Author name code: sturrock
ADS astronomy entries on 2022-09-14
author:"Sturrock, Peter A."
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Title: Neutrino-Flux Variability, Nuclear-Decay Variability, and
Their Apparent Relationship
Authors: Sturrock, P. A.
Bibcode: 2022SSRv..218...23S
Altcode: 2022arXiv220305069S
Analysis of Homestake, Gallex and GNO measurements reveals evidence
of variability of presumed solar-neutrino-flux measurements. Analysis
of Super-Kamiokande neutrino records over the interval May 1996 to
July 2001 reveals oscillations at 9.43 year−1 and 12.6
year−1, both well within a range of frequencies (6-16
year−1) that, according to helioseismology, could be
related to internal solar rotation.
Title: An Oscillation Evident in Both Solar Neutrino Data and Radon
Decay Data
Authors: Sturrock, P. A.; Fischbach, E.; Piatibratova, O.; Steinitz,
G.; Scholkmann, F.
Bibcode: 2019arXiv190711749S
Altcode:
Analyses of neutrino measurements acquired by the Super-Kamiokande
Neutrino Observatory (SK, for the time interval 1996 - 2001) and of
radon decay measurements acquired by the Geological Survey of Israel
(GSI, for the time interval 2007 - 2017) yield remarkably consistent
detections of the same oscillation: frequency 9.43 +/- 0.04 year-1 (SK),
9.44 +/- 0.04 year-1 (GSI); amplitude 6.8 +/- 1.7 % (SK), 7.0 +/- 1.0 %
(GSI); phase 124 +/- 15 deg. (SK), 124 +/- 9 deg. (GSI). We briefly
discuss possible hypotheses that may be relevant to this experimental
result.
Title: The Detection of Solar Neutrinos by Radon Decay
Authors: Sturrock, Peter
Bibcode: 2019HEAD...1711215S
Altcode:
By comparison with the neutrino detection rate of 12 per day by the
Super-Kamiokande Neutrino Observatory (SKO), a radon-decay experiment
at the Geological Survey of Israel (GSI) in Jerusalem yields 260 gamma
detections per second, of which a few percent are attributable to a
solar influence. An oscillation at 9.43 year-1is detected
by both SKO and GSI with the same depth of modulation (7%) and the
same phase. An oscillation at this frequency has also been reported by
Alexeyev et al. in the decay of 213Po. Related oscillations
in GSI data at 7.43 year-1and 8.43 year-1suggest
that these three oscillations are attributable to a solar core that
rotates with a sidereal rotation rate of 8.43 year-1about
an axis approximately orthogonal to that of the convection zone. The
physical process responsible for the influence of neutrinos on nuclear
decays is currently unknown.
Title: Analysis of gamma radiation from a radon source. II:
Indications of influences of both solar and cosmic neutrinos on
beta decays
Authors: Sturrock, P. A.; Steinitz, G.; Fischbach, E.
Bibcode: 2018APh...100....1S
Altcode:
In the first article in this series, we reported an analysis of 29,000
hourly measurements of gamma radiation associated with the decay of
radon gas in a sealed container at the Geological Survey of Israel
(GSI) Laboratory in Jerusalem (Sturrock et al., 2012). We now report
an analysis of a full 10 years of operation that yields over 85,000
hourly gamma measurements. To avoid possible confusion with seasonal
environmental influences, we pay special attention to oscillations
with frequencies in a band relevant to solar rotation, identifying
two striking oscillations with frequencies 11.35 year-1
and 12.63 year-1, which we have found to be prominent also
in decay data acquired at the Brookhaven National Laboratory (Sturrock
et al., 2016). The 12.63 year-1 frequency agrees with the
synodic rotational frequency (the frequency as observed on Earth) of
the radiative zone as determined by helioseismology. Significantly,
the more prominent rotational oscillations occur in pairs separated by
1 year-1, indicating that the solar sources of modulation
rotate about axes that are oblique with respect to the normal to the
ecliptic. It is notable that one of a triplet of such oscillations
has exactly the same frequency (9.43 year-1) as the
most significant oscillation in Super-Kamiokande measurements,
suggesting that the experiment is responding to the influence of
neutrinos. As found in our previous article, the annual oscillation is
(counter-intuitively) stronger by day (with phase of maximum near 0.5,
i.e. mid-year, suggestive of a cosmic source) than by night (with
phase of maximum near zero, as expected for a solar source). This
day-night asymmetry in the measurements may be understood in terms
of a combined influence of asymmetries in the experiment and in the
relevant nuclear processes. Spectrograms (with axes local hour of
day and frequency) formed from the ambient temperature and pressure
and the supply voltage differ significantly from the corresponding
spectrogram formed from the gamma measurements. We have been unable
to identify any environmental influence or experimental artifact,
or any combination thereof, which can duplicate these statistically
highly significant patterns found in the GSI data.
Title: Concerning the variability of nuclear decay rates: Rebuttal
of an article by Pomme et al. [1]
Authors: Sturrock, P. A.; Steinitz, G.; Fischbach, E.
Bibcode: 2018APh....98....9S
Altcode:
Pomme et al. have recently analyzed one year of GSI (Geological Survey
of Israel) radon data, and claimed that "GSI radon measurements are
unsuited for studying the variability of decay constants because the
data are strongly influenced by environmental conditions such as solar
irradiance and rainfall" [1]. They also claim that "the existence
of cyclic variations in the decay constant is refuted." We find that
these claims are not supported by analysis of GSI data.
Title: The Life and Times of a Dissident Scientist
Authors: Sturrock, Peter Andrew
Bibcode: 2017SoPh..292..147S
Altcode:
No abstract at ADS
Title: Analysis of Ten Years of Radon-Chain Decay Measurements:
Evidence of Solar Influences and Inferences Concerning Solar Internal
Structure and the Role of Neutrinos
Authors: Sturrock, P. A.; Steinitz, G.; Fischbach, E.
Bibcode: 2017arXiv170503010S
Altcode:
Gamma radiation associated with radon decay exhibits variations in both
time of year and time of day. The annual oscillation has its maximum
value in June, suggestive of a galactic influence. Measurements made
at midnight show strong evidence of an influence of solar rotation, but
measurements made at noon do not. We find several pairs of oscillations
with frequencies separated by 1 cycle per year that is suggestive of an
influence of rotation that is oblique with respect to the normal to the
ecliptic. We suggest that beta decays may be stimulated by neutrinos
and that the decay products tend to travel in the same direction as
the neutrinos. We estimate the relevant cross section.
Title: Comparative Analyses of Brookhaven National Laboratory Nuclear
Decay Measurements and Super-Kamiokande Solar Neutrino Measurements:
Neutrinos and Neutrino-Induced Beta-Decays as Probes of the Deep
Solar Interior
Authors: Sturrock, P. A.; Fischbach, E.; Scargle, J. D.
Bibcode: 2016SoPh..291.3467S
Altcode: 2016SoPh..tmp..173S
An experiment carried out at the Brookhaven National Laboratory over
a period of almost 8 years acquired 364 measurements of the beta-decay
rates of a sample of 32Si and, for comparison, of a sample
of 36Cl. The experimenters reported finding "small periodic
annual deviations of the data points from an exponential decay …
of uncertain origin". We find that power-spectrum and spectrogram
analyses of these datasets show evidence not only of the annual
oscillations, but also of transient oscillations with frequencies
near 11 year−1 and 12.5 year−1. Similar
analyses of 358 measurements of the solar neutrino flux acquired by
the Super-Kamiokande neutrino observatory over a period of about 5
years yield evidence of an oscillation near 12.5 year−1
and another near 9.5 year−1. An oscillation near 12.5
year−1 is compatible with the influence of rotation
of the radiative zone. We suggest that an oscillation near 9.5
year−1 may be indicative of rotation of the solar core,
and that an oscillation near 11 year−1 may have its origin
in a tachocline between the core and the radiative zone. Modulation
of the solar neutrino flux may be attributed to an influence of the
Sun's internal magnetic field by the Resonant Spin Flavor Precession
(RSFP) mechanism, suggesting that neutrinos and neutrino-induced beta
decays can provide information about the deep solar interior.
Title: Analysis of beta-decay data acquired at the
Physikalisch-Technische Bundesanstalt: Evidence of a solar influence
Authors: Sturrock, P. A.; Steinitz, G.; Fischbach, E.; Parkhomov,
A.; Scargle, J. D.
Bibcode: 2016APh....84....8S
Altcode: 2016arXiv160503088S
According to an article entitled Disproof of solar influence
on the decay rates of 90Sr/90Y by Kossert and Nähle of the
Physikalisch-Technische Bundesanstalt (PTB) [1], the PTB measurements
show no evidence of variability. We show that, on the contrary,
those measurements reveal strong evidence of variability, including an
oscillation at 11 year-1 that is suggestive of an influence
of internal solar rotation. An analysis of radon beta-decay data
acquired at the Geological Survey of Israel (GSI) Laboratory for the
same time interval yields strong confirmation of this oscillation.
Title: Comparative Analysis of Brookhaven National Laboratory
Nuclear Decay Data and Super-Kamiokande Neutrino Data: Indication
of a Solar Connection
Authors: Sturrock, P. A.; Fischbach, E.
Bibcode: 2015arXiv151108770S
Altcode:
An experiment carried out at the Brookhaven National Laboratory from
February 1982 to December 1989 acquired 364 measurements of the
beta-decay rates of a sample of 36Cl and of a sample of 32Si. The
experimenters reported finding small periodic annual deviations
of the data points from an exponential decay - of uncertain
origin. We here analyze this dataset by power spectrum analysis and
by forming spectrograms and phasegrams. We confirm the occurrence
of annual oscillations but we also find evidence of oscillations in
a band of frequencies appropriate for the internal rotation of the
Sun. Both datasets show clear evidence of a transient oscillation
with a frequency of 12.7 cycles per year that falls in the range of
rotational frequencies for the solar radiative zone. We repeat these
analyses for 358 neutrino measurements acquired by Super-Kamiokande
over the interval May 1986 to August 2001. Spectrogram analysis yields
a strong and steady oscillation at about 9.5 cycles per year and an
intermittent oscillation with frequency in the range 12.5 - 12.7 cycles
per year. We attribute the former to rotation of the solar core and the
latter to rotation in the radiative zone. Since the flux of neutrinos
(8B neutrinos) responsible for the Super-Kamiokande measurements is
known, we are able to estimate the cross sections for the beta-decay
oscillations at 12.7 cycles per year. These estimates are found to
be 10-21.6 cm-2 for 36Cl and 10-18.4 cm-2 for 32Si. We suggest that
the beta-decay process is influenced by neutrinos, and that the solar
neutrino flux is modulated by magnetic field in the deep solar interior
by Resonant Spin Flavor Precession.
Title: Indications of R-mode Oscillations in SOHO/MDI Solar Radius
Measurements
Authors: Sturrock, P. A.; Bush, R.; Gough, D. O.; Scargle, J. D.
Bibcode: 2015ApJ...804...47S
Altcode: 2015arXiv150301039S
Analysis of solar radius measurements acquired by the Michelson Doppler
Imager on the Solar and Heliospheric Observatory spacecraft supports
previously reported evidence of solar internal r-mode oscillations
in Mt Wilson radius data and in 90Sr beta-decay data. The
frequencies of these oscillations are compatible with oscillations in
a putative inner tachocline that separates a slowly rotating core from
the radiative envelope.
Title: Erratum: "Analysis of Beta-decay Rates for Ag108,
Ba133, Eu152, Eu154, Kr85, Ra226, and Sr90, Measured at the
Physikalisch-technische Bundesanstalt from 1990 to 1996" (2014, apj, 794, 42)
Authors: Sturrock, P. A.; Fischbach, E.; Jenkins, J.
Bibcode: 2014ApJ...796..149S
Altcode:
No abstract at ADS
Title: Analysis of Beta-Decay Rates for Ag108, Ba133, Eu152, Eu154,
Kr85, Ra226, and Sr90, Measured at the Physikalisch-Technische
Bundesanstalt from 1990 to 1996
Authors: Sturrock, P. A.; Fischbach, E.; Jenkins, J.
Bibcode: 2014ApJ...794...42S
Altcode: 2014arXiv1408.3090S
We present the results of an analysis of measurements of the
beta-decay rates of Ag108, Ba133, Eu152, Eu154, Kr85, Ra226, and
Sr90 acquired at the Physikalisch-Technische Bundesanstalt from 1990
through 1995. Although the decay rates vary over a range of 165 to 1
and the measured detector current varies over a range of 19 to 1, the
detrended and normalized count rate measurements exhibit a sinusoidal
annual variation with amplitude in the small range 0.068%-0.088% (mean
0.081%, standard deviation 0.0072%, a rejection of the zero-amplitude
hypothesis) and phase-of-maximum in the small range 0.062-0.083
(January 23 to January 30). In comparing these results with those
of other related experiments that yield different results, it may be
significant that this experiment, at a standards laboratory, seems to
be unique in using a 4π detector. These results are compatible with a
solar influence, and do not appear to be compatible with an experimental
or environmental influence. It is possible that Ba133 measurements
are also subject to a non-solar (possibly cosmic) influence.
Title: Comparative study of beta-decay data for eight nuclides
measured at the Physikalisch-Technische Bundesanstalt
Authors: Sturrock, P. A.; Fischbach, E.; Javorsek, D.; Jenkins, J. H.;
Lee, R. H.; Nistor, J.; Scargle, J. D.
Bibcode: 2014APh....59...47S
Altcode:
We present the results of time-series analyses of data, kindly
provided by the Physikalisch-Technische Bundesanstalt, concerning
the beta-decays of Ag108, Ba133, Cs137, Eu152, Eu154, Kr85, Ra226,
and Sr90. From measurements of the detector currents, we find evidence
of annual oscillations (especially for Ra226), and for several solar
r-mode oscillations. It is notable that the frequencies of these
r-mode oscillations correspond to exactly the same sidereal rotation
rate (12.08 year-1) that we have previously identified in
r-mode oscillations detected in both Mt Wilson solar diameter data and
Lomonosov Moscow State University Sr90 beta-decay data. Ba133 is found
to be anomalous in that current measurements for this nuclide have a
much larger variation (by 4 σ) than those of the other nuclides. It
is interesting that analysis of variability measurements in the PTB
files yields strong evidence for an oscillation for Ba133 but only
weak evidence for Ra226.
Title: A Possible Role of Neutrinos in Stimulating Beta Decays and
its Significance for Solar Physics
Authors: Sturrock, Peter A.; Fischbach, Ephraim; Jenkins, Jere
Bibcode: 2014AAS...22421102S
Altcode:
We find evidence from measurements of Ag108, Ba133, Eu152, Eu154,
Ra226 and Sr90 (Physikalisch-Technische Bundesanstalt, Germany),
Rn222 (Geological Survey of Israel), Co60, Pu239, and Sr90 (Lomonosov
Moscow State University, Russia), Cl36 and Si32 (Brookhaven National
Laboratory, USA) and Mn54 (Purdue University, USA) that beta-decay rates
tend to be variable, and that the Sun is responsible for some - perhaps
all - of the variability. One variation is an annual oscillation with
amplitude about 0.1% and maximum in January or February, presumably
related to the annually varying Sun-Earth distance. We also find
evidence for two rotational modulations, one with a measured (synodic)
frequency of about 12.5 year-1 (an absolute, sidereal frequency
of 13.5 year-1), due perhaps to processes in the radiative zone,
and another with a synodic frequency of about 11 year-1 (12 year-1
sidereal), due perhaps to processes in an inner tachocline between
the core and the radiative zone. A steep gradient in angular velocity
(as in a tachocline) is known to be unstable and generate r-mode
oscillations. These may be detectable as Rieger-type oscillations in
the outer tachocline, and to similar oscillations (with correspondingly
lower frequencies, in proportion to the sidereal rotation frequencies)
in the inner tachocline. We find evidence for such r-mode oscillations
not only in beta-decay data, but also in solar diameter data. A possible
explanation of the apparent beta-decay variability is that decays may be
stimulated by neutrinos. Since the flavor composition of the neutrino
flux can be modified by the Sun’s internal magnetic field (via
Resonant Spin Flavor Precession), magnetohydrodynamic processes in the
deep solar interior may be detectable on Earth as neutrino-stimulated
beta-decay fluctuations. Experiments suggest that a nuclide such as
32Si has a beta-decay-equivalent-cross-section of order 10-25 cm2,
larger than the neutrino-equivalent-cross-section of an electron or
proton by about 1019. If this proves to be correct, then less than
1 picogram of 32Si would yield the same solar-neutrino-induced event
rate as the Super-Kamiokande Observatory.
Title: Power-Spectrum Analysis of Reconstructed DAMA Data
Authors: Sturrock, P. A.; Fischbach, E.; Gruenwal, J. T.; Javorsek, D.,
II; Jenkins, J. H.; Lang, R. F.; Lee, R. H.; Nistor, J.; Scargle, J.
Bibcode: 2013arXiv1304.8112S
Altcode:
Claims by the DAMA (DArk MAtter) collaboration to have detected an
annually varying signal consistent with models of dark matter appear to
be at variance with results from other dark-matter searches. To further
understand the DAMA results, we have carried out an independent analysis
of DAMA data reconstructed from published figures. In addition to
reexamining the Lomb-Scargle and chi-square analyses previously carried
out by the DAMA collaboration, we carry out two new likelihood analyses
and a new chi-square analysis, focusing attention on the treatment of
experimental errors and binning. We confirm the existence of an annual
oscillation, with a maximum in early June, but at a lower significance
level than previously reported.
Title: Spectral content of 22Na/44Ti decay data:
implications for a solar influence
Authors: O'Keefe, D.; Morreale, B. L.; Lee, R. H.; Buncher, John B.;
Jenkins, J. H.; Fischbach, Ephraim; Gruenwald, T.; Javorsek, D.;
Sturrock, P. A.
Bibcode: 2013Ap&SS.344..297O
Altcode: 2012arXiv1212.2198O; 2013Ap&SS.tmp....3O
We report a reanalysis of data on the measured decay rate ratio
22Na/44Ti which were originally published by
Norman et al., and interpreted as supporting the conventional hypothesis
that nuclear decay rates are constant and not affected by outside
influences. We find upon a more detailed analysis of both the amplitude
and the phase of the Norman data that they actually favor the presence
of an annual variation in 22Na/44Ti, albeit
weakly. Moreover, this conclusion holds for a broad range of parameters
describing the amplitude and phase of an annual sinusoidal variation
in these data. The results from this and related analyses underscore
the growing importance of phase considerations in understanding the
possible influence of the Sun on nuclear decays. Our conclusions with
respect to the phase of the Norman data are consistent with independent
analyses of solar neutrino data obtained at Super-Kamiokande-I and
the Sudbury Neutrino Observatory (SNO).
Title: UV and EUV Emissions at the Flare Foot-points Observed by AIA
Authors: Qiu; J.; Sturrock; Z.
Bibcode: 2013enss.confE..40Q
Altcode:
A solar flare is composed of impulsive energy release events by
magnetic reconnection, which forms and heats flare loops. Recent
studies have revealed a two-phase evolution pattern of UV 1600Å
emission at the feet of these flare loops: a rapid rise lasting for
a few minutes, followed by a gradual decay on timescales of a few
tens of minutes. These signatures are indicative of instantaneous
lower-atmosphere response to impulsive energy deposition, and the
subsequent plasma evolution in the overlying corona that is heated and
then cools down. Multiple band EUV observations by AIA further reveal
very similar signatures at the foot-points of flare loops. We report
the coordinated and spatially resolved observations of UV and EUV
emissions at the foot-points of a C3.2 thermal flare, and discuss the
governing mechanism of the two-phase evolution of the flare foot-point
emissions with a simple conductive heating model.
Title: An analysis of apparent r-mode oscillations in solar activity,
the solar diameter, the solar neutrino flux, and nuclear decay
rates, with implications concerning the Sun's internal structure
and rotation, and neutrino processes
Authors: Sturrock, P. A.; Bertello, L.; Fischbach, E.; Javorsek, D.;
Jenkins, J. H.; Kosovichev, A.; Parkhomov, A. G.
Bibcode: 2013APh....42...62S
Altcode: 2012arXiv1211.6352S
This article presents a comparative analysis of solar activity data, Mt
Wilson diameter data, Super-Kamiokande solar neutrino data, and nuclear
decay data acquired at the Lomonosov Moscow State University (LMSU). We
propose that salient periodicities in all of these datasets may be
attributed to r-mode oscillations. Periodicities in the solar activity
data and in Super-Kamiokande solar neutrino data may be attributed to
r-mode oscillations in the known tachocline, with normalized radius
in the range 0.66-0.74, where the sidereal rotation rate is in the
range 13.7-14.6 year-1. We propose that periodicities
in the Mt Wilson and LMSU data may be attributed to similar r-mode
oscillations where the sidereal rotation rate is approximately
12.0 year-1, which we attribute to a hypothetical "inner"
tachocline separating a slowly rotating core from the radiative zone. We
also discuss the possible role of the Resonant Spin Flavor Precession
(RSFP) process, which leads to estimates of the neutrino magnetic
moment and of the magnetic field strength in or near the solar core.
Title: The Case for a Solar Influence on Certain Nuclear Decay Rates
Authors: Sturrock, Peter; Fischbach, Ephraim; Javorsek, Daniel, II;
Jenkins, Jere; Lee, Robert
Bibcode: 2013arXiv1301.3754S
Altcode:
Power-spectrum analyses of the decay rates of certain nuclides
reveal (at very high confidence levels) an annual oscillation and
periodicities that may be attributed to solar rotation and to solar
r-mode oscillations. A comparison of spectrograms (time-frequency
displays) formed from decay data and from solar neutrino data reveals
a common periodicity with frequency 12.5 year-1, which is indicative of
the solar radiative zone. We propose that the neutrino flux is modulated
by the solar magnetic field (via Resonant Spin Flavor Precession)
in that region, and we estimate the force and the torque that could
be exerted on a nuclide by the solar neutrino flux.
Title: Evidence for a Solar Influence on Gamma Radiation from Radon
Authors: Sturrock, P. A.; Steinitz, G.; Fischbach, E.; Javorsek, D.;
Jenkins, J.
Bibcode: 2012AGUFMSH13A2249S
Altcode:
We have analyzed 29,000 measurements of gamma radiation associated with
the decay of radon confined to an airtight vessel at the Geological
Survey of Israel (GSI) Laboratory in Jerusalem between January 28 2007
and May 10 2010. These measurements exhibit strong variations in time
of year and time of day, which may be due in part to environmental
influences. However, time-series analysis reveals a number of strong
periodicities, including two at approximately 11.2 year-1 and 12.5
year-1. We consider it significant that these same oscillations
have previously been detected in nuclear-decay data acquired at the
Brookhaven National Laboratory and at the Physiklisch-Technische
Bundesanstalt. We have suggested that these oscillations are due
to some form of solar radiation (possibly neutrinos) that has its
origin in the deep solar interior. A curious property of the GSI
data is that the annual oscillation is much stronger in daytime
data than in nighttime data, but the opposite is true for all other
oscillations. Time-frequency analysis also yields quite different
results from daytime and nighttime data. These procedures have also been
applied to data collected from subsurface geological sites in Israel,
Tenerife, and Italy, which have a variety of geological and geophysical
scenarios, different elevations, and depths below the surface ranging
from several meters to 1000 meters. In view of these results, and in
view of the fact that there is at present no clear understanding of the
behavior of radon in its natural environment, there would appear to be
a need for multi-disciplinary research. Investigations that clarify
the nature and mechanisms of solar influences may help clarify the
nature and mechanisms of geological influences.
Title: Study of nuclear decays during a solar eclipse: Thule
Greenland 2008
Authors: Javorsek, D.; Brewer, M. C.; Buncher, J. B.; Fischbach, E.;
Gruenwald, J. T.; Heim, J.; Hoft, A. W.; Horan, T. J.; Kerford, J. L.;
Kohler, M.; Lau, J. J.; Longman, A.; Mattes, J. J.; Mohsinally, T.;
Newport, J. R.; Petrelli, M. A.; Stewart, C. A.; Jenkins, J. H.; Lee,
R. H.; Morreale, B.; Morris, D. B.; Mudry, R.; O'Keefe, D.; Terry,
B.; Silver, M. A.; Sturrock, P. A.
Bibcode: 2012Ap&SS.342....9J
Altcode: 2012Ap&SS.tmp..260J
Recent efforts to determine the cause of anomalous experimental
nuclear decay fluctuations suggests a possible solar influence. Here
we report on the results from several nuclear decay experiments
performed at Thule Air Base in Greenland during the solar eclipse
on 1 August 2008. Thule was ideal for this experiment due to its
proximity to the magnetic north pole which amplified changes in the
charged particle flux and provided relatively stabilized conditions
for nearly all environmental factors. An exhaustive list of relevant
factors were monitored during the eclipse to help rule out possible
systematic effects in the event of unexpected results. We included
measurements of temperature, pressure, and humidity as well as power
supply outputs, neutron count rates, and the Earth's local electric
and magnetic fields. Nuclear decay measurements of 14C,
90Sr, 99Tc, 210Bi, 234Pa,
and 241Am were made using Geiger-Müller (GM) ionization
chambers. Although our data exhibit no evidence for a statistically
significant change in the decay rate of any nuclide measured during the
1 August 2008 solar eclipse, small anomalies remain to be understood.
Title: Additional experimental evidence for a solar influence on
nuclear decay rates
Authors: Jenkins, Jere H.; Herminghuysen, Kevin R.; Blue, Thomas E.;
Fischbach, Ephraim; Javorsek, Daniel; Kauffman, Andrew C.; Mundy,
Daniel W.; Sturrock, Peter A.; Talnagi, Joseph W.
Bibcode: 2012APh....37...81J
Altcode: 2012arXiv1207.5783J
Additional experimental evidence is presented in support of the recent
hypothesis that a possible solar influence could explain fluctuations
observed in the measured decay rates of some isotopes. These data
were obtained during routine weekly calibrations of an instrument
used for radiological safety at The Ohio State University Research
Reactor using 36Cl. The detector system used was based on
a Geiger-Müller gas detector, which is a robust detector system with
very low susceptibility to environmental changes. A clear annual
variation is evident in the data, with a maximum relative count
rate observed in January/February, and a minimum relative count rate
observed in July/August, for seven successive years from July 2005
to June 2011. This annual variation is not likely to have arisen from
changes in the detector surroundings, as we show here.
Title: Searches for solar-influenced radioactive decay anomalies
using spacecraft RTGs
Authors: Krause, D. E.; Rogers, B. A.; Fischbach, E.; Buncher, J. B.;
Ging, A.; Jenkins, J. H.; Longuski, J. M.; Strange, N.; Sturrock, P. A.
Bibcode: 2012APh....36...51K
Altcode: 2012arXiv1205.7015K
Experiments showing a seasonal variation of the nuclear decay rates of
a number of different nuclei, and decay anomalies apparently related to
solar flares and solar rotation, have suggested that the Sun may somehow
be influencing nuclear decay processes. Recently, Cooper searched for
such an effect in 238Pu nuclei contained in the radioisotope
thermoelectric generators (RTGs) on board the Cassini spacecraft. In
this paper we modify and extend Cooper's analysis to obtain constraints
on anomalous decays of 238Pu over a wider range of models,
but these limits cannot be applied to other nuclei if the anomaly is
composition-dependent. We also show that it may require very high
sensitivity for terrestrial experiments to discriminate among some
models if such a decay anomaly exists, motivating the consideration
of future spacecraft experiments which would require less precision.
Title: Analysis of gamma radiation from a radon source: Indications
of a solar influence
Authors: Sturrock, P. A.; Steinitz, G.; Fischbach, E.; Javorsek, D.;
Jenkins, J. H.
Bibcode: 2012APh....36...18S
Altcode: 2012arXiv1205.0205S
This article presents an analysis of about 29,000 measurements of gamma
radiation associated with the decay of radon in a sealed container
at the Geological Survey of Israel (GSI) Laboratory in Jerusalem
between 28 January 2007 and 10 May 2010. These measurements exhibit
strong variations in time of year and time of day, which may be due
in part to environmental influences. However, time-series analysis
reveals a number of periodicities, including two at approximately 11.2
year-1 and 12.5 year-1. We have previously found
these oscillations in nuclear-decay data acquired at the Brookhaven
National Laboratory and at the Physiklisch-Technische Bundesanstalt, and
we have suggested that these oscillations are attributable to some form
of solar radiation that has its origin in the deep solar interior. A
curious property of the GSI data is that the annual oscillation is much
stronger in daytime data than in nighttime data, but the opposite is
true for all other oscillations. This may be a systematic effect but,
if it is not, this property should help narrow the theoretical options
for the mechanism responsible for decay-rate variability.
Title: The Case for a Solar Influence on Certain Nuclear Decay Rates
Authors: Sturrock, Peter; Fischbach, Ephraim; Javorsek, Daniel, II;
Jenkins, Jere
Bibcode: 2012aww..confE..10S
Altcode:
No abstract at ADS
Title: Flares in the Crab Nebula Driven by Untwisting Magnetic Fields
Authors: Sturrock, Peter; Aschwanden, Markus J.
Bibcode: 2012ApJ...751L..32S
Altcode: 2012arXiv1205.0039S
The recent discovery of PeV electrons from the Crab Nebula, produced
on rapid timescales of one day or less with a sharply peaked gamma-ray
spectrum without hard X-rays, challenges traditional models of diffusive
shock acceleration followed by synchrotron radiation. Here, we outline
an acceleration model involving a DC electric field parallel to the
magnetic field in a twisted toroidal field around the pulsar. Sudden
developments of resistivity in localized regions of the twisted field
are thought to drive the particle acceleration, up to PeV energies,
resulting in flares. This model can reproduce the observed timescales
of T ≈ 1 day, the peak photon energies of U Φ, rr ≈
1 MeV, maximum electron energies of U e, rr ≈ 1 PeV,
and luminosities of L ≈ 1036 erg s-1.
