are
studied. Phenomena under study include:(1) wave motions, particularly
Alfven and fast mode waves, (2) the formation of standing shocks in
the inner heliosphere as a result of momentum and/or heat addition
to the wind and (3) coronal transient phenomena where momentum and/or
heat are deposited in the corona to produce transient plasma heating
and/or mass ejections. Also included are the theoretical investigation
of spectroscopic plasma diagnostics for the inner heliosphere and the
analysis of existing Skylab and other relevant data.
Title: Impulsive Phenomena in a Small Active Region
Authors: Withbroe, G. L.; Habbal, S. R.; Ronan, R.
Bibcode: 1985SoPh...95..297W
Altcode:
The temporal and spatial variations of EUV emission from a small
growing active region were investigated. Frequent localized short
term (∼ few minutes) fluctuations in EUV emission were observed
throughout the 7.2 hr interval when the most continuous observations
were acquired. Approximately 20% of the 5 ″ x 5 ″ pixels had
intensity variations exceeding a factor of 1.3 for the chromospheric
Lα line, a factor of 1.5 for lines formed in the chromospheric-coronal
transition region and a factor of 1.4 for the coronal Mg x line. A
subflare in the region produced the largest intensity enhancements,
ranging from a factor of ∼ 2.3 for the chromospheric Lα line to ∼
8 for the transition region and coronal lines. The EUV fluctuations
in this small active region are similar to those observed in coronal
bright points, suggesting that impulsive heating is an important,
perhaps dominant form of heating the upper chromospheric and lower
coronal plasmas in small magnetic bipolar regions. The responsible
mechanism most likely involves the rapid release of magnetic energy,
possibly associated with the emergence of magnetic flux from lower
levels into the chromosphere and corona.
Title: PROBING THE SUN'S SECRETS: An Advanced Solar Observatory
Authors: Withbroe, George L.
Bibcode: 1985ivnt.book..181W
Altcode:
No abstract at ADS
Title: Physics of the inner heliosphere 1-1OR0 plasma diagnostics
and models
Authors: Withbroe, G. L.
Bibcode: 1984sao..reptS....W
Altcode:
The physics of solar wind flow in the acceleration region and
impulsive phenomena in the solar corona is studied. The study of
magnetohydrodynamic wave propagation in the corona and the solutions
for steady state and time dependent solar wind equations gives
insights concerning the physics of the solar wind acceleration region,
plasma heating and plasma acceleration processes and the formation
of shocks. Also studied is the development of techniques for placing
constraints on the mechanisms responsible for coronal heating.
Title: Plasma diagnostics for the outer solar corona - UV and XUV
Fe XII lines
Authors: Withbroe, G. L.; Raymond, J. C.
Bibcode: 1984ApJ...285..347W
Altcode:
The formation of the UV and XUV spectral lines of Fe XII in the outer
corona was investigated. The results indicate that these lines can be
an important tool for probing the physical conditions in the coronal
regions where the solar wind is generated. The Fe XII lines can be
particularly useful for determining outflow velocities of heavy ions
in the solar wind and for providing critical empirical constraints
on energy transport and dissipation mechanisms in the solar wind
acceleration region. Application of the theoretical calculations
to existing UV, EUV, and XUV observations of the low corona provide
evidence that: (1) the inclusion of the effects of resonances in the
collision strengths for the low-lying levels of Fe XII is important,
(2) that the contributions of resonances for these levels are even
larger than the estimates given in the present paper, and (3) that
the collision strengths used here yield populations for these levels
which are accurate to a factor of 2. These results have implications
concerning the accuracy of abundances and densities derived from
observations of the Fe XII lines in the low corona.
Title: Temporal and Spatial Variations of Solar Coronal Bright Points
Observed with the VLA
Authors: Habbal, S. R.; Cowell, A.; Ronan, R.; Withbroe, G. L.;
Shevgaonkar, R.; Kundu, M.
Bibcode: 1984BAAS...16..929H
Altcode:
No abstract at ADS
Title: Impulsive Phenomena in a Small Active Region
Authors: Withbroe, G. L.; Habbal, S. R.; Ronan, R.
Bibcode: 1984BAAS...16R.528W
Altcode:
No abstract at ADS
Title: Evidence for Supersonic Solar Wind Velocities at 2.1
R⊙
Authors: Kohl, J. L.; Weiser, H.; Withbroe, G. L.; Zapata, C. A.;
Munro, R. H.
Bibcode: 1984BAAS...16..531K
Altcode:
No abstract at ADS
Title: Spatial and Temporal Variations of Solar Coronal Loops
Authors: Ronan, R. S.; Habbal, S. R.; Withbroe, G. L.
Bibcode: 1984BAAS...16..529R
Altcode:
No abstract at ADS
Title: MHD waves and turbulence in the sun and interplanetary medium.
Authors: Barnes, A.; Goldstein, M.; Hollweg, J.; Mariska, J.;
Matthaeus, W.; Smith, C.; Smith, E.; Stein, R.; Withbroe, G.; Woo, R.
Bibcode: 1984NASRP1120....4B
Altcode:
Contents: Introduction. Global oscillations of the sun. Observations
related to waves or turbulence in the solar atmosphere. Local waves
in the solar atmosphere: theoretical considerations. Interplanetary
hydromagnetic fluctuations. Recent studies of the interplanetary plasma
based on turbulence theory. Effects of waves and turbulence of the
solar wind.
Title: The Solar Wind Generation Experiment for SPARTAN Mission 201
Authors: Kohl, J. L.; Weiser, H.; Withbroe, G. L.; Munro, R. H.
Bibcode: 1984uxsa.coll...29K
Altcode: 1984uxsa.conf...29K; 1984IAUCo..86...29K
No abstract at ADS
Title: Evidence for Temporal Variations in Polar Plumes
Authors: Withbroe, G. L.
Bibcode: 1983SoPh...89...77W
Altcode:
In order to place empirical constraints on possible plasma heating
processes and acceleration mechanisms for mass flows in polar plumes,
we studied the variability of the O VI and MgX emissions from four
plumes observed by the Harvard Skylab experiment. The observations
consist of a 40 min sequence of spectroheliograms acquired with ∼2 min
temporal resolution. We found that the MgX emission from each plume had
a strong `dc' component and that any variations, if present, occurred
at approximately the 10% (of the mean) level or less. This implies
that temporal variations in the density and/or temperature were 5%
or less. There were some statistically significant variations in the
measured MgX signals. Two of the plumes decreased in brightness by
approximately 10% during the 40 min period of the observations. In
addition two plumes exhibited short-term (few minute) variations
which appear to be statistically significant at a confidence level of
>90%. The latter variations (if real) appear to be due to small
(∼2 × 104 K) fluctuations in temperature caused by
fluctuations in the local plasma heating rate.
Title: Spectroscopic measurements of solar wind generation.
Authors: Kohl, J. L.; Withbroe, G. L.; Zapata, C. A.; Noci, G.
Bibcode: 1983NASCP.2280..47K
Altcode: 1983sowi.conf...47K
Spectroscopically observable quantities are described which are
sensitive to the primary plasma parameters of the solar wind's source
region. The method is discussed in which those observable quantities are
used as constraints in the construction of empirical models of various
coronal structures. Simulated observations are used to examine the
fractional contributions to observed spectral intensities from coronal
structures of interest which co-exist with other coronal structures
along simulated lines-of-sight. The sensitivity of spectroscopic
observables to the physical parameters within each of those structures
is discussed.
Title: The role of spicules in heating the solar atmosphere
Implications of EUV observations
Authors: Withbroe, G. L.
Bibcode: 1983ApJ...267..825W
Altcode:
Although spicules hae been obseved for many years, very little is
known about their role in the transport of mass and energy between the
chromosphere and the higher layers of the atmospere. Athay and Holzer
(1982) demonstrated that the rise and fall of spicular material can
supply the thermal energy required for heating the upper chromosphere,
transition, and possibly corona. The proposed mechanism depends upon
assumptions about the fate of spicules after they disappear from view
in the visual spectrum where observations are limited to spectral lines
formed at chromospheric temperatures. The present investigation is
concerned with an analysis of meaurements of the spatial and temporal
variations of EUV emission near the solar limb. The obtained results
place empirical constraints on the fate of spicules after they disappear
from view in the visible spectrum and thereby place constraints on
their role in the transport of mass and energy between the chromosphere
and corona.
Title: Rapid magnetic energy release, its possible role in coronal
heating and solar wind acceleration
Authors: Withbroe, G. L.; Habbal, S. R.
Bibcode: 1983sao..reptR....W
Altcode:
Studies of the EUV emission from coronal bright points, active
regions and apicules suggest that stochastic mechanisms may plan an
important role in heating the solar atmosphere at chromospheric and
coronal levels. In small magnetic bipolar regions (spatial extent
< 1') the observed EUV variations suggest that impulsive heating
at chromospheric and coronal levels appears to be very important,
possibly the dominant form of heating. The mechanism most likely
involves rapid release of magnetic energy, possibly associated with the
emergence of magnetic flux from lower levels into the chromosphere
and corona. In larger scale (> 1') magnetic bipolar regions,
there is evidence for both quasi-steady and impulsive heating,
with quasi-steady heating dominating. This heating could be caused
by either a mechanism such as steady-state current dissipation, or
by a stochastic process whose integrated effect (resulting from the
smoothing caused by finite radiative and conductive cooling times)
yields a nearly constant radiative output. The widespread variability of
the emission in spectral lines formed at transition region temperatures
(100000 < T < 1000000 K) provides evidence that impulsive energy
releases are a common, nearly continuous phenomenon in bipolar magnetic
regions. However, at the present time we do not know what fraction of
the total energy deposition in the atmosphere (chromosphere and low
corona) originates in impulsive phenomena.