Title: Power spectrum analysis of LMSU (Lomonosov Moscow State
University) nuclear decay-rate data: Further indication of r-mode
oscillations in an inner solar tachocline
Authors: Sturrock, P. A.; Parkhomov, A. G.; Fischbach, E.; Jenkins,
J. H.
Bibcode: 2012APh....35..755S
Altcode: 2012arXiv1203.3107S
This article presents a power-spectrum analysis of 2350 measurements
of the 90Sr-90Y decay process acquired over the interval August 4 2002
to February 6 2009 at the Lomonosov Moscow State University. As we
have found for other long sequences of decay measurements, the power
spectrum is dominated by a very strong annual oscillation. However,
we also find a set of low-frequency peaks, ranging from 0.26 to 3.98
year-1, which are very similar to an array of peaks in
a power spectrum formed from Mt Wilson diameter measurements. The
Mt Wilson measurements have been interpreted in terms of r-mode
oscillations in a region where the sidereal rotation frequency is
12.08 year-1. We find that the LMSU measurements may also
be attributed to the same type of r-mode oscillations in a solar
region with the same sidereal rotation frequency. We propose that
these oscillations occur in an inner tachocline that separates the
radiative zone from a more slowly rotating solar core.
Title: Analysis of Radon Decay Data and its Implications for Physics,
Geophysics, and Solar Physics.
Authors: Sturrock, Peter A.; Fischbach, E.; Jenkins, J. H.; Steinitz,
G.
Bibcode: 2012AAS...22020514S
Altcode:
We present an analysis of about 29,000 measurements of gamma radiation
associated with the decay of radon in a sealed container at the
Geological Survey of Israel (GSI) Laboratory in Jerusalem between
January 28 2007 and May 10 2010. These measurements exhibit strong
variations in time of year and time of day, which may be due in part to
environmental influences. However, time-series analysis also reveals a
number of periodicities, notably at 11.2 year-1 and 12.5 year-1, which
we have found in other nuclear-decay data --including data acquired
at the Brookhaven National Laboratory and the Physiklisch-Technische
Bundesanstalt-- which we attribute to a solar influence. A distinct
property of the GSI results is that the annual oscillation is much
stronger in daytime data than in nighttime data, but the opposite
is true for all other oscillations. We speculate on possible
interpretations of this curious result. Solar neutrinos remain our
prime suspect as the agent responsible for beta-decay anomalies. These
results have implications for physics (that nuclear decay rates are not
constant and may be stimulated); for geophysics (that the variability
of radon measurements cannot be ascribed entirely to atmospheric and
solid-earth processes); and for solar physics (that the Sun contains an
inner tachocline, separating a slowly rotating core from the radiative
zone, which has properties similar to those of the outer tachocline
separating the radiative zone from the convection zone). This work
was supported by DOE grant DE-AC-02-76ER071428.
Title: Flares in the Crab Nebula Driven by Untwisting Magnetic Fields
Authors: Sturrock, Peter A.; Aschwanden, M. J.
Bibcode: 2012AAS...22040708S
Altcode:
The recent discovery of PeV electrons from the Crab nebula, produced on
rapid time scales of one day or less with a sharply peaked gamma-ray
spectrum without hard X-rays, challenges traditional diffusive shock
acceleration models followed by synchrotron radiation. Here we outline
an acceleration model involving a DC electric field, parallel to the
magnetic field, in a twisted toroidal field in the nebula.. Sudden
developments of resistivity in localized regions of the twisted field
are thought to drive the flares and associated particle acceleration up
to PeV energies. This model can reproduce the observed time scales of
about 1 day, the peak photon energies of about 1 MeV, maximum electron
energies of about 1 PeV, and a luminosity of about 1036 erg s-1.
Title: Corroboration for the influence of a component of solar
irradiance on subsurface radon signals
Authors: Steinitz, G.; Piatibratova, O.; Kotlarsky, P.; Sturrock,
P.; Maritn, C.
Bibcode: 2012EGUGA..14.1209S
Altcode:
Rn-222 occurs at highly varying levels as a trace component in
subsurface air (geogas). This high variability is traced by alpha and
gamma activity due to the decay of radon and its progeny. Nuclear
radiation from radon in geogas and in experiments using air+radon
within a confined volume exhibits systematic temporal variations. These
variations are composed of periodic and non-periodic signals spanning
several orders of magnitude in time - from annual to daily and
sub-daily durations. Analysis of extensive data sets from three key
sites 200 km apart in the arid desert of southern Israel [1-3] and from
a 5-year experiment using alpha and gamma detectors [4] demonstrate
that the periodic variations, observed to a depth of >100 meters,
are related to an above surface driver probably due to a component of
solar irradiance. Insight was also derived from the long term variations
in the geological and the experimental time series [5], indicated by the
occurrence of multi-year variations, and clear semiannual and ternary
annual signals which are in addition to the annual periodicity. New
confirmations are based on recognizing further cyclic phenomena, some
of which are not linked with Earth related periodicities. A likehood
analysis of the alpha and gamma time series in a long-term experiment
is performed. A Combined Power Statistic formed from the gamma, alpha-H
and alpha-L sensors inside the experimental tank shows that the time
series of the gamma radiation contains an annual periodicity as well
as a clear semi-annual and possibly a ternary-annual periodicity. The
same analysis also resolves additional periodicities in the frequency
range of 10-15 yr-1 in the gamma time series which are indicative of a
relationship to rotation of the sun around its axis [6]. Observation of
solar periodicities in the temporal pattern of the nuclear radiation
of radon is a significant independent substantiation for the notion
of the influence of a component in solar irradiance. An independent
confirmation of the solar effect in the experimental data is obtained
by observing day time and night time patterns. "Specgrams" of the power
as a function of frequency and hour of day show that the peak of the
annual periodicity occurs at daytime while the semi-annual and solar
periodicities are seen to be prominent at night. This is interpreted
to indicate a differentiation in the nuclear radiation from radon as a
function of rotation of Earth. - i.e. when Earth faces the sun and when
the sun is completely obstructed. This feature is also demonstrated
using Continuous Wavelet Transform (CWT) analysis on separate time
series composed of day-time and night-time measurements. Applying the
CWT analysis yields different frequency-time variation patterns for
day-time and night-time measurements in the experimental data. This
confirms the utilization of the CWT analysis for detecting the
phenomena. Using the CWT analysis tool the day- and night-time
difference in radon time series is also detected at subsurface
geological sites from Israel, Tenerife and Italy. These sites are from
different geological and geophysical scenarios, different elevations and
span depths from several meters to around 1000m below the surface. New
multi disciplinary prospects for the research are indicated in terms of
a) the radioactive behavior of radon in above surface and subsurface
air, b) an above surface geophysical driver for this behavior and,
c) the influence of a component of solar irradiation. 1. Steinitz,
G., O. Piatibratova, and S. M. Barbosa, 2007. Radon daily signals
in the Elat Granite, southern Arava, Israel, J. Geophys. Res., 112,
B10211, doi:10.1029/2006JB004817. 2. Steinitz, G., Piatibratova,
O., 2010a. Radon signals in the Gavnunim intrusion, Makhtesh Ramon,
Israel. Geophys. J. Int. 180, 651-665. 3. Steinitz, G. and Piatibratova,
O., 2010. Radon signals at the Roded site, Southern Israel, Solid Earth,
1, 99-109, doi:10.5194/se-1-99-2010. 4. Steinitz, G., Piatibratova,
O., Kotlarsky, P., 2011. Possible effect of solar tides on radon
signals. Journal of Environmental Radioactivity, 102, 749-765. doi:
10.1016/j.jenvrad.2011.04.002. 5. Steinitz, G., Piatibratova, O.,
Kotlarsky, P., 2011. Solar radiation tidal forcing of radon signals in
subsurface air. Geophysical Research Abstracts, Vol. 13, EGU2011-733,
2011 6. Sturrock, P.A., Buncher , J.B., Fischbach, E., Gruenwald, J.T.,
Javorsek, D., Jenkins, J.H., Lee, R.H., Mattes, J.J., Newport, J.R.,
2010b. Power Spectrum Analysis of Physikalisch-Technische Bundesanstalt
Decay-Rate Data: Evidence for Solar Rotational Modulation. Solar
Physics, 267, 251-265. DOI: 10.1007/s11207-010-9659-4
Title: Evidence for Solar Influences on Nuclear Decay Rates
Authors: Fischbach, E.; Jenkins, J. H.; Buncher, J. B.; Gruenwald,
J. T.; Sturrock, P. A.; Javorsek, D.
Bibcode: 2011cls..conf..168F
Altcode: 2010arXiv1007.3318F
Recent reports of periodic fluctuations in nuclear decay data of
certain isotopes have led to the suggestion that nuclear decay rates
are being influenced by the Sun, perhaps via neutrinos. Here we present
evidence for the existence of an additional periodicity that appears
to be related to the Rieger periodicity well known in solar physics.
Title: Evidence from Helioradiology of an Inner Tachocline in the Sun
Authors: Sturrock, P. A.; Bertello, L.; Fischbach, E.; Jenkins, J. H.
Bibcode: 2011AGUFMSH13B1931S
Altcode:
One can make a good case that the Rieger and related solar oscillations
may be understood as r-mode oscillations. The frequencies of these
oscillations fit the formula 2*m*nu/(l*(l+1)), where l and m (two
of the three spherical harmonic indices) take the values m = 1, l =
2,3,4,..., (the third index n does not affect the mode frequency),
and the sidereal rotation frequency nu = 13.7 year-1. This value of
the rotation frequency indicates that these oscillations occur in the
tachocline, which separates the radiative zone from the convection
zone. There is now strong evidence that beta decay rates are not
constant, and there is a persuasive case that the Sun is responsible
for variations in these rates. This new source of solar observational
data, for which we propose the name "helioradiology," yields evidence
that the solar core rotates more slowly than the radiative zone. This
raises the possibility that there is a second, "inner," tachocline
that separates the core from the radiative zone. This possibility
in turn suggests that there may be a second group of "Rieger-like"
oscillations that have their origin in this inner tachocline. We present
evidence for such oscillations, derived from helioradiology data and
also from the long-term diameter measurements acquired at the Mount
Wilson Observatory.
Title: Further Evidence Suggestive of a Solar Influence on Nuclear
Decay Rates
Authors: Sturrock, P. A.; Fischbach, E.; Jenkins, J. H.
Bibcode: 2011SoPh..272....1S
Altcode: 2011SoPh..tmp..318S; 2011SoPh..tmp..196S; 2011SoPh..tmp..138S;
2011SoPh..tmp..293S; 2011arXiv1105.1335S; 2011SoPh..tmp..265S
Recent analyses of nuclear decay data show evidence of variations
suggestive of a solar influence. Analyses of datasets acquired at the
Brookhaven National Laboratory (BNL) and at the Physikalisch-Technische
Bundesanstalt (PTB) both show evidence of an annual periodicity
and of periodicities with sidereal frequencies in the neighborhood
of 12.25 year−1 (at a significance level that we have
estimated to be 10−17). It is notable that this implied
rotation rate is lower than that attributed to the solar radiative
zone, suggestive of a slowly rotating solar core. This leads us to
hypothesize that there may be an "inner tachocline" separating the
core from the radiative zone, analogous to the "outer tachocline"
that separates the radiative zone from the convection zone. The Rieger
periodicity (which has a period of about 154 days, corresponding to a
frequency of 2.37 year−1) may be attributed to an r-mode
oscillation with spherical-harmonic indices l=3,m=1, located in the
outer tachocline. This suggests that we may test the hypothesis of a
solar influence on nuclear decay rates by searching BNL and PTB data
for evidence of a "Rieger-like" r-mode oscillation, with l=3,m=1,
in the inner tachocline. The appropriate search band for such an
oscillation is estimated to be 2.00 - 2.28 year−1. We
find, in both datasets, strong evidence of a periodicity at 2.11
year−1. We estimate that the probability of obtaining
these results by chance is 10−12.
Title: Concerning the Phases of the Annual Variations of Nuclear
Decay Rates
Authors: Sturrock, P. A.; Buncher, J. B.; Fischbach, E.; Javorsek,
D., ii; Jenkins, J. H.; Mattes, J. J.
Bibcode: 2011ApJ...737...65S
Altcode: 2011arXiv1106.2374S
Recent analyses of data sets acquired at the Brookhaven National
Laboratory and at the Physikalisch-Technische Bundesanstalt both
show evidence of pronounced annual variations, suggestive of a solar
influence. However, the phases of decay-rate maxima do not correspond
precisely to the phase of minimum Sun-Earth distance, as might then
be expected. We here examine the hypothesis that decay rates are
influenced by an unknown solar radiation, but that the intensity of
the radiation is influenced not only by the variation in Sun-Earth
distance, but also by a possible north-south asymmetry in the solar
emission mechanism. We find that this can lead to phases of decay-rate
maxima in the range 0-0.183 or 0.683-1 (September 6 to March 8) but
that, according to this hypothesis, phases in the range of 0.183-0.683
(March 8 to September 6) are "forbidden." We find that phases of the
three data sets analyzed here fall in the allowed range.
Title: Evidence for Time-Varying Nuclear Decay Rates: Experimental
Results and Their Implications for New Physics
Authors: Fischbach, Ephraim; Jenkins, Jere H.; Sturrock, Peter A.
Bibcode: 2011arXiv1106.1470F
Altcode:
Unexplained annual variations in nuclear decay rates have been
reported in recent years by a number of groups. We show that data
from these experiments exhibit not only variations in time related
to Earth-Sun distance, but also periodicities attributable to solar
rotation. Additionally, anomalous decay rates coincident in time with a
series of solar flares in December 2006 also point to a solar influence
on nuclear decay rates. This influence could arise from some flavor
of solar neutrinos, or through some other objects we call "neutrellos"
which behave in some ways like neutrinos. The indication that neutrinos
or neutrellos must interact weakly in the Sun implies that we may
be able to use data on time-varying nuclear decay rates to probe the
interior of the Sun, a technique which we may call "helioradiology".
Title: Analysis of Experiments Exhibiting Time-Varying Nuclear Decay
Rates: Systematic Effects or New Physics?
Authors: Jenkins, Jere H.; Fischbach, Ephraim; Sturrock, Peter A.;
Mundy, Daniel W.
Bibcode: 2011arXiv1106.1678J
Altcode:
Since the 1930s, and with very few exceptions, it has been assumed
that the process of radioactive decay is a random process, unaffected
by the environment in which the decaying nucleus resides. There have
been instances within the past few decades, however, where changes in
the chemical environment or physical environment brought about small
changes in the decay rates. But even in light of these instances,
decaying nuclei that were undisturbed or un-"pressured" were thought
to behave in the expected random way, subject to the normal decay
probabilities which are specific to each nuclide. Moreover, any
"non-random" behavior was assumed automatically to be the fault of
the detection systems, the environment surrounding the detectors,
or changes in the background radiation to which the detector was
exposed. Recently, however, evidence has emerged from a variety
of sources, including measurements taken by independent groups at
Brookhaven National Laboratory, Physikalisch-Technische Bundesanstalt,
and Purdue University, that indicate there may in fact be an influence
that is altering nuclear decay rates, albeit at levels on the order
of $10^{-3}$. In this paper, we will discuss some of these results,
and examine the evidence pointing to the conclusion that the intrinsic
decay process is being affected by a solar influence.
Title: Helioradiology: A New View Of The Deep Solar Interior:
Indications Of A Slowly Rotating Core And An Inner Tachocline
Authors: Sturrock, Peter A.; Fischbach, E.; Jenkins, J. H.
Bibcode: 2011SPD....42.0201S
Altcode: 2011BAAS..43S.0201S
Analyses of several radionuclide experiments give strong evidence that
decay rates are NOT constant (as we have all been led to believe). To
date, there is evidence for three periodicities: one with an annual
period; a second with a period of order one month; and one that is
approximately semi-annual. The first may be attributed partly to the
eccentricity of the Earth's orbit, and partly to a north-south asymmetry
in whatever solar radiation is responsible for the variations. The
second may be attributed to the influence of solar rotation; however,
the synodic period is in the range 30 - 33 days, indicative of a slowly
rotating region - presumably the core. The third may be interpreted
as a Rieger oscillation, except that it occurs in an inner tachocline
(separating the core from the radiative zone) rather than in the outer
tachocline, that separates the radiative zone from the convection
zone. The mechanism by which the Sun influences nuclear decay rates
is presently unknown. There are reasons to suspect that neutrinos
are involved, but this would require that neutrinos have previously
unsuspected properties. This work was supported by the NSF grant
AST-0607572 and DOE grant DE-AC-02-76ER071428.
Title: Power Spectrum Analysis of Physikalisch-Technische
Bundesanstalt Decay-Rate Data: Evidence for Solar Rotational
Modulation
Authors: Sturrock, P. A.; Buncher, J. B.; Fischbach, E.; Gruenwald,
J. T.; Javorsek, D.; Jenkins, J. H.; Lee, R. H.; Mattes, J. J.;
Newport, J. R.
Bibcode: 2010SoPh..267..251S
Altcode: 2010SoPh..tmp..193S; 2010arXiv1010.2225S
Evidence for an anomalous annual periodicity in certain nuclear-decay
data has led to speculation on a possible solar influence on nuclear
processes. We have recently analyzed data concerning the decay rates of
36Cl and 32Si, acquired at the Brookhaven National
Laboratory (BNL), to search for evidence that might be indicative of
a process involving solar rotation. Smoothing of the power spectrum by
weighted-running-mean analysis leads to a significant peak at frequency
11.18 year−1, which is lower than the equatorial synodic
rotation rates of the convection and radiative zones. This article
concerns measurements of the decay rates of 226Ra acquired
at the Physikalisch-Technische Bundesanstalt (PTB) in Germany. We
find that a similar (but not identical) analysis yields a significant
peak in the PTB dataset at frequency 11.21 year−1, and
a peak in the BNL dataset at 11.25 year−1. The change in
the BNL result is not significant, since the uncertainties in the BNL
and PTB analyses are estimated to be 0.13 year−1 and 0.07
year−1, respectively. Combining the two running means by
forming the joint power statistic leads to a highly significant peak
at frequency 11.23 year−1. We will briefly comment on
the possible implications of these results for solar physics and for
particle physics.
Title: Power Spectrum Analysis of Mount Wilson Solar Diameter
Measurements: Evidence for Solar Internal r-mode Oscillations
Authors: Sturrock, P. A.; Bertello, L.
Bibcode: 2010ApJ...725..492S
Altcode: 2010arXiv1010.0261S
This paper presents a power-spectrum analysis of 39,024 measurements of
the solar diameter made at the Mount Wilson Observatory from 1968.670 to
1997.965. This power spectrum contains a number of very strong peaks. We
find that eight of these peaks agree closely with the frequencies of
r-mode oscillations for a region of the Sun where the sidereal rotation
frequency is 12.08 year-1. We estimate that there is less
than one chance in 106 of finding this pattern by chance.
Title: Nuclear Decay Variations: New Solar Observations and Possible
New Flare Predictors
Authors: Sturrock, P. A.; Fischbach, E.; Jenkins, J.
Bibcode: 2010AGUFMSH43B1821S
Altcode:
There are many ground-based solar observatories, and more than
a few space-based observatories. They give highly detailed and
high-cadence information about the Sun’s surface and atmosphere,
and (by way of helioseismology) less detailed information about the
radiative zone and convection zone. Neutrino observatories can in
principle yield information about the solar core, but very little
has been achieved along those lines so far. The recent discovery of
variability of beta-decay rates offers a new opportunity. There are
now three lines of evidence linking this variability to the Sun. One
promising scenario is that the solar neutrino flux can induce beta
decays. Current evidence indicates that beta-decay measurements have
much higher sensitivity and can run at much higher cadence, than direct
measurements of the neutrino flux. Such measurements therefore offer
the prospect of greatly improved information about the structure and
activity of the solar core. In addition, there is tantalizing evidence
of a linkage between decay-rate fluctuations and solar flares. These
recent discoveries therefore offer the prospect of a new type of solar
observatory that will open a window on the solar core, that may offer
a predictive capability concerning solar activity, and which—compared
with other types of observatory—should be quite inexpensive.
Title: Power spectrum analyses of nuclear decay rates
Authors: Javorsek, D.; Sturrock, P. A.; Lasenby, R. N.; Lasenby, A. N.;
Buncher, J. B.; Fischbach, E.; Gruenwald, J. T.; Hoft, A. W.; Horan,
T. J.; Jenkins, J. H.; Kerford, J. L.; Lee, R. H.; Longman, A.; Mattes,
J. J.; Morreale, B. L.; Morris, D. B.; Mudry, R. N.; Newport, J. R.;
O'Keefe, D.; Petrelli, M. A.; Silver, M. A.; Stewart, C. A.; Terry, B.
Bibcode: 2010APh....34..173J
Altcode: 2010arXiv1007.0924J
We provide the results from a spectral analysis of nuclear decay data
displaying annually varying periodic fluctuations. The analyzed data
were obtained from three distinct data sets: 32Si and
36Cl decays reported by an experiment performed at the
Brookhaven National Laboratory (BNL), 56Mn decay reported
by the Children's Nutrition Research Center (CNRC), but also performed
at BNL, and 226Ra decay reported by an experiment performed
at the Physikalisch-Technische Bundesanstalt (PTB) in Germany. All
three data sets exhibit the same primary frequency mode consisting
of an annual period. Additional spectral comparisons of the data to
local ambient temperature, atmospheric pressure, relative humidity,
Earth-Sun distance, and their reciprocals were performed. No common
phases were found between the factors investigated and those exhibited
by the nuclear decay data. This suggests that either a combination
of factors was responsible, or that, if it was a single factor, its
effects on the decay rate experiments are not a direct synchronous
modulation. We conclude that the annual periodicity in these data
sets is a real effect, but that further study involving additional
carefully controlled experiments will be needed to establish its origin.
Title: Power spectrum analysis of BNL decay rate data
Authors: Sturrock, P. A.; Buncher, J. B.; Fischbach, E.; Gruenwald,
J. T.; Javorsek, D.; Jenkins, J. H.; Lee, R. H.; Mattes, J. J.;
Newport, J. R.
Bibcode: 2010APh....34..121S
Altcode: 2010arXiv1006.4848S
Evidence for an anomalous annual periodicity in certain nuclear decay
data has led to speculation concerning a possible solar influence
on nuclear processes. As a test of this hypothesis, we here search
for evidence in decay data that might be indicative of a process
involving solar rotation, focusing on data for 32Si and
36Cl decay rates acquired at the Brookhaven National
Laboratory. Examination of the power spectrum over a range of
frequencies (10-15 year -1) appropriate for solar synodic
rotation rates reveals several periodicities, the most prominent being
one at 11.18 year -1 with power 20.76. We evaluate the
significance of this peak in terms of the false-alarm probability,
by means of the shuffle test, and also by means of a new test (the
"shake" test) that involves small random time displacements. The last
two tests are the more robust, and indicate that the peak at 11.18
year -1 would arise by chance only once out of about 10
7 trials. However, the fact that there are several peaks
in the rotational search band suggests that modulation of the count
rate involves several low-Q oscillations rather than a single high-Q
oscillation, possibly indicative of a partly stochastic process. To
pursue this possibility, we investigate the running-mean of the
power spectrum, and identify a major peak at 11.93 year -1
with peak running-mean power 4.08. Application of the shuffle test
indicates that there is less than one chance in 10 11of
finding by chance a value as large as 4.08. Application of the shake
test leads to a more restrictive result that there is less than one
chance in 10 15 of finding by chance a value as large as
4.08. We find that there is notable agreement in the running-mean
power spectra in the rotational search band formed from BNL data and
from ACRIM total solar irradiance data. Since rotation rate estimates
derived from irradiance data have been found to be closely related to
rotation rate estimates derived from low-energy solar neutrino data,
this result supports the recent conjecture that solar neutrinos may be
responsible for variations in nuclear decay rates. We also carry out
a similar comparison with local temperature measurements, but find no
similarity between power spectra formed from BNL measurements and from
local temperature measurements.
Title: False-alarm Probability in Relation to Oversampled Power
Spectra, with Application to Super-Kamiokande Solar Neutrino Data
Authors: Sturrock, Peter A.; Scargle, Jeffrey D.
Bibcode: 2010ApJ...718..527S
Altcode: 2010arXiv1006.0546S
The term "false-alarm probability" denotes the probability that at least
one out of M independent power values in a prescribed search band of a
power spectrum computed from a white-noise time series is expected to be
as large as or larger than a given value. The usual formula is based on
the assumption that powers are distributed exponentially, as one expects
for power measurements of normally distributed random noise. However,
in practice, one typically examines peaks in an oversampled power
spectrum. It is therefore more appropriate to compare the strength of
a particular peak with the distribution of peaks in oversampled power
spectra derived from normally distributed random noise. We show that
this leads to a formula for the false-alarm probability that is rather
more conservative than the familiar formula. We also show how to combine
these results with a Bayesian method for estimating the probability of
the null hypothesis (that there is no oscillation in the time series),
and we discuss as an example the application of these procedures to
Super-Kamiokande solar neutrino data.
Title: Evidence for a Solar Influence on Nuclear Decay Rates
Authors: Sturrock, Peter A.; Buncher, J. B.; Fischbach, E.; Gruenwald,
J. T.; Javorsek, D., II; Jenkins, J. H.; Lee, R.; Mattes, J. T.;
Newport, J. R.
Bibcode: 2010AAS...21640011S
Altcode: 2010BAAS...41..856S
Analyses of data acquired during two experiments at the Brookhaven
National Laboratory (BNL) and one at the Physikalisch-Technische
Bundesanstalt in Germany have yielded strong evidence for an annual
variation of some nuclear decay rates. Since the Sun-Earth distance
has an annual period, it is possible that some radiation from the Sun
plays a role. We here present evidence in support of this conjecture. The low-energy solar-neutrino flux as detected by the Homestake and
GALLEX experiments, and the total solar irradiance as measured by the
ACRIM experiment, both exhibit a periodicity of about 12 year-1. We
infer that the solar core rotates at this synodic frequency, and
that nuclear burning in the core is not spherically symmetric. If
neutrinos influence some decay rates, the same periodicity may be
manifested in decay measurements. We have for this reason carried
out a power-spectrum analysis of measurements made at BNL over a
7-year interval of the decay rates of 32Si and 36Cl. This analysis
yields strong evidence for a cluster of periodicities centered on
12 year-1, such as one might obtain from stochastic fluctuations of
nuclear burning in a rotating core. These results imply that
some nuclear decay rates are influenced either by solar neutrinos
or by some other form of radiation that has its origin in the solar
core. This work was supported by the NSF grant AST-0607572 and
DOE grant DE-AC-02-76ER071428.
Title: Variation in Nuclear Decay Rates as a Possible Predictor of
Solar Flares
Authors: Sturrock, P. A.; Buncher, J.; Fischbach, E.; Gruenwald, J.;
Javorsek, D.; Jenkins, J.; Krause, D.; Mattes, J.
Bibcode: 2009AGUFMSH21C..07S
Altcode:
Jenkins and Fischbach (Astroparticle Physics, 31, 407, 2009) have
recently found evidence for fluctuations in the decay rates of
radioactive isotopes in association with solar flares. Jenkins et
al. (Astroparticle Physics, 32, 42, 2010) have also found strong
evidence for annual variations in measurements of decay rates
acquired at the Brookhaven National Laboratory (BNL) and at the
Physikalisch-Technische Bundesanstalt (PTB) in Germany. If these
claims are confirmed, they pose important questions in particle
physics and in solar physics, with the intriguing possibility
that such measurements may lead to procedures for predicting the
occurrence of some solar flares. The purpose of this presentation is
to discuss these questions. The strongest feature of the variability
of isotopic decay rates is an annual variation in both BNL and
PTB data. The phases of these variations rule out the possibility
that they are due either to the annual variation in temperature or
to the annual variation in Sun-Earth distance. However, we found
some time ago that the solar neutrino flux, as measured at Earth,
is influenced not only by the varying Sun-Earth distance, but also
by the variation in the heliospheric latitude of the Sun-Earth vector
(Sturrock,Walther, and Wheatland, Astrophys. J., 507, 978, 1998). The
phases of the annual variation in the BNL and PTB data are consistent
with the combined effect of varying Sun-Earth distance and varying
heliospheric latitude. This result suggests that the decay rates may
be influenced by solar neutrinos. This interpretation would require
a revision of neutrino physics. In order to check this hypothesis,
it would clearly be desirable to be able to compare decay data with
neutrino data. The difficulty is that the decay-rate variations amount
to only a few parts in 10,000. This is far too small a fraction to be
detectable in neutrino data. However, we have recently found that there
is a close association between variations in the solar neutrino flux
and variations in solar irradiance. Hence we may, with caution, use
irradiance data as a proxy for neutrino data. This has the advantage
that irradiance data has been measured several times a day with very
high accuracy for over thirty years. We shall present recent results
on the comparison of decay data and irradiance data, and comment on
possible processes that might explain these associations. This work was
supported by the National Science Foundation through grant AST-0607572.
Title: Reexamination of Possible Bimodality of GALLEX Solar-Neutrino
Data
Authors: Sturrock, P. A.
Bibcode: 2009SoPh..260..245S
Altcode: 2009arXiv0904.4236S
The histogram formed from published capture-rate measurements for the
GALLEX solar-neutrino experiment is bimodal, showing two distinct
peaks. However, the histogram formed from published measurements
derived from the similar Gallium Neutrino Observatory (GNO) experiment
is unimodal, showing only one peak. Nevertheless, the two experiments
differ in run durations: GALLEX runs are either three weeks or four
weeks (approximately) in duration, whereas GNO runs are all about four
weeks in duration. When we form three-week and four-week subsets of
the GALLEX data, we find that the relevant histograms are unimodal. The
upper peak arises mainly from the three-week runs, and the lower peak
from the four-week runs. The four-week subset of the GALLEX dataset
is found to be similar to the GNO dataset. A recent re-analysis of
GALLEX data leads to a unimodal histogram.
Title: A Bayesian Assessment of p-Values for Significance Estimation
of Power Spectra and an Alternative Procedure, with Application to
Solar Neutrino Data
Authors: Sturrock, P. A.; Scargle, J. D.
Bibcode: 2009ApJ...706..393S
Altcode: 2009arXiv0904.1713S
The usual procedure for estimating the significance of a peak in a power
spectrum is to calculate the probability of obtaining that value or a
larger value by chance (known as the "p-value"), on the assumption that
the time series contains only noise—typically that the measurements
are derived from random samplings of a Gaussian distribution. However,
since the use of p-values in other contexts is known to be misleading,
it seems prudent to examine the implications of using p-values for
significance estimation of power spectra. We really need to know
the probability that the time series is—or is not—compatible
with the "null hypothesis" that the measurements are derived from
noise. This probability can be calculated by Bayesian analysis,
but this requires one to specify and evaluate a second hypothesis
that the time series does contain a contribution other than noise. We
show that the requirement that the p-value should be identical to the
probability that the null hypothesis is true leads to an unacceptable
form for the likelihood function associated with this hypothesis. We
claim that, for this reason, the p-value is not an acceptable method
for significance estimation of a power spectrum. In order to obtain
an acceptable significance estimate, it is necessary to explicitly
consider a second hypothesis, and the key challenge is to identify an
appropriate likelihood function for this hypothesis. We first propose
four simple conditions that it seems reasonable to impose on this
function. We then examine a general functional form for the function,
and find the simplest form (which has one free parameter) that meets
these conditions. We then define two different ways of combining
information derived from two independent power estimates. One procedure
is to calculate the post-probabilities of the null hypothesis, convert
these to odds-values, and sum the log-odds. The second procedure is
to combine the p-values using a procedure due to R.A. Fisher, and to
calculate the corresponding post-probability and hence the corresponding
log-odds. It seems sensible—even if not logically essential—to
seek a likelihood function for which the two procedures lead to the
same answer. We find that this consistency condition may be satisfied,
to good approximation, by a special case of the previously proposed
likelihood function. We find that the resulting significance estimates
are considerably more conservative than those usually associated
with the p-values. As two examples, we apply the new procedure to two
recent analyses of solar neutrino data: (1) power spectrum analysis of
Super-Kamiokande data and (2) the combined analysis of radiochemical
neutrino data and irradiance data.
Title: Combined Analysis of Solar Neutrino and Solar Irradiance Data:
Further Evidence for Variability of the Solar Neutrino Flux and Its
Implications Concerning the Solar Core
Authors: Sturrock, P. A.
Bibcode: 2009SoPh..254..227S
Altcode: 2008arXiv0805.3686S
A search for any particular feature in any single solar neutrino
dataset is unlikely to establish variability of the solar neutrino
flux since the count rates are very low. It helps to combine datasets,
and in this article we examine data from both the Homestake and GALLEX
experiments. These show evidence of modulation with a frequency of 11.85
year−1, which could be indicative of rotational modulation
originating in the solar core. We find that precisely the same frequency
is prominent in power spectrum analyses of the ACRIM irradiance data for
both the Homestake and GALLEX time intervals. These results suggest that
the solar core is inhomogeneous and rotates with a sidereal frequency of
12.85 year−1. From Monte Carlo calculations, it is found
that the probability that the neutrino data would by chance match the
irradiance data in this way is only 2 parts in 10 000. This rotation
rate is significantly lower than that of the inner radiative zone
(13.97 year−1) as recently inferred from analysis of
Super-Kamiokande data, suggesting that there may be a second, inner
tachocline separating the core from the radiative zone. This opens up
the possibility that there may be an inner dynamo that could produce
a strong internal magnetic field and a second solar cycle.
Title: Evidence for r-Mode Oscillations in Super-Kamiokande Solar
Neutrino Data
Authors: Sturrock, P. A.
Bibcode: 2008SoPh..252..221S
Altcode: 2008SoPh..tmp..156S; 2008arXiv0802.3399S
There has for some time been evidence of variability in radiochemical
solar neutrino measurements, but this evidence has seemed suspect
since the Cerenkov experiments have not shown similar evidence of
variability. The present reanalysis of Super-Kamiokande data shows
strong evidence of r-mode oscillations. The frequencies of these
oscillations correspond to a region with a sidereal rotation rate
of 13.97 year−1. This estimate is incompatible with the
rotation rate in the convection zone but is compatible with current
estimates of the rotation rate in the radiative zone. The excitation of
r modes in the radiative zone may be due to a velocity field originating
in or related to the nuclear-burning core.
Title: Solar Neutrino Variability and Its Implications for Solar
Physics and Neutrino Physics
Authors: Sturrock, P. A.
Bibcode: 2008ApJ...688L..53S
Altcode: 2008arXiv0810.2755S
Recent coordinated power-spectrum analyses of radiochemical solar
neutrino data and the solar irradiance have revealed a highly
significant, high-Q common modulation at 11.85 yr-1. Since
the stability of this frequency points to an explanation in terms of
rotation, this result may be attributable to non-spherically-symmetric
nuclear burning in a solar core with sidereal rotation frequency 12.85
yr-1. The variability of the amplitude (on a timescale of
years) suggests that the relevant nuclear burning is variable as well
as asymmetric. Recent analysis of Super-Kamiokande solar neutrino data
has revealed r-mode-type modulations with frequencies corresponding to
a region with sidereal rotation frequency 13.97 yr-1. If
this modulation is attributed to the RSFP (resonant spin flavor
precession) process, it provides a measurement of the rotation rate
deep in the radiative zone. These two results suggest that the core
rotates significantly more slowly than the radiative zone. If one
accepts an upper limit of 7 MG for the Sun's internal magnetic field,
an RSFP interpretation of the Super-Kamiokande results leads to a lower
limit of 10-12 Bohr magnetons for the neutrino transition
magnetic moment.
Title: Time Frequency Analysis of GALLEX and GNO Solar Neutrino Data
Authors: Sturrock, P. A.
Bibcode: 2008SoPh..252....1S
Altcode: 2008SoPh..tmp..157S
Time - frequency analysis of data from the GALLEX and GNO solar
neutrino experiments shows that some features in power-spectrum
analyses of those datasets are due to aliasing (a result of the fact
that run durations tend to be small multiples of one week). Displays
formed from the published GALLEX data show a sharp discontinuity
that we attribute to some systematic effect. We therefore normalize
data for each of the four experiments in the GALLEX series and
concatenate the resulting normalized data. This step effectively
removes the presumed systematic effect. To help understand the effect
of aliasing, we form time - frequency displays of the two principal
modulations found in the data, at 11.87 year−1 and at
13.63 year−1. We also form time - frequency displays
of datasets formed by subtracting these modulations from the actual
(normalized) data. The results suggest that the true principal
modulation is that at 11.87 year−1. Comparison with
helioseismology data suggests that modulation may be occurring in the
core, perhaps resulting from inhomogeneities and fluctuations in the
nuclear-burning process, and that the sidereal rotation rate of the
core is 12.87 year−1, or 408 nHz.
Title: A Bayesian approach to power-spectrum significance estimation,
with application to solar neutrino data
Authors: Sturrock, P. A.
Bibcode: 2008arXiv0809.0276S
Altcode:
The usual procedure for estimating the significance of a peak in
a power spectrum is to calculate the probability of obtaining that
value or a larger value by chance, on the assumption that the time
series contains only noise (e.g. that the measurements were derived
from random samplings of a Gaussian distribution). However, it is
known that one should regard this P-Value approach with caution. As
an alternative, we here examine a Bayesian approach to estimating the
significance of a peak in a power spectrum. This approach requires that
we consider explicitly the hypothesis that the time series contains
a periodic signal as well as noise. The challenge is to identify a
probability distribution function for the power that is appropriate
for this hypothesis. We propose what seem to be reasonable conditions
to require of this function, and then propose a simple function that
meets these requirements. We also propose a consistency condition, and
check to see that our function satisfies this condition. We find that
the Bayesian significance estimates are considerably more conservative
than the conventional estimates. We apply this procedure to three
recent analyses of solar neutrino data: (a) bimodality of GALLEX data;
(b) power spectrum analysis of Super-Kamiokande data; and (c) the
combined analysis of radiochemical neutrino data and irradiance data.
Title: Analysis of Bimodality in Histograms Formed from GALLEX and
GNO Solar Neutrino Data
Authors: Sturrock, P. A.
Bibcode: 2008SoPh..249....1S
Altcode: 2008SoPh..tmp...70S; 2007arXiv0711.0216S
A histogram display of the solar neutrino capture-rate measurements
made by the GALLEX experiment appears to be bimodal, but that of
the follow-on GNO experiment does not. To assess the significance
of these results, we introduce a "bimodality index" based on the
probability-transform procedure. This confirms that the GALLEX
measurements are indeed bimodal (at the 99.98% confidence level) and
that the GNO measurements are not. Tracking the bimodality index as a
function of time shows that the strongest contribution to bimodality
comes from runs 42 to 62 (i.e., from the time interval 1995.1 to
1996.9). The bimodality index for the first half (runs 1 through
33) is 2.56, whereas that for the second half (runs 33 through 65)
is 7.05. A power-spectrum analysis shows a similar distinction: The
peaks in the power spectrum formed from the second half are stronger
than those in the power spectrum formed from the first half, suggesting
that bimodality and rotational modulation are related.
Title: Analysis and Packaging of Radiochemical Solar Neutrino Data:
A Bayesian Approach
Authors: Sturrock, P. A.; Wheatland, M. S.
Bibcode: 2008SoPh..247..217S
Altcode: 2007arXiv0706.2192S; 2008SoPh..tmp....4S
According to current practice, the results of each run of a
radiochemical solar neutrino experiment comprise an estimate of the
flux and upper and lower error estimates. These estimates are derived
by a maximum-likelihood procedure from the times of decay events in
the analysis chamber. This procedure has the following shortcomings:
(a) published results sometimes include negative flux estimates; (b)
even if the flux estimate is non-negative, the probability distribution
function implied by the flux and error estimates will extend into
negative territory; and (c) the overall flux estimate derived from
the results of a sequence of runs may differ substantially from an
estimate made by a "global" analysis of all of the timing data taken
together. These defects indicate that the usual "packaging" of data
in radiochemical solar neutrino experiments provides an inadequate
summary of the data, which implies a loss of information. This article
reviews this problem from a Bayesian perspective, and we suggest an
alternative scheme for the packaging of radiochemical solar neutrino
data, which we believe is free from these shortcomings.
Title: Time-Frequency Analysis of GALLEX and GNO Solar Neutrino Data:
Evidence Suggestive of Asymmetric and Variable Nuclear Burning
Authors: Sturrock, P. A.
Bibcode: 2008arXiv0802.3370S
Altcode:
Time-frequency analysis of data from the GALLEX and GNO solar neutrino
experiments shows that some features in power-spectrum analyses of those
datasets are due to aliasing. We normalize data for each of the four
experiments in the GALLEX series, concatenate the resulting normalized
data, and then form time-frequency displays. We also form time-frequency
displays of the two principal modulations found in the data, at 11.87
yr-1 and at 13.63 yr-1, and of the datasets formed by subtracting these
modulations from the actual (normalized) data. The results suggest that
the true modulation is that at 11.87 yr-1, consistent with the results
of our earlier analysis of Homestake solar neutrino data. Comparison
with helioseismology data indicates that modulation is occurring either
in the radiative zone just below the tachocline, presumably by the RSFP
(resonant spin-flavor precession) process, or in the core, presumably
due to inhomogeneities and fluctuations in the nuclear-burning process.
Title: An Extension of the Chi-Square Procedure for Non-NORMAL
Statistics, with Application to Solar Neutrino Data
Authors: Sturrock, P. A.
Bibcode: 2008SoPh..247....3S
Altcode:
Using the chi-square statistic, one may conveniently test whether a
series of measurements of a variable are consistent with a constant
value. However, that test is predicated on the assumption that the
appropriate probability distribution function (pdf) is normal in
form. This requirement is usually not satisfied by experimental
measurements of the solar neutrino flux. This article presents an
extension of the chi-square procedure that is valid for any form of
the pdf. This procedure is applied to the GALLEX-GNO dataset, and it is
shown that the results are in good agreement with the results of Monte
Carlo simulations. Whereas application of the standard chi-square test
to symmetrized data yields evidence significant at the 1% level for
variability of the solar neutrino flux, application of the extended
chi-square test to the unsymmetrized data yields only weak evidence
(significant at the 4% level) of variability.
Title: Comparative Analysis of Super-Kamiokande and SNO Solar-Neutrino
Data and the Photospheric Magnetic Field
Authors: Sturrock, P. A.
Bibcode: 2006SoPh..239....1S
Altcode: 2006SoPh..tmp...91S; 2006hep.ph...10065S
We carry out a comparative analysis of Super-Kamiokande, SNO, and
photospheric magnetic-field data for the interval in which these
datasets overlap. This proves to be the interval of operation
of the D2O phase of the SNO experiment. Concerning
solar-rotational modulation, we find that the magnetic-field power
spectrum shows the strongest peaks at the second and sixth harmonics
of the solar synodic rotation frequency [i.e., at 3νrot
and 7νrot]. We find that the restricted Super-Kamiokande
dataset has a strong modulation at the second harmonic, as we found
to be the case for the complete Super-Kamiokande dataset. The SNO
D2O dataset exhibits weak modulation at that frequency,
but shows strong modulation in the band corresponding to the sixth
harmonic (too high a frequency to be detectable in the Super-Kamiokande
dataset, which is available only in five-day bins, whereas SNO data is
available in one-day bins). We estimate the significance level of the
correspondence of the Super-Kamiokande second-harmonic peak with the
corresponding magnetic-field peak to be 0.0004, and the significance
level of the correspondence of the SNO D2O sixth-harmonic
peak with the corresponding magnetic-field peak to be 0.009. By
estimating the amplitude of the modulation of the solar-neutrino flux
at the second harmonic from the restricted Super-Kamiokande dataset,
we find that the weak power at that frequency in the SNO D2O
power spectrum is not particularly surprising. We also examine power
spectra in the neighborhood of 9.43 year−1, which is
the frequency of a particularly strong modulation in the entire
Super-Kamiokande dataset. There is no peak at this frequency in the
power spectrum formed from the restricted Super-Kamiokande dataset. It
is therefore not surprising that we find (in agreement with the recent
analysis by the SNO collaboration) that this peak does not show up in
the SNO D2O dataset either.
Title: Comparative analysis of GALLEX and GNO solar neutrino data
Authors: Sturrock, P. A.; Caldwell, D. O.; Scargle, J. D.
Bibcode: 2006APh....26..174S
Altcode: 2004hep.ph....9064S
Since the GALLEX and GNO datasets were derived from closely related
experiments, there is a natural tendency to merge them. This is perhaps
appropriate for any analysis based on the hypothesis that the solar
neutrino flux is constant, but it is not necessarily appropriate for
an analysis that allows for possible variability, since the GALLEX and
GNO experiments belong to different solar cycles. Moreover, we find
significant differences between the GALLEX and GNO datasets. It appears,
from inspection of the time series and histograms, that GNO measurements
are compatible with the assumption that the solar neutrino flux is
constant, but GALLEX measurements are not. Furthermore, power-spectrum
analysis yields evidence of rotational modulation in GALLEX data
but not in GNO data. We compare our results with those of Pandola,
who claims that GALLEX-GNO data show no evidence for variability.
Title: Power-Spectrum Analysis of Super-Kamiokande Solar Neutrino
Data, Taking into Account Asymmetry in the Error Estimates
Authors: Sturrock, P. A.; Scargle, J. D.
Bibcode: 2006SoPh..237....1S
Altcode: 2006hep.ph....1251S; 2006SoPh..tmp....4S
The purpose of this article is to carry out a power-spectrum analysis
of the Super-Kamiokande five-day dataset that takes account of the
asymmetry in the error estimates. Whereas for symmetrical error
estimates the likelihood analysis involves a linear optimization
procedure, for asymmetrical error estimates it involves a nonlinear
optimization procedure. For most frequencies there is little difference
between the power spectra derived from analyses of symmetrized
error estimates and from asymmetrical error estimates, but this is
not the case for the principal peak in the power spectrum at 9.43
yr −1. A likelihood analysis that takes account of the
error asymmetry leads to a peak with power 13.24 at that frequency,
and a Monte Carlo analysis shows that there is a chance of only 0.1%
of finding a peak this big or bigger in the search band 1 - 36 yr
−1. From this perspective, power-spectrum analysis that
takes account of asymmetry of the error estimates gives evidence
for variability that is significant at the 99.9% level. We comment
briefly on an apparent discrepancy between power-spectrum analyses of
the Super-Kamiokande and SNO solar neutrino experiments.
Title: Power-spectrum analyses of Super-Kamiokande solar neutrino
data: Variability and its implications for solar physics and neutrino
physics
Authors: Sturrock, P. A.; Caldwell, D. O.; Scargle, J. D.; Wheatland,
M. S.
Bibcode: 2005PhRvD..72k3004S
Altcode: 2004hep.ph....8017S
Since rotational or similar modulation of the solar neutrino flux
would seem to be incompatible with the currently accepted theoretical
interpretation of the solar neutrino deficit, it is important to
determine whether or not such modulation occurs. There have been
conflicting claims as to whether or not power-spectrum analysis
of the Super-Kamiokande solar neutrino data yields indication of
variability. Comparison of these claims is complicated by the fact that
the relevant articles may use different data sets, different methods of
analysis, and different procedures for significance estimation. The
purpose of this article is to clarify the role of power-spectrum
analysis. To this end, we analyze primarily the Super-Kamiokande 5-day
data set, and we use a standard procedure for significance estimation as
used by the Super-Kamiokande collaboration. We then analyze this data
set, with this method of significance estimation, using six methods
of power-spectrum analysis. Five of these have been used in published
articles, and the other is a method that might have been used. We
find that, with one exception, the results of these calculations are
consistent with those of previously published analyses. We find that
the power of the principal modulation (that at 9.43yr-1)
is greater in analyses that take account of error estimates than in
the basic Lomb-Scargle analysis that does not take account of error
estimates. The corresponding significance level ranges between 98%
and 99.3%, depending on the details of the analysis. Concerning the
recent article by Koshio, we find that we can reproduce the results
of his power-spectrum analysis but not the results of his Monte
Carlo simulations, and we have a suggestion that may account for
the difference. We also comment on a recent article by Yoo et al. We
discuss, in terms of subdominant processes, possible neutrino-physics
interpretations of the apparent variability of the Super-Kamiokande
measurements, and we suggest steps that could be taken to resolve the
question of variability of the solar neutrino flux.
Title: Evidence for solar neutrino flux variability and its
implications
Authors: Caldwell, D. O.; Sturrock, P. A.
Bibcode: 2005APh....23..543C
Altcode: 2003hep.ph....9191C
Although KamLAND apparently rules out resonant-spin-flavor-precession
(RSFP) as an explanation of the solar neutrino deficit, the solar
neutrino fluxes in the Cl and Ga experiments appear to vary with solar
rotation. Added to this evidence, summarized here, a power spectrum
analysis of the Super-Kamiokande data reveals significant variation
in the flux matching a dominant rotation rate observed in the solar
magnetic field in the same time period. Three frequency peaks, all
related to this rotation rate, can be explained quantitatively. A
Super-Kamiokande paper reported no time variation of the flux, but
showed the same peaks, there interpreted as statistically insignificant,
due to an inappropriate analysis. This modulation is small (7%) in
the Super-Kamiokande energy region (and below the sensitivity of the
Super-Kamiokande analysis) and is consistent with RSFP as a subdominant
neutrino process in the convection zone. The data display effects that
correspond to solar-cycle changes in the magnetic field, typical of
the convection zone. This subdominant process requires new physics: a
large neutrino transition magnetic moment and a light sterile neutrino,
since an effect of this amplitude occurring in the convection zone
cannot be achieved with the three known neutrinos. It does, however,
resolve current problems in providing fits to all experimental estimates
of the mean neutrino flux, and is compatible with the extensive evidence
for solar neutrino flux variability.
Title: Combined and Comparative Analysis of Power Spectra
Authors: Sturrock, P. A.; Scargle, J. D.; Walther, G.; Wheatland, M. S.
Bibcode: 2005SoPh..227..137S
Altcode: 2005astro.ph..2050S
In solar physics, especially in exploratory stages of research,
it is often necessary to compare the power spectra of two or more
time series. One may, for instance, wish to estimate what the power
spectrum of the combined data sets might have been, or one may wish to
estimate the significance of a particular peak that shows up in two
or more power spectra. One may also on occasion need to search for a
complex of peaks in a single power spectrum, such as a fundamental and
one or more harmonics, or a fundamental plus sidebands, etc. Visual
inspection can be revealing, but it can also be misleading. This
leads one to look for one or more ways of forming statistics,
which readily lend themselves to significance estimation, from two
or more power spectra. We derive formulas for statistics formed from
the sum, the minimum, and the product of two or more power spectra. A
distinguishing feature of our formulae is that, if each power spectrum
has an exponential distribution, each statistic also has an exponential
distribution. The statistic formed from the minimum power of two or more
power spectra is well known and has an exponential distribution. The
sum of two or more powers also has a well-known distribution that is
not exponential, but a simple operation does lead to an exponential
distribution. Concerning the product of two or more power spectra,
we find an analytical expression for the case n = 2, and a procedure
for computing the statistic for n > 2. We also show that some quite
simple expressions give surprisingly good approximations.
Title: Comparative Analysis of Super-Kamiokande 10-day-bin and
5-day-bin Datasets
Authors: Sturrock, P. A.; Caldwell, D. O.; Scargle, J. D.; Walther,
G.; Wheatland, M. S.
Bibcode: 2004AAS...204.5301S
Altcode: 2004BAAS...36..755S
The Super-Kamiokande Collaboration has released two datasets suitable
for time-series analysis: one packaged in 10-day bins and, more
recently, one packaged in 5-day bins. We have analyzed both datasets by
a likelihood power-spectrum procedure that is to be preferred over the
more usual Lomb-Scargle procedure since it takes account of all of the
available data, whereas the Lomb-Scargle procedure uses only a fraction
of the data. Analysis of these two datasets yields power spectra that
are similar but have some notable differences. Comparative analysis
of these two datasets shows that the significant differences are due
to aliasing. Since each dataset represents highly regular sampling,
a modulation at frequency vM will be accompanied by alias
periodicities at frequencies ěrt vT - vM
ěrt and at vT + vM, where vT is the
sampling frequency. As indications of real oscillations, we have looked
for peaks in the two power spectra which are strong in both, but for
which the power in the 5-day power spectrum is larger than that in
the 10-day power spectrum. This plot identifies three peaks of special
interest. One of these may be attributed to modulation associated with
solar rotation, and the other two may be attributed to modulation
associated with an internal r-mode oscillation. These periodicities
appear to be statistically significant. We thank the Super-Kamiokande
consortium for making these datasets available. This work was supported
by NSF grant AST-0097128 and DOE grant DE-FG03-91ER40618.
Title: Comments on `Possible Role of MHD Waves in Heating the Solar
Corona' by Dwivedi and Pandey
Authors: Klimchuk, J. A.; Porter, L. J.; Sturrock, P. A.
Bibcode: 2004SoPh..221...47K
Altcode:
We comment on the recent paper by Dwivedi and Pandey (Solar Physics216,
59, 2003). Parts of that paper closely reproduce, without reference,
material that we had published previously, while other parts that
deviate from our earlier analysis contain several critical flaws. We
show that magnetoacoustic waves are capable of heating the corona with
a modest enhancement in the coefficient of compressive viscosity.
Title: A Code of Ethics for Referees?
Authors: Sturrock, Peter A.
Bibcode: 2004EOSTr..85R.160S
Altcode:
I have read with interest the many letters commenting on the pros and
cons of anonymity for referees. While I sympathize with writers who
have suffered from referees who are incompetent or uncivil, I also
sympathize with those who argue that one would simply exchange one set
of problems for another if journals were to require that all referees
waive anonymity. Perhaps there is a more direct way to address the
issue. It may help if guidelines for referees were to include a code
of ethics.
Title: Analysis of Super-Kamiokande 5 Day Measurements of the Solar
Neutrino Flux
Authors: Sturrock, P. A.
Bibcode: 2004ApJ...605..568S
Altcode: 2003hep.ph....9239S
Data in 5 day bins, recently released by the Super-Kamiokande
consortium, have been analyzed by a likelihood procedure that
has certain advantages over the Lomb-Scargle procedure used by the
consortium. The two most prominent peaks in the power spectrum of the
10 day data were at 9.42 and 26.57 yr-1, and it was clear
that one was an alias of the other caused by the regularity of the
binning. There were reasons to believe that the 9.42 yr-1
peak was an alias of the 26.57 yr-1 peak, but analysis
of the 5 day data makes it clear that the reverse is the case. In
addition to a strong peak near 9.42 yr-1, we find peaks at
43.72 and 39.28 yr-1. After comparing this analysis with a
power-spectrum analysis of magnetic field data, we suggest that these
three peaks may be attributed to a harmonic of the solar rotation rate
and to an r-mode oscillation with spherical harmonic indices l=2, m=2.
Title: Time-Series Analysis of Super-Kamiokande Measurements of the
Solar Neutrino Flux
Authors: Sturrock, P. A.
Bibcode: 2003ApJ...594.1102S
Altcode: 2003hep.ph....4073S
A recently released data set of Super-Kamiokande data comprises 184
bins of about 10 days each, from 1996 May to 2001 July. The power
spectrum of the acquisition times has a huge peak at frequency ν=35.98
(period 10.15 days), where frequencies are measured in cycles per year,
leading to severe aliasing of the power spectrum that complicates the
analysis. The strongest peak in the range 0-100 in a power spectrum
formed by a likelihood procedure is at ν=26.57 (period 13.75 days)
with S=11.26. For the range 0-40, the second-strongest peak is at 9.42
(period 38.82 days) with S=7.3. Since 26.57+9.42=35.99, we infer that
the weaker peak at 9.42 is an alias of the stronger at 26.57. When we
subtract the oscillation at 26.57 from the data, the resulting CLEAN
spectrum has no peak with power in excess of 6.3 in the range 0-100, and
none with power in excess of 5.0 in the range 0-40. We note that 26.57
falls in the band 26.36-27.66, formed from twice the range of synodic
rotation frequencies of an equatorial section of the Sun. We find from
the shuffle test that the probability of obtaining a peak of S=11.26
or more by chance in this band is 0.1%. This new result therefore
supports previous evidence, found in Homestake and GALLEX-GNO data,
for rotational modulation of the solar neutrino flux. The frequency
25.57 yr-1 points to a source of modulation at or near
the tachocline.
Title: Statistics of the Chi-Square Type, with Application to the
Analysis of Multiple Time-Series Power Spectra
Authors: Sturrock, P. A.; Wheatland, M. S.
Bibcode: 2003astro.ph..7353S
Altcode:
It is often necessary to compare the power spectra of two or more
time series: one may, for instance, wish to estimate what the power
spectrum of the combined data sets might have been, or one may wish
to estimate the significance of a particular peak that shows up in two
or more power spectra. Also, one may occasionally need to search for a
complex of peaks in a single power spectrum, such as a fundamental and
one or more harmonics, or a fundamental plus sidebands, etc. Visual
inspection can be revealing, but it can also be misleading. This
leads one to look for one or more ways of forming statistics, which
readily lend themselves to significance estimation, from two or more
power spectra. The familiar chi-square statistic provides a convenient
mechanism for combining variables drawn from normal distributions, and
one may generalize the chi-square statistic to be any function of any
number of variables with arbitrary distributions. In dealing with power
spectra, we are interested mainly in exponential distributions. One
well-known statistic, formed from the sum of two or more variables
with exponential distributions, satisfies the gamma distribution. We
show that a transformation of this statistic has the convenient
property that it has an exponential distribution. We introduce two
additional statistics formed from two or more variables with exponential
distributions. For certain investigations, we may wish to study the
minimum power (as a function of frequency) drawn from two or more
power spectra. In other investigations, it may be helpful to study
the product of the powers. We give numerical examples and an example
drawn from our solar-neutrino research.
Title: Implications of the variability of the solar neutrino flux
Authors: Caldwell, D. O.; Sturrock, P. A.
Bibcode: 2003NuPhS.124..239C
Altcode:
Analyses of the Cl and Ga solar neutrino data yield statistically
compelling evidence for rotational (and related) modulations of the
solar neutrino flux. While a neutrino transition magnetic moment and
the Resonant-Spin-Flavor-Precession (RSFP) process have given at least
as good a fit to time-averaged solar data as any other solution, the
observed variability fits no present solution. The Cl data show mainly a
synodic rotation frequency of 12.88 y-1 (period 28.4 d) which
display a latitudinal effect, just as does exactly the same frequency
seen by SXT in coronal X-rays. While each data set has some of the
other's dominant frequency, that of Ga is mainly 13.59 y-1,
but it is equatorial, just as are the SXT coronal X-rays of that
same frequency. The Ca data in narrow bins show one peak of nearly
non-oscillational flux value and the other of about half that, with
bimodality at the 99.99% CL. Convolution with SOHO/MDI helioseismology
data shows the Ca effect is on the solar equator in the convection
zone at 0.8 Rsolar, yielding exactly the E/Δm2
value used for RSFP solutions to suppress 7Be neutrinos;
hence Δm2 ~ 10-8 eV2. The data can be
explained by two rotating solar fields, the higher latitude one being
anchored in the radiative zone, the tilt of the solar axis, and the Ga
data being nearly all pp neutrinos produced at ~ 0.2 Rsolar,
whereas the others come from the solar center (~ 0.05 Rsolar)
. Supported in part by the National Science Foundation and NASA.
Title: Further Evidence for Neutrino Flux Variability from
Super-Kamiokande Data
Authors: Caldwell, D. O.; Sturrock, P. A.
Bibcode: 2003hep.ph....5303C
Altcode:
While KamLAND apparently rules out Resonant-Spin-Flavor-Precession
(RSFP) as an explanation of the solar neutrino deficit, the solar
neutrino fluxes in the Cl and Ga experiments vary with solar rotation
rates. Added to this evidence, summarized here, a power spectrum
analysis of the Super-Kamiokande data reveals (99.9% CL) an oscillation
in the band of twice the equatorial rotation frequencies of the solar
interior. An m=2 magnetic structure and RSFP, perhaps as a subdominant
process, would give this effect. Solar cycle data changes are seen,
as expected for convection zone modulations.
Title: Time-Series Analysis of Solar Neutrino Data: Evidence for
Rieger-type Periodicities and their Interpretation as R-Modes
Authors: Sturrock, P. A.