Title: Solar wind and coronal structure.
Authors: Withbroe, G. L.
Bibcode: 1983ESAJ....7..341W
Altcode:
Spectroscopic diagnostic techniques used to determine the coronal source
region of the solar wind, and results of preliminary applications
are examined. The topics reviewed are magnetic fields, coronal mass
ejections, coronal holes, flow velocities, coronal temperatures, fine
spatial structure, and future observational programs. The physical
mechanisms responsible for plasma heating, solar-wind acceleration, the
transport of mass momentum and energy, and the spatial differentiation
of chemical abundances are also discussed. Among the data presented
are Skylab's white-light coronagraph photograph of a coronal transient,
X-ray photographs of the corona, and spectroheliograms showing bright
points overlying polar plumes, and macrospicules.
Title: New Observations of the Extended Ultraviolet Corona
Authors: Kohl, J. L.; Weiser, H.; Withbroe, G. L.; Munro, R. H.;
Noci, G.
Bibcode: 1982BAAS...14..976K
Altcode:
No abstract at ADS
Title: EUV spectroscopic plasma diagnostics for the solar wind
acceleration region
Authors: Kohl, J. L.; Withbroe, G. L.
Bibcode: 1982ApJ...256..263K
Altcode:
Possibilities are considered for probing physical conditions in the
solar corona with strong EUV resonance lines from ions such as N V, O
VI, Ne VIII, Mg X, and Si XII. Through measurements of the intensities
and profiles of EUV spectral lines with coronagraphic instrumentation
employing normal incidence reflecting optics, it is possible to
acquire information on electron, proton, and ion temperatures and
velocity distributions; electron, H I, and ion densities; mass flow
and nonthermal velocities; and chemical abundances. This information
will provide critical empirical constraints on physical processes
responsible for plasma heating, solar wind acceleration, and transport
of mass, momentum, and energy in the solar corona, as well as providing
constraints on theoretical models for solar and stellar coronae and
mass loss.
Title: Analysis of coronal H I Lyman alpha measurements from a rocket
flight on 1979 April 13
Authors: Withbroe, G. L.; Kohl, J. L.; Weiser, H.; Noci, G.; Munro,
R. H.
Bibcode: 1982ApJ...254..361W
Altcode:
It is noted that measurements of the profiles of resonantly scattered
hydrogen Lyman-alpha coronal radiation have been used in determining
hydrogen kinetic temperatures from 1.5 to 4 solar radii from sun
center in a quiet region of the corona. Proton temperatures derived
using the line widths decrease with height from 2.6 x 10 to the 6th
K at 1.5 solar radii to 1.2 x 10 to the 6th K at 4 solar radii. These
measurements, together with temperatures for lower heights determined
from earlier Skylab and eclipse data, suggest that there is a
maximum in the quiet coronal proton temperature at about 1.5 solar
radii. Comparison of measured Lyman-alpha intensities with those
calculated using a representative model for the radial variation of
the coronal electron density yields information on the magnitude of
the electron temperature gradient and suggests that the solar wind
flow was subsonic for distances less than 4 solar radii.
Title: Probing the solar wind acceleration region using spectroscopic
techniques.
Authors: Withbroe, G. L.; Kohl, J. L.; Weiser, H.; Munro, R. H.
Bibcode: 1982SSRv...33...17W
Altcode:
Measurements of the intensities and profiles of UV and EUV spectral
lines can provide a powerful tool for probing the physical
conditions in the solar corona out to 8 R ⊙ and
beyond. We discuss here how measurements of spectral line radiation
in conjunction with measurements of the white light K-corona can
provide information on electron, proton and ion temperatures and
velocity distribution functions; densities; chemical abundances and
mass flow velocities. Because of the fundamental importance of such
information, we provide a comprehensive review of the formation of
coronal resonance line radiation, with particular emphasis on the H i
Lα line, and discuss observational considerations such as requirements
for rejection of stray light and effects of emission from the geocorona
and interplanetary dust. Finally, we summarize some results of coronal H
i Lα and white light observations acquired on sounding rocket flights.
Title: 1980 rocket coronagraph measurements of the solar wind
acceleration region.
Authors: Withbroe, G. L.; Kohl, J. L.; Munro, R. H.; Weiser, H.
Bibcode: 1982SAOSR.392A..99W
Altcode: 1982csss....2...99W
Spectroscopic measurements of temperatures, densities and flow
velocities in the solar wind acceleration region provide critical
empirical constraints on solar stellar wind theory. Preliminary results
of an analysis of H I Lyman-alpha and white light measurements made on
16 February 1980 in a polar coronal region are reported. The hydrogen
kinetic temperatures in the observed region were found to be nearly
constant with THI approximately equals 10 degrees K at
heliocentric distances between 1.5 and 4 solar radii. The outflow
velocities were found to be subsonic indicating that the critical
point in the observed region was located at r approximately greater
than 4 solar radii.
Title: Solar EUV, XUV and soft X-ray telescope facilities
Authors: Withbroe, G. L.
Bibcode: 1982sao..rept.....W
Altcode:
Facility class, high resolution instrumentation can enable maximum
spatial, spectral and temporal resolutions and provide understanding of
the complex physical conditions in the outer solar atmosphere and the
mechanisms responsible for these conditions. The scientific rationale
for facility class instruments operating in the EUV, XUV, and soft X
ray spectral ranges are discussed. Possible configurations for these
facilities and priorities for their development are considered.
Title: The Spacelab Lyman-Alpha and White Light Coronagraphs Program
Authors: Kohl, J. L.; Withbroe, G. L.; Weiser, H.; MacQueen, R. M.;
Munro, R. H.
Bibcode: 1981SSRv...29..419K
Altcode:
The Harvard-Smithsonian Center for Astrophysics and the High Altitude
Observatory have defined a joint coronagraphs experiment for a
future Spacelab mission. The instrumentation package would include an
ultraviolet light coronagraph to measure the intensity and profiles of
spectral lines formed between 1.2 and 8 solar radii from Sun center and
a white light coronagraph to measure the intensity and polarization
of visible light. The overall goals of the joint program are to use
new coronal plasma diagnostic techniques to understand the physical
processes and mechanisms operating in the solar corona, to understand
the acceleration of high-speed and low-speed solar wind streams and to
extrapolate this knowledge to other stars in order to help understand
the physics of stellar coronae and stellar mass loss.
Title: Mechanical heating in the transition region.
Authors: Withbroe, G.
Bibcode: 1981NASSP.450..321W
Altcode: 1981suas.nasa..321W
Attention is focused on the energy balance in the transition region and
the role that mechanical heating plays in determining the temperature
density structure of this region in a stellar atmosphere. Because of
its role as the interface layer through which mass and energy flow
between the chromospheres and corona, direct deposition of mechanical
energy is a relatively unimportant factor in the overall energy balance
in the transition region, except in the uppermost layers where the
temperature approaches coronal values.
Title: Results of Ly-α Coronagraphic Observations Following the
1980 Eclipse
Authors: Weiser, H.; Kohl, J. L.; Munro, R. H.; Withbroe, G. L.
Bibcode: 1981BAAS...13R.913W
Altcode:
No abstract at ADS
Title: Coronal Outflow Velocities: 1980 Rocket Measurements
Authors: Munro, R. H.; Kohl, J. L.; Weiser, H.; Withbroe, G. L.
Bibcode: 1981BAAS...13..912M
Altcode:
No abstract at ADS
Title: Analysis of Extreme Ultraviolet Spectroheliograms of Solar
Prominences
Authors: Kanno, M.; Withbroe, G. L.; Noyes, R. W.
Bibcode: 1981SoPh...69..313K
Altcode:
The optical depth at the head of the Lyman continuum, τH,
is determined at a number of positions in three hedgerow prominences
using spectroheliograms (5″ × 5″ resolution) of C IIIλ 977,
LC λ896, and O IV λ554 observed with the Harvard experiment
on Skylab. At heights greater than 10″ above the limb the
maximum value of τH is 30 to 50, which occurs at the
central part of the prominences. For one of the prominences the
determination of τH is found to be consistent with data from
spectroheliograms of Mg X λ625. The degree of ionization of hydrogen is
estimated from the intensity of LC λ896 at τH ≫ 1. In the
central part of a model prominence NP/NHI≤1.9
for a reasonable range of the electron densities, where NP
and NHI are the proton density and the neutral hydrogen
density, respectively.
Title: Spatial and Temporal Variations of EUV Coronal Bright Points
Authors: Habbal, S. R.; Withbroe, G. L.
Bibcode: 1981SoPh...69...77H
Altcode:
This paper reports results of an analysis of Skylab observations
of coronal bright points made in EUV spectral lines formed in the
chromosphere, chromospheric-coronal transition region and corona. The
most important result is that the observed bright points exhibited
large variations in EUV emission over time scales as short as 5.5 min,
the temporal resolution of the data. In most cases strong enhancements
in the coronal line were accompanied by strong enhancements in the
chromospheric and transition region lines. The intensity variations
appear to take place within substructures of the bright points, which
most likely consist of miniature loops evolving on time scales of a few
minutes. Coronal cooling times derived from the data are consistent with
an intermittent, impulsive coronal heating mechanism for bright points.
Title: Activity and outer atmospheres of the sun and stars
Authors: Praderie, F.; Spicer, D. S.; Withbroe, G. L.
Bibcode: 1981aoa..conf.....P
Altcode: 1981aoa..conf.....B; 1981SAAS...11.....B; 1981QB528.P73......
No abstract at ADS
Title: Physics of static loop structures and scaling laws.
Authors: Withbroe, G. L.