Bibcode: 2003SPD....34.0805S
Altcode: 2003BAAS...35..822S
Power-spectrum analysis of the Homestake and GALLEX-GNO radiochemical
solar neutrino data has shown evidence of the effects of solar rotation
and indications of two oscillations that are well known in solar
physics: one at about 154 days period (the Rieger periodicity) and
another at about 52 days period. We speculate that these periodicities,
and another well known periodicity at about 77 days, are due to r-mode
oscillations with spherical harmonic indices l = 3 and m = 1, 2, and
3. In the rotating frame, these would have frequencies fR/6, fR/3,
and fR/2, where fR is the sidereal rotation rate where the waves are
excited. We have combined power spectra formed from both neutrino
datasets, and then tested the combined spectrum for the presence of
peaks at four related frequencies: the above three r-mode frequencies,
and the corresponding synodic frequency fR - 1. In the range 0 - 20
y-1, we find a strong peak at 13.88 y-1 which falls in the rotation
frequency range of the radiative zone. By applying the shuffle test,
we find that the probability of obtaining by chance a peak this big or
bigger in this range is less than 0.1%. This analysis suggests that
Rieger-type periodicities are caused by r-mode oscillations in the
radiative zone, and that these oscillations may lead to modulation of
the solar neutrino flux, probably by the RSFP (Resonant Spin Flavor
Precession) mechanism. This research was supported by the National
Science Foundation.
Title: Variability of the Solar Neutrino Flux
Authors: Sturrock, P. A.
Bibcode: 2003SPD....34.2605S
Altcode: 2003BAAS...35R.854S
The question of variability of the solar neutrino flux is important for
particle physics and also for solar physics. It is generally believed
that the solar neutrino flux is constant and that the deficit can
be explained by the MSW (Mikhevev-Smirnov-Wolfenstein) effect which
converts electron neutrinos into mu or tau neutrinos as they propagate
through the dense solar interior. Variability of the neutrino flux would
indicate that the MSW effect must be supplemented by some other process
such as Resonant Spin-Flavor Precession (RSFP) that changes a neutrino
into an antineutrino of different flavor. This process can explain
variability since it involves the Sun's internal magnetic field. If
(as is likely) the magnetic field is not cylindrically symmetric, the
RSFP process would lead to modulation at the synodic rotation frequency
and/or a harmonic of this frequency. We present the results
of time-series analysis of solar-neutrino data from the Homestake,
GALLEX-GNO, SAGE, and Super-Kamiokande experiments. We find evidence
for modulation at 12.88 y-1, consistent with the rotation rate of the
radiative zone, at 13.59 y-1, consistent with the rotation rate of the
deep convection zone, and at 26.57 y-1, consistent with the harmonic
of the rotation rate at or near the tachocline. We present estimates
of the statistical significance of these results, and we discuss the
significance of the bimodal structure of the histogram of GALLEX-GNO
flux estimates. If the present evidence for variability of the
solar neutrino flux is substantiated by future analysis of additional
data, neutrino measurements may yield new insight into the strength,
structure, and variability of the Sun's internal magnetic field. This work was supported by the National Science Foundation.
Title: Combined and Comparative Time-Series Spectrum Analysis
Authors: Sturrock, P. A.
Bibcode: 2003astro.ph..4148S
Altcode:
It is often necessary to compare the power spectra of two or more time
series. One may, for instance, wish to estimate what the power spectrum
of the combined data sets might have been. One might also wish to
estimate the significance of a particular peak that shows up in two or
more power spectra. Visual comparison can be revealing, but it can also
be misleading. This leads one to look for one or more ways of forming
statistics, which lend themselves to significance estimation, from two
or more power spectra. We here propose two such statistics, one that is
most useful for the combined study of two or more similar time series,
and another that is more useful for the study of dissimilar time series.
Title: Preliminary Time-Series Analysis of Super-Kamiokande
Measurements of the Solar Neutrino Flux
Authors: Sturrock, P. A.; Caldwell, D. O.
Bibcode: 2002AAS...20113002S
Altcode: 2002BAAS...34.1314S
We report an analysis of an early release of Super-Kamiokande data
comprising 184 bins, about 10 days each, from May 1996 to July
2001. Flux estimates vary over a range of more than 2:1, and the
mean ratio of error estimates to flux estimates is 0.14. Due to the
regularity of the binning, the power spectrum of the acquisition times
has a huge peak (power S > 120) at frequency nu = 35.98, where
frequencies are measured in cycles per year and power measurements are
such that the probability of obtaining a peak of strength S or more by
chance at a specified frequency is exp(-S). Such regularity inevitably
leads to aliasing of a power spectrum. The strongest peak in the range
0 - 100 in a power spectrum formed by a relative-likelihood procedure is
at nu = 26.57 with S = 11.1. For the range 0 - 40, the second-strongest
peak is at nu = 9.41 with S = 7.33. Since 26.57 + 9.41 = 35.98, it is
probable that the weaker peak at 9.41 is an alias of the stronger at
26.57. Indeed, when we subtract the 26.57 oscillation from the data,
the resulting "CLEAN" spectrum has no peak stronger than S >6.1 in
the range 0 - 100, and none stronger than 5.5 in the range 0 - 40. We
note that 26.57 falls in the band 26.46 - 27.66, formed from twice
the range of synodic rotation frequencies of an equatorial section
of the solar convection zone. Such oscillations, attributable to "m
= 2" structures, are not uncommon in solar data. We find from the
shuffle test that the probability of obtaining a peak of S = 11.1
or more by chance in this band is 0.2%. This new result therefore
supports previous evidence, found in Homestake and GALLEX-GNO data,
for rotational modulation of the solar neutrino flux. We thank the
Super-Kamiokande consortium for making this data available. This work
was supported by NSF grant AST-0097128 and DOE grant DE-FG03-91ER40618.
Title: Pre-eruptive Coronal Model for a Magnetic Flux-tube
Authors: Weber, M. A.; Sturrock, P. A.
Bibcode: 2002AAS...200.2006W
Altcode: 2002BAAS...34Q.674W
Aly conjectured that the energy of a closed magnetic-field configuration
above the photosphere cannot exceed the energy of the corresponding
open-field configuration with the same normal field distribution at the
photosphere. This limitation, later proved by Aly for a planar geometry
and by Sturrock for a curved geometry, has important consequences for
modeling coronal dynamics, especially solar eruptions such as flares and
CMEs, that involve the release of magnetic energy. The above analyses
were based on the assumption that all field lines are connected to the
photosphere. However, one can conceive of a pre-eruption configuration
involving magnetic flux that does not thread the photosphere. A toroidal
current-carrying wire embedded in a dipolar arcade can have arbitrarily
large magnetic energy relative to the potential configuration as its
radius goes to zero, but this would be an unphysical model for the
solar corona. We inquire into whether there exist force-free field
solutions with ``disconnected'' flux and energy greater than the
open-field energy. We examine a magnetic-field model comprising a
toroidal, force-free flux tube in the equatorial plane, restrained
by an overlying arcade with dipole boundary conditions, analyzing the
configuration by the generating-function (Grad-Shafranov) method. We
solve the equations numerically by an iterative procedure, relaxing
the flux-tube and the dipole field separately, alternately allowing
their interface to adjust. We confirm that it is indeed possible for
the energy of such a closed magnetic-field configuration to exceed the
Aly-Sturrock limit. However, it requires such a large amount of twist
that the flux-tube would be unstable in a full 3-D MHD treatment. We
gratefully acknowledge that this research was supported by NASA grants
NAS 8-37334 and NAG 5-9784.
Title: Variability of the Solar Neutrino Flux
Authors: Sturrock, P. A.; Scargle, J. D.; Walther, G.; Weber, M. A.;
Wheatland, M. S.
Bibcode: 2002AAS...200.8904S
Altcode: 2002BAAS...34..791S
Several tests of the available data provide evidence for variability of
the solar neutrino flux. The variance of the Homestake measurements is
larger than expected of a constant flux, and varies with heliographic
latitude. The Homestake power spectrum contains a peak at 12.88
y-1 (period 28.4 days), corresponding to a sidereal
rotation frequency of 440 nHz, close to that of the radiative zone. The
power spectrum of GALLEX-GNO data contains the 12.88 y-1
peak and a stronger peak at 13.59 y-1 (period 26.9 days),
corresponding to a sidereal rotation frequency of 462 nHz, that of the
equatorial convection zone at normalized radius 0.85. Further evidence
for time variation comes from the bimodality of the GALLEX-GNO and SAGE
histograms. Joint spectrum analysis of the Homestake and GALLEX-GNO
data yields evidence for the influence of r-mode oscillations [with
l = 3, m = \{1,2,3\}] associated with the same sidereal rotation rate
(13.88 y-1 or 440 nHz) found previously. The periods of these
oscillations (158, 79, and 53 days, respectively) are close to those of
known Rieger-type oscillations, and therefore point to the radiative
zone as the source of these oscillations. A subset of these tests,
selected to be independent, yield results that could arise by chance
from a constant flux with probabilities ranging from 0.1 to 0.0001. If
there are no relevant experimental systematic effects, and if the tests
are valid and statistically independent, the combined estimates yield a
probability of 10-15 that the results are compatible with a
constant flux. A variable flux implies that neutrinos have a significant
magnetic moment, and that neutrino measurements may be used to probe
the Sun's internal magnetic field and internal dynamics. This work
was supported by NASA grants NAS 8-37334 and NAG 5-9784, NSF grant
AST-0097128, and the NASA Applied Information Systems Research Program.
Title: Solar Neutrino Flux: Implications of Intrinsic Variability
Authors: Caldwell, D. O.; Sturrock, P. A.
Bibcode: 2002APS..APR.X7002C
Altcode:
The Resonance-Spin-Flavor-Precession (RSFP) process helps explain
the evidence for the solar neutrino flux variability presented in the
previous abstract. This requires a νe transition magnetic
moment as could be found in proposed experiments. The RSFP process gives
a good fit to all solar neutrino data. Like the SMA fit, the resonance
is near the 0.86 MeV ^7Be line, but the RSFP resonance asymptotes to
1/2, unlike unity for the SMA, so it gives a flat spectrum as measured
by the water detectors. The solar rotation rate deduced from the Ga
(and also seen in the Cl data) is at a solar density which gives the
same E/Δ m^2 value for the resonance position as that required for a
fit to all the solar data. This remarkable agreement yields for E=0.86
MeV a Δ m^2 ~ 10-8 eV^2. Details of the flux variability
require more complexity than just RSFP, but (as would be expected from
the Δ m^2) the MSW LOW solution also contributes. The two overlapping
resonances produce the observed bimodal Ga rate distribution, while
giving very little variability at the energy of the water detectors
where the LOW and RSFP effects are nearly the same.
Title: Solar Neutrino Flux: Evidence for Intrinsic Variability
Authors: Sturrock, P.; Walther, G.; Weber, M.; Scargle, J.;
Wheatland, M.
Bibcode: 2002APS..APR.X7001S
Altcode:
Analyses of Homestake and GALLEX-GNO data yield persuasive evidence for
rotational modulation and related modulations of the solar neutrino
flux. We find in Homestake data evidence that (1) the variance is
significantly larger than that found in Monte Carlo simulations; (2)
the power spectrum contains a significant peak at 12.88 y-1
(period 28.4 days); (3) the spectrum also contains four sidebands
displaced by ± 1 y-1 and ± 2 y-1; (4) the
variance of the data shows a significant heliographic N/S asymmetry;
(5) a time series reconstructed from power spectrum analysis exhibits a
heliographic-latitude-dependent variance; and (6) the spectrum formed
from the variance of the reconstructed flux has a notable peak at
1 y-1. We find from analysis of GALLEX-GNO data that (7)
there is a significant periodicity at 13.59 y-1 (period
26.9 days); and (8) the histogram is bimodal. From a comparative
analysis of Homestake and GALLEX-GNO data, we find (9) evidence for
variations attributable to r-mode oscillations with l = 3, m = 1,2,3
in a region with synodic rotation rate 12.88 y-1. From
analysis of X-ray data acquired by the SXT instrument on Yohkoh, we
find that the corona exhibits two discrete rotation rates, and that
(10) the coronal rotation frequencies are virtually identical to the
principal frequencies in the Homestake and GALLEX-GNO spectra.
Title: Comparative Analysis of GALLEX-GNO Solar Neutrino Data and
SOHO/MDI Helioseismology Data: Further Evidence for Rotational
Modulation of the Solar Neutrino Flux
Authors: Sturrock, Peter A.; Weber, Mark A.
Bibcode: 2002ApJ...565.1366S
Altcode: 2001astro.ph..3154S
Recent histogram analysis of GALLEX-GNO and SAGE data indicates that
the solar neutrino flux, in the energy range of gallium experiments,
varies on a timescale of weeks. Such variability could be caused by
modulation of the neutrino flux by an inhomogeneous magnetic field in
the solar interior if neutrinos have a nonzero magnetic moment. We may
then expect the detected neutrino flux to oscillate with a frequency set
by the synodic rotation frequency in the region of the solar interior
that contains the magnetic structure. We investigate this possibility
by carrying out a comparative analysis of the GALLEX-GNO solar neutrino
data and estimates of the solar internal rotation rate derived from the
MDI helioseismology experiment on the SOHO spacecraft. We find that
while the Lomb-Scargle spectrum does not show a significant peak in
the band appropriate to the radiative zone, it does show two closely
spaced peaks in the band appropriate to the convection zone. In order
to explore the relationship of these features to the Sun's internal
rotation, we introduce a ``resonance statistic'' that is a measure of
the degree of ``resonance'' of oscillations in the neutrino flux and the
solar rotation as a function of radius and latitude. A two-dimensional
map of the resonance statistic indicates that the modulation is
occurring in the convection zone, near the equator. In order to derive a
significance estimate for this result, we next evaluate the integral of
this statistic over selected equatorial sections corresponding to the
convection zone and the radiative zone. This statistic yields strong
evidence that modulation is occurring in the convection zone and no
evidence that modulation is occurring in the radiative zone.
Title: Differential Rotation of the Soft-X-Ray Corona over a Solar
Cycle
Authors: Weber, M. A.; Sturrock, P. A.
Bibcode: 2002mwoc.conf..347W
Altcode:
The Yohkoh Soft X-ray Telescope has provided unprecedented, high
spatial and temporal resolution of the solar corona in X-rays for
nearly a complete activity cycle. Building upon earlier work, we
perform time-series analysis on bins of the full-disk images (SFDs)
to describe the differential rotation of the corona over latitude and
cycle phase. The bins are formed by integrating over localized regions
in heliographic longitude and latitude. We find that the rotation
signal in the data comprises a few (usually two) components which
are relatively rigid with respect to time and latitude. The relative
strength of these components varies over latitude, which may be the
reason previous analyses have indicated a ``slightly differential''
rotation profile over latitude.
Title: Comparative Analysis of Solar Neutrino Data and SXT X-ray Data
Authors: Sturrock, P. A.; Weber, M. A.
Bibcode: 2002mwoc.conf..323S
Altcode:
There is some evidence that the low-energy component of the solar
neutrino flux exhibits rotational modulation. The power spectrum
of the GALLEX-GNO neutrino data has a peak at 13.59 +/- 0.06 y-1
(period = 26.88 +/- 0.12 days), that is within the band of synodic
rotation rates of the solar convection zone. In order to relate the
neutrino time series to the Sun's internal rotation, we have formed a
"resonance statistic" that is a measure of the degree of "resonance"
of the neutrino flux with the Sun's internal rotation, as determined by
MDI. A map of this statistic indicates that the source of the modulation
of the solar neutrino flux is located deep in the convection zone. We
have now carried out a comparative analysis of GALLEX-GNO neutrino
data and SXT X-ray data. We have formed the logarithm of the mean
daily X-ray flux (to de-emphasize active regions) and then formed
the mean power spectrum for five 15-degree latitude bands centered
on 30S, 15S, the equator, 15N, and 30N. The mean spectrum peaks at
13.54 +/- 0.08 y-1 (period = 26.98 +/- 0.16 days). Taking account of
the error bars, the neutrino peak frequency and SXT peak frequency
are indistinguishable. We find that the neutrino and X-ray waveforms
are approximately in anti-phase. We have also formed a map of the
resonance statistic formed from the SXT power spectrum and the MDI
rotation estimates. The neutrino-rotation and X-ray-rotation resonance
maps are very similar, and both point to the same location deep in the
convection zone. These results suggest that modulation of the low-energy
solar neutrino flux and long-lived quasi-rigid rotation of the corona
have a common cause. It seems possible that a magnetic structure deep
in the convection zone leads to (a) an enhancement of the X-ray flux,
and (b) a diminution of the observed neutrino flux. This diminution
could be caused by any one of several proposed mechanisms by which an
electron neutrino, with non-zero magnetic moment and non-zero mass, may
be converted into a neutrino of different flavor and/or opposite spin.
Title: Comparative Analysis of GALLEX-GNO Neutrino Data, SOHO-MDI
Helioseismology Data, and SXT X-ray Data
Authors: Sturrock, P. A.; Weber, M. A.
Bibcode: 2001AGUSM..SP22A07S
Altcode:
There have been many claims of correlation between solar
neutrino measurements and various solar indices, including coronal
brightness. These claims have been greeted with skepticism, largely
on the grounds that there is no obvious mechanism to explain the
correlation. We review our recent comparative analysis of GALLEX-GNO
neutrino data and SOHO-MDI measurements of internal solar rotation,
which yields evidence of rotational modulation of the solar neutrino
flux. We attribute this modulation to the influence of internal
magnetic structures on neutrino propogation. The coronal X-ray flux
also exhibits rotational modulation. From this viewpoint, some kind of
correlation between neutrino measurements and X-ray measurements is
to be expected. We compare the spectra of the two time series with
each other and with the distribuition of rotation frequencies in
the solar interior. We also examine the correlation spectrum, which
gives information about the frequencies responsible for correlation,
and about the relative phases of the two oscillations. In order to
relate these new studies with earlier studies (which did not involve
spectrum analysis), we process the X-ray data in just the same way
that the neutrino experiments process the solar neutrino flux. In this
way we obtain a sequence of proxy X-ray measurements corresponding
to the same start times, end times, and decay time, that apply to the
GALLEX-GNO runs. We can then carry out a simple correlation analysis
of the neutrino and X-ray run sequences. We shall present the results
of these studies and compare these results with earlier claims of
correlation between neutrino measurements and solar indices. We wish
to acknowledge support by NASA grants NAS 8-37334 and NAGW-2265 and
NSF grant ATM-9910215.
Title: Energy Content of a Possible Pre-CME Magnetic Field
Configuration
Authors: Weber, M. A.; Sturrock, P. A.
Bibcode: 2001AGUSM..SH51B05W
Altcode:
The total free energy of coronal magnetic-field configurations is
significant for studies of solar eruptions such as flares and CMEs. It
was conjectured by Aly that the energy of a closed magnetic-field
configuration above the photosphere cannot exceed the energy of
the corresponding open-field configuration with the same normal
field distribution at the photosphere. This conjecture was later
analyzed by Aly for a planar geometry and by Sturrock for a curved
geometry. However, these analyses both involved the assumption that
all field lines thread the photosphere. Since one can conceive of a
pre-eruption configuration involving magnetic flux that does not thread
the photosphere, it is interesting to determine whether this variation
can lead to models for which the magnetic energy exceeds the Aly
limit. We have therefore examined a force-free field model comprising
a toroidal twisted flux-tube, above the solar equator, held in place
by an overlying dipolar field. We consider only magnetic stresses, and
analyze the configuration by the generating-function (Grad-Shafranov)
method. We solve the equations numerically by an iterative procedure,
relaxing the flux-tube field and the dipole field in turn. We find
that it is indeed possible for the energy of a closed magnetic-field
configuration to exceed the Aly limit. This work was supported in part
by NASA grant NSS 8-37334.
Title: Histogram Analysis of GALLEX, GNO, and SAGE Neutrino Data:
Further Evidence for Variability of the Solar Neutrino Flux
Authors: Sturrock, Peter A.; Scargle, Jeffrey D.
Bibcode: 2001ApJ...550L.101S
Altcode: 2000astro.ph.11228S
If the solar neutrino flux were constant, as is widely assumed, the
histogram of flux measurements would be unimodal. On the other hand,
sinusoidal or square-wave modulation (either periodic or stochastic)
may lead to a bimodal histogram. We here present evidence that the
neutrino flux histogram is in fact bimodal. We analyze all available
data from gallium experiments, coordinating results from the GALLium
EXperiment and the Gallium Neutrino Observatory experiment into one data
set and adopting results from the Soviet-American Gallium Experiment
as another data set. The two histograms, from the two data sets, are
consistent in showing peaks in the ranges 45-75 and 90-120 SNU, with a
valley in between. By combining the data into one data set, we may form
more detailed histograms; these strengthen the case that the flux is
bimodal. A preliminary statistical analysis indicates that the bimodal
character of the solar neutrino flux is highly significant. Since
the upper peak is close to the expected flux (120-140 SNU), we may
infer that the neutrino deficit is due to time-varying attenuation
of the flux produced in the core. We estimate the timescale of this
variation to be in the range 10-60 days. Attenuation that varies on
such a timescale is suggestive of the influence of solar rotation
and points toward a process involving the solar magnetic field in
conjunction with a nonzero neutrino magnetic moment.
Title: Metastable Magnetic Configurations and Their Significance
for Solar Eruptive Events
Authors: Sturrock, Peter A.; Weber, Mark; Wheatland, Michael S.;
Wolfson, Richard
Bibcode: 2001ApJ...548..492S
Altcode:
Solar flares and coronal mass ejections (CMEs) involve the sudden
release of magnetic energy that can lead to the ejection from the Sun of
large masses of gas with entrained magnetic field. In dynamical systems,
such sudden events are characteristic of metastable configurations that
are stable against small perturbations but unstable to sufficiently
large perturbations. Linear stability analysis indicates whether
or not the first requirement is met, and energetic analysis can
indicate whether or not the second requirement is met: if a magnetic
configuration that is stable against small perturbations can make a
transition to a lower energy state, then it is metastable. In this
paper, we consider a long twisted flux tube, anchored at both ends
in the photosphere and restrained by an overlying magnetic arcade. We
argue from a simple order-of-magnitude calculation that, for appropriate
parameter values, it is energetically favorable for part of the flux
tube to erupt into interplanetary space, even when the configuration
is stable according to linear MHD stability theory. The properties
of metastable magnetic configurations may be relevant to CMEs and to
other explosive astrophysical events such as solar flares.
Title: Histogram Analysis of GALLEX, GNO and SAGE Neutrino Data:
Further Evidence for Variability of the Solar Neutrino Flux
Authors: Sturrock, P. A.; Scargle, J. D.
Bibcode: 2000AAS...197.3107S
Altcode: 2000BAAS...32.1448S
If the solar neutrino flux were constant, as is widely assumed, the
histogram of flux measurements would be unimodal. On the other hand,
sinusoidal or square-wave modulation may lead to a bimodal histogram. We
here present evidence that the neutrino flux histogram is in fact
bimodal. We analyze all available data from gallium experiments,
coordinating results from the GALLEX and GNO experiments into one
data set, and adopting results from the SAGE experiment as another
data set. The two histograms, from the two data sets, are consistent
in showing peaks in the range 45 - 75 SNU and 90 - 120 SNU, and a
valley in between. By combining the data into one data set, we may form
more detailed histograms; these strengthen the case that the flux is
bimodal. A preliminary statistical analysis indicates that the bimodal
character of the solar neutrino flux is highly significant. A bimodal
flux distribution points towards variability, and variability points
towards a nonzero neutrino magnetic moment. We wish to acknowledge
support (for PAS) by NASA grants NAS 8-37334 and NAGW-2265 and NSF
grant ATM-9910215 and (for JDS) by the NASA Applied Information Systems
Research Program.
Title: A Maximum-Entropy Approach to Hypothesis Testing: An
Alternative to the p-Value Approach
Authors: Sturrock, P. A.
Bibcode: 2000AAS...197.2204S
Altcode: 2000BAAS...32R1438S
In problems of the Bernoulli type, an experiment or observation yields
a count of the number of occurrences of an event, and this count is
compared with what it to be expected on the basis of a specified and
unremarkable hypothesis. The goal is to determine whether the results
support the specified hypothesis, or whether they indicate that some
extraordinary process is at work. This evaluation is often based on the
``p-value" test according to which one calculates, on the basis of the
specific hypothesis, the probability of obtaining the actual result or a
``more extreme" result. Textbooks caution that the p-value does not give
the probability that the specific hypothesis is true, and one recent
textbook asserts ``Although that might be a more interesting question
to answer, there is no way to answer it." The Bayesian approach does
make it possible to answer this question. As in any Bayesian analysis,
it requires that we consider not just one hypothesis but a complete
set of hypotheses. This may be achieved very simply by supplementing
the specific hypothesis with the maximum-entropy hypothesis that covers
all other possibilities in a way that is maximally non-committal. This
procedure yields an estimate of the probability that the specific
hypothesis is true. This estimate is found to be more conservative
than that which one might infer from the p-value test.
Title: An Optimization Approach to Reconstructing Force-free Fields
Authors: Wheatland, M. S.; Sturrock, P. A.; Roumeliotis, G.
Bibcode: 2000ApJ...540.1150W
Altcode:
A new method for reconstructing force-free magnetic fields from their
boundary values, based on minimizing the global departure of an initial
field from a force-free and solenoidal state, is presented. The method
is tested by application to a known nonlinear solution. We discuss
the obstacles to be overcome in the application of this method to the
solar case: the reconstruction of force-free fields in the corona from
measurements of the vector magnetic field in the low atmosphere.
Title: Coronal X-Ray Brightness and Photospheric Magnetic Field:
A Study in Correlations
Authors: Wolfson, Richard; Roald, Colin B.; Sturrock, P. A.; Weber,
Mark A.
Bibcode: 2000ApJ...539..995W
Altcode:
We have examined correlations between coronal X-ray emission from the
Yohkoh Soft X-Ray Telescope (SXT) and photospheric magnetic field
measurements from the Michelson Doppler Imager (MDI) on SOHO. Our
data sets span a 521 day period beginning 1996 July 25, and we have
averaged the data temporally into one bin per day and spatially into
nine latitude bins, each spanning 15°. We find strong correlations
between SXT and MDI data at all but extreme latitudes. Phase shifting
one data set relative to the other shows that the correlation always
peaks at zero shift, indicating that coronal X-ray emission is always
most strongly related to the photospheric field at the same time
(essentially, the same longitude). However, higher order peaks occur for
phase shifts of the order of 1 solar rotation, and a detailed analysis
shows that the exact phasing of these higher order peaks is consistent
with differential rotation of persistent magnetic structures in the
photosphere. Cross-correlation between SXT and MDI data from different
latitude bins shows that the high-latitude coronal X-ray emission
is most strongly correlated with the photospheric field at -30°
and +30°. Although this correlation is probably due to projection
effects, a less likely interpretation is that the coronal magnetic
field, on average, spreads from the photosphere to higher latitudes
in the corona. Finally, we compute actual X-ray energy fluxes from
the SXT data and show that the correlation between X-ray flux and
photospheric magnetic field is in reasonable quantitative agreement
with a simple model for coronal heating based on the reconnection of
magnetic elements in the chromospheric network.
Title: Coronal Heating: Energy Release Associated with Chromospheric
Magnetic Reconnection
Authors: Roald, Colin B.; Sturrock, P. A.; Wolfson, Richard
Bibcode: 2000ApJ...538..960R
Altcode:
We examine a one-dimensional circularly symmetric supergranulation
reconnection model with typical quiet-Sun values. In this model,
the assumed source rate of elements determines heating, because all
emerged elements eventually annihilate; the assumed collision cross
section determines mean field-the more efficient the interaction,
the fewer elements exist at any time; and the effective element
diffusivity determines the ratio of field strengths in the network
and cell interior. Power-law indices for the variation of the heating
flux with the mean magnetic field were computed in order to allow
comparisons to observations. The indices are found to be in the range
1.9-2.0, and the only parameter that was found to have much effect on
them was the effective element diffusivity, where the index declines
roughly logarithmically with decreasing diffusivity. Even this effect
is fairly shallow, however; a tenfold reduction in diffusivity only
lowers the power-law index from 1.9 to 1.7.
Title: Energetic Considerations Concerning Coronal Mass Ejections
Authors: Sturrock, P. A.; Wheatland, M. E.; Wolfson, R.
Bibcode: 2000SPD....31.0282S
Altcode: 2000BAAS...32..825S
One of the current models for explaining coronal mass ejections (CMEs)
comprises a twisted flux tube, anchored at each end in the photosphere
and confined by an overlying magnetic arcade. It is known that the
flux tube becomes MHD unstable if it is twisted sufficiently. However,
linear theory does not tell us what would be the result of such an
instability. An onset of instability can be either explosive or
non-explosive. In the present context, the former could lead to
the eruption of part of the flux tube into interplanetary space,
i.e. to a CME. On the other hand, the latter would lead only to a
slow re-structuring of the magnetic configuration with no dramatic
effects. We can gain some insight into this distinction by considering
the energy required to produce the kind of eruption that could explain
a CME. We make a simple estimate of this requirement by comparing the
energy before and after an eruption. The former is essentially the
free energy of a twisted flux tube of given length - the excess of the
energy of the twisted flux tube over the energy of the corresponding
untwisted flux tube. The latter comprises the energy of that part
of the flux tube which extends into interplanetary space, together
with the energy which is required to create an opening in the arcade
sufficiently large to permit the penetration of the flux tube. This
work was supported in part by NASA grants NAS 8-37334 and NAG 5-4038.
Title: Temperature Structure of the Quiet Corona: An SXT-SUMER
Discrepancy
Authors: Wolfson, Richard; Roald, Colin B.; Sturrock, P. A.; Lemen,
J.; Shirts, P.
Bibcode: 2000ApJ...529..570W
Altcode:
The Soft X-ray Telescope (SXT) on Yohkoh and the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) spectrometer on the Solar
and Heliospheric Observatory (SOHO) are both capable of providing
measures of temperature in the solar corona. A recent SUMER-based
study of a quiet coronal region suggests an isothermal plasma in the
range from 1.03 to 1.5 solar radii. In this work, we have analyzed
part of the same region using SXT data and find a temperature that
increases with height. This is consistent with earlier SXT-based
coronal temperature studies but obviously disagrees with SUMER results
for the same region. The SUMER study reveals a lower scale height for
emission in the Fe X, Fe XI, and Fe XII lines than for the lines of
lighter elements, an effect that may be attributable to gravitational
stratification. Because iron lines contribute heavily to the X-ray
emission detected with SXT, it is reasonable to suspect that the
more rapid decrease in iron abundance at higher altitudes might be
responsible for the SXT-SUMER discrepancy. We have therefore explored
the effect on SXT temperatures of altering individually the abundances
of all 14 elements used in standard SXT temperature calculations. We
find that only iron and carbon have any significant effect but that
this effect is not nearly sufficient to account for the SXT-SUMER
discrepancy.
Title: Solar Neutrinos as a Possible Diagnostic of the Solar
Magnetic Field
Authors: Sturrock, P. A.
Bibcode: 2000ASPC..206...83S
Altcode: 2000hesp.conf...83S
No abstract at ADS
Title: Rotational Signature and Possible R-Mode Signature in the
GALLEX Solar Neutrino Data
Authors: Sturrock, P. A.; Scargle, J. D.; Walther, G.; Wheatland, M. S.
Bibcode: 1999ApJ...523L.177S
Altcode: 1999astro.ph..4278S
Recent analysis of the Homestake data has yielded evidence that the
solar neutrino flux varies in time--more specifically, that it exhibits
a periodic variation that may be attributed to rotational modulation
occurring deep in the solar interior, either in the tachocline or
in the radiative zone. Here we present a spectral analysis of the
GALLEX data that yields supporting evidence for this rotational
modulation. The most prominent peak in the power spectrum occurs
at the synodic frequency of 13.08 yr-1 (cycles per year)
and is estimated to be significant at the 0.1% level. It appears that
the most likely interpretation of this modulation is that the electron
neutrinos have nonzero magnetic moment, so that they oscillate between
left-hand (detectable) and right-hand (nondetectable) chiralities
as they traverse the Sun's internal magnetic field. This oscillation
could account for the neutrino deficit. The second strongest peak in
the GALLEX spectrum has a period of 52 days, and this period occurs
in other solar data as well. We suggest that this periodicity and also
the Rieger 154 day periodicity, which shows up in many solar parameters
and in the Homestake data, are due to r-mode oscillations.
Title: Chromospheric Magnetic Reconnection and its Implication for
Coronal Heating
Authors: Sturrock, P. A.; Roald, C. B.; Wolfson, R.
Bibcode: 1999ApJ...524L..75S
Altcode:
According to recent data analyses, the relationship between the
coronal energy flux density and the photospheric magnetic flux density
is approximately power law; estimates of the exponent tend to be
noninteger and fall in the range 1-2. The index is closer to 2 for
quiet regions and closer to 1 for active regions. We here examine this
relationship on the basis of a recent model of coronal heating. We
assume that the coronal energy flux is derived from reconnection of
neighboring flux tubes at the level of the chromosphere, and we examine
the rate at which such reconnection would occur in terms of a simple
kinetic-theory model. In this model, flux elements appear randomly
within supergranulation cells, are carried into the network according
to a prescribed velocity field, and cancel in the network due to
``collisions'' between elements of opposite polarity. For any limited
range of magnetic flux density, the relationship is approximately
power law. We find that the power-law index is in the range 1-2: for
weak fields it is close to 2, and for strong fields it is close to 1,
in agreement with available evidence.
Title: Chromospheric magnetic reconnection and its possible
relationship to coronal heating.
Authors: Sturrock, P. A.; Roald, C. B.; Wolfson, R.
Bibcode: 1999BAAS...31.1236S
Altcode:
No abstract at ADS
Title: Chromospheric Magnetic Reconnection and its Possible
Relationship to Coronal Heating
Authors: Sturrock, P. A.; Roald, C. B.; Wolfson, R.
Bibcode: 1999AAS...194.1618S
Altcode: 1999BAAS...31..852S
It has been clear since the Skylab era that coronal heating is related
to the coronal magnetic field. This may be due to the influence
of magnetic field on wave heating mechanisms. It may also be due to
"nanoflares," involving magnetic reconnection in the corona, as proposed
by Parker and others. It is also possible that reconnection at the
chromospheric level may be important. The chromosphere is a favorable
site for reconnection, since the resistivity is highest in that region
- specifically at the temperature-minimum location. Chromospheric
reconnection can lead to coronal heating in several ways including
direct Joule heating, the response of the coronal magnetic field to
a sudden change in connectivity at the chromospheric level, and the
generation and subsequent dissipation of high-frequency Alfven and
magneto-acoustic waves. The last possibility could contribute also to
the heating and propulsion of the solar wind, as suggested by Axford
and others, since high-frequency waves can be dissipated by cyclotron
damping. We examine some of the processes involved in a scenario
for coronal heating which is based on chromospheric reconnection. We
also examine a simple analytical model for the random emergence of
magnetic elements within supergranulation cells, the convection of
these elements into the network, and the cancellation of elements of
opposite polarity within the network. This model leads to a prediction
concerning the relationship between the mean coronal energy flux and
the mean photospheric magnetic flux density for quiet regions. It also
leads to an estimate of the rate of injection of chromospheric matter
into the corona that may be compared with estimates of the rate of
downflow in the transition region. This work was supported in part by
NASA grants NAS 8-37334 and NAG 5-4038.
Title: Chromospheric Magnetic Reconnection and Its Possible
Relationship to Coronal Heating
Authors: Sturrock, P. A.
Bibcode: 1999ApJ...521..451S
Altcode:
Coronal heating is clearly related to the coronal magnetic field. This
may be due to a passive role of the magnetic field in modifying wave
propagation and dissipation or to an active role resulting from the
liberation of magnetic energy by reconnection or in some other way. The
purpose of this article is to examine the consequences of reconnection
at the chromospheric level rather than in the corona. We note that
the chromosphere is indeed a favorable site for reconnection to occur,
since the resistivity is greatest in that region--specifically at the
temperature-minimum location. Chromospheric reconnection can lead to
coronal heating by Joule heating, by the generation and subsequent
dissipation of high-frequency Alfvén and magnetacoustic waves, or
by the response of the coronal magnetic field to a sudden change in
connectivity. The second process could also contribute to heating of
the solar wind, since high-frequency Alfvén waves can be absorbed by
cyclotron damping. We note also that chromospheric reconnection could
inject sufficient chromospheric gas into the corona to balance the
known steady downflow of coronal gas through the transition region. It
is also possible that chromospheric reconnection plays a role in the
first ionization potential effect.
Title: Coronal X-ray Brightness and Photospheric Magnetic Field:
A Simple Model
Authors: Roald, C. B.; Wolfson, R.; Sturrock, P. A.
Bibcode: 1999AAS...194.1616R
Altcode: 1999BAAS...31..852R
We discuss the possibility that the energy that heats the corona
originates in magnetic reconnection in the chromosphere, with reference
to a simple 1D supergranulation model. In this model, magnetic elements
are assumed to be brought up to the surface by convection in the
interior of supergranules, then carried to the network by outflow. They
are meanwhile buffetted by randomly-directed granulation flows, leading
to collisions (and apparent cancellation via post-reconnection magnetic
relaxation) between neighbouring elements. For reasonable assumptions
about the magnetic element production rate, sufficient energy to power
the quiet corona is released. Numerical analysis of the model allows
us to compute the relationship between the heating flux and the mean
unsigned magnetic field in the supergranule. We consider a range of
parameters and compute power-law fits for each, then compare these
predictions to observations from Yohkoh SXT and SOHO MDI. This work
was supported by NASA grants NAS 8-37334 and NAG 5-4038.
Title: Coronal X-ray Brightness and Photospheric Magnetic Field:
Observational Correlations
Authors: Wolfson, R.; Roald, C. B.; Sturrock, P. A.
Bibcode: 1999AAS...194.1617W
Altcode: 1999BAAS...31..852W
We have formed time series of photospheric magnetic field data from
the Michelson Doppler Imager (MDI) on SOHO and of coronal X-ray flux
from the Soft X-ray Telescope (SXT) on Yohkoh. The data are averaged to
give one datum per day for each of nine latitude bins on the central
meridian, for the mean SXT energy flux, the mean magnetic field B,
and the mean field magnitude |B|. Data from both instruments overlap
for a 521-day period beginning 25 July 1996. Analyzing the two time
series for this period, we find strong correlations between coronal
X-ray brightness and the magnitude of the photospheric magnetic field
at all but extreme latitudes, and these correlations persist when the
general trend in the data -- presumably due to the solar cycle --
is removed. The inferred relation between X-ray flux and the field
magnitude |B| takes the form of a power law, which we compare with
simple models that also predict a power-law relation. We have also
formed cross correlations involving different time or latitude bins. The
former show that the strongest correlations always occur for SXT and
MDI data from the same time. Strong correlations also result when
data are separated in time by integer multiples of a solar rotation,
suggesting the presence of persistent structures at the photosphere
and/or in the corona. The spatial analysis shows that at low latitudes
the strongest correlation occurs between SXT and MDI data from the same
latitude bins. At higher latitudes, however, the SXT data correlate
most strongly with MDI data from lower latitudes, suggesting that the
magnetic field spreads from the low-latitude photosphere to higher
latitudes in the corona. This work was supported by NASA grants
NAG5-6118 and NAS 8-37334.
Title: Rotational and Related Periodicities in the Homestake and
GALLEX Neutrino Data
Authors: Sturrock, P. A.; Walther, G.; Wheatland, M. S.
Bibcode: 1999HEAD....4.3908S
Altcode: 1999BAAS...31..743S
If neutrinos have a sufficiently strong magnetic moment, the solar
neutrino flux will be modulated by the Sun's internal magnetic field. We
have spectrum-analyzed the Homestake data, looking for evidence of
periodic modulation in the range 12.6 - 13.3 y(-1) due to structures
in the radiative zone that has a sidereal rotation rate in the range
13.6 - 14.3 y(-1) . We find a peak at 12.88 y(-1) . The estimated
probability of finding such a peak in the search band by chance is
about 3%. We also find sidebands at 11.88, 12.88, 14.88 and 15.88 y(-1)
, attributable to a seasonal modulation due to the tilt of the solar
axis. The estimated probability of this combination occurring by chance
is about 0.2%. We have more recently examined the GALLEX data and find
that the strongest peak in the range 1 to 20 cycles per year occurs
at 13.10 y(-1) , close to the value found in the Homestake data. The
estimated probability of finding such a periodicity in the search band
by chance is less than 0.1%. There is evidence for some other well
known solar periodicities in the neutrino data: a peak at 2.32 cycles
per year (period = 157 days) in the Homestake data, and a peak at 7.00
cycles per year (period = 52 days) in the GALLEX data. We propose that
these periodicities [together with another well known periodicity at
4.67 cycles per year (period = 78 days)] are due to internal r-mode
oscillations. We suggest that these modulations in the neutrino flux may
be understood in terms of the RSFP (resonant spin flavor precession)
mechanism proposed by Akhmedov and others. This interpretation leads
to an estimate of Delta m(2) and to a lower limit for the neutrino
magnetic moment. This work was supported in part by Air Force grant
F49620-95-1-008 and NASA grants NAS 8-37334 and NAGW-5-4038.
Title: The Waiting-Time Distribution of Solar Flare Hard X-Ray Bursts
Authors: Wheatland, M. S.; Sturrock, P. A.; McTiernan, J. M.
Bibcode: 1998ApJ...509..448W
Altcode:
A waiting-time distribution is constructed for 8 yr of solar flare
hard X-ray bursts observed by the ICE/ISEE 3 spacecraft. The observed
distribution is compared with a simulated waiting-time distribution
produced by a time-dependent Poisson process constructed using rates
estimated from the observations. The observed distribution shows an
overabundance of short waiting times (10 s-10 minutes) in comparison
with the simulation. This result implies that the hard X-ray bursts
are not independent events. The implications of this result for the
existence of sympathetic flaring and to models of flare statistics are
discussed, and the result is compared with previous determinations of
waiting-time distributions for solar hard X-ray events.
Title: Apparent Latitudinal Modulation of the Solar Neutrino Flux
Authors: Sturrock, P. A.; Walther, G.; Wheatland, M. S.
Bibcode: 1998ApJ...507..978S
Altcode:
We examine the solar neutrino flux, as measured by the Homestake
neutrino detector, to search for evidence of a dependence upon the
solar latitude of the Earth-Sun line that varies from 7.25d south in
mid-March to 7.25d north in mid-September. Although the flux does
not obviously show any dependence on latitude, we do find evidence
for a dependence of the variance of the flux upon latitude. When
data from 108 runs of the Homestake experiment are divided into four
quartiles, sorted according to latitude, we find that the northernmost
quartile exhibits a larger variance than the other three. By applying
the shuffle test, we estimate the probability that this could have
occurred by chance to be in the range 1%-2%. For more detailed
information, we examine a ``reconstructed flux'' formed from our recent
maximum likelihood spectrum analysis. This procedure indicates that
the variance is largest at about 6.5d north. We also find that the
spectrum of the variance of the reconstructed flux has a notable peak
at 1 cycle y-1 tending to confirm a latitude dependence of
the variance. We also examine the 12.88 cycle yr periodicity described
in our recent paper and find that the amplitude of the periodicity is
greater for the northernmost quartile than for the other quartiles. We
suggest that these effects may be attributed to resonant spin-flavor
precession of left-hand-helicity electron neutrinos in the magnetic
field of the solar radiative zone.
Title: Environmental Conditions Responsible for Solar Activity
Authors: Sturrock, Peter A.
Bibcode: 1998STIN...0111579S
Altcode:
During the seven years that this program was active at Stanford
University, the group working with Professor Sturrock investigated many
aspects of the conditions responsible for solar activity. Their results
are presented in detail in their publications. A list of publications,
sorted by topic, is included in the report. The following is a brief
summary of the major advances.
Title: Is the Solar Cycle Due to a Dynamo Process?
Authors: Sturrock, Peter A.
Bibcode: 1998sers.conf..427S
Altcode:
No abstract at ADS
Title: Search for Periodicities in the Homestake Solar Neutrino Data
Authors: Sturrock, P. A.; Walther, G.; Wheatland, M. S.
Bibcode: 1997ApJ...491..409S
Altcode:
We evaluate a χ2 statistic to test against the Homestake
data the hypothesis that the neutrino flux from the Sun is constant. We
use estimates of standard deviations derived 1000 simulations of the
sequence of 108 runs, and we also use two procedures for deriving
proxies for the standard deviation from the experimental data. All
tests indicate that the hypothesis should be rejected; the significance
level ranges from 5.8% to 0.1%. We also search for evidence of
periodicities in the neutrino flux by evaluating the log likelihood of
finding the actual count rates in a model in which the neutrino flux
is modulated with a sinusoidal term. We consider a range of values of
the frequency (0-20 cycles yr-1) and, for each frequency,
adjust the modulation parameters to maximize the likelihood. We find
no evidence of modulation at the frequency of the solar cycle. A 1000
shuffle test and 1000 simulations using error estimates taken from the
simulations yield no evidence for either the quasi-biennial (2.2 yr)
periodicity or the Rieger (157 day) periodicity. However, simulations
based on the experimental error estimates yield significance levels
of 1% and 2.7% for the quasi-biennial periodicity, and 2% and 0.2%
for the Rieger periodicity. We have also looked for evidence
of modulation at a frequency that might be related to the solar
rotation frequency. We have adopted a search band of 12.4-13.1 cycles
yr-1, corresponding to the 1 year lower sideband (synodic
frequency) of the rotation frequency of the Sun's radiative zone, as
estimated from helioseismology. There is indeed a peak in that band,
at 12.88 cycles yr-1, that according to the simulation test
is significant at the 3% level. However, we also find evidence of four
sidebands near 10.88, 11.88, 13.88, and 14.88 cycles yr-1
that may be due to the departure of the rotational axis from the
normal to the ecliptic. We introduce a correlation measure formed
from the powers at a ``fundamental'' and at four sidebands. None of
1000 shuffle tests, and only one of 1000 simulations, yield values of
the correlation measure as large as that formed from the experimental
data. These tests offer support, at the 0.1% and 0.2% significance
level, respectively, for the proposition that the neutrino flux
is modulated at a frequency that could be the synodic frequency
corresponding to a sidereal rotational frequency of 13.88 cycles
yr-1 (440 nHz) of the Sun's radiative zone.
Title: Search for Periodicities in the Homestake Solar Neutrino Data
Authors: Sturrock, P. A.; Walther, G.; Wheatland, M. S.
Bibcode: 1997BAAS...29.1121S
Altcode:
No abstract at ADS
Title: Test for Constancy of the Solar Neutrino Flux as Measured by
the Homestake Neutrino Experiment
Authors: Walther, G.; Sturrock, P. A.; Wheatland, M. S.
Bibcode: 1997BAAS...29.1121W
Altcode:
No abstract at ADS
Title: Coronal Heating and the Vertical Temperature Structure of
the Quiet Corona
Authors: Wheatland, M. S.; Sturrock, P. A.; Acton, L. W.
Bibcode: 1997ApJ...482..510W
Altcode:
The radial variation of temperature in the inner corona is examined
using long-exposure Yohkoh images of two regions of diffuse (quiet)
corona. The results indicate a steady radial increase of temperature for
both regions, out to 0.7 and 0.95 solar radii above the limb. We find
that the filter-ratio data for the two regions is well fitted in each
case by integration over the line of sight of a spherically symmetric
model atmosphere in hydrostatic equilibrium and with a temperature
profile due to a conserved inward heat flux. An Abel inversion process
is also applied to the data, and this gives results consistent with
the spherically symmetric, conserved-heat flux model. These results
imply that the nonthermal energy responsible for heating these regions
of the quiet corona is being deposited beyond the observed range of
heights. However, the diffuse regions we examined are believed to be
partly closed-field regions, and so, the radial models require careful
interpretation. We discuss the implications for coronal heating in
these regions.
Title: Coronal Heating and the Photospheric Magnetic Field
Authors: Parnell, C. E.; Sturrock, P. A.
Bibcode: 1997SPD....28.0506P
Altcode: 1997BAAS...29..909P
Since magnetic field typically plays a role (either active or passive)
in coronal heating theories, it may be possible to evaluate these
theories by investigating the relationship between the coronal energy
budget (the total power requirement of the corona) and measurable
properties of the photospheric magnetic field. The X-ray flux is a
useful proxy for the total power required to maintain the corona, so we
have examined the relationship between the total X-ray flux, as measured
by the GOES instruments, and the total magnetic flux, as estimated
from the NSO instrumentation at Kitt Peak. We use this relationship to
test the recent proposal that coronal heating is due to sudden magnetic
relaxation. According to this concept, reconnection in the chromosphere
of the footpoint regions of two oppositely directed flux tubes leads to
a new flux tube, with widely separated footpoints, which erupts rapidly
and generates sound waves that heat the corona. We adopt a simple
"kinetic theory" model for the photospheric and chromospheric processes,
and so obtain an estimate of the magnetic flux reconnection rate in
terms of the mean field strength and of the parameters (diameter, flux
and random speed) that characterize the elementary flux elements. The
sudden magnetic relaxation model gives a simple relation between the
magnetic flux budget and the coronal energy budget. In this way, we
obtain a theoretical relationship between the coronal energy budget and
the mean photospheric magnetic field strength that we compare with the
available observational data. This work was supported by NASA grants
NAS 8-37334 and NAGW-2265, and by Air Force grant F49620-95-1-0008.
Title: Avalanche Models of Solar Flares and the Distribution of
Active Regions
Authors: Wheatland, M. S.; Sturrock, P. A.
Bibcode: 1996ApJ...471.1044W
Altcode:
Avalanche models of solar flares successfully reproduce the power-law
distribution of flare frequency as a function of energy. However,
the model distributions have been produced for a single numerical
grid, representing a single active region on the Sun. Here we
convolve the distribution owing to an avalanche grid with each of
two observationally determined active region size distributions. The
resulting energy distributions are power laws (with index α ≍ 1.5)
below about 1031 ergs, but they gradually steepen with
energy. The resulting distributions are compared with a flare energy
distribution derived from International Cometary Explorer satellite
observations. Qualitative agreement is found between the model and
observed distributions, although the observations favor a simple
power-law model distribution with a somewhat steeper index (≍1.71).
Title: A Conjecture Concerning the Rieger and Quasi-Biennial Solar
Periodicities
Authors: Sturrock, P. A.
Bibcode: 1996astro.ph..9150S
Altcode:
It has been established that the Rieger periodicity of approximately
153 days is part of a complex of periodicities, all multiples of
a basic period of approximately 25.5 days. However, it has not
been clear why the sixth subharmonic of this periodicity should be
preferentially manifested. We here note that if the Sun contains two
rotating elements, with different periods and different axes, a special
situation will arise if the two periods have a lowest common multiple,
for in this case the relative configuration of the two rotators would
repeat exactly at that (LCM) period. This chain of thought leads us to
suspect that the Sun contains a second rotating element with rotational
period in the range 21 - 22.5 days.
Title: An Apparent Periodicity in the Gallex, Homestake and Kamiokande
Neutrino Data
Authors: Sturrock, P. A.; Walther, G.
Bibcode: 1996astro.ph..9151S
Altcode:
In order to explore a recent proposal that the solar core may contain
a component that varies periodically with a period in the range 21.0
- 22.4 days, due either to rotation or to some form of oscillation,
we have examined the time series formed from measurements of the
solar neutrino flux by means of the GALLEX, Homestake and Kamiokande
experiments. Direct Fourier transform analysis of the Homestake data
shows that the most prominent peak in the entire spectrum (examined
down to 5 days period) is found at a frequency of approximately 17.2
y-1 corresponding to a period of approximately 21.3 days. According
to the "shuffle test," the probability of finding this large a peak
in the prescribed search band is about 0.03%, if it is assumed that
there is no correlation between count rate and time. The GALLEX and
Kamiokande data are examined in a way that searches for similarity
in the shapes of the two spectra in sliding windows in frequency. We
find that the "spectral correlation measure" peaks at 17.2 y-1, and
the shuffle test indicates that the probability of finding this large
a peak at a specified frequency is 2%, if it is again assumed that
for each time series there is no correlation between count rate and
time. The combined significance estimate is of order 1 part in 105
that the results are due to chance, on the assumption that there is
no real structure to the count-rate time series.
Title: Coronal Heating in the Quiet Corona
Authors: Wheatland, M.; Sturrock, P.
Bibcode: 1996AAS...188.3308W
Altcode: 1996BAAS...28Q.869W
The radial variation of temperature in the inner corona is examined
using long exposure Yohkoh images for two regions of diffuse (quiet)
corona. The results indicate a steady radial increase of temperature
for both regions, out to 0.7 and 0.9 solar radii above the limb,
respectively. We find that the filter ratio data for the two regions
is well fitted in each case by integration over the line of sight
of a model radial atmosphere in hydrostatic equilibrium and with
a temperature profile due to a conserved inward heat flux. An Abel
inversion process is also applied to the data, and this gives results
consistent with the radially symmetric, conserved heat flux model. These
results imply that the non-thermal energy responsible for heating these
pieces of the quiet corona is being deposited beyond the observed range
of heights. However, the diffuse regions we examined are believed to be
mainly closed field regions, and so the radial models require careful
interpretation. We discuss the implications for coronal heating in these
regions, and compare this result with other recent determinations of
the temperature in the inner corona. This work was supported in part
by NASA grant NAS 8-37334. The authors acknowledge also support from
Air Force grant F49620-95-1-0008 and NASA grant NAGW-2265.
Title: Is a Dynamo Process Essential for Explaining the Solar Cycle?
Authors: Sturrock, P. A.
Bibcode: 1996AAS...188.3309S
Altcode: 1996BAAS...28Q.869S
The magnetic field at the solar photosphere is highly structured and
time-variable, suggesting that it is generated and regenerated by
a dynamo process that occurs within or at the base of the convection
zone. However, it is proving difficult to explain all the properties of
the solar cycle, and to match the rotational velocity profiles obtained
by means of helioseismological observations, within the context of a
dynamo model. Furthermore, there is some evidence that the neutrino
flux is time varying, and that the variation is correlated with the
solar cycle. This fact, if it proves to be correct, would be difficult
to understand on the basis of a dynamo model, unless the neutrino has a
magnetic moment, which would require that the neutrino has a non-zero
mass. For these and other reasons, it is perhaps prudent to question
the assumption that dynamo action is essential for explaining the solar
cycle. One way to seek to determine whether dynamo action is essential
is to look for an alternative. If the neutrino flux is time variable,
this may indicate that nuclear burning is not steady, in which case
it is likely that it is not spherically symmetric either. Nuclear
burning that is neither steady nor spherically symmetric must be
expected to lead to hydrodynamic flows within the Sun. It will be
argued that a certain flow pattern, and a certain associated magnetic
field pattern, can readily reproduce some of the salient properties
of the solar cycle. This work was supported in part by Air Force grant
F49620-95-1-008 and NASA grant NAGW-2265.
Title: Yokhoh Soft X-Ray Telescope Images of the Diffuse Solar Corona
Authors: Sturrock, P. A.; Wheatland, M. S.; Acton, L. W.
Bibcode: 1996ApJ...461L.115S
Altcode:
During the interval 1992 May 3--15, an extended region (out to 1.5
solar radii) of diffuse, stable corona crossed the northeast limb
of the Sun. This region underlaid a coronal streamer as revealed by
the Mauna Loa Coronagraph of the High Altitude Observatory. During
this passage, the soft X-ray telescope on Yohkoh obtained a number of
high-quality pairs of images, closely spaced in time, through the two
thinnest analysis filters. Analysis of these data indicates that (1)
the temperature increases steadily with height and (2) the variation
of temperature with radius is consistent with a conserved inward
heat flux. These results imply that the magnetic field configuration
was substantially open out to 1.5 solar radii and that there was no
significant coronal heating below that height in that region. It appears
that this region was being heated by nonthermal energy deposited beyond
1.5 solar radii.
Title: Zooming in on the redshift problem
Authors: Sturrock, P. A.
Bibcode: 1996Ap&SS.244..159S
Altcode:
Scientific inference offers a way to help organize and clarify
our thinking about controversial areas of science such as the
redshift problem. Scientists typically devote considerable effort
to evaluating the probability that data relevant to a controversial
area may be due to the “null hypothesis” (i.e. that there is no
new phenomenon). However, it is usually not clear whether a small
probability for the null hypothesis can be interpreted as a high
probability for some other hypothesis, if only for the reason that the
alternative hypothesis may not be specified, and it is not clear how
strong a case is required to establish the new hypothesis. Thinking
about such topics can be clarified by a simple procedure based on
the methods of scientific inference. This procedure is referred to
as “ZOOM” for “Zero-Order Organizing Model”. This article
proposes a ZOOM for the redshift problem, and presents the results of
a preliminary trial.
Title: Interpretation of SXT Data Concerning the Diffuse Corona
Authors: Sturrock, P. A.; Wheatland, M. S.; Acton, L. W.
Bibcode: 1996mpsa.conf..417S
Altcode: 1996IAUCo.153..417S
No abstract at ADS
Title: Perspectives on Solar Flares
Authors: Sturrock, P. A.
Bibcode: 1996ASPC...95...42S
Altcode: 1996sdit.conf...42S
No abstract at ADS
Title: Coronal Heating by Sudden Magnetic Relaxation
Authors: Sturrock, P. A.
Bibcode: 1996ASPC..111..105S
Altcode: 1997ASPC..111..105S
If two flux tubes of opposite polarity come into contact in the
chromosphere, reconnection has several consequences: (a) flux elements,
as seen in magnetographs, appear to have "cancelled;" (b) small regions
in the chromosphere will be heated; (c) cool gas is ejected upwards;
(d) most of the cool gas subsequently returns to the chromosphere,
giving rise to a downflow as seen in transition-region lines; (e)
the sudden relaxation of the flux tubes will lead to high-frequency
Alfvén waves. In a closed-field region, the Alfvén waves will be
standing waves that are damped by exciting sound waves in the corona;
dissipation of these sound waves offers an explanation of coronal
heating. In an open-field region such as a coronal hole, the Alfvén
waves will be traveling waves that are damped at greater heights,
leading to both coronal heating and high-speed solar wind. Depending
on the magnetic topology, the upward motion of cool gas may have the
form of a spicule, that is a small form of a flare surge, or may be
more closely related to a flare spray. This scenario appears to lead
to conditions that could be helpful in understanding the FIP effect.
Title: Asymptotic Analysis of Force-free Magnetic Fields of
Cylindrical Symmetry
Authors: Sturrock, P. A.; Antiochos, S. K.; Roumeliotis, G.
Bibcode: 1995ApJ...443..804S
Altcode:
It is known from computer calculations that if a force-free
magnetic-field configuration is stressed progressively by footpoint
displacements, the configuration expands and approaches the open
configuration with the same surface flux distribution, and, in the
process, the energy of the field increases progressively. Analysis
of a simple model of force-free fields of cylindrical symmetry leads
to simple asymptotic expressions for the extent and energy of such a
configuration. The analysis is carried through for both spherical and
planar source surfaces. According to this model, the field evolves
in a well-behaved manner with no indication of instability or loss
of equilibrium.
Title: Observations of Coronal Temperature Structure by Yohkoh
Authors: Acton, L. W.; Culhane, J. L.; Lemen, J. R.; Sturrock, P. A.
Bibcode: 1995SPD....26..615A
Altcode: 1995BAAS...27..964A
No abstract at ADS
Title: Coronal Hard X-ray Sources in Solar Flares
Authors: Wheatland, M. S.; Sturrock, P. A.
Bibcode: 1995SPD....26.1321W
Altcode: 1995BAAS...27..991W
No abstract at ADS
Title: Interpretation of SXT Data Concerning the Diffuse Corona
Authors: Sturrock, P. A.; Acton, L. W.
Bibcode: 1995SPD....26..616S
Altcode: 1995BAAS...27..964S
No abstract at ADS
Title: Environmental conditions responsible for solar activity
Authors: Sturrock, Peter A.