Bibcode: 1981sars.work..199W
Altcode:
The use of quasi-static models in the study of the physical processes
occurring in the magnetic flux loops making up the visible, EUV and
X-ray corona in solar active regions is considered. The quasi-static
loop models are based on steady-state energy equations for a static
plasma in a section of a symmetrical loop with specified boundary
conditions, from which values of parameters such as loop length,
pressure, maximum temperature and differential emission measure may
be derived that are consistent with those observed. The models also
provide insight into mechanisms controlling mass exchange between
the chromosphere and the corona, and the role of changes in coronal
heating in the loops in initiating the mass flows. Investigations
into the properties of quasi-static models for coronal loops
have also demonstrated the insensitivity of the loop longitudinal
temperature-density structure to parameters characterizing hypothetical
steady-state heating functions.
Title: Activity and Outer Atmosphere of the Sun
Authors: Withbroe, G. L.
Bibcode: 1981aoa..conf....1W
Altcode: 1981SAAS...11....1W
No abstract at ADS
Title: Measurements of coronal kinetic temperatures from 1.5 to 3
solar radii
Authors: Kohl, J. L.; Weiser, H.; Withbroe, G. L.; Noyes, R. W.;
Parkinson, W. H.; Reeves, E. M.; Munro, R. H.; MacQueen, R. M.
Bibcode: 1980ApJ...241L.117K
Altcode:
A rocket-borne Lyman-alpha coronagraph has been used to make the first
measurements of the spectral line profile of resonantly scattered
hydrogen Lyman-alpha coronal radiation between 1.5 and 3 solar
radii. These data provide, for the first time, direct measurements of
coronal temperatures above 1.5 solar radii. Data were obtained in a
coronal hole, quiet region, and streamer. The widths of the profiles
from the quiet region decrease with height and correspond to a steady
decrease in hydrogen kinetic temperature, with increasing radius, from
about 2.5 million K at r = 2 solar radii to about 1 million K at r =
9 solar radii. In the coronal hole the measured line widths indicate
a kinetic temperature of 1.8 million K at r = 2.5 solar radii.
Title: Coronagraphic H I Lyman-Alpha Observations following the 1980
Solar Eclipse
Authors: Weiser, H.; Kohl, J. L.; Parkinson, W. H.; Withbroe, G. L.
Bibcode: 1980BAAS...12R.917W
Altcode:
No abstract at ADS
Title: The Spacelab Lyman-Alpha and White-Light Coronagraphs Program
Authors: Kohl, J. L.; MacQueen, R. W.; Withbroe, G. L.; Munro, R.;
Weiser, H.
Bibcode: 1980BAAS...12..793K
Altcode:
No abstract at ADS
Title: Implications of Lyman α Measurements on Coronal Electron
and Proton Temperatures between 2.0 and 4.0 R⊙
Authors: Withbroe, G. L.; Kohl, J. L.; Weiser, H.
Bibcode: 1980BAAS...12Q.917W
Altcode:
No abstract at ADS
Title: (Invited Paper) Spectroscopy of the Corona between 1 and 8
Solar Radii
Authors: Withbroe, G.; Kohl, J.
Bibcode: 1980BAAS...12..544W
Altcode:
No abstract at ADS
Title: Solar Maximum Mission
Authors: Bohlin, J. David; Frost, Kenneth J.; Burr, Peter T.; Guha,
Arun K.; Withbroe, George L.
Bibcode: 1980SoPh...65....5B
Altcode:
The scientific objective of the Solar Maximum Mission is to understand
the physics of solar flares. A description is provided for the SMM
spacecraft, the scientific planning activity, the observing vprogram
and the guest investigator program associated with the mission.
Title: Contribution to Solar Physics from extreme-ultraviolet
observations
Authors: Huber, M. C. E.; Withbroe, G. L.
Bibcode: 1980fsoo.conf..146H
Altcode:
No abstract at ADS
Title: Lyman Alpha Line Profiles from 1.5 to 3.0 Solar Radii.
Authors: Kohl, J. L.; Weiser, H.; Withbroe, G. L.; Munro, R. H.;
Parkinson, W. H.; Reeves, E. M.
Bibcode: 1979BAAS...11..398K
Altcode:
No abstract at ADS
Title: Lyman-α and White Light Observations of the Outer Solar
Corona.
Authors: Munro, R. H.; Kohl, J. L.; MacQueen, R. M.; Noyes, R. W.;
Parkinson, W. H.; Weiser, H.; Withbroe, G. L.
Bibcode: 1979BAAS...11..398M
Altcode:
No abstract at ADS
Title: Contributions to solar physics from extreme-ultraviolet
observations.
Authors: Huber, M. C. E.; Withbroe, G. L.
Bibcode: 1979MmArc.106..146H
Altcode:
No abstract at ADS
Title: Discussion
Authors: Gaizauskas, V.; Heyvaerts, J.; Hirayama, T.; Pneuman, G. W.;
Spicer, D. S.; Withbroe, G. L.; Zirin, H.
Bibcode: 1979phsp.coll..301G
Altcode: 1979IAUCo..44..301G
No abstract at ADS
Title: Temperature gradients in the inner corona.
Authors: Mariska, J. T.; Withbroe, G. L.
Bibcode: 1978SoPh...60...67M
Altcode:
Emission gradient curves for extreme ultraviolet (EUV) resonance lines
of O VI and Mg X have been constructed from spectroheliograms of quiet
limb regions observed with the Harvard experiment on Skylab. An analysis
of these data suggests that the coronal temperature rises throughout
the height range 1.03R⊙≤r≤1.3R⊙. This
result implies that in quiet regions there is significant coronal
heating beyond r = 1.3R⊙.
Title: The thermal phase of a large solar flare.
Authors: Withbroe, G. L.
Bibcode: 1978ApJ...225..641W
Altcode:
EUV and X-ray observations are used to derive the differential emission
measures, temperatures, densities, radiative and conductive cooling
rates, and thermal energy content of a class 2B flare that occurred on
September 7, 1973. The results of the analysis indicate that (1) most of
the flare plasma was at temperatures between 3 and 10 million degrees;
(2) the peak temperature decreased with time from about 8 million K to
5 million K over a period of 3.5 hours; (3) the differential emission
measure steadily decreased with time at nearly all temperatures; (4)
both radiation and conduction were important cooling mechanisms for the
plasma at temperatures above 100,000 K; and (5) a substantial amount of
energy, of the order of 3 x 10 to the 31st power ergs, was deposited
in the flare loops after flare maximum. The empirically determined
flare parameters are compared with similar parameters derived from a
simple theoretical loop model.
Title: Models for solar coronal holes
Authors: Withbroe, G. L.
Bibcode: 1978sao..rept.....W
Altcode:
This report summarizes several investigations of coronal holes and
quiet regions. Temperature-density models for those regions have been
derived from EUV observations. It is found that the coronal temperature,
density, and temperature gradient are lower in coronal holes than in
quiet regions. There is evidence for a positive temperature gradient
to heights of 0.3 solar radii in quiet regions and 2.5 solar radii in
coronal holes.
Title: Contribution to Solar Physics from extreme-ultraviolet
observations
Authors: Huber, M. C. E.; Withbroe, G. L.
Bibcode: 1978fsoo.conf..146H
Altcode:
No abstract at ADS
Title: EUV analysis of polar plumes.
Authors: Ahmad, I. A.; Withbroe, G. L.
Bibcode: 1977SoPh...53..397A
Altcode:
Three polar plumes were studied using Skylab Mg X and O VI data. The
plumes lie within the boundaries of a polar coronal hole. We find that
the mean temperature of the plumes is about 1.1 × 106 K
and that they have a small vertical temperature gradient. Densities
are determined and found consistent with white light analyses. The
variation of density with height in the plumes is compared with that
expected for hydrostatic equilibrium. As is the case for other coronal
features, polar plumes will be a source of solar wind if the magnetic
field lines are open. On the basis of the derived plume model and
estimates of the numbers of plumes in polar coronal holes, it appears
that polar plumes contain about 15% of the mass in a typical polar
hole and occupy about 10% of the volume.
Title: Radio and EUV observations of a coronal hole.
Authors: Dulk, G. A.; Sheridan, K. V.; Smerd, S. F.; Withbroe, G. L.
Bibcode: 1977SoPh...52..349D
Altcode:
We present observations of a coronal hole made with the EUV
spectroheliometer of the Harvard College aboard Skylab and with `high
resolution' (2-4') radio telescopes at Culgoora and Fleurs Australia and
Bonn, West Germany. We attempt to derive the density and temperature
distributions in the transition region and inner corona from the
combined observations. No one `standard' model can explain both sets
of observations; characteristically, models based on EUV data yield
higher radio brightnesses than are observed, while models based on
radio data yield lower EUV line intensities than are observed. The
discrepancy is essentially that the electron density inferred from
the EUV data is about three times that inferred from the radio data.
Title: Photometric calibration of the EUV spectroheliometer on ATM.
Authors: Reeves, E. M.; Timothy, J. G.; Huber, M. C. E.; Withbroe,
G. L.
Bibcode: 1977ApOpt..16..849R
Altcode:
This paper describes the derivation of the preflight photometric
calibration of the UV spectrometer on Skylab. The calibration of the
orbiting instrument through cross-comparison with two rocket instruments
is discussed in assessing the observed changes in response to quiet
solar regions during the mission. Formulas are presented for the
determination of the instrument sensitivity, and an uncertainty of plus
or minus 35% is assigned over most of the 296-1340-A wavelength range.
Title: Skylab EUV Observations of the 7 September 1973 Flare.
Authors: Withbroe, G. L.; Vernazza, J. E.
Bibcode: 1977BAAS....9..299W
Altcode:
No abstract at ADS
Title: The solar boron abundance.
Authors: Kohl, J. L.; Parkinson, W. H.; Withbroe, G. L.