Bibcode: 1995stan.reptQ....S
Altcode:
Solar coronal activity is of concern to the Air Force primarily
because of the terrestrial effects of coronal mass ejections and solar
flares. Coronal mass ejections can lead to geomagnetic disturbances
that in turn cause magnetospheric substorms. This geomagnetic
activity disturbs the ionosphere, especially in the polar regions,
interfering with radio propagation. Ionizing radiation (UV and X-ray)
and particle events from solar flares can also lead to ionospheric
disturbances. Furthermore, major flares pose serious hazards to
astronauts. During the past three years, the Stanford group has
obtained significant theoretical insights into the driving mechanism
of eruptive events in the solar corona. The question of what causes
coronal eruptions inevitably leads to questions concerning the plasma
conditions and magnetic field configurations in which eruptions
occur. In particular, we have grappled with the long-standing issue
of how the coronal plasma is maintained at a temperature of several
million degrees, while the underlying surface of the sun that is visible
in white light has a temperature of only a few thousand degrees. Our
work over the past three years has taken us closer to the goal of
being able to predict the imminent onset of solar flares and coronal
mass ejections.
Title: The Possible Role of MHD Waves in Heating the Solar Corona
Authors: Porter, Lisa J.; Klimchuk, James A.; Sturrock, Peter A.
Bibcode: 1994ApJ...435..482P
Altcode:
The possible role of waves in the heating of the solar corona has
been investigated. A general dispersion relation has been derived for
waves propagating in a homogeneous plasma subject to dissipation by
viscosity and thermal conduction. The dissipation mechanisms have been
incorporated self-consistently into the equations, and no assumptions
about the strength of the damping have been made. Solutions of the
sixth-order dispersion relation provide information on how the damping
of both slow and fast mode waves depends upon the plasma density,
temperature, field strength, and angle of propagation relative to the
background magnetic field. We provide a detailed comparison to the
standard approach, which is to solve for the wave quantities in the
absence of dissipation and then to use these quantities in expressions
for the heating due to viscosity and thermal conduction.
Title: The Possible Role of High-Frequency Waves in Heating Solar
Coronal Loops
Authors: Porter, Lisa J.; Klimchuk, James A.; Sturrock, Peter A.
Bibcode: 1994ApJ...435..502P
Altcode:
We investigate the role of high-frequency waves in the heating of
solar active region coronal loops. We assume a uniform background
magnetic field, and we introduce a density stratification in a
direction perpendicular to this field. We focus on ion compressive
viscosity as the damping mechanism of the waves. We incorporate
viscosity self-consistently into the equations, and we derive a
dispersion relation by adopting a slab model, where the density inside
the slab is greater than that outside. Such a configuration supports
two types of modes: surface waves and trapped body waves. In order
to determine under what conditions these waves may contribute to the
heating of active regions, we solve our dispersion relation for a
range of densities, temperatures, magnetic field strengths, density
ratios, wavevector magnitudes, wavevector ratios, and slab widths. We
find that surface waves exhibit very small damping, but body waves can
potentially damp at rates needed to balance radiative losses. However,
the required frequencies of these body waves are very high. For
example, the wave frequency must be at least 5.0/s for a slab density
of 109,5/cc, a slab temperature of 106,5 K, a
field strength of 100 G, and a density ratio of 5. For a slab density
of 1010/cc, this frequency increases to 8.8/s. Although
these frequencies are very high, there in no observational evidence
to rule out their existence, and they may be generated both below the
corona and at magnetic reconnection sites in the corona. However, we
do find that, for slab densities of 1010/cc or less, the
dissipation of high-frequency waves will be insufficient to balance
the radiative losses if the magnetic field strength exceeds roughly
200 G. Because the magnetic field is known to exceed 200 G in many
active region loops, particularly low-lying loops and loops emanating
from sunspots, it is unlikely that high-frequency waves can provide
sufficient heating in these regions.
Title: Asymptotic Forms for the Energy of Force-free Magnetic Field
Configurations of Translational Symmetry
Authors: Sturrock, P. A.; Antiochos, S. K.; Klimchuk, J. A.;
Roumeliotis, G.
Bibcode: 1994ApJ...431..870S
Altcode:
It is known from computer calculations that if a force-free
magnetic field configuration is stressed progressively by footpoint
displacements, the configuration expands and approaches the open
configuration with the same surface flux distribution and the
energy of the field increases progressively. For configurations of
translational symmetry, it has been found empirically that the energy
tends asymptotically to a certain functional form. It is here shown
that analysis of a simple model of the asymptotic form of force-free
fields of translational symmetry leads to and therefore justifies
this functional form. According to this model, the field evolves in
a well-behaved manner with no indication of instability or loss of
equilibrium.
Title: Observations of Enhanced Coronal Heating in Sheared MAgnetic
Fields
Authors: Moore, R. T.; Porter, J.; Roumeliotis, G.; Tsuneta, S.;
Shimizu, T.; Sturrock, P. A.; Acton, L. W.
Bibcode: 1994kofu.symp...89M
Altcode:
From superposition of Yohkoh SXT images on MSFC vector magnetograms of
two active regions, we find: (1) coronal heating is enhanced at sites of
strong magnetic shear, and (2) this heating is produced by microflares.
Title: Microflaring at the Feet of Large Active Region Loops
Authors: Porter, J.; Moore, R. T.; Roumeliotis, G.; Shimizu, T.;
Tsuneta, S.; Sturrock, P. A.; Acton, L. W.
Bibcode: 1994kofu.symp...65P
Altcode:
By superposing Yohkoh SXT images on an MSFC magnetogram of an active
region, we find that the brightest loops in the bipolar magnetic
envelope spanning the active region are rooted near a compact site
of mixed polarity and microflaring. Apparently, the enhanced coronal
heating in these high loops is a consequence of the microflaring and/or
related magnetic activity at this end site.
Title: Plasma Physics
Authors: Sturrock, Peter Andrew
Bibcode: 1994plph.book.....S
Altcode:
1. Introduction; 2. Basic concepts; 3. Orbit theory - uniform fields;
4. Adiabatic invariants; 5. Orbit theory; 6. Electromagnetic waves in
a cold electron plasma; 7. Electromagnetic waves in an electron-ion
plasma; 8. Two-stream instability; 9. Electrostatic oscillations in a
plasma of non-zero temperature; 10. Collision theory; 11. MHD equations;
12. Magnetohydrodynamics; 13. Force-free magnetic configurations;
14. Waves in MHD systems; 15. Magnetohydrodynamic stability;
16. Variational principle for MHD systems; 17. Resistive instabilities;
18. Stochastic processes; 19. Interaction of particles and waves.
Title: A Numerical Study of the Sudden Eruption of Sheared Magnetic
Fields
Authors: Roumeliotis, George; Sturrock, Peter A.; Antiochos, Spiro K.
Bibcode: 1994ApJ...423..847R
Altcode:
We investigate the quasi-static evolution of an idealized magnetic
configuration in the solar corona that is subjected to photospheric
shearing motions. The initial, unsheared field in our calculations
is a magnetic dipole located at the center of the Sun. The assumed
photospheric shearing motions are latitude-dependent and antisymmetric
about the equator. The quasi-static evolution of the coronal field
is calculated using the magneto-frictional method. A key difference
between our study and previous work is that the outer computational
boundary is placed exceedingly far from the solar surface where the
shearing motions are applied. This is achieved by writing the basic
equations of the magneto-frictional method in terms of the logarithm
of radial distance. We find that initially, the coronal magnetic field
expands steadily as the footpoint displacement is increased. However,
when the footpoint displacement exceeds a certain critical amount,
the qualitative behavior of the evolving field suddenly changes,
so that the outward expansion of the field lines becomes a much more
rapidly increasing function of the footpoint displacement. We propose
that this sudden transition to a regime with very sensitive dependence
on boundary conditions plays an important role in the onset of eruptive
phenomena in the solar atmosphere.
Title: Plasma physics. an introduction to the theory of astrophysical,
geophysical, and laboratory plasmas
Authors: Sturrock, Peter A.
Bibcode: 1994ppai.book.....S
Altcode:
No abstract at ADS
Title: The Asymptotic Behavior of Force-Free Magnetic-Field
Configurations
Authors: Sturrock, P. A.; Klimchuk, J. A.; Roumeliotis, G.; Antiochos,
S. K.
Bibcode: 1994ASPC...68..219S
Altcode: 1994sare.conf..219S
No abstract at ADS
Title: Plasma Physics, An Introduction to the Theory of Astrophysical,
Geophysical and Laboratory Plasmas
Authors: Sturrock, Peter Andrew
Bibcode: 1994ppit.book.....S
Altcode:
No abstract at ADS
Title: Environmental conditions responsible for solar activity
Authors: Sturrock, Peter A.
Bibcode: 1993stan.reptR....S
Altcode:
During the past year, the Stanford group has continued its
investigations into the origins of solar coronal activity. Solar
activity occurs within a complex magnetic environment, which is
determined by the entire history of magnetic flux emergence and surface
flows at the underlying photosphere. One of the main achievements has
been the development of a technique to reconstruct the coronal magnetic
field above active regions from measurements of the magnetic field
at the photosphere. To complement this empirical tool, the authors
have continued theoretical work on the influence of photospheric
shearing motions on the configuration and energy content of coronal
fields. This work is shedding light on the nature of eruptive phenomena
such as coronal mass ejections. They have also intensively evaluated
the role of magnetohydrodynamic waves and reconnection in heating the
solar atmosphere, and identified a number of promising coronal heating
scenarios that will require detailed numerical modeling.
Title: Collisional Damping of Magnetoacoustic Waves in the Solar
Corona
Authors: Porter, Lisa A.; Sturrock, Peter A.; Klimchuk, James A.
Bibcode: 1993BAAS...25.1203P
Altcode:
No abstract at ADS
Title: Asymptotic Forms for the Energy of Force Free Magnetic-Field
Configurations
Authors: Sturrock, P. A.; Roumeliotis, G.; Antiochos, S.
Bibcode: 1993BAAS...25.1218S
Altcode:
No abstract at ADS
Title: Evidence for a Fundamental Period of the Sun and Its Relation
to the 154 Day Complex of Periodicities
Authors: Bai, T.; Sturrock, P. A.
Bibcode: 1993ApJ...409..476B
Altcode:
We have analyzed the longitude distributions of major flares observed in
the 1955-1991 interval, referring them to coordinate systems rotating
about axes tilted with respect to the rotation axis of the solar
envelope. We find that the longitude distribution exhibits the largest
modulation in the coordinate system with the following parameters:
rotation period, 25.50 days; tilt angle of the rotation axis, 40 deg;
tilt direction, toward the position of the earth on December 4 in its
orbit around the sun. We interpret this as being due to an obliquely
rotating structure (or a wave pattern rotating about an oblique axis)
which has two exciters. We identify the period of 25.50 days as the
fundamental period of the hypothetical 'clock' proposed by Bai and
Sturrock (1991). The periods of the subharmonics are 51.0, 76.5,
102.0, 127.5, and 153.0 days, in agreement with periodicities found
from analysis of flare occurrence times.
Title: Physics of solar activity
Authors: Sturrock, Peter A.
Bibcode: 1993stan.reptQ....S
Altcode:
The aim of the research activity was to increase our understanding
of solar activity through data analysis, theoretical analysis,
and computer modeling. Because the research subjects were diverse
and many researchers were supported by this grant, a select few key
areas of research are described in detail. Areas of research include:
(1) energy storage and force-free magnetic field; (2) energy release
and particle acceleration; (3) radiation by nonthermal electrons; (4)
coronal loops; (5) flare classification; (6) longitude distributions
of flares; (7) periodicities detected in the solar activity; (8)
coronal heating and related problems; and (9) plasma processes.
Title: Microflaring at the feet of large active region loops
Authors: Porter, Jason; Moore, Ron; Roumeliotis, George; Shimizu,
Toshifumi; Tsuneta, Saku; Sturrock, Peter; Acton, Loren
Bibcode: 1993STIN...9670891P
Altcode:
By superposing Yohkoh SXT images on an MSFC magnetogram of an active
region, we find that the brightest loops in the bipolar magnetic
envelope spanning the active region are rooted near a compact site
of mixed polarity and microflaring. Apparently, the enhanced coronal
heating in these high loops is a consequence of the microflaring and/or
related magnetic activity at this end site.
Title: Environmental conditions responsible for solar activity
Authors: Sturrock, Peter A.
Bibcode: 1992stan.reptQ....S
Altcode:
This report describes progress toward understanding the theoretical
basis for solar activity. One of our key accomplishments has been
the insight we have gained into the eruption of coronal magnetic
structures. Roumeliotis, Sturrock, and Antiochos have made numerical
and analytic calculations which indicate that coronal magnetic fields
being sheared by convective motions acting on their photospheric
footpoints evolve smoothly until the shear surpasses a certain critical
amount. After that, the coronal field exhibits very sensitive dependence
on the photospheric boundary conditions, in the sense that small
changes in the footpoint displacements produce huge changes in the
height of the coronal field. We propose that this nonlinear behavior
of sheared magnetic fields is the explanation for eruptive phenomena
such as coronal mass ejections and solar flares. We are also developing
several approaches for understanding coronal heating. In particular,
Sturrock has proposed a model in which turbulent reconnection
deep within the chromosphere produces local heating as well as a
burst of magnetohydrodynamic waves that propagate upward to heat the
corona. Roumeliotis is working on the theory that twisted flux loops in
the corona undergo an internal resistive kink instability that unwinds
the internal field and releases magnetic energy to heat the loop.
Title: Eruptions of Magnetic-Field Configurations
Authors: Sturrock, P. A.; Roumeliotis, G.
Bibcode: 1992AAS...181.5506S
Altcode: 1992BAAS...24.1212S
No abstract at ADS
Title: Search for Evidence of a Clock Related to the Solar 154 Day
Complex of Periodicities
Authors: Sturrock, P. A.; Bai, T.
Bibcode: 1992ApJ...397..337S
Altcode:
Evidence indicates that the 154-day periodicity in solar activity may
be part of a complex of periodicities that are approximate multiples of
25.8 d, which suggests that the sun contains a 'clock' with frequency
in the range 440-463 nHz. To search for evidence of this clock, the
daily Greenwich sunspot areas and daily Zurich sunspot numbers have been
Fourier-analyzed. The Zurich data show a strong peak that may clearly
be identified with the fundamental frequency, while the Greenwich data
show a peak that may be the harmonic of the fundamental frequency. A
model is discussed which provides a kinematical interpretation of the
sunspot spectrum.
Title: Search for evidence of a clock related to the solar 154 day
complex of periodicities
Authors: Sturrock, P. A.; Bai, T.
Bibcode: 1992STIN...9220916S
Altcode:
Evidence that has recently been compiled (Bai and Sturrock 1991)
indicates that the enigmatic 154-day periodicity in solar activity may
be viewed as part of a complex of periodicities that are approximate
multiples of 25.8 days, suggesting that the Sun contains a 'clock'
with frequency in the range 440 to 463 nano Hz. The clock may comprise
either an oscillator or a rotator, each of which may be either real
or virtual. We have reconsidered a previous spectrum analysis of
the Zurich sunspot-number sequence by Knight, Schatten, and Sturrock
(1979) which revealed a sharp, persistent and significant periodicity
with a period of 12.072 days, corresponding to a frequency of about
958.8 nano Hz. This periodicity may be regarded as the (second) upper
sideband of the second harmonic (2nuR + 2nuE)
of a fundamental frequency of 447.7 nano Hz that is clearly within
the search band. In this expression, nuR is the sidereal
frequency of the hypothetical rotator and nuE is the
frequency (31.69 nano Hz) of the Earth in its orbital motion around
the Sun. In analyzing sunspot area data derived from the Greenwich
data set, and on noting that any frequency is defined only to within
the Nyquist frequency, we find clear evidence not only for the upper
sideband of the second harmonic, but also for the second harmonic
(2nuR) and the lower sideband of the second harmonic
(2nuR - 2nuE). There is no strong peak at the
fundamental frequency in the Greenwich data, but there is in the Zurich
sunspot data. The effect of a linear oscillator is, to the lowest order
in the amplitude, the same as the combined effect of two rotators of
opposite polarities. A rotator that has arbitrary orientation with
respect to the ecliptic may influence the outer layers of the Sun and
thereby modulate the occurrence of solar activity such as sunspots. By
analyzing a simple model, we find that such a rotator would influence
surface activity in such a way that the spectrum of a 'signal' (such
as the record of sunspots), as seen from the Earth, would contain
components with frequencies that are certain integral combinations
of nuR and nuE. The amplitudes of the various
components depend sensitively on theta, the angle between the axis of
the rotator and the axis of the Earth's orbital motion. This simple
model therefore offers a kinematical (but not dynamical) interpretation
of the sunspot spectrum. The present analysis, while offering support of
our conjectures that the Sun contains a clock that regulates the 154-day
complex of periodicities, cannot distinguish between an osillator or a
rotator (that might be a traveling wave), nor between a real rotator or
a virtual rotator (that might be an apparent traveling wave due to the
aliasing effect of an oscillator in a rotating system). Further analysis
of sunspot and other data sets will be required to confirm the existence
of such clock and (if it is real) to determine its physical nature.
Title: Cylindrically Symmetric Force-free Magnetic Fields
Authors: Porter, Lisa J.; Klimchuk, James A.; Sturrock, Peter A.
Bibcode: 1992ApJ...385..738P
Altcode:
The magnetofrictional method was used to study the energy buildup
in stressed coronal fields possessing cylindrical symmetry. Four
different nonlinear, force-free magnetic-field configurations were
examined. It was determined that, in all cases, a reasonable amount
of twist in the field lines can produce enough free magnetic energy
to power a typical flare. Furthermore, it was found that the rate of
energy buildup is enhanced if the greatest twist and/or the magnetic
flux is concentrated closer to the neutral line. It is thought that
the open-field configuration (a configuration for which the field
lines extend to infinity and the current is confined to a current
sheet separating outgoing and incoming field lines) is the limiting
state as one imposes infinite shear. The results of this work do not
contradict this theory once numerical errors are taken into account.
Title: The Emerging Picture of Eruptive Solar Flares
Authors: Sturrock, P. A.
Bibcode: 1992ComAp..16...71S
Altcode:
No abstract at ADS
Title: The Emerging Picture of Eruptive Solar Flares
Authors: Sturrock, P. A.
Bibcode: 1992LNP...399..397S
Altcode: 1992esf..coll..397S; 1992IAUCo.133..397S
No abstract at ADS
Title: An oblique rotator in the Sun and 154-day and related
periodicities.
Authors: Bai, T.; Sturrock, P. A.
Bibcode: 1992BAAS...24.1077B
Altcode:
No abstract at ADS
Title: Three-dimensional Force-free Magnetic Fields and Flare
Energy Buildup
Authors: Klimchuk, J. A.; Sturrock, P. A.
Bibcode: 1992ApJ...385..344K
Altcode:
The 'magneto-frictional' method is used to compute fully 3D models
of force-free magnetic fields. Beginning with a potential field
produced by a point dipole buried below the solar surface, the magnetic
footpoints at the photosphere are displaced to investigate the buildup
of magnetic energy. Reasonable footpoint shearing displacements are
found to be able to increase the total magnetic energy by at least
one-third. The energy buildup is greater when the shearing displacements
are concentrated closer to the magnetic neutral line. Roughly half
of the energy buildup is free magnetic energy. The absolute quantity
of free magnetic energy (10 exp 30-33 ergs, depending on the scaling
of the models) is sufficient to explain solar flares. No evidence for
'loss of equilibrium' was found.
Title: Maximum Energy of Semi-infinite Magnetic Field Configurations
Authors: Sturrock, P. A.
Bibcode: 1991ApJ...380..655S
Altcode:
This article addresses the conjecture by Aly (1984) that the
maximum-energy state of magnetic field configurations that have
a given flux distribution on a given surface is the open-field
configurations. It is first shown that the existence of a maximum-energy
configuration depends upon the topology of the source surface: for a
multiply connected surface there is no maximum-energy state. However,
the magnetic energy is known to be bounded above for a wide class of
simply connected surfaces, and it is shown that in this case there
must be a field configuration that has maximum energy. Furthermore,
for this configuration the energy is stationary under arbitrary small
footprint displacements that leave the surface flux distribution
unchanged. It is then shown that this condition leads to the result
that either Bn, the normal component of magnetic field, of jn, the
normal component of current, must vanish at each point on the source
surface. This condition is met by the open configuration but not
by any other configuration. The implications of this result for the
understanding of flares and of coronal mass ejections are discussed.
Title: The 154-day and Related Periodicities of Solar Activity are
Subharmonics of a 25.8-day Clock
Authors: Bai, T.; Sturrock, P. A.
Bibcode: 1991BAAS...23.1027B
Altcode:
No abstract at ADS
Title: The 154-day and related periodicities of solar activity as
subharmonics of a fundamental period
Authors: Bai, T.; Sturrock, P. A.
Bibcode: 1991Natur.350..141B
Altcode:
IN 1984 a periodicity of 154 days was found in the record of solar
flare activity1 from 1980 to 1983. Since then, the same
periodicity has been found in many different measures of solar flare
activity during cycle 21 (soft X-ray peak flux1; hard X-ray
emission2,3; H α flare activity4; microwave peak
flux5; production of inter-planetary electrons6
and protons7; 10-cm radio flux8) as well as in
sunspot area9,10. The cause of this 154-day periodicity,
which has also been discovered in solar cycles 19 and 20 (refs 7, 11)
remains unknown, but a suggestion that it was related to enhanced flare
activity in certain longitude bands has been ruled out3. Here
we show that periodicities of 51, 78, 104 and 129 days, in addition
to the 154-day period, can often be detected in flare and sunspot
records. These periods are close to integral multiples (by factors of
2, 3, 4, 5 and 6) of 25.8 days, suggesting that they are subharmonics
of a fundamental period.
Title: Search for Evidence for an Oblique Rotator within the Sun
Authors: Sturrock, P. A.; Bai, T.
Bibcode: 1991BAAS...23.1028S
Altcode:
No abstract at ADS
Title: Simulated SXT Observations of Coronal Loops
Authors: Dixon, W. W.; Klimchuk, J. A.; Sturrock, P. A.; Lemen, J. R.
Bibcode: 1991LNP...387..297D
Altcode: 1991fpsa.conf..297D
We have simulated the appearance of two static coronal loops as they
might be observed by the Soft X-ray Telescope onboard the Solar-A
spacecraft. One loop corresponds to a non-flaring active region loop,
and the other corresponds to a post-flare loop. We find that the
loops have fundamentally different appearances: the quiescent loop is
brightest at its apex, while the hotter post-flare loop is brightest
at, or near, its base (depending on the particular X-ray filter assumed
for the observations).
Title: Maximum Energy of Semi-infinite Magnetic-Field Configurations
Authors: Sturrock, P. A.
Bibcode: 1991LNP...387..224S
Altcode: 1991fpsa.conf..224S
No abstract at ADS
Title: The 154-Day Periodicity of Solar Activity as a Subharmonic
of a 25.8-Day Clock
Authors: Bai, T.; Sturrock, P. A.
Bibcode: 1990BAAS...22.1225B
Altcode:
No abstract at ADS
Title: Is There an Oblique Rotator Within the Sun?
Authors: Sturrock, P. A.; Bai, T.
Bibcode: 1990BAAS...22Q1225S
Altcode:
No abstract at ADS
Title: Episodic Coronal Heating
Authors: Sturrock, P. A.; Dixon, W. W.; Klimchuk, J. A.; Antiochos,
S. K.
Bibcode: 1990ApJ...356L..31S
Altcode:
A study is made of the observational consequences of the hypothesis
that there is no steady coronal heating, the solar corona instead
being heated episodically, such that each short burst of heating
is followed by a long period of radiative cooling. The form of the
resulting contribution to the differential emission measure (DEM), and
to a convenient related function (the differential energy flux, DEF) is
calculated. Observational data for the quiet solar atmosphere indicate
that the upper branch of the DEM, corresponding to temperatures above
100,000 K, can be interpreted in terms of episodic energy injection
at coronal temperatures.
Title: Flare Energy Buildup and the Stressing of 3-D Coronal
Magnetic Fields
Authors: Klimchuk, J. A.; Sturrock, P. A.
Bibcode: 1990BAAS...22..900K
Altcode:
No abstract at ADS
Title: Cylindrically-Symmetric Force-Free Magnetic Fields
Authors: Porter, L. J.; Klimchuk, J. A.; Sturrock, P. A.
Bibcode: 1990BAAS...22..853P
Altcode:
No abstract at ADS
Title: Cascade Model of Gamma-Ray Bursts
Authors: Sturrock, P. A.; Harding, A. K.; Daugherty, J. K.
Bibcode: 1989ApJ...346..950S
Altcode:
If, in a neutron star magnetosphere, an electron is accelerated to
an energy of 10 to the 11th or 12th power eV by an electric field
parallel to the magnetic field, motion of the electron along the curved
field line leads to a cascade of gamma rays and electron-positron
pairs. This process is believed to occur in radio pulsars and gamma
ray burst sources. Results are presented from numerical simulations
of the radiation and photon annihilation pair production processes,
using a computer code previously developed for the study of radio
pulsars. A range of values of initial energy of a primary electron was
considered along with initial injection position, and magnetic dipole
moment of the neutron star. The resulting spectra was found to exhibit
complex forms that are typically power law over a substantial range
of photon energy, and typically include a dip in the spectrum near
the electron gyro-frequency at the injection point. The results of
a number of models are compared with data for the 5 Mar., 1979 gamma
ray burst. A good fit was found to the gamma ray part of the spectrum,
including the equivalent width of the annihilation line.
Title: Force-free Magnetic Fields: Is There a ``Loss of Equilibrium''?
Authors: Klimchuk, J. A.; Sturrock, P. A.
Bibcode: 1989ApJ...345.1034K
Altcode:
This paper examines concept in solar physics that is known as loss of
equilibrium in which a sequence of force-free magnetic fields, said to
represent a possible quasi-static evolution of solar magnetic fields,
reaches a critical configuration beyond which no acceptable solution
of the prescribed form exists. This concept is used to explain eruptive
phenomena ranging from solar flares to coronal mass ejections. Certain
sequences of force-free configurations are discussed that exhibit
a loss of equilibrium, and it is argued that the concept is devoid
of physical significance since each sequence is defined a way that
does not represent an acceptable thought experiment. For example, the
sequence may be defined in terms of a global constraint on the boundary
conditions, or the evolution of the sequence may require the creation
of mgnetic flux that is not connected to the photosphere and is not
present in the original configuration. The global constraints typically
occur in using the so-called generating function method. An acceptance
thought experiment is proposed to specify the field configuration
in terms of photospheric boundary conditions comprising the normal
component of the field and the field-line connectivity. Consider a
magnetic-field sequence that, when described in terms of a generating
function, exhibits a loss of equilibrium and show that, when one instead
defines the sequence in terms of the corresponding boundary conditions,
the sequence is well behaved.
Title: Episodic Coronal Heating and the Solar Differential Emission
Measure
Authors: Sturrock, P. A.; Klimchuk, J. A.; Antiochos, S. K.
Bibcode: 1989BAAS...21R1186S
Altcode:
No abstract at ADS
Title: Cascade Model of Gamma-Ray Bursts
Authors: Sturrock, P. A.; Harding, A. K.; Daugherty, J. K.
Bibcode: 1989BAAS...21..768S
Altcode:
No abstract at ADS
Title: An Episodic Model of Coronal Heating
Authors: Sturrock, P. A.; Antiochos, S. K.
Bibcode: 1989BAAS...21R.829S
Altcode:
No abstract at ADS
Title: Force-Free Magnetic Fields: Is there a "Loss of Equilibrium?"
Authors: Klimchuk, J. A.; Sturrock, P. A.
Bibcode: 1989BAAS...21R.855K
Altcode:
No abstract at ADS
Title: The Role of Eruption in Solar Flares
Authors: Sturrock, Peter A.
Bibcode: 1989SoPh..121..387S
Altcode: 1989IAUCo.104..387S
This article focuses on two problems involved in the development of
models of solar flares. The first concerns the mechanism responsible
for eruptions, such as erupting filaments or coronal mass ejections,
that are sometimes involved in the flare process. The concept of
`loss of equilibrium' is considered and it is argued that the concept
typically arises in thought-experiments that do not represent acceptable
physical behavior of the solar atmosphere. It is proposed instead
that such eruptions are probably caused by an instability of a plasma
configuration. The instability may be purely MHD, or it may combine both
MHD and resistive processes. The second problem concerns the mechanism
of energy release of the impulsive (or gradual) phase. It is proposed
that this phase of flares may be due to current interruption, as was
originally proposed by Alfvén and Carlqvist. However, in order for this
process to be viable, it seems necessary to change one's ideas about the
heating and structure of the corona in ways that are outlined briefly.
Title: Energy conversion in solar flares.
Authors: Sturrock, P. A.
Bibcode: 1989GMS....54..181S
Altcode: 1989opss.conf..181S; 1989sspp.conf..181S
Flares involve a sequence of energy conversion processes beginning
with the initial stressing of the magnetic field and ending with
radiation. This article is concerned primarily with the processes by
which magnetic energy is suddenly converted into other forms.
Title: Classification of solar flares.
Authors: Bai, T.; Sturrock, P. A.
Bibcode: 1989ARA&A..27..421B
Altcode:
The authors organize this paper as follows. First they discuss the
historical background before the SMM launch. Then, they review the
recent developments made by observations with SMM, Hinotori, and other
contemporary satellites and ground-based observatories. Based on the
observations discussed, they classify solar flares into the following
five classes: thermal hard X-ray flares, nonthermal hard X-ray flares,
impulsive gamma-ray/proton flares, gradual gamma-ray/proton flares,
and quiescent filament-eruption flares. The authors examine the roles of
filament eruptions in flare development. They discuss theoretical ideas
related to processes occurring in different classes of flares. Closing
remarks are given.
Title: Coronal Magnetic Fields Produced by Photospheric Shear
Authors: Klimchuk, J. A.; Sturrock, P. A.; Yang, W. -H.
Bibcode: 1988ApJ...335..456K
Altcode:
The magnetofrictional method for computing force-free fields is used
to examine the evolution of the magnetic field of a line dipole,
when there is relative shearing motion between the two polarities. It
is found that the energy of the sheared field can be arbitrarily
large compared with the potential field. It is also found that it is
possible to fit the magnetic energy, as a function of shear amplitude,
by a simple functional form. The fit parameters depend only on the
distribution of normal field in the photosphere and the form of the
shearing displacement. They show that the energy is relatively more
enhanced if the shear occurs: (1) where the normal field is strongest;
and/or (2) in the inner region of the dipole, near the axis; and/or
(3) over a large fraction of the dipole area.
Title: Force-free magnetic fields: Is there a loss of equilibrium
Authors: Klimchuk, James A.; Sturrock, Peter A.
Bibcode: 1988STIN...8921717K
Altcode:
This paper examines concept in solar physics that is known as loss of
equilibrium in which a sequence of force-free magnetic fields, said to
represent a possible quasi-static evolution of solar magnetic fields,
reaches a critical configuration beyond which no acceptable solution
of the prescribed form exists. This concept is used to explain eruptive
phenomena ranging from solar flares to coronal mass ejections. Certain
sequences of force-free configurations are discussed that exhibit
a loss of equilibrium, and it is argued that the concept is devoid
of physical significance since each sequence is defined a way that
does not represent an acceptable thought experiment. For example, the
sequence may be defined in terms of a global constraint on the boundary
conditions, or the evolution of the sequence may require the creation
of magnetic flux that is not connected to the photosphere and is not
present in the original configuration. The global constraints typically
occur in using the so-called generating function method. An acceptable
thought experiment is proposed to specify the field configuration
in terms of photospheric boundary conditions comprising the normal
component of the field and the field-line connectivity. Consider a
magnetic-field sequence that, when described in terms of a generating
function, exhibits a loss of equilibrium and show that, when one instead
defines the sequence in terms of the corresponding boundary conditions,
the sequence is well behaved.
Title: Cascade model of gamma-ray bursts: Power-law and
annihilation-line components
Authors: Harding, A. K.; Sturrock, P. A.; Daugherty, J. K.
Bibcode: 1988STIN...8827998H
Altcode:
If, in a neutron star magnetosphere, an electron is accelerated to
an energy of 10 to the 11th or 12th power eV by an electric field
parallel to the magnetic field, motion of the electron along the curved
field line leads to a cascade of gamma rays and electron-positron
pairs. This process is believed to occur in radio pulsars and gamma
ray burst sources. Results are presented from numerical simulations
of the radiation and photon annihilation pair production processes,
using a computer code previously developed for the study of radio
pulsars. A range of values of initial energy of a primary electron was
considered along with initial injection position, and magnetic dipole
moment of the neutron star. The resulting spectra was found to exhibit
complex forms that are typically power law over a substantial range
of photon energy, and typically include a dip in the spectrum near
the electron gyro-frequency at the injection point. The results of
a number of models are compared with data for the 5 Mar., 1979 gamma
ray burst. A good fit was found to the gamma ray part of the spectrum,
including the equivalent width of the annihilation line.
Title: Coronal magnetic fields produced by photospheric shear
Authors: Klimchuk, James A.; Sturrock, Peter A.; Yang, Wei-Hong
Bibcode: 1988cmfp.book.....K
Altcode:
The magneto-frictional method for computing force-free fields examines
the evolution of the magnetic field of a line dipole, when there is
relative shearing motion between the two polarities. The energy of the
sheared field can be arbitrarily large compared with the potential
field. It is possible to fit the magnetic energy, as a function
of shear amplitude, by a simple functional form. The fit parameters
depend only on the distribution of normal field in the photosphere and
the form of the shearing displacement. The energy is relatively more
enhanced if the shear occurs: (1) where the normal field is strongest;
(2) in the inner region of the dipole, near the axis; or (3) over a
large fraction of the dipole area.
Title: Coronal Magnetic Fields Produced by Photospheric Shear
Authors: Klimchuk, J. A.; Sturrock, P. A.; Yang, W. -H.
Bibcode: 1988BAAS...20..716K
Altcode:
No abstract at ADS
Title: Cascade Model of Gamma-Ray Bursts
Authors: Sturrock, P. A.; Harding, A. K.; Daugherty, J. K.
Bibcode: 1988BAAS...20..685S
Altcode:
No abstract at ADS
Title: Coronal magnetic fields produced by photospheric shear
Authors: Sturrock, P. A.; Yang, W. -H.
Bibcode: 1987cmfp.book.....S
Altcode:
The magneto-frictional method is used for computing force free fields to
examine the evolution of the magnetic field of a line dipole, when there
is relative shearing motion between the two polarities. It found that
the energy of the sheared field can be arbitrarily large compared with
the potential field. It is also found that it is possible to fit the
magnetic energy, as a function of shear, by a simple functional form.
Title: Book Review - Physics of the Sun
Authors: Sturrock, P. A.; Holzer, T. E.; Mihalas, D. M.; Ulrich,
R. K.; Carson, T. R.
Bibcode: 1987Obs...107..173S
Altcode:
No abstract at ADS
Title: The 152-day periodicity of the solar flare occurrence rate
Authors: Bai, Taeil; Sturrock, Peter A.
Bibcode: 1987Natur.327..601B
Altcode:
The occurrence rate of solar flares exhibits a periodicity of about 152
days. This periodicity was discovered from analyses of flares observed
with the Solar Maximum Mission (SMM), and confirmed by analysis of
flares observed by other observatories. This periodicity was also
discovered from the flare rate of solar cycle 20 (1965-75). The cause
of the 152-day periodicity still remains a mystery. But answers to
the following questions will enhance our understanding of it. (1) Is
the periodicity a local or a global phenomenon? (2) Is the periodicity
due to the interaction of 'hotspots' rotating at different rates such
that they align with one another once every 152-day period? (3) Is the
periodicity due to the interaction of rotating features originating
from g-mode oscillations? Here we report our analysis of 'major flares'
observed with the Hard X-ray Burst Spectrometer (HXRBS) aboard SMM
and we conclude that the 152-day periodicity is a global phenomenon,
and that the answers to questions (2) and (3) are negative.
Title: The Gradual Phase of Energy Release in Solar Flares
Authors: Sturrock, P. A.; Bai, T.
Bibcode: 1987BAAS...19..921S
Altcode:
No abstract at ADS
Title: Book Review - Physics of the Sun
Authors: Sturrock, P. A.
Bibcode: 1987Sci...236.1009S
Altcode:
No abstract at ADS
Title: Solar flares and magnetic topology
Authors: Sturrock, P. A.
Bibcode: 1987SoPh..113...13S
Altcode: 1982SoPh..113...13S; 1987STIN...8820244S
This article is a very brief review and comparison of the observational
properties of flares and theoretical concepts of models of flares,
especially the concepts of magnetic topology and its evolution. We
examine the "environmental" aspects of flare behavior. Some of these
aspects must be consequences of unknown processes occurring below the
photosphere. Other aspects involve structures--such as filaments--that
are closely related to flares. We then examine properties of flares
to try to distinguish the different phases of energy release that can
occur in the course of a flare. Finally we offer a schematic scenario
and attempt to interpret these phases in terms of this scenario.
Title: Book-Review - Physics of the Sun - VOL.1 - the Solar
Interior - VOL.2 - the Solar Atmosphere - VOL.3 - Astrophysics and
Solar-Terrestrial Relations
Authors: Sturrock, P. A.; Holzer, T. E.; Mihalas, D. M.; Ulrich, R. K.
Bibcode: 1987ApL....25..267S
Altcode:
No abstract at ADS
Title: On the 152-day periodicity of the solar flare occurrence rate
Authors: Bai, Taeil; Sturrock, Peter A.
Bibcode: 1986STIN...8721838B
Altcode:
The occurrence rate of solar flares exhibits a periodicity of about
152 days. This periodicity was discovered from analyses of flares
observed with the Solar Maximum Mission (SMM), and confirmed with
flares observed by other observatories. This periodicity was also
discovered from the flare rate of solar cycle 20 (1965 to 1975). The
cause of the 152 day periodicity still remains a mystery. But answers
to the following questions will enhance our understanding of it: (1)
Is the periodicity a local or global phenomenon? (2) Is the periodicity
due to interactions of hot spots rotating at different rates such that
they align with one another once in every 152-day period? (3) Is the
periodicity due to interactions of rotating features originating from
g-mode oscillations? Analyzing major flares observed with the Hard X
Ray Burst Spectrometer (HXRBS) aboard SMM concludes that the 152 day
periodicity is a global phenomenon.
Title: Force-free Magnetic Fields: The Magneto-frictional Method
Authors: Yang, W. H.; Sturrock, P. A.; Antiochos, S. K.
Bibcode: 1986ApJ...309..383Y
Altcode:
The problem under discussion is that of calculating magnetic field
configurations in which the Lorentz force j x B is everywhere zero,
subject to specified boundary conditions. We choose to represent
the magnetic field in terms of Clebsch variables in the form B =
grad alpha x grad beta. These variables are constant on any field
line so that each field line is labeled by the corresponding values
of alpha and beta. When the field is described in this way, the most
appropriate choice of boundary conditions is to specify the values
of alpha and beta on the bounding surface. We show that such field
configurations may be calculated by a magneto-frictional method. We
imagine that the field lines move through a stationary medium, and
that each element of magnetic field is subject to a frictional force
parallel to and opposing the velocity of the field line. This concept
leads to an iteration procedure for modifying the variables alpha and
beta, that tends asymptotically towards the force-free state. We apply
the method first to a simple problem in two rectangular dimensions,
and then to a problem of cylindrical symmetry that was previously
discussed by Barnes and Sturrock (1972). In one important respect,
our new results differ from the earlier results of Barnes and Sturrock,
and we conclude that the earlier article was in error.
Title: Gamma-Ray Burst Spectra from Electromagnetic Cascades
Authors: Harding, A. K.; Sturrock, P. A.; Daugherty, J. K.
Bibcode: 1986BAAS...18Q.928H
Altcode:
No abstract at ADS
Title: Book-Review - Physics of the Sun - V.I - the Solar Interior
- V.II - the Solar Atmosphere - V.III - Astrophysics and Solar /
Terrestrial Relations
Authors: Sturrock, P. A.; Holzer, T. E.; Mihalas, D. M.; Ulrich,
R. K.; Parker, E. N.
Bibcode: 1986Natur.323..210S
Altcode:
No abstract at ADS
Title: The Differential Emission Measure of Transiently Heated
Coronal Loops
Authors: Antiochos, S. K.; Sturrock, P. A.
Bibcode: 1986BAAS...18..901A
Altcode:
No abstract at ADS
Title: Book-Review - Physics of the Sun
Authors: Sturrock, P. A.
Bibcode: 1986Sci...232.1654S
Altcode:
No abstract at ADS
Title: Book-Review - Physics of the Sun
Authors: Sturrock, P. A.
Bibcode: 1986S&T....71Q.579S
Altcode:
No abstract at ADS
Title: A flare-induced cascade model of γ-ray bursts
Authors: Sturrock, P. A.
Bibcode: 1986Natur.321...47S
Altcode:
Although there is no agreement concerning the model and mechanisms
responsible for γ-ray bursts, it is generally agreed that they are
produced by neutron stars1. With few exceptions2,
it is thought that an intense magnetic field plays a key role. The
favoured radiation mechanism is optically thin synchrotron
radiation3, but it is difficult to find any way of
maintaining the electron energy since the radiation cooling time is
extremely short. As a resolution of this difficulty, I propose that
the basic energy-release mechanism is a flare in the magnetosphere of
a neutron star. This involves reconnection that leads to an electric
field parallel to the magnetic field. This accelerates an electron
along the magnetic field, producing high-energy γ rays (by curvature
radiation) that promptly annihilate in the magnetic field, resulting
in an electron-positron cascade as in radio pulsars4. This
model offers an explanation of the continuum spectrum, of the 511-keV
annihilation line, and possibly of the optical radiation that seems
to accompany some γ-ray bursts.
Title: Evolution of Our Understanding of Solar Flares
Authors: Sturrock, P. A.
Bibcode: 1986BAAS...18..687S
Altcode:
No abstract at ADS
Title: Physics of the Sun. Vol. I: The solar interior. Vol. II:
The solar atmosphere. Vol. III: Astrophysics and solar-terrestrial
relations.
Authors: Sturrock, P. A.; Holzer, T. E.; Mihalas, D. M.; Ulrich, R. K.
Bibcode: 1986psvi.book.....S
Altcode:
No abstract at ADS
Title: Accretion Disk Flares
Authors: Sturrock, P. A.; Yang, W.
Bibcode: 1986IAUS..119..411S
Altcode:
No abstract at ADS
Title: Physics of the sun. Volume 3: Astrophysics and
solar-terrestrial relations
Authors: Sturrock, P. A.; Holzer, T. E.; Mihalas, D. M.; Ulrich, R. K.
Bibcode: 1986psun....3.....S
Altcode:
No abstract at ADS
Title: Physics of the sun. Volume 2: The solar atmosphere
Authors: Sturrock, P. A.; Holzer, T. E.; Mihalas, D. M.; Ulrich, R. K.
Bibcode: 1986psun....2.....S
Altcode:
Aspects related to the solar interior are discussed, taking into account
thermonuclear reactions in the solar interior, atomic and radiative
processes in the solar interior, hydrodynamic and hydromagnetic
phenomena in the deep solar interior, rotation and magnetic fields,
solar waves and oscillations, and observations and theories of solar
convection, global circulation, and magnetic fields. In a discussion
of the solar atmosphere, attention is given to the radiation output,
the chromospheric fine structure, physical processes in the solar
corona, magnetic energy storage and conversion in the solar atmosphere,
the acceleration and propagation of solar flare energetic particles,
solar radio emission, and structure, dynamics, and heating of the solar
atmosphere. Other subjects explored are concerned with astrophysics and
solar-terrestrial relations. The formation of the sun and its planets
is considered along with the solar neutrino problem, solar and stellar
magnetic activity, the effects of solar electromagnetic radiation on
the terrestrial environment, and the effect of the solar wind.
Title: Rapid fluctuations in solar flares.
Authors: Sturrock, Peter A.
Bibcode: 1986NASCP2449....1S
Altcode: 1986rfsf.nasa....1S; 1986STIN...8713387S
Study of rapid fluctuations in the emission of radiation from
solar flares provides a promising approach for probing the
magneto-plasma structure and plasma processes that are responsible
for a flare. Fluctuations that occur on a sub-second time-scale may be
due to magnetic islands that develop in current sheets during magnetic
reconnection. Magnetic field configurations that might produce solar
flares are divided into a number of categories, depending on: whether
or not there is a filament; whether there is no current sheet, a closed
current sheet, or an open current sheet; and whether the filament (if
present) erupts into the corona, or is ejected completely from the sun's
atmosphere. Analysis of the properties of these possible configurations
is compared with different types of flare, and to Bai's subdivision of
gamma-ray/proton events. The article ends with a number of theoretical
questions related to the study of rapid fluctuations in solar flares.
Title: Physics of the sun
Authors: Sturrock, P. A.; Holzer, T. E.; Mihalas, D. M.; Ulrich, R. K.
Bibcode: 1986psun....1.....S
Altcode: 1986QB521.P48......
Aspects related to the solar interior are discussed, taking into account
thermonuclear reactions in the solar interior, atomic and radiative
processes in the solar interior, hydrodynamic and hydromagnetic
phenomena in the deep solar interior, rotation and magnetic fields,
solar waves and oscillations, and observations and theories of solar
convection, global circulation, and magnetic fields. In a discussion
of the solar atmosphere, attention is given to the radiation output,
the chromospheric fine structure, physical processes in the solar
corona, magnetic energy storage and conversion in the solar atmosphere,
the acceleration and propagation of solar flare energetic particles,
solar radio emission, and structure, dynamics, and heating of the solar
atmosphere. Other subjects explored are concerned with astrophysics and
solar-terrestrial relations. The formation of the sun and its planets
is considered along with the solar neutrino problem, solar and stellar
magnetic activity, the effects of solar electromagnetic radiation on
the terrestrial environment, and the effect of the solar wind.
Title: A Flare-Induced Cascade Model of Gamma-Ray Bursts
Authors: Sturrock, P. A.
Bibcode: 1985BAAS...17..850S
Altcode:
No abstract at ADS
Title: Extragalactic variable radio sources
Authors: Sturrock, P. A.
Bibcode: 1985ApJ...293...52S
Altcode:
Radio emission from a plasmoid that expands in a nonspherically
symmetric manner is analyzed. The properties of this model are
compared with the results of Andrews et al. (1978) and Epstein
et al. (1982) concerning the values of beta derived for standard
(delayed) radio sources. Mechanisms that might produce plasmoids that
expand progressively in length while retaining substantially constant
cross-sections are briefly discussed.
Title: Calculation of Nonlinear Force-Free Magnetic Fields
Authors: Sturrock, P. A.; Yang, W.
Bibcode: 1985BAAS...17..641S
Altcode:
No abstract at ADS
Title: Spicules and surges
Authors: Blake, M. L.; Sturrock, P. A.
Bibcode: 1985ApJ...290..359B
Altcode:
The authors adopt the position that spicules, macrospicules, and
surges are manifestations of the same phenomenon occurring on different
scales. They search for a mechanism that can be successfully applied
to explain the phenomenon on all three scales. It is found that the
Pikel'ner model, according to which gas is transported in a sequence
of "magnetic sacks" which may, for instance, form as the result of
reconnection, can reproduce the kinematic properties of spicules and
surges. A modification of this mechanism, involving two different
magnetic field configurations, can explain the collimation of spicules
and surges. The implications of the Pikel'ner mechanism for the heating
of the solar corona are examined.
Title: Summary proceedings of the Standford Workshop on Solar Flare
Prediction held in Paris on 28 February - 1 March 1985
Authors: Antiochos, S. K.; Bai, T.; Sturrock, P. A.
Bibcode: 1985STIN...8623543A
Altcode:
A workshop on The Prediction of Solar Activity was held at Meudon
Observatory in France in June 1984. During that meeting, a number
of participants from the United States expressed interest in meeting
together to discuss this topic with a view to exploring what actions
might be taken to improve our predictive capability. This document
contains abstracts of presentations made at the meeting.
Title: Energy Release in Solar Flares
Authors: Sturrock, P. A.; Kaufmann, P.; Smith, D. F.
Bibcode: 1985IAUS..107..293S
Altcode:
The authors discuss the question how many phases of energy release
are involved in flares and what are their characteristics.
Title: Obituary - Wilcox, John-Marsh
Authors: Walker, A. B. C., Jr.; Helliwell, R. A.; Sturrock, P. A.
Bibcode: 1984QJRAS..25..534W
Altcode: 1984QJRAS..25..534.
No abstract at ADS
Title: Physical aspects of the prediction of solar flares
Authors: Sturrock, P. A.
Bibcode: 1984STIN...8519915S
Altcode:
The properties of a solar flare depend critically on the preflare
magnetic-field configuration and the way that this configuration evolves
during the flare process. The flare process often, if not always,
involves the eruption of a filament or similar structure, possibly
leading to complete ejection from the Sun. This eruption will generate
an extensive current sheet: reconnection of this sheet contributes
to the gradual phase and perhaps also to the impulsive phase. It
is proposed that reconnection of a current sheet (pre-existing, or
generated by filament eruption) is required for a gamma-ray event or
a particle event. A particle event requires also an escape mechanism
that could be provided either by a pre-existing open current sheet or
by the ejection of the magnetic-field configuration associated with
a filament. Following these guidelines, it is possible to propose a
classification of flares into seven categories and to propose whether or
not each category will lead to the following phenomena: mass ejection,
shock wave, gamma-ray emission, and particle event.
Title: Energy Release in Solar Flares
Authors: Sturrock, P. A.; Kaufman, P.; Moore, R. L.; Smith, D. F.
Bibcode: 1984SoPh...94..341S
Altcode:
We examine observational evidence concerning energy release in solar
flares. We propose that different processes may be operative on four
different time scales: (a) on the sub-second time scale of `sub-bursts'
which are a prominent feature of mm-wave microwave records; (b) on the
few-seconds time scale of `elementary bursts' which are a prominent
feature of hard X-ray records; (c) on the few-minutes time scale of
the impulsive phase; and (d) on the tens-of-minutes or longer time
scale of the gradual phase.
Title: Energy Release in Solar Flares
Authors: Sturrock, P. A.; Kaufmann, P.; Moore, R. L.; Smith, D. F.
Bibcode: 1984BAAS...16..890S
Altcode:
No abstract at ADS
Title: Extragalactic radio sources
Authors: Sturrock, P. A.
Bibcode: 1984STIN...8426557S
Altcode:
The standard model for extragalactic variable radio sources comprises
an isotropically expanding plasmoid with frozen magnetic flux and an
electron distribution which evolves adiabatically. This model leads to
the following relaton between the peak luminosity L nu, m
and the relevant frequency num which are functions of
time: Lnu,m is proportional to num(n) where N =
(7n + 5)/(4n + 5). In this expression, n is the spectral index in
the optically thin part of the spectrum, where L nu is
proportional to nu (-n). For n in the range 0.5 to 1.5, the standard
model yields N in the range 1.2 to 1.4. By contrast, analysis of
observational data yields estimates of N in a small range about the
mean value 0.4, in clear contradiction with the standard model.
Title: Spicules and surges
Authors: Blake, M. L.; Sturrock, P. A.
Bibcode: 1984STIN...8516727B
Altcode:
It is argued that spicules, macrospicules and surges are manifestations
of the same phenomenon occurring on different scales. A mechanism that
can be successfully applied to explain the phenomenon on all three
scales is sought.
Title: Progress in the study of homologous flares on the sun - Part II
Authors: Woodgate, B. E.; Martres, M. -J.; Smith, J. B., Jr.; Strong,
K. T.; McCabe, M. K.; Machado, M. E.; Gaizauskas, V.; Stewart, R. T.;
Sturrock, P. A.
Bibcode: 1984AdSpR...4g..11W
Altcode: 1984AdSpR...4...11W
Studies of groups of homologous flares in active regions in
1980 have been made using a variety of space and ground based
instruments. Detailed properties of three of these groups have been
studied, and are combined to form a possible sequence of events.
Title: Energy release in solar flares
Authors: Sturrock, P. A.; Kaufmann, P.; Moore, R. L.; Smith, D. F.
Bibcode: 1984ersf.rept.....S
Altcode:
This document presents observational evidence concerning energy
release in solar flares. It is proposed that a different process may
be operative on four different time scales: (1) on the sub-second time
scale of sub-bursts which are a prominent feature of mm-wave microwave
records; (2) on the few-seconds time scale of elementary bursts which
are a prominent feature of hard X-ray records; (3) on the few-minutes
time scale of the impulsive phase; and (4) on the tens-of-minutes
or longer time scale of the gradual phase. It is proposed that the
concentration of magnetic field into magnetic knots at the photosphere
has important consequences for the coronal magnetic-field structure
such that the magnetic field in this region may be viewed as an array
of elementary flux tubes. The release of the free energy of one such
tube may produce an elementary burst. The development of magnetic
islands during this process may be responsible for the sub-bursts. The
impulsive phase may be simply the composite effect of many elementary
bursts. It is also proposed that the gradual phase of energy release,
with which flares typically begin and with which many flares end,
involves a steady process of reconnection, whereas the impulsive phase
involves a more rapid stochastic process of reconnection which is
a consequence of mode interaction. In the case of two-ribbon flares,
the late part of the gradual phase may be attributed to reconnection of
a large current sheet which is being produced as a result of filament
eruption. A similar process may be operative in smaller flares.
Title: A Model for Extragalactic Variable Radio Sources
Authors: Sturrock, P. A.
Bibcode: 1983BAAS...15Q.944S
Altcode:
No abstract at ADS
Title: A Model of Spicules and Surges
Authors: Sturrock, P. A.; Blake, M. L.
Bibcode: 1983BAAS...15Q.717S
Altcode:
No abstract at ADS
Title: Spicules and surges. Part 1: Examination of two possible models
Authors: Blake, M. L.; Sturrock, P. A.
Bibcode: 1983STIN...8330347B
Altcode:
We adopt the position that spicules, macrospicules and surges are
manifestations of the same phenomenon occurring on different scales. We
therefore search for a mechanism which can be successfully applied
to explain the phenomenon on all three scales. We first consider the
possibility that the mechanism is the same as that which operates in
producing the solar wind, except that the divergence of the magnetic
ducts is much more rapid. We find that the mechanism fails to explain
spicules, macrospicules or surges. For instance, if it produces speeds
typical of spicules, the maximum height is much too small; if it
reproduces the height, the required velocities are much too high. We
also consider a variant of this mechanism proposed by Uchida in which
the gas pressure is supplemented by the magnetic pressure of a gas
composed of plasmoids. This mechanism also fails for similar reasons.
Title: Energy release in solar flares
Authors: Sturrock, P. A.; Kaufmann, P.; Smith, D. F.
Bibcode: 1982ersf.rept.....S
Altcode:
This report examines observational information concerning various phases
of the solar-flare process: (a) Recent evidence strongly suggests
that the soft X-ray emission before and after the impulsive phase
should be regarded as one process--the gradual phase. (b) Microwave
and X-ray data indicate that the impulsive phase is comprised of a
large number of similar bursts of energy release. (c) Large flares are
usually preceded by filament eruptions, and it is possible tht the same
process occurs on a smaller scale for smaller flares. We propose that
most flares are initiated by the eruption of a filament. The eruption
opens up magnetic field lines to form a large current sheet. This
current sheet may persist as a coronal streamer, or it may immediately
reconnect. Reconnection of this current sheet is responsible for the
gradual phase of a flare. Since magnetic field at the photospheric level
is concentrated into small knots of high field strength, the coronal
magnetic field may be regarded as an aggregation of small flux tubes,
each with an internal current, adjacent tubes being separated by current
sheets. The gradual phase of a flare may leave the fine-scale current
system undisturbed, in which case the flare has only a gradual phase.
Title: Temperature minimum heating in solar flares by resistive
dissipation of Alfvén waves
Authors: Emslie, A. G.; Sturrock, P. A.
Bibcode: 1982SoPh...80...99E
Altcode:
We examine the possibility that the strong heating produced at
temperature-minimum levels during solar flares is due to resistive
dissipation of Alfvén waves generated by the primary energy release
process in the corona. It is shown how, for suitable parameters,
these waves can carry their energy essentially undamped into the
temperature-minimum layers and can then produce a degree of heating
consistent with observations.
Title: The acceleration and propagation of solar flare energetic
particles
Authors: Forman, M. A.; Ramaty, R.; Zweibel, E. G.; Holzer, T. E.;
Mihalas, D.; Sturrock, P. A.; Ulrich, R. K.
Bibcode: 1982STIN...8329162F
Altcode:
Observations and theories of particle acceleration in solar flares
are reviewed. The most direct signatures of particle acceleration
in flares are gamma rays, X-rays and radio emissions produced by the
energetic particles in the solar atmosphere and energetic particles
detected in interplanetary space and in the Earth's atmosphere. The
implication of these observations are discussed. Stochastic and shock
acceleration as well as acceleration in direct electric fields are
considered. Interplanetary particle propagation is discussed and
an overview of the highlights of both current and promising future
research is presented.
Title: Examination of time series through randomly broken windows
Authors: Sturrock, P. A.; Shoub, E. C.
Bibcode: 1982ApJ...256..788S
Altcode:
The study of many astronomical problems involves a consideration
of time series. The present investigation was prompted by a problem
related to the determination of normal modes of oscillation of the
sun. It is desirable to have an approach for obtaining an estimate
of the accuracy with which oscillation modes may be determined
when it appears possible to observe the sun over a long interval of
time losing some blocks of time because of cloud cover. The present
investigation has the objective to develop a model for addressing
problems of this type. After presentation of a few general formulae,
the problem is considerably simplified by supposing that observations
are made over a large number N of equal time intervals, each of
length t, so that the total time interval T is given by T = Nt. With
certain additional simplifying assumptions, attention is given to the
statistical properties of two functions which are representative of
'randomly broken' window functions.
Title: Bimodel energy release in solar flares.
Authors: Sturrock, P. A.; Smith, D. F.
Bibcode: 1982BAAS...14..608S
Altcode:
No abstract at ADS
Title: Bimodel Energy Release in Solar Flares
Authors: Sturrock, P. A.; Smith, D. F.
Bibcode: 1982BAAS...14..607S
Altcode:
No abstract at ADS
Title: The cooling and condensation of flare coronal plasma
Authors: Antiochos, S. K.; Sturrock, P. A.
Bibcode: 1982ApJ...254..343A
Altcode:
A model is investigated for the decay of flare heated coronal
loops in which rapid radiative cooling at the loop base creates
strong pressure gradients which, in turn, generate large (supersonic)
downward flows. The important features of this model which distinguish
it from previous models of flare cooling are: (1) Most of the thermal
energy of the coronal plasma may be lost by mass motion rather than
by conduction or coronal radiation. (2) Flare loops are not isobaric
during their decay phase, and large downward velocities are present
near the footpoints. (3) The differential emission measure has a
strong temperature dependence. These results can account for recent
observations of compact flare loops that are not consistent with the
previous cooling models.
Title: Temperature minimum heating in solar flares by resistive
dissipation of Alfven waves
Authors: Emslie, A. G.; Sturrock, P. A.
Bibcode: 1981STIN...8210975E
Altcode:
The possibility that the strong heating produced at temperature-minimum
levels during solar flares is due to resistive dissipation of Alfven
waves generated by the primary energy release process in the corona is
studied. It is shown how, for suitable parameters, these waves can carry
their energy essentially undamped into the temperature-minimum layers
and can then produce a degree of heating consistent with observations.
Title: Coronal heating by stochastic magnetic pumping
Authors: Sturrock, P. A.; Uchida, Y.
Bibcode: 1981ApJ...246..331S
Altcode:
Recent observational data cast serious doubt on the widely held
view that the sun's corona is heated by traveling waves (acoustic or
magnetohydrodynamic). It is here proposed that the energy responsible
for heating the corona is derived from the free energy of the coronal
magnetic field derived from motion of the 'feet' of magnetic field
lines in the photosphere. Stochastic motion of the feet of magnetic
field lines leads, on the average, to a linear increase of magnetic
free energy with time. This rate of energy input is calculated for a
simple model of a single thin flux tube. The model appears to agree
well with observational data if the magnetic flux originates in small
regions of high magnetic field strength as proposed by Tarbell et
al. (1979). On combining this energy input with estimates of energy
loss by radiation and of energy redistribution by thermal conduction,
scaling laws are obtained for density and temperature in terms of
length and coronal magnetic field strength.
Title: The cooling and condensation of flare coronal plasma
Authors: Antiochos, S. K.; Sturrock, P. A.