Bibcode: 1977ApJ...212L.101K
Altcode:
Positive evidence for the presence of boron in the sun is reported,
and the chemical abundance of boron in the photosphere is derived from
photoelectric measurements of the solar spectrum near 2500 A obtained
with a rocketborne high-resolution spectrometer. Short sections
of the spectrum in the vicinities of the B I lines at 2496.772
and 2497.723 A are plotted. The photospheric boron abundance is
determined primarily by analyzing the solar-center spectrum near the
first of the two lines in the framework of several single-component
photospheric models. The logarithmic boron abundance obtained is 2.6,
with an estimated uncertainty of plus or minus 0.3 dex, on the scale
where that of hydrogen is 12.0. This value is shown to be in excellent
agreement with that predicted for a nucleosynthesis model in which Li,
Be, and B are produced by cosmic-ray spallation.
Title: The chromospheric and transition layers in coronal holes.
Authors: Withbroe, G. L.
Bibcode: 1977chhs.conf..145W
Altcode:
No abstract at ADS
Title: Physics of an active region loop system.
Authors: Levine, R. H.; Withbroe, G. L.
Bibcode: 1977SoPh...51...83L
Altcode:
The structure of the active region loops is investigated by the study
of a loop complex which undergoes a dramatic evacuation of most of
the mass it contains. The need for continual energy deposition in
loops is emphasized by the apparent cessation of energy input to the
loops studied and their subsequent behavior. Estimates are made of
the energy necessary to form and to maintain the loops, and of the
relative importance of radiation and thermal conduction as energy loss
mechanisms. Models based on the observed EUV emission are used to place
limits on the size of loops seen in various lines and on the density
and temperature structure. We find that the cool cores of active region
loops are likely to be no more than a few hundred kilometers in radius
and that several such cool threads may be imbedded in a common hot
outer sheath. The primary energy loss on a large scale is radiation
with thermal conduction contributing to local disturbances. There is
a tendency for the development of apparently unstable condensations
or knots along the length of a loop. Higher resolution observations
will be necessary to confirm some of our predictions.
Title: Mass and Energy Flow in the Solar Atmosphere - Implications
of SKYLAB Observations
Authors: Withbroe, G.
Bibcode: 1977ebhs.coll..263W
Altcode: 1977IAUCo..36..263W
No abstract at ADS
Title: Mass and energy flow in the solar chromosphere and corona.
Authors: Withbroe, G. L.; Noyes, R. W.
Bibcode: 1977ARA&A..15..363W
Altcode:
The work reviews some investigations into the mass and energy
flow in the solar chromosphere and corona; the objective of these
investigations is the development of a physical model that will not
only account for the physical conditions in the outer atmosphere of
the sun, but can also be applied to the study of the outer atmospheres
of other stars. Particular attention is given to mass and energy flow
in regions with weak and strong magnetic fields, to observational
evidence for wave heating and systematic mass flows, and to heating
mechanisms. Consideration is given throughout to mechanisms of energy
input and energy loss.
Title: Investigations of solar flares, quiet and active regions
based on EUV and radio observations
Authors: Withbroe, G. L.; Vernazza, J. E.
Bibcode: 1976hco..rept.....W
Altcode:
This report summarizes several investigations of the quiet and active
solar atmosphere. It includes a discussion of a technique for studying
the physical conditions in active region loops and the application of
the technique to loops in McMath region 12628 and loops associated
with the 7 September 1973 proton flare in McMath region 12507. The
report also summarizes some work on coronal hole models, models for
the chromosphere and an investigation of relationships between flare
rates and 8.6 mm brightness temperatures.
Title: Active region flare rates and 8.6 mm brightness temperatures.
Authors: Withbroe, G. L.; Vernazza, J. E.
Bibcode: 1976SoPh...50..127W
Altcode:
The relationship between the flaring rates and 8.6 mm brightness
temperatures of active regions has been analyzed. We find that as the
8.6 mm brightness temperature of an active region increases, a larger
proportion of the energy released by the region in the form of flares is
contained in progressively larger flares. At all temperatures subflares
are the most frequent event. At intermediate and high temperatures
about 10% of the events are flares of importance 1 or larger with
flares of importance 2 or larger contributing an increasing fraction
of these events as the brightness temperature increases.
Title: Analysis of EUV limb brightening observations from ATM. II:
Influence of spicules.
Authors: Withbroe, G. L.; Mariska, J. T.
Bibcode: 1976SoPh...48...21W
Altcode:
A comparison of limb brightening measurements with theoretical limb
brightening curves calculated for simple atmospheric models indicates
that a significant fraction of the EUV emission from lines formed
in the transition layer comes from spicules. We find that spicules
contribute about 20% of the total quiet Sun intensity for lines of the
C II, C III, N III, and O VI ions. The uncertainty in the magnitude of
the percentage is about a factor of 2. The EUV-emission scale heights
above the limb are consistent with the assumption that the variation
with height of the number of EUV-emitting spicules is the same as for
Hα-emitting spicules. Optical depths derived for the C II λ1335 and
C III λ977 lines yield estimates for the pressure P = neT
in the transition layer, log P = 14.7±0.5, that are in good agreement
with pressures derived under the assumption that the transition layer
is in pressure equilibrium with the chromosphere and corona.
Title: The Quiet Sun in the Extreme Ultraviolet
Authors: Reeves, E. M.; Vernazza, J. E.; Withbroe, G. L.
Bibcode: 1976RSPTA.281..319R
Altcode: 1976RSLPT.281..319R
Observations of the quiet Sun with the Harvard extreme ultraviolet
spectrometer on the Skylab mission are reported for the chromosphere,
transition region, and corona. The changing structure of the
network is examined over the temperature range from 104
to 1.5 × 106 K, and the distribution of intensities in
the cell interiors and the network examined from the standpoint of
creating characteristic models. Observations of traces of periodic
oscillations at 300 s in the cells for T <= 2 × 104
is reported together with the absence of any periodic contributions at
higher temperatures or periodic effects at any height in the network
elements. Frequent non-periodic brightenings are observed, however,
and their characteristics discussed. Observations of the increased
thickness of the transition region in coronal holes, as well as
other properties are discussed in limited detail. Observations of the
centre-to-limb behaviour of transition region and coronal lines are
used to construct coronal models, and the assumptions of spherical
symmetry evaluated from the intensity data. The effects of spicules
on the limb and disk data are discussed in relation to the observations.
Title: Extreme-ultraviolet transients observed at the solar pole.
Authors: Withbroe, G. L.; Jaffe, D. T.; Foukal, P. V.; Huber, M. C. E.;
Noyes, R. W.; Reeves, E. M.; Schmahl, E. J.; Timothy, J. G.; Vernazza,
J. E.
Bibcode: 1976ApJ...203..528W
Altcode:
Extreme-ultraviolet (EUV) observations of two polar transient features
('macrospicules') are described. These features appear to be caused
by jets of chromospheric material that shoot upward to a height of
35,000 km above the limb and then fall back into the chromosphere,
reaching terminal velocities of about 140 km/s. On the basis of a
model developed from the EUV measurements, it is found that the energy
required to produce each event is about 3 by 10 to the 26th power ergs,
about two orders of magnitude more than that required to produce an
ordinary spicule. This indicates that macrospicules may be an important
factor in the energy balance of the chromosphere and corona.
Title: Initial results from the EUV spectroheliometer on ATM
Authors: Reeves, E. M.; Timothy, J. G.; Foukal, P. V.; Huber, M. C. E.;
Noyes, R. W.; Vernazza, J. E.; Withbroe, G. L.; Schmahl, E. J.
Bibcode: 1976skls.conf...73R
Altcode:
The Harvard College Observatory photoelectric spectroheliometer on
the Apollo Telescope Mount operated correctly in orbit from May 29,
1973 to February 7, 1974. During this period, many thousands of
spatial and spectral scans at extreme ultraviolet wavelengths were
recorded during observations of a variety of solar features. The
construction and modes of operation of the instrument are outlined,
and the principal scientific results from a preliminary analysis of
the data are described.
Title: The Analysis of XUV Emission Lines
Authors: Withbroe, G. L.
Bibcode: 1975SoPh...45..301W
Altcode:
A technique for analyzing measurements of XUV spectral line intensities
is described. Application of the technique to OSO-4 and OSO-6 spectra
indicates that the mean coronal temperature is 2.1 × 106 K
in typical active solar regions and that the mean coronal temperature
in typical quiet regions ranges from 1.5 × 106 to 2.1
× 106 K. One active region spectrum shows evidence for
substantial quantities of coronal material with 2 × 106 <
T < 3.5 × 106 K. Measurements from limb spectra show
evidence that (1) coronal abundances of N and O are low relative to
heavier elements; or (2) that the ionization equilibrium calculations
used may contain systematic errors; or (3) that the XUV intensity
measurements may be incorrectly calibrated.
Title: Active region flare rates and 8.6 millimeter brightness
temperatures, 2
Authors: Withbroe, G. L.; Vernazza, J. E.
Bibcode: 1975hco..rept.....W
Altcode:
The relationship between the flaring rate and 8.6 mm brightness
temperatures of active regions has been analyzed. As the 8.6 mm
brightness temperature of an active region increases, the energy
released by the region is contained in larger and larger flares. At
low temperatures subflares are dominant, at intermediate temperatures
most of the events are either subflares or class 1 flares and at high
temperatures class 2 or greater flares release most of the energy. The
results of the study indicate that measurements of 8.6 mm brightness
temperatures can be used to predict the rate of flaring of active
regions.
Title: Analysis of EUV Limb-Brightening Observations from ATM. I:
Model for the Transition Layer and the Corona
Authors: Mariska, J. T.; Withbroe, G. L.
Bibcode: 1975SoPh...44...55M
Altcode:
Limb-brightening curves for EUV resonance lines of O VI and Mg X
have been constructed from spectroheliograms (5″ resolution)
of quiet limb regions observed with the Harvard experiment on
Skylab. The observations are interpreted with a simple model for
the transition layer and the corona. A comparison of theoretical and
observed limb-brightening curves indicates that the lower boundary of
the corona, where Te= 106K, is at a height of
about 8000 km in typical quiet areas. For 1.01 R⊙≲r1.25
R⊙, the corona can be represented by a homogeneous model in
hydrostatic equilibrium with a temperature of 106K for 1.01
R⊙≲r<1.1 R⊙ and 1.1 × 106K
for r≳1.1 R⊙. The model for the transition layer is
inhomogeneous, with the temperature gradient a factor of 3 shallower
in the network than in the intranetwork regions. It appears that
spicules should be included in the model in order to account for the
penetration into the corona of cool (Te<106K)
EUV-emitting material to heights up to 20000 km above the limb.
Title: Time variations in extreme-ultraviolet emission lines and
the problem of coronal heating.
Authors: Vernazza, J. E.; Foukal, P. V.; Huber, M. C. E.; Noyes,
R. W.; Reeves, E. M.; Schmahl, E. J.; Timothy, J. G.; Withbroe, G. L.
Bibcode: 1975ApJ...199L.123V
Altcode:
We have analyzed the time structure of the intensity of solar
chromospheric and coronal extreme-ultraviolet lines, obtained by
the Harvard College Observatory spectrometer aboard Skylab. We find
changes in the intensity of up to 50 percent in times as short as
1 minute, but not periodic oscillations. Some evidence is found for
the presence of shock waves in the chromosphere and the transition
region. It is suggested that the solar chromosphere and corona are
heated by nonperiodic waves.
Title: EUV Analysis of an Active Region
Authors: Raghavan, N.; Withbroe, G. L.
Bibcode: 1975SoPh...43..117R
Altcode:
A sequence of extreme ultraviolet (EUV) spectroheliograms of McMath
region No. 10283 were obtained by the Harvard College Observatory
experiment on OSO-6. The lines OVIλ1032 Mg × λ625, Si XII λ499 and
Fe XVI λ 335 were used to determine coronal temperatures and densities
above the active region. A comparison of theoretical and observed line
ratios yielded coronal temperatures of 2.2 to 2.3 × 106K
above the active region and 2.0 to 2.1 × 106K in the
surrounding area. The temperatures derived from ratios involving the
O VI intensities are systematically higher than the others. This is
attributed to an error in the theoretical O VI intensities.
Title: Physics of an Active Region Loop Event.
Authors: Levine, R. H.; Withbroe, G. L.
Bibcode: 1975BAAS....7Q.460L
Altcode:
No abstract at ADS
Title: INVITED PAPER - Solar Structure in the Extreme Ultraviolet.
Authors: Withbroe, G. L.
Bibcode: 1975BAAS....7..478W
Altcode:
No abstract at ADS
Title: Extreme Ultraviolet Solar Limb Brighteness Observations
Authors: Mariska, J. T.; Withbroe, G. L.
Bibcode: 1975BAAS....7Q.460M
Altcode:
No abstract at ADS
Title: Extreme Ultraviolet Solar Limb Brightening Observations of
Lithium-Like Ions
Authors: Mariska, J. T.; Withbroe, G. L.
Bibcode: 1975BAAS....7..354M
Altcode:
No abstract at ADS
Title: Polar Transients Observed in the EUV
Authors: Withbroe, G. L.; Jaffe, D.
Bibcode: 1975BAAS....7..354W
Altcode:
No abstract at ADS
Title: EUV Observations of the Active Sun from the Harvard Experiment
on ATM
Authors: Noyes, R. W.; Foukal, P. V.; Huber, M. C. E.; Reeves, E. M.;
Schmahl, E. J.; Timothy, J. G.; Vernazza, J. E.; Withbroe, G. L.
Bibcode: 1975IAUS...68....3N
Altcode:
Some extreme UV observations of solar active regions made with a
scanning spectroheliometer are described. Spectroheliograms constructed
from digital data using a computer-driven cathode-ray tube display show
clearly how the appearance of an active region changes as a function
of temperature. Flare studies indicate that the impulsive rise in
EUV emission occurs essentially simultaneously at all levels from the
transition zone to the corona. Observations of sunspots reveal a very
intense emission in transition zone lines. A matrix of Mg x rasters
covering the entire sun reveals several hundred bright points having
dimensions of 30 arc seconds or less. Other observations include
coronal holes and prominences.
Title: Extreme-Ultraviolet Observations of Coronal Holes: Initial
Results from SKYLAB
Authors: Huber, M. C. E.; Foukal, P. V.; Noyes, R. W.; Reeves, E. M.;
Schmahl, E. J.; Timothy, J. G.; Vernazza, J. E.; Withbroe, G. L.
Bibcode: 1974ApJ...194L.115H
Altcode:
We compare the appearance and physical parameters of the solar
chromosphere, transition zone, and corona in areas of coronal holes
with that of quiet areas outside the hole. Measurements of the height
of emission of various ions in a coronal hole appearing at the polar
limb give a quantitative indication of the increased thickness of the
transition zone underlying coronal holes.
Title: Initial results from the EUV spectroheliometer on ATM.
Authors: Reeves, E. M.; Timothy, J. G.; Foukal, P. V.; Huber, M. C. E.;
Noyes, R. W.; Schmahl, E. J.; Vernazza, J. E.; Withbroe, G. L.
Bibcode: 1974aiaa.conf.....R
Altcode:
The Harvard College Observatory photoelectric spectroheliometer on
the Apollo Telescope Mount operated correctly in orbit from May 29,
1973 to Feb. 7, 1974. During this period many thousands of spatial and
spectral scans at extreme ultraviolet wavelengths were recorded during
observations of a variety of solar features. The construction and modes
of operation of the instrument are outlined and the principal scientific
results from a preliminary analysis of the data are described.
Title: Active region flare rates and 8.6 MM brightness temperatures
Authors: Withbroe, G. L.; Vernazza, J. E.
Bibcode: 1974STIN...7522247W
Altcode:
The relationship between flare rate and 8.6 mm brightness temperature
was analyzed using data from 99 active regions present on the solar disk
in 1969 and 1970. The rate of flaring appears to increase exponentially
with 8.6 mm brightness temperature Tb, for Tb -
9200 K. For higher temperatures, the rate of flaring appears to remain
nearly constant, independent of Tb. The resulting empirical
relationship provides a quantitative means of estimating flare rates
from an easily measured parameter, the 8.6 mm brightness temperature.
Title: Extreme Ultraviolet Solar Spectra from Skylab-Apollo Telescope
Mount.
Authors: Dupree, A. K.; Foukal, P. V.; Huber, M. C. E.; Noyes, R. W.;
Reeves, E. M.; Schmahl, E. J.; Timothy, J. G.; Vernazza, J. E.;
Withbroe, G. L.
Bibcode: 1974BAAS....6..349D
Altcode:
No abstract at ADS
Title: Extreme Ultraviolet Solar Observations from the Harvard
ATM Experiment
Authors: Withbroe, G. L.; Foukal, P. K.; Huber, M. C. E.; Noyes,
R. W.; Reeves, E. M.; Schmahl, E. J.; Timothy, J. G.; Vernazza, J. E.
Bibcode: 1974BAAS....6V.297W
Altcode:
No abstract at ADS
Title: ATM Observations of the Time Dependent Intensity Fluctuations
in the Extreme Ultraviolet
Authors: Vernazza, J. E.; Foukal, P. K.; Huber, M. C. E.; Noyes,
R. W.; Reeves, E. M.; Schmahl, E. J.; Timothy, J. G.; Withbroe, G. L.
Bibcode: 1974BAAS....6R.296V
Altcode:
No abstract at ADS
Title: Solar Prominences in the Extreme Ultraviolet as Observed from
the Apollo Telescope Mount
Authors: Schmahl, E. J.; Foukal, P. V.; Huber, M. C. E.; Noyes, R. W.;
Reeves, E. M.; Timothy, J. G.; Vernazza, J. E.; Withbroe, G. L.
Bibcode: 1974SoPh...39..337S
Altcode:
Observations of quiescent solar prominences with the Harvard College
Observatory spectrometer abroad Skylab show that prominence material is
optically thick in the Lyman alpha line and the Lyman continuum. The
color temperature of the Lyman continuum has a mean of 6600 K and
an upward gradient toward the top of the prominence. The departure
coefficient of the ground state of hydrogen is found to be of the
order of unity as expected from theory.
Title: Observations of the Chromospheric Network: Initial Results
from the Apollo Telescope Mount
Authors: Reeves, E. M.; Foukal, P. V.; Huber, M. C. E.; Noyes, R. W.;
Schmahl, E. J.; Timothy, J. G.; Vernazza, J. E.; Withbroe, G. L.
Bibcode: 1974ApJ...188L..27R
Altcode:
A preliminary analysis of early data taken by the HCO spectrometer on
Skylab shows that the solar chromospheric network can be clearly seen
with varying contrast in the extreme-ultraviolet emission characteristic
of temperatures between 10 v K (the Lyman continuum) and 3 X 10 K (0
vi). In the emission of Mg x, a coronal line formed at about 1.5 X 108
K, the network is generally unrecognizable. This is interpreted as being
due to a spreading of the magnetic field lines of the network boundary
in the height interval corresponding to the temperature difference
between 3 X 10 and 1.5 X 108 K. We note that in certain anomalous cases,
bright points of the network are seen to extend with high contrast and
essentially unchanged in their cross-section through the full range of
temperatures characteristic of the chromosphere, transition region,
and low corona. Subject headings: granules and supergranules, solar-
spectra, ultraviolet
Title: Solar EUV Photoelectric Observations from SKYLAB
Authors: Reeves, E. M.; Foukal, P. V.; Huber, M. C. E.; Noyes, R. W.;
Schmahl, E. J.; Timothy, J. G.; Vernazza, J. E.; Withbroe, G. L.
Bibcode: 1974IAUS...57..497R
Altcode:
No abstract at ADS
Title: A Comparison of EUV Spectroheliograms and Photospheric
Magnetograms
Authors: Gurman, Joseph B.; Withbroe, George L.; Harvey, John W.
Bibcode: 1974SoPh...34..105G
Altcode:
A comparison of EUV data from the Harvard College Observatory
experiment on OSO-6 with photospheric magnetograms from Kitt Peak
National Observatory indicates a bipartite relationship between values
of the longitudinal field strength B and Mg x intensity I averaged over
square areas 35″ × 35″: in quiet regions ¦B¦ ∼ Ik,
where 0.0 ≲ k ≲ 0.3, and in active regions ¦B¦ ∼ I. From these
relationships we infer that ¦B¦ ∼ ne2k
in quiet regions and ¦B¦ ∼ ne2 in active
regions. In addition, the photospheric field beneath a coronal hole
is found to be virtually identical to that beneath normal quiet regions.
Title: EUV spectroscopy with the Harvard Skylab experiment.
Authors: Withbroe, G. L.
Bibcode: 1974JOSA...64R1375W
Altcode:
No abstract at ADS
Title: A Study of the Active Region McMath 12417 with the Harvard
ATM EUV Spectrometer.
Authors: Foukal, P. V.; Huber, M. C. E.; Noyes, R. W.; Reeves, E. M.;
Schmahl, E. J.; Timothy, J. G.; Vernazza, J. E.; Withbroe, G. L.
Bibcode: 1973BAAS....5..432F
Altcode:
No abstract at ADS
Title: Preliminary Solar Extreme Ultraviolet Observations from the
ATM with the Harvard Instrument.
Authors: Reeves, E. M.; Foukal, P. K.; Huber, M. C. E.; Noyes, R. W.;
Schmahl, E. J.; Timothy, J. G.; Vernazza, J. E.; Withbroe, G. L.
Bibcode: 1973BAAS....5..419R
Altcode:
No abstract at ADS
Title: ATM Observations of Solar Flares in the Extreme Ultraviolet.
Authors: Noyes, R. W.; Foukal, P. V.; Huber, M. C. E.; Reeves, E. M.;
Schmahl, E. J.; Timothy, J. G.; Vernazza, J. E.; Withbroe, G. L.
Bibcode: 1973BAAS....5..433N
Altcode:
No abstract at ADS
Title: Solar Prominences-in the EUV as Observed from ATM.
Authors: Schmahl, E. J.; Foukal, P. V.; Huber, M. C. E.; Noyes, R. W.;
Reeves, E. M.; Timothy, J. G.; Vernazza, J. E.; Withbroe, G. L.
Bibcode: 1973BAAS....5..432S
Altcode:
No abstract at ADS
Title: Observations of a Coronal Hole Boundary in the Extreme
Ultraviolet.
Authors: Huber, M. C. E.; Foukal, P. V.; Noyes, R. W.; Reeves, E. M.;
Schmahl, E. J.; Timothy, J. G.; Vernazza, J. E.; Withbroe, G. L.
Bibcode: 1973BAAS....5..446H
Altcode:
No abstract at ADS
Title: The Harvard Experiment on OSO-6: Instrumentation, Calibration,
Operation, and Description of Observations
Authors: Huber, Martin C. E.; Dupree, A. K.; Goldberg, Leo; Noyes,
R. W.; Parkinson, W. H.; Reeves, E. M.; Withbroe, George L.
Bibcode: 1973ApJ...183..291H
Altcode:
The Harvard experiment carried by OS 0-6 was an extreme-ultraviolet
(EUV) spectrometerspectroheliometer with wavelength range 285-1385 A,
spatial and spectral bandwidth 35 x 35 (arc sec)2 and 3 A, respectively;
the instrumeflt acquired data that have been deposited with the National
Space Science Data Center and World Data Center A at the Goddard Space
Flight Center in Greenbelt, Maryland, and are now available in their
entirety to the scientific community. This paper describes aspects
of the experiment that are relevant to potential users of the data:
instrument configuration and parameters, laboratory and inflight
calibrations, as well as operational capabilities and procedures. We
also report the observations obtained and, where relevant, list
the nature, number, and dates of observations. Subject headings:
atmospheres, solar - instruments - solar activity - spectra, solar -
spectra, ultraviolet
Title: Models of the Chromospheric-Coronal Transition Layer and
Lower Corona Derived from Extreme-Ultraviolet Observations
Authors: Withbroe, George L.; Gurman, Joseph B.
Bibcode: 1973ApJ...183..279W
Altcode:
intensities of nine resonance lines from ions in the lithium and
sodium isoelectronic sequences are used to derive models for the
chromospheric-coronal transition layer and the corona in quiet and
active solar regions. The resulting models are combined with models
derived in previous studies to determine how the coronal temperature
and the conductive flux from the corona to the chromosphere vary as
a function of the electron pressure P = n,T in the lower corona. The
coronal temperature ranges from 106 K in coronal "holes" to 2.5 x 106
K in active regions. The conductive flux varies approximately as for P
3.0 >c 1015 and remains constant at a value of about 6 x 106 ergs 1
for P > 3.0 x 1015. Subject headings:chromosphere, solar - corona,
solar - coronal lines - spectra, solar - spectra, ultraviolet
Title: The Extreme-Ultraviolet Spectrum of a Solar Active Region
Authors: Dupree, A. K.; Huher, M. C. E.; Noyes, R. W.; Parkinson,
W. H.; Reeves, E. M.; Withbroe, G. L.
Bibcode: 1973ApJ...182..321D
Altcode:
Extreme-ultraviolet spectra ( 370 A) of the brightest point in McMath
Region 10266 and of the quiet solar atmosphere are presented as measured
by the Harvard scanning spectrometer on 0S0-6. Line identifications
and physical parameters of the active region are discussed. Subject
headings: line identifications - spectra, solar - spectra, ultraviolet
Title: Flare Rates and Coronal Density Evolution of Active Regions
Authors: Smith, Stephen P.; Withbroe, George L.
Bibcode: 1973BAAS....5R.280S
Altcode:
No abstract at ADS
Title: A Model for the Polar Transition Layer and Corona for
November 1967
Authors: Withbroe, George L.; Wang, Yi-Ming
Bibcode: 1972SoPh...27..394W
Altcode:
A model for the chromospheric-coronal transition layer and lower corona
has been constructed for the south polar region. EUV observations
acquired by the Harvard OSO-4 experiment in the fall of 1967 were used
in the analysis. The observations can be explained with a simple model
consisting of two types of regions. One region has a temperature-density
structure similar to that in models developed for typical equatorial
quiet areas. The other region has a corona in which the temperature
and density are a factor of about 2 lower and the chromospheric-coronal
temperature gradient is less steep by a factor of 4.
Title: Extreme-Ultraviolet Emission from Solar Prominences
Authors: Noyes, R. W.; Dupree, A. K.; Huber, M. C. E.; Parkinson,
W. H.; Reeves, E. M.; Withbroe, G. L.
Bibcode: 1972ApJ...178..515N
Altcode:
Spectra and spectroheliograms of prominences have been obtained at
wavelengths 300 A < A < 1400 A from instruments aboard the OSO 4
and OSO 6 spacecraft. Quiescent prominences appear in emission above
the limb for all strong lines formed at temperatures below 3 x 10 K,
but not at higher temperatures. The gas pressure in the 10 K transition
zone around prominences is approximately equal to that in the cooler
(6300 K) central regions. The temperature and the hydrogen ground-state
departure coefficient in the central regions are determined from
the Lymancontinuum spectrum. Prominences on the disk (filaments) are
visible in absorption in many lines, especially those at wavelengths
below the hydrogen Lyman limit at 912 A. The fractional absorption,
averaged over the spectrometer aperture, decreases regularly with
increasing temperature of line formation. The hydrogen La and Lfl lines
show only slight absorption relative to chromospheric lines lying on
top of the Lyman continuum.
Title: Observing Programs in Solar Physics during the 1973 ATM
Skylab Program
Authors: Reeves, E. M.; Noyes, R. W.; Withbroe, G. L.
Bibcode: 1972SoPh...27..251R
Altcode:
No abstract at ADS
Title: Properties of a Coronal "hole" Derived from Extreme-Ultraviolet
Observations
Authors: Munro, Richard H.; Withbroe, George L.
Bibcode: 1972ApJ...176..511M
Altcode:
A coronal <`hole" is characterized by significant deficiency in
the intensity of coronal emission lines, yet there is little change
in lines and continua formed below 800,000 K except for the He I and
He ii emission features. Comparison of the hole with the normal quiet
Sun indicates that the electron pressure is reduced hy a factor of 3,
the coronal temperature is lower hy 600,000 K, and the temperature
gradient in the chromospheric-coronal transition layer is less steep by
an order of magnitude. The apparent insensitivity of the lines formed
in the transition layer to the physical conditions of the hole implies
that the conductive flux from the corona is proportional to the square
of the electron pressure.
Title: The Solar Euv-Emitting Plasma (invited Paper)
Authors: Noyes, R. W.; Withbroe, G. L.
Bibcode: 1972SSRv...13..612N
Altcode: 1972IAUCo..14..612N
No abstract at ADS
Title: The Derivation of Temperature Gradient and Electron Density
Maps from EUV Spectroheliograms
Authors: Withbroe, George L.
Bibcode: 1972SoPh...25..116W
Altcode:
We discuss spatial variations in electron density at the base of the
corona and in the temperature gradient in the chromospheric-coronal
transition layer as determined from analysis of maps constructed
from Mgx and OVI spectroheliograms. Both the mapping techniques
and results of analyzing EUV spectra from OSO 6 observations are
presented. Comparisons of these maps with photospheric magnetograms and
spectroheliograms made in chromospheric EUV lines and continua indicate
that the electron density and temperature gradient in the transition
layer tend to be enhanced in areas where the photospheric magnetic
field and chromospheric EUV emission are enhanced. Relationships among
the coronal electron density, transition-layer temperature gradient,
chromospheric emission, and photospheric magnetic field strength
are derived.
Title: Properties of a Coronal "Hole" from EUV Observations
Authors: Munro, R. H.; Withbroe, G. L.
Bibcode: 1972BAAS....4R.388M
Altcode:
No abstract at ADS
Title: Solar Flares in the Extreme Ultraviolet. I. The Observations
Authors: Wood, A. T., Jr.; Noyes, R. W.; Dupree, A. K.; Huber,
M. C. E.; Parkinson, W. H.; Reeves, E. M.; Withbroe, G. L.
Bibcode: 1972SoPh...24..169W
Altcode:
Solar-flare observations in the extreme ultraviolet (300-1350 Å) are
reported. Some 269 flares observed by the Harvard College Observatory
(HCO) experiment on OSO 4 and 211 flares observed by the HCO experiment
on OSO 6 have been analyzed. The flares were observed in spectral
lines and continua emitted by many ionic species over a temperature
range from 104 to 3.5 × 106 K. The EUV data
have been correlated with X-ray, Hα, and radio observations, and a
significant number of EUV bursts not associated with reported Hα,
X-ray, or radio bursts have been iden tified and investigated. The
results indicate that these latter EUV events are less energetic by
about a factor of 2 than EUV bursts associated with — F subflares.
Title: Coronal Electron Density Maps for 7 March, 1970, Derived from
Mgx λ625 Spectroheliograms (Papers presented at the Proceedings
of the International Symposium on the 1970 Solar Eclipse, held in
Seattle, U. S. A. , 18-21 June, 1971.)
Authors: Withbroe, G. L.; Dupree, A. K.; Goldberg, L.; Huber,
M. C. E. .; Noyes, R. W.; Parkinson, W. H.; Reeves, E. M.
Bibcode: 1971SoPh...21..272W
Altcode:
We have analyzed daily Mgx λ 625 spectroheliograms acquired by the
Harvard College Observatory experiment on OSO-6 for a 28-day period
centered on 7 March, 1970, the date of a well-observed total solar
eclipse. These data are used to construct maps of the variation across
the solar disk of the electron density at the base of the corona. The
correspondence of high and low density regions with regions of enhanced
and reduced emission in white light and Mgx pictures made during or
near the time of the eclipse are described.
Title: Electron Densities Derived from Line Intensity Ratios:
Beryllium Isoelectronic Sequence
Authors: Munro, Richard H.; Dupree, A. K.; Withbroe, George L.
Bibcode: 1971SoPh...19..347M
Altcode:
A direct method for determining electron densities from emission
line intensities of ions in the beryllium isoelectronic sequence is
described and then applied to the analysis of extreme ultraviolet
CIII and OV spectra from both quiet and active areas in the solar
transition region. The results are consistent with a value of
NeTe = 6 × 1014 cm-3K
for the quiet Sun at temperatures of 5 × 104 to 3 ×
105K. Electron densities are approximately five times
greater in active regions than in the quiet Sun.
Title: The Chemical Composition of the Photosphere and the Corona
Authors: Withbroe, George L.
Bibcode: 1971spas.conf..127W
Altcode:
No abstract at ADS
Title: A Comparison of Solar EUV Intensities and K-Coronameter
Measurements
Authors: Withbroe, George L.
Bibcode: 1971SoPh...18..458W
Altcode:
Characteristics of the emission observed above the solar limb in
four EUV lines, SIXIIλ499, MgXλ625, NeVIIIλ770, and OVIλ1032 are
discussed. The mean temperature of the corona derived from the ratios
of the intensities of SIXIIλ499 and MgXλ625 is 1.8 million K. There
do not appear to be significant temperature differences in regions with
low EUV intensities and those with high EUV intensities, suggesting
that the EUV emission from the lithium-like ions depends primarily on
the integral of ne2 along the line of sight.
Title: EUV emission lines: Density sensitive multiplet ratios.
Authors: Dupree, A. K.; Munro, R. H.; Noyes, R. W.; Withbroe, G. L.
Bibcode: 1971BAAS....3Q.260D
Altcode:
No abstract at ADS
Title: Real Time Control of the Observing Program of an Orbiting
Solar Observatory
Authors: Reeves, E. M.; Huber, M. C. E.; Withbroe, G. L.; Noyes, R. W.
Bibcode: 1971IAUS...41..336R
Altcode:
No abstract at ADS
Title: Solar EUV observations: Lines of lithium-like ions.
Authors: Withbroe, G. L.; Noyes, R. W.
Bibcode: 1971BAAS....3S.265W
Altcode:
No abstract at ADS
Title: The density and vibrational distribution of molecular oxygen
in the lower thermosphere
Authors: Reid, R. H. G.; Withbroe, George L.
Bibcode: 1970P&SS...18.1255R
Altcode: 1970P&SS...18.1255W
Observations of solar ultraviolet radiation from the satellite
OSO-IV are analysed. The atmospheric absorption of 1032 Å (O VI)
can be reproduced theoretically by a static diffusion model of the O
2, density above 120 km with a density of (3.6 ± 0.4) x 10
10cm -3 at 120 km. The atmospheric absorption
of 1335 Å (CII) appears to require an effective absorption cross
section of O 2 that decreases with increasing altitude. The
decrease could result from an increasing vibrational development of
O 2, such that the fraction of molecules in the ground
vibrational state is less than about 0.9 at 130 km, 0.7 at 150 km and
0.5 above 160 km.
Title: OSO-VI: Surges, Flares, and the Development of Active Regions
Authors: Reeves, E. M.; Dupree, A. K.; Goldberg, L.; Huber, M. C. E.;
Noyes, R. W.; Parkinson, W. H.; Withbroe, G. L.
Bibcode: 1970BAAS....2R.215R
Altcode:
No abstract at ADS
Title: OSO-VI: The EUV Spectrum of Solar-Active Regions
Authors: Dupree, A. K.; Goldberg, L.; Huber, M. C. E.; Noyes, R. W.;
Parkinson, W. H.; Reeves, E. M.; Withbroe, G. L.
Bibcode: 1970BAAS....2..191D
Altcode:
No abstract at ADS
Title: Extreme Ultraviolet Observations of Active Regions in the
Chromosphere and the Corona
Authors: Noyes, Robert W.; Withbroe, George L.; Kirshner, Robert P.
Bibcode: 1970SoPh...11..388N
Altcode:
New observations of solar active regions have been obtained by
the Harvard College Observatory EUV spectroheliometer aboard the
OSO-IV spacecraft. From the observations we have determined the
enhancement in active regions of the emission from ions formed at
various temperatures in the chromosphere and corona. The results are
in accord with a simple model of active regions, for which the active
region pressure is about 5 times the quiet sun pressure; the temperature
gradient in the transition zone is about 5 times the quiet sun value;
and the coronal temperature above active regions is slightly increased.
Title: OSO-VI: The Harvard Experiment
Authors: Huber, M. C. E.; Dupree, A. K.; Goldberg, L.; Noyes, R. W.;
Parkinson, W. H.; Reeves, E. M.; Withbroe, G. L.
Bibcode: 1970BAAS....2S.200H
Altcode:
No abstract at ADS
Title: Solar XUV Limb Brightening Observations. II: Lines Formed in
the Chromospheric-Coronal Transition Region
Authors: Withbroe, George L.
Bibcode: 1970SoPh...11..208W
Altcode:
Limb brightening of XUV lines of the ions CIII NIII, NIV, OIII, OIV,
OV and SiIV is compared with that predicted by a modified version of a
coronal model developed by Dupree and Goldberg. Systematic differences
between the predicted and observed limb brightening are found. These
differences can be eliminated by introducing into the model the effects
of spicules that extend up into the chromospheric-coronal transition
region. The spicules are assumed to be opaque to radiation between
500 and 900 Å because of absorption in the hydrogen Lyman continuum.
Title: Solar XUV Limb Brightening Observations. I: The Lithium-Like
Ions
Authors: Withbroe, George L.
Bibcode: 1970SoPh...11...42W
Altcode:
OSO-IV observations of the equatorial limb brightening of XUV resonance
lines of NV, O VI, Ne VIII, Mg X and Si XII are interpreted with a
modified version of a coronal model developed by Dupree and Goldberg
(1967). Good agreement is obtained between the observed limb brightening
and that predicted by the model. The sensitivity of the predicted
limb-brightening curves to changes in parameters describing the model
is discussed. Coronal abundances for N, O, Ne, Mg, and Si are obtained.
Title: Solar XUV Limb Brightening Observations II. Lines Formed in
the Chromospheric-Coronal Transition Region
Authors: Withbroe, G. L.
Bibcode: 1969cctr.conf...93W
Altcode:
No abstract at ADS
Title: Solar XUV Limb Brightening Observations I. The Lithium-Like
Ions
Authors: Withbroe, G. L.
Bibcode: 1969cctr.conf...55W
Altcode:
No abstract at ADS
Title: Extreme Ultraviolet Observations of Active Regions in the
Chromosphere and the Corona
Authors: Noyes, R. W.; Withbroe, G. L.; Kirshner, R. P.
Bibcode: 1969cctr.conf..125N
Altcode:
No abstract at ADS
Title: The Photospheric Abundance of Iron
Authors: Withbroe, George L.
Bibcode: 1969SoPh....9...19W
Altcode:
The center-to-limb variation of equivalent widths of 198 FeI lines in
the spectral region 5500 to 7000 Å was studied with five photospheric
models. The gf-values of Corliss and Warner (1964) were used in
the analysis. The photospheric iron abundance was found to vary with
excitation potential. This can be explained by a systematic error in the
gf-values of high excitation lines and an error of 250 to 500K in the
temperature of the arcs used for measuring the gf-values. Departures
from LTE in the solar FeI lines are also a possibility. The adopted
photospheric abundance of iron, log(NFe/NH)
is - 5.2.
Title: OSO-IV Observations of uv Limb Brightening
Authors: Withbroe, George L.
Bibcode: 1969BAAS....1S.296W
Altcode:
No abstract at ADS
Title: The Solar [Fe II] Lines
Authors: Withbroe, George L.
Bibcode: 1969ApJ...156.1177W
Altcode:
Theoretical equivalent widths for solar [Fe ii] lines calculated with
five photospheric models are corn- pared with observed values. This Note
describes new calculations of the theoretical equivalent widths of the
solar [Fe ii] lines made with five recent photospheric models. These
lines are important because they are the only photospheric lines that
give evidence of a photospheric iron abundance in good agreement
with the coronal abundances found by several investigators (e.g.,
Goldberg, Kopp, and Dupree 1964). The equivalent widths of the [Fe ii]
lines were originally calculated by Garstang (1952), using his own
theoretical oscillator strengths, the model atmosphere of Goldberg
and Pierce (1959), and the photospheric iron abundance determined by
Goldberg, Muller, and Aller (1960). Garstang concluded that the [Fe u]
lines would be absent from the solar spectrum unless the theoretical
equivalent widths could be increased by a factor of 20. Warner (1964)
found a number of coincidences of [Fe ii] lines with unidentified
features in the lJtrecht (1960) atlas which he interpreted as evidence
for a photospheric iron abundance 20 times larger than the accepted
value. However, Kodiara (1964) sug- gested that the coincidences were
due to chance. More recently Swings (1965, 1966) has examined the
problem using high-resolution tracings of the solar spectrum obtained
by him and Neven, Delbouille, and Roland at the Jungfraujoch Scientific
Station. He found twenty features that can be attributed to [Fe II], and
he measured equivalent widths of nine of them. Their relative strengths
are in good agreement with Garstang's theoretical values. There is also
good agreement between the predicted and observed wavelengths (within
± 0.01 A) and half-widths. This is evidence that the identifications
are correct. A comparison of the equivalent widths observed by Swings
with those computed by Garstang gives an iron abundance, log NFe/NH
= -4.18. This value is 1.27 dex (1.27 dex = 101.27) larger than the
photospheric abundance, log NFe/NH = -5.45, determined from permitted
lines of Fe i and Fe ii (Warner 1968). Swings (1966) and Gasson and
Pagel (1966) have suggested that this difference in abundance should
be reduced by a factor of 0.14 to 0.4 dex to allow for an incorrect
electron pressure in the atmosphere used by Garstang. In order to
estimate better the influence of the assumed model photosphere
on the iron abundance derived from [Fe ii] lines, we calculated
new theoretical equivalent widths for these lines using Garstang's
oscillator strengths and five photospheric models: models of Elste
(1967), Hoiweger (1967), and Mutschlecner (1963), the Utrecht Refer-
ence Model (Heintze, Hubenet, and de Jager 1964), and a three-stream
model developed by Elste (1967). Local thermodynamic equilibrium was
assumed. Table 1 lists Garstang's theoretical equivalent widths for
the [Fe ii] lines, equivalent widths computed for Elste's photospheric
model for log NFe/NH = -5.43 and for log NFe/NH = -4.40, and equivalent
widths measured by Swings. A comparison of Swings's equivalent widths
with the new theoretical values suggests log NFe/NH = -4.40. The iron
abundance determined with Hoiweger's model, Mutschlecner's model, the
Utrecht Reference Model, and the three-stream model are, respectively,
-4.35, -4.38 ,-4.35, and -4.37. The mean abundance for the five models
is -4.37. This abundance is 0.19 dex smaller than the value derived
with Garstang's theoretical equivalent widths. However, the abundance
derived from the [Fe ii] lines is still an order of magnitude larger
than other recent determinations. For example, Goldberg, 117
Title: The differences between quiet and active regions measured by
spectroheliograms in the neutral helium resonance lines
Authors: Hearn, A. G.; Noyes, R. W.; Withbroe, G. L.
Bibcode: 1969MNRAS.144..351H
Altcode:
Spectroheliograms of the 537 and 584 A lines of neutral helium
were obtained in November 1967 by the Harvard spectroheliometer on
OSO-IV. The increased intensities of these lines in active regions
cannot be explained by an increased electron temperature. Calculations
show that the variation of the ratio of the intensity of the 537 A line
to the 584 A line as a function of the intensity of the 584 A line
is consistent with the layers emitting these lines having a higher
electron density in the active regions. The calculations require the
layer emitting the neutral helium lines in a quiet region to have an
electron temperature of 32000 K and an electron density of 4.5 X 1010
cm-3. The error in this electron density may be a factor of 3. The
active regions that have been observed require an increase in the
electron density of up to times that of a quiet region.
Title: Ultraviolet Solar Images from Space
Authors: Goldberg, Leo; Noyes, Robert W.; Parkinson, William H.;
Reeves, Edmond M.; Withbroe, George L.
Bibcode: 1968Sci...162...95G
Altcode:
No abstract at ADS
Title: Preliminary EUV Spectroheliograms from OSO-IV
Authors: Noyes, R. W.; Goldberg, L.; Parkinson, W. H.; Reeves, E. M.;
Withbroe, G. L.
Bibcode: 1968AJS....73R..73N
Altcode:
The Harvard OSO-I V spectrometer-spectroheliometer has provided pictures
of the sun over a wide range of wavelengths originating from different
heights in the solar atmosphere, from the low chromosphere through the
corona. Lines from H I through Si XII have been observed against the
solar disk showing structure on the disk both in active regions and, in
certain cases, well above the limb. The data allow a close comparison
with simultaneous ground-based coronal observations. Representative
spectroheliograms in lines of increasing ionization potentials are
used to illustrate the size, structure, and development of active
regions on the limb and on the disk at different heights in the solar
atmosphere. Preliminary observations of limb brightening, instensity
of active regions, and flare activity are presented.
Title: The Center-Limb Behavior of Solar Molecular Lines
Authors: Withbroe, George L.
Bibcode: 1968SoPh....3..146W
Altcode:
The center-limb behavior of C2, CH, CN, CO, and MgH lines
have been analyzed using five photospheric models. A three-stream model
developed by G. Elste gave the most satisfactory results, providing
evidence for the existence of inhomogeneities in the photospheric
layers - 2.5 ⩽ log τ5000 ⩽ -0.5.
Title: An Analysis of CH in the Solar Atmosphere
Authors: Withbroe, George L.
Bibcode: 1967ApJ...147.1117W
Altcode:
Center-limb observations of selected lines in the band system of the CH
molecule are used to study the upper photosphere. The observations are
interpreted using several photospheric models including an inhomogeneous
three-stream model. As a first approximation the assumption of LTE
appears to be adequate for the CII lines. A turbulence model was
deduced from the center-limb behavior of the CII equivalent widths
and the profile of X4248.944 A. For the microturbulence in the upper
photosphere, -2.5< log r5ooo < -o 5, we found a radial velocity
of 1.2 1 0.2 km/sec and a ratio between the tangential and radial
components of 1 2 1 0.2. For the macroturbulence in the same layers we
found a radial component of 1 0 1 0 5 km/sec and a tangential component
of 1.7 1 0.5 km/sec.
Title: Photospheric Abundance of Iron.
Authors: Withbroe, George L.
Bibcode: 1967AJ.....72T.837W
Altcode:
The center-limb variation of the equivalent widths of 198 Fe
I lines in the spectral region 5500 to 7000 A have been studied
with four photospheric models. The gf values of Corliss and Warner
(Astrophys. J. Suppi. 8, 395, 1964) were used in the analysis. The
photospheric abundance of iron was determined as a function of limb
position and as a function of excitation potential Xe of the lines. The
abundance does not vary significantly with position on the solar disk;
however, it does seem to depend upcn excitation potential. The iron
abundance decreases with increasing excitation potential for 1 ~ X~~
4 V and increases for 4&Xex~5 V. The minimum in abundance at Xe
4 V corresponds closely to an ~nflection point in the calibration
curve used to de~ne the absolute scale of Corliss and Warner's gf
values. Huber and Tobey (Scientific Report Xo. 16, Harvard College
Observatory Shock Tube Spectroscopy Laboratory, 1967) have found
evidence that this calibration curve is incorrect for lines with
X~> 6 V, where Xa is the excitation potential of the upper level
of a transition. If Corliss and Warner's gf values are changed in the
manner suggested by Huber and Tobey's data, the solar iron abundance
decreases with increasing Xex over the range 1 ~ X~& 5 V. The
results suggest that the excitation temperature of the Fe I lines is
5000K cooler than the photospheric local electron temperature or that
there is a corresponding temperaturedependent error in the gf values.
Title: An Analysis of CH in the Solar Atmosphere.
Authors: Withbroe, George Lund
Bibcode: 1965PhDT.........7W
Altcode:
No abstract at ADS