Bibcode: 1981STIN...8127029A
Altcode:
A model is investigated for the decay of flare heated coronal loops
in which rapid radiative cooling at the loop base creates strong
pressure gradients which, in turn, generate large (supersonic)
downward flows. The coronal material cools and 'condenses' onto
the flare chromosphere. The features which distinguish this model
from previous models of flare cooling are: (1) most of the thermal
energy of the coronal plasma may be lost by mass motion rather than
by conduction or coronal radiation; (2) flare loops are not isobaric
during their decay phase, and large downward velocities are present
near the footpoints; (3) the differential emission measure q has a
strong temperature dependence.
Title: Temperature Minimum Heating in Solar Flares by Resistive
Dissipation of Alfvén Waves
Authors: Emslie, A. G.; Sturrock, P. A.
Bibcode: 1981BAAS...13R.543E
Altcode:
No abstract at ADS
Title: The Structure of a Force-Free Coronal Loop
Authors: Wear, K. A.; Antiochos, S. K.; Emslie, A. G.; Sturrock, P. A.
Bibcode: 1981BAAS...13..542W
Altcode:
No abstract at ADS
Title: On the Mechanism of Solar Spicules
Authors: Blake, M. L.; Sturrock, P. A.
Bibcode: 1981BAAS...13..914B
Altcode:
No abstract at ADS
Title: The Structure of a Force Free Magnetic Flux Tube
Authors: Wear, K. A.; Antiochos, S. K.; Sturrock, P. A.
Bibcode: 1981BAAS...13..915W
Altcode:
No abstract at ADS
Title: Book Review - Solar Flares
Authors: Sturrock, P. A.; Valnicek, B.
Bibcode: 1981SSRv...28..109S
Altcode:
No abstract at ADS
Title: Examination of Time Series Through Randomly Broken Windows
Authors: Sturrock, P. A.
Bibcode: 1980BAAS...12..816S
Altcode:
No abstract at ADS
Title: Coronal heating by stochastic magnetic pumping
Authors: Sturrock, P. A.; Uchida, Y.
Bibcode: 1980chsm.bookR....S
Altcode:
Recent observational data cast serious doubt on the widely held
view that the sun:s corona is heated by traveling waves (acoustic or
magnetohydrodynamic). It is here proposed that the energy responsible
for heating the corona is derived from the free energy of the coronal
magnetic field derived from motion of the :feet: of magnetic field
lines in the photosphere. Stochastic motion of the feet of magnetic
field lines leads, on the average, to a linear increase of magnetic
free energy with time. This rate of energy input is calculated for a
simple model of a single thin flux tube. The model appears to agree
well with observational data if the magnetic flux originates in small
regions of high magnetic field strength as proposed by Tarbell, Title
and Schoolman. On combining this energy input with estimates of energy
loss by radiation and of energy redistribution by thermal conduction,
we obtain scaling laws for density and temperature in terms of length
and coronal magnetic field strength.
Title: Coronal heating by stochastic magnetic pumping
Authors: Sturrock, P. A.; Uchida, Y.
Bibcode: 1980chsm.bookQ....S
Altcode:
Recent observational data cast serious doubt on the widely held
view that the Sun's corona is heated by traveling waves (acoustic or
magnetohydrodynamic). It is proposed that the energy responsible for
heating the corona is derived from the free energy of the coronal
magnetic field derived from motion of the 'feet' of magnetic field
lines in the photosphere. Stochastic motion of the feet of magnetic
field lines leads, on the average, to a linear increase of magnetic free
energy with time. This rate of energy input is calculated for a simple
model of a single thin flux tube. The model appears to agree well with
observational data if the magnetic flux originates in small regions
of high magnetic field strength. On combining this energy input with
estimates of energy loss by radiation and of energy redistribution by
thermal conduction, we obtain scaling laws for density and temperature
in terms of length and coronal magnetic field strength.
Title: Is the galactic corona produced by galactic flares
Authors: Sturrock, P. A.; Stern, R.
Bibcode: 1980ApJ...238...98S
Altcode:
The effect of the differential rotation of the disk of the galaxy on
magnetic field which penetrates the disk is considered. The magnetic
field will be progressively distorted from a potential (current-free)
form and will at some stage become unstable. We expect, from knowledge
of solar flares, that an MHD instability, a resistive instability,
or a combination of the two, will result in the release of the excess
magnetic energy, and that part of the released energy will be converted
into heat. By estimating the energy release and the rate at which this
process will occur and by assuming that this energy input is balanced
by radiation, we obtain estimates of the parameters of the resulting
plasma. It appears that this process alone can heat a galactic corona
to temperatures of order one-million K.
Title: Coronal Heating by Stochastic Magnetic Pumping
Authors: Sturrock, P. A.; Uchida, Y.
Bibcode: 1980BAAS...12..516S
Altcode:
No abstract at ADS
Title: a Sunspot Reriodicity and the Solar Rotation
Authors: Knight, J. W.; Sturrock, P. A.; Schatten, K. H.
Bibcode: 1980NASCP2098..175K
Altcode: 1980sscs.nasa..175K
A least squares power spectrum analysis of daily sunspot numbers
for the last 122 years yielded a statistically significant peak at
12.0715 plus or minus .002 days period. This feature at 11.685 days
(sidereal) of the sunspot spectrum is discussed in relation to the
peak at 12.22 days (sidereal) which Dicke found in his oblateness
data. The data is attributed to the Sun's core if the core rotates at
either 12.0715 days or 24.1430 days period (synodic). It is suggested
that spacecraft observations combined with correlative analysis of
solar surface features between eastern and western hemispheres could
further reveal a basic core periodicity. A Dicke type space oblateness
experiment is discussed for providing better photospheric observations
than a ground instrument to determine the core periodicity.
Title: Book-Review - Solar Flares
Authors: Sturrock, P. A.; Maran, S. P.
Bibcode: 1980ApL....21...80S
Altcode:
No abstract at ADS
Title: Uncertainty in estimates of the number of extraterrestrial
civilizations
Authors: Sturrock, P. A.
Bibcode: 1980ASSL...83...59S
Altcode: 1980sslu.meet...59S; 1980sslu.conf...59S
No abstract at ADS
Title: Solar flares
Authors: Sturrock, P. A.
Bibcode: 1980sfsl.work.....S
Altcode:
Papers are presented on the current understanding of the physics of
solar flares based on Skylab and other observations and theoretical
considerations. Specific aspects of the solar flare problem considered
include the preflare state, primary energy release, energetic particles,
the impulsive phase, the chromosphere and transition region, mass
ejections and the thermal X-ray flare plasma. Attention is also given
to the various flare models, and the total radiative and mechanical
energy outputs of the solar flare of Sept. 5, 1973, are estimated.
Title: Flare models
Authors: Sturrock, P. A.
Bibcode: 1980sfsl.work..411S
Altcode: 1980sofl.symp..411S
The current status of solar flare modeling is reviewed. Primary
and secondary observational features that a proposed flare model
should be capable of explaining are discussed, including energy
storage and release, particle acceleration, mass ejection, heating
of the temperature minimum region, X-ray, EUV, UV, visible and radio
emission and mass flow. Consideration is then given to the twisted
flux tube paramagnetic recombination model of Gold and Hoyle (1960),
the current model of Alfven and Carlqvist (1967), closed current-sheet
models such as those of Syrovatskii (1966, 1969, 1977) and Uchida and
Sakurai (1977), open-field models such as those of Carmichael (1964)
and Barnes and Sturrock (1972), the emerging flux model of Heyvaerts
and Priest (1974, 1977, 1978) and the loop-flare models of Spicer
(1977) and Colgate (1978). It is noted that no one model can yet
account for all the observational features, and that there may turn
out to be several types of flare, each requiring its own explanation.
Title: Positron production by pulsars.
Authors: Sturrock, P. A.; Baker, K. B.
Bibcode: 1979ApJ...234..612S
Altcode:
Analytical calculations based on the 'polar-cap light-cylinder' (PCLC)
(Sturrock, 1971a) and 'polar-cap force-balance' (PCFB) (Roberts and
Sturrock, 1972,3) pulsar models show that in either case the intensity
of the 511 keV gamma-ray line from the galactic center can be explained
as the result of the annihilation of positrons produced by pulsars. The
Crab pulsar (braking index approximately 2.5) is estimated to have a
power budget of 10 to the 38th ergs/s, and to produce a total number of
10 to the 51.7th positrons. It is suggested that positron annihilation
can be supplied by pulsars if the birthrate of pulsars in the galactic
center is 10 to the -8.2nd/s.
Title: Is the Galactic Corona Produced by Galactic Flares?
Authors: Sturrock, P. A.; Stern, R.
Bibcode: 1979BAAS...11..705S
Altcode:
No abstract at ADS
Title: Steady State Condensation of Coronal Flare Plasma
Authors: Antiochos, S. K.; Sturrock, P. A.
Bibcode: 1979BAAS...11..697A
Altcode:
No abstract at ADS
Title: Is the galactic corona produced by galactic flares?
Authors: Sturrock, P. A.; Stern, R.
Bibcode: 1979STIN...7930130S
Altcode:
The effect of the differential rotation of the disk of the Galaxy on
magnetic field which penetrates the disk is considered. The magnetic
field will be progressively distorted from a potential (current-free)
form and will at some stage become unstable. It is expected that an
MHD instability, a resistive instability, or a combination of the two,
will result in the release of the excess magnetic energy and that part
of the released energy will be converted into heat. By estimating the
energy release and the rate at which this process will occur and by
assuming that this energy input is balanced by radiation, estimates
were obtained of the parameters of the resulting plasma. It appears
that this process alone can heat a galactic corona to temperatures of
order 10 to the 6th power K.
Title: Flare models: Chapter 9 of solar flares
Authors: Sturrock, P. A.
Bibcode: 1979STIN...7923873S
Altcode:
By reviewing the properties of solar flares analyzed by each of the
seven teams of the Skylab workshop, a set of primary and secondary
requirements of flare models are derived. A number of flare models
are described briefly and their properties compared with the primary
requirements. It appears that, at this time, each flare model has some
strong points and some weak points. It has not yet been demonstrated
that any one flare model meets all the proposed requirements.
Title: Positron production by pulsars
Authors: Sturrock, P.; Baker, K. B.
Bibcode: 1979STIN...7921986S
Altcode:
Calculations based on two specific pulsar models show that in
either case the 511 keV gamma-ray line from the galactic center can
be explained as the as the result of the annihilation of positrons
produced by pulsars.
Title: A sunspot periodicity and its possible relation to solar
rotation.
Authors: Knight, J. W.; Schatten, K. H.; Sturrock, P. A.
Bibcode: 1979ApJ...227L.153K
Altcode:
A least-squares power-spectrum analysis of 122 years of Zurich daily
sunspot numbers yields a statistically significant peak at a 12.0715
+ or - 0.002 day period. This feature of the sunspot spectrum may be
associated with the peak at 12.22 days (sidereal) which Dicke (1976)
found in his oblateness data, and may be attributable to the sun's core
if it rotates at either a 12.0715-day or a 24.1430-day period (synodic).
Title: Impacts of Solar System Environment on Man and Man on the
Environment
Authors: Sturrock, P. A.
Bibcode: 1979spp2.conf.1269S
Altcode:
No abstract at ADS
Title: Electric field in pulsar magnetospheres.
Authors: Baker, K. B.; Knight, J. W.; Sturrock, P. A.
Bibcode: 1978BAAS...10..730B
Altcode:
No abstract at ADS
Title: Evaporative cooling of flare plasma.
Authors: Antiochos, S. K.; Sturrock, P. A.
Bibcode: 1978ApJ...220.1137A
Altcode:
We investigate a one-dimensional loop model for the evaporative
cooling of the coronal flare plasma. The important assumptions are that
conductive losses dominate radiative cooling and that the evaporative
velocities are small compared with the sound speed. We calculate the
profile and evolution of the temperature and verify the accuracy of
our assumptions for plasma parameters typical of flare regions. The
model is in agreement with soft X-ray observations on the evolution of
flare temperatures and emission measures. The effect of evaporation
is to greatly reduce the conductive heat flux into the chromosphere
and to enhance the EUV emission from the coronal flare plasma.
Title: Extraterrestrial Intelligent Life (Correspondence)
Authors: Sturrock, P. A.
Bibcode: 1978QJRAS..19..521S
Altcode:
No abstract at ADS
Title: Reverse current in solar flares.
Authors: Knight, J. W.; Sturrock, P. A.
Bibcode: 1977ApJ...218..306K
Altcode:
We examine the proposal that impulsive X-ray bursts are produced by
high-energy electrons streaming from the corona to the chromosphere. It
is known that the currents associated with these streams are so high
that either the streams do not exist or their current is neutralized
by a reverse current. Analysis of a simple model in which the reverse
current is stable indicates that the primary electron stream leads to
the development of an electric field in the ambient corona which (a)
decelerates the primary beam and (b) produces a neutralizing reverse
current. It appears that, in some circumstances, this electric field
could prevent the primary beam from reaching the chromosphere. In
any case, the electric field acts as an energy exchange mechanism,
extracting kinetic energy from the primary beam and using it to heat
the ambient plasma. This heating is typically so rapid that it must
be expected to have important dynamical consequences.
Title: Polar Electric Fields of Aligned Magnetized Neutron Stars.
Authors: Baker, K. B.; Sturrock, P. A.
Bibcode: 1977BAAS....9..562B
Altcode:
No abstract at ADS
Title: An Overview of the Energy-Flow Problem in Flares (Concluding
Remarks) (Proceedings of the Meeting `How Can Flares be Understood?',
held during the 16th General Assembly of the IAU in Grenoble, France,
on 27 August, 1976.)
Authors: Sturrock, P. A.
Bibcode: 1977SoPh...53..299S
Altcode:
No abstract at ADS
Title: Particle acceleration in axisymmetric, magnetized neutron stars
Authors: Baker, K. B.; Sturrock, P. A.
Bibcode: 1977STIN...7726044B
Altcode:
The potential drop in the polar cap region of a rotating, magnetized
neutron star is found assuming that the magnetic field is dipolar,
with the field aligned (or anti-aligned) with the rotation axis. The
curvature of the field lines is of critical importance. Charge flow
is assumed to be along magnetic field lines. The electric field has a
maximum at radius 1.5 R and the magnitude and functional form of the
current is determined.
Title: Radiation mechanisms and magnetospheric structure of pulsars.
Authors: Sturrock, P. A.; Baker, K. B.
Bibcode: 1977NASCP...2...99S
Altcode: 1977scgr.nasa...99S; 1977NASCP.002...99S
Considerations made in developing a model of pulsars are
explored. Observational data seems to support the argument that pulsar
magnetospheres may contain large masses of plasma. The cascade process
resulting from pair creation enables one to interpret the X-ray emission
from the Crab and Vela pulsars as synchrotron radiation. On the other
hand, the optical radiation from the Crab pulsar is best understood as
coherent curvature radiation. Radio emission is interpreted as curvature
radiation produced by charge bunches moving along magnetic-field
lines. Certain tests of this model are proposed.
Title: Force free magnetic fields and solar activity
Authors: Sturrock, P. A.; Barnes, C. W.
Bibcode: 1976suiprrept.....S
Altcode:
This study, aimed at the prediction of solar flares, centers on
devising methods for calculating magnetic field structures in the
solar atmosphere. Force-free fields comprise an important class
of magnetic-field structures which may be calculated by relaxation
techniques. Models under active consideration involve spherical boundary
surfaces and cylindrical symmetry. Study of the energy of such field
configurations indicates that, for sufficiently large shear, force-free
fields will be unstable against perturbations leading to eruption. The
condition for this instability and the mechanism of instability have
been investigated. The studies are related to erupting prominences
and coronal transients, as well as solar flares.
Title: Reverse current in solar flares
Authors: Knight, J. W.; Sturrock, P. A.
Bibcode: 1976rcsf.rept.....K
Altcode:
The theory that impulsive X ray bursts are produced by high
energy electrons streaming from the corona to the chromosphere is
investigated. Currents associated with these streams are so high
that either the streams do not exist or their current is neutralized
by a reverse current. Analysis of a simple model indicates that the
primary electron stream leads to the development of an electric field
in the ambient corona which decelerates the primary beam and produces a
neutralizing reverse current. It appears that, in some circumstances,
this electric field could prevent the primary beam from reaching
the chromosphere. In any case, the electric field acts as an energy
exchange mechanism, extracting kinetic energy from the primary beam
and using it to heat the ambient plasma. This heating is typically so
rapid that it must be expected to have important dynamical consequences.
Title: Solar activity geomagnetic field and terrestrial weather
Authors: Knight, J. W.; Sturrock, P. A.
Bibcode: 1976Natur.264..239K
Altcode:
IT has long been known that geomagnetic disturbances tend to recur
after ~27 d (refs 1-4). More recently, this effect has been associated
with the rotation of the interplanetary magnetic field5-8,
and some evidence for a relation between the interplanetary magnetic
field and terrestrial weather has also been found9,10. The
interplanetary magnetic field is usually characterised by either
two or four sectors, and this pattern rotates with a fairly well
defined period of ~27.1+/-0.1 d (ref. 7). Such a periodicity leads
naturally to the use of spectral analysis as an independent test of
the reported association between the interplanetary magnetic field
structure and terrestrial weather. We have obtained data on the
geomagnetic activity index Ap for the 1964-70 from the
National Oceanic and Atmospheric Administration and the vorticity area
index used by Wilcox and his colleagues in their analysis9
for the same interval. We wish to form spectra of both time series and
examine the spectra for common features which may be associated with
solar related phenomena. Specifically we look for peaks in the power
spectra of both time series with periods near 27.1 d.
Title: Solar flares
Authors: Sturrock, P. A.
Bibcode: 1976NatH...85...71S
Altcode:
The study of solar flares is reviewed, and attention is drawn to:
prediction of flares and their properties, effects exerted by
flares on the earth, and possible astrophysical implications of
flare studies. Emission of X-rays by the corona and by flares, UV
emission, and production of hydrogen-alpha (red) light and gamma rays
by flares and associations with solar layers are reviewed. Prediction
of the time and circumstances of occurrence of flares, and associated
magnetic field and other properties, is acknowledged as a crucial
goal of flare research. The effect of solar flares on aurorae and on
the geomagnetic field, on radio transmission and radar performance,
and on power distribution networks is pointed out. A possible analogy
between flares and phenomena associated with quasars and explosions
in galaxies is ventured.
Title: Evaporative cooling of flare plasma
Authors: Antiochos, S. K.; Sturrock, P. A.
Bibcode: 1976STIN...7714971A
Altcode:
A one-dimensional loop model for the evaporative cooling of the coronal
flare plasma was investigated. Conductive losses dominated radiative
cooling, and the evaporative velocities were small compared to the sound
speed. The profile and evolution of the temperature were calculated. The
model was in agreement with soft X-ray observations on the evolution
of flare temperatures and emission measures. The effect of evaporation
was to greatly reduce the conductive heat flux into the chromosphere
and to enhance the EUV emission from the coronal flare plasma.
Title: An Evaporative Model of Flare Loops.
Authors: Antiochos, S. K.; Sturrock, P. A.
Bibcode: 1976BAAS....8R.555A
Altcode:
No abstract at ADS
Title: The Reverse Current in Solar Flares.
Authors: Knight, J. W.; Sturrock, P. A.
Bibcode: 1976BAAS....8..495K
Altcode:
No abstract at ADS
Title: Influence of magnetic field structure on the conduction
cooling of flare loops.
Authors: Antiochos, S. K.; Sturrock, P. A.
Bibcode: 1976SoPh...49..359A
Altcode:
A simple model facilitates calculation of the influence of magnetic
field configuration on the conduction cooling rate of a hot post-flare
coronal plasma. The magnetic field is taken to be that produced
by a line dipole or point dipole at an arbitrary depth below the
chromosphere. For the high temperatures (T ≳ 107 K)
produced by flares, the plasma may remain static and isobaric. The
influence of the field is such as to increase the heat flux (per unit
area) into the chromosphere, but to decrease the total conduction
cooling of the flare plasma. This leads to a significant enhancement
of the total energy radiated by the flare plasma.
Title: Pulsar extinction.
Authors: Sturrock, P. A.; Baker, K.; Turk, J. S.
Bibcode: 1976ApJ...206..273S
Altcode:
The radiation properties of pulsars are reinvestigated in the context
of the 'PCFB' model, according to which the radiation originates at
the polar caps and the magnetic-field lines change from a closed to an
open configuration at the 'force-balance' or 'corotation' radius. Major
attention is given to the condition for electron-positron pair creation,
which leads, in turn, to an extinction condition whereby any pulsar
will cease to be a radio emitter after its period has increased beyond
a certain value. This extinction condition is derived on the basis of
a model where the magnetic field is the same as that of a point dipole
located at the center of the star; effects of dipole distortion are
also considered. A comparison of the results with observational data
shows that most pulsars satisfy or nearly satisfy the pair-creation
condition for undistorted dipoles and seem to satisfy the extinction
condition. It is noted that pulsars which should be extinguished
according to the undistorted-dipole model need not be if the magnetic
field is sufficiently distorted at the polar caps.
Title: The relevance of solar flares to astrophysics.
Authors: Sturrock, P. A.; Knight, J. W.
Bibcode: 1976SoPh...47..401S
Altcode:
The physical mechanisms associated with solar flares are reviewed. The
relevance of flare mechanisms to other astrophysical phenomena is
discussed. In this context, specific models of quasars and radio
galaxies, Sco X-1 and gamma-ray bursts are examined.
Title: Report on the solar physics - plasma physics workshop. held
at Stanford University, 17 - 20 September 1974.
Authors: Sturrock, P. A.; Baum, P. J.; Beckers, J. M.; Newman, C. E.;
Priest, E. R.; Rosenberg, H.; Smith, D. F.; Wentzel, D. G.
Bibcode: 1976SoPh...46..411S
Altcode:
This report summarizes the proceedings of a meeting held on
17-20 September 1974, at Stanford University. The purpose was to
explore plasma physics problems which arise in the study of solar
physics. Sessions were concerned with specific questions including
the following: Is the solar plasma thermal or non-thermal? What
spectroscopic data are required? What types of magnetic field structures
exist? Do MHD instabilities occur? Do resistive or non-MHD instabilities
occur? What mechanisms of particle acceleration have been proposed? What
information do we have concerning shock waves? Very few questions were
answered categorically but, for each question, there was discussion
concerning the observational evidence, theoretical analyses, and
existing or potential laboratory and numerical experiments.
Title: Magnetic Models of Solar Flares
Authors: Sturrock, P. A.
Bibcode: 1976saop.book..163S
Altcode:
No abstract at ADS
Title: Magnetic models of solar flares.
Authors: Sturrock, P. A.
Bibcode: 1976npsa.conf..144S
Altcode:
No abstract at ADS
Title: The distribution of redshifts of quasars and related objects.
Authors: Knight, J. W.; Sturrock, P. A.; Switzer, P.
Bibcode: 1976ApJ...203..286K
Altcode:
A statistical analysis of some 386 redshifts is conducted together
with a numerical simulation of 100 sets of synthetic redshifts to
evaluate the possibility that a short-wavelength periodic modulation
may be present in the redshift distribution of quasars and related
compact objects. A previous analysis by Burbidge and O'Dell (1972)
is reviewed, and the inclusion of absorption redshifts in the data
set is discussed. The results of the present analysis are found not
to support claims for the presence of periodic modulations in redshift
distribution.
Title: A model of coronal holes.
Authors: Adams, W. M.; Sturrock, P. A.
Bibcode: 1975ApJ...202..259A
Altcode:
It has been noted that coronal holes appear to be associated with
regions of diverging magnetic field in the corona. We set out to test
the hypothesis that coronal holes may be caused by an increased flow
of energy into the solar wind resulting directly from this diverging
magnetic field pattern. Simple models were devised to approximate
the energy flow down into the transition region and up into the solar
wind as a function of the temperature, density, and rate of field line
divergence in the corona. By assuming the rate of mechanical energy
influx into the corona to be constant, it was then possible to solve
numerically for the coronal temperature and density as a function of
the rate of field line divergence. The results of these calculations
demonstrate that a diverging field pattern can, indeed, bring about
reductions in the temperature and density at the base of the corona
comparable to those observed in coronal holes.
Title: Clusters in the distribution of pulsars in period, pulse-width,
and age
Authors: Baker, K. B.; Sturrock, P. A.
Bibcode: 1975STIN...7610939B
Altcode:
The question of whether pulsars form a single group or whether pulsars
come in two or more different groups is discussed. It is proposed that
such groups might be related to several factors such as the initial
creation of the neutron star, or the orientation of the magnetic field
axis with the spin axis. Various statistical models are examined.
Title: The solar atmosphere and the structure of active regions
Authors: Sturrock, P. A.
Bibcode: 1975suiprreptQ....S
Altcode:
Numerical analyses of solar activities are presented. The effect of
these activities on aircraft and weather conditions was studied. Topics
considered are: (1) solar flares; (2) solar X-rays; and (3) solar
magnetic fields (charts are shown).
Title: Force free magnetic fields and solar activity
Authors: Sturrock, P. A.; Barnes, C. W.
Bibcode: 1975STIN...7621113S
Altcode:
This report, aimed at the prediction of solar flares, centers on
devising methods for calculating magnetic field structures in the
solar atmosphere. Force-free fields comprise an important class
of magnetic-field structures which may be calculated by relaxation
techniques. Models of force-free fields with cylindrical symmetry,
based on a spherical boundary surface, were calculated. Evaluation of
the energy of such structures provides information about the eruption
of closed-field patterns to form open current sheets which can then
lead to solar flares.
Title: Stanford Workshop on Extraterrestrial civilization Opening
a new Scientific Dialog
Authors: Carlson, J. B.; Sturrock, P. A.
Bibcode: 1975OrLi....6..459C
Altcode:
A workshop, held at Stanford University on August 29 and 30, 1974,
brought together two groups of scientists interested in extraterrestrial
civilization (ETC). Group A is comprised of scientists studying the
problem theoretically in terms of physical, astronomical and biological
knowledge, and those considering searching for extraterrestrial
radio signals which might provide evidence for ETC. Group B comprises
scientists pursuing the UFO problem their activities comprise analysis
of soft evidence such as eye-witness reports, and of hard evidence such
as photographs. Discussion at the Workshop centered on the following
topics: the existence of ETC; interstellar travel; interstellar
communication; human contact with ETC; UFO evidence; evaluation of the
UFO phenomenon; and assessment of our ignorance. It was generally agreed
that radio search for ETC is a promising endeavor. Althought it was
agreed that study of the UFO problem is a justifiable pursuit, members
of Group A chose to remain skeptical in the absence of unimpeachable
evidence concerning the nature of the phenomenon.
Title: Pulsar extinction.
Authors: Sturrock, P. A.; Baker, K.; Turk, J. S.
Bibcode: 1975puex.book.....S
Altcode: 1975STIN...7529969S
Radio emission from pulsars, attributed to an instability associated
with the creation of electron-positron pairs from gamma rays was
investigated. The condition for pair creation therefore lead to an
extinction condition. The relevant physical processes were analyzed
in the context of a mathematical model, according to which radiation
originated at the polar caps and magnetic field lines changed from a
closed configuration to an open configuration at the force balance or
corotation radius.
Title: Calculation of Solar Force Free Magnetic Field Structures.
Authors: Barnes, C. W.; Sturrock, P. A.
Bibcode: 1975BAAS....7R.459B
Altcode:
No abstract at ADS
Title: Solar Activity, Geomagnetic Field and Terrestrial Weather.
Authors: Knight, J. W.; Sturrock, P. A.
Bibcode: 1975BAAS....7..474K
Altcode:
No abstract at ADS
Title: Clusters in the Distribution of Pulsars in Period, Pulse
Width and Age
Authors: Baker, K. B.; Sturrock, P. A.
Bibcode: 1975BAAS....7R.455B
Altcode:
No abstract at ADS
Title: Thermal Instability in Loop Prominence Systems
Authors: Antiochos, S. K.; Sturrock, P. A.
Bibcode: 1975BAAS....7..472A
Altcode:
No abstract at ADS
Title: Reply to Billings Concerning `Two-fluid Model of the Solar
Corona'
Authors: Knight, J. W.; Newman, C. E.; Sturrock, P. A.
Bibcode: 1975SoPh...41..371K
Altcode:
No abstract at ADS
Title: Search for correlation between geomagnetic disturbances
and mortality
Authors: Lipa, B. J.; Barnes, C. W.; Sturrock, P. A.; Feinleib, M.;
Rogot, E.
Bibcode: 1975STIN...7520189L
Altcode:
Statistical evaluation of death rates in the U.S.A. from heart diseases
or stroke did not show any correlation with measured geomagnetic
pulsations and thus do not support a claimed relationship between
geomagnetic activity and mortality rates to low frequency fluctuations
of the earth's magnetic field.
Title: A Model of Coronal Holes
Authors: Adams, W. M.; Sturrock, P. A.
Bibcode: 1975BAAS....7..358A
Altcode:
No abstract at ADS
Title: Optical radiation from the Crab pulsar.
Authors: Sturrock, P. A.; Petrosian, V.; Turk, J. S.
Bibcode: 1975ApJ...196...73S
Altcode:
Possible mechanisms for producing the optical radiation from the Crab
pulsar are proposed and discussed. There are severe difficulties in
interpreting the radiation as being produced by an incoherent process,
whether it be synchrotron radiation, inverse-Compton radiation, or
curvature radiation. It is proposed, therefore, that radiation in the
optical part of the spectrum is coherent. In the polar cap model,
a small bunch of electrons and positrons forms near each primary
electron as a result of the pair-production cascade process. Turbulent
electric field components associated with large-scale bunching may
lead to separation of the electrons and positrons in space and in
energy, with the result that coherent radiation may be produced by the
electrons, the positrons, or both. Calculations, which involve a number
of simplifying assumptions, indicate that the optical radiation from
the Crab pulsar can be understood in this way if the mass of the star
is approximately 0.3 solar mass. Various consequences of this model,
which may be subjected to observational test, are discussed.
Title: Centrifugal instability of the jovian magnetosphere and its
interaction with the solar wind
Authors: Michel, F. C.; Sturrock, P. A.
Bibcode: 1974P&SS...22.1501M
Altcode:
The outer regions ( r > 2.3 Rj; Rj = radius
of Jupiter) of the magnetosphere of Jupiter will systematically
accumulate plasma. If sufficient plasma accumulates, the field lines
must open to allow the plasma to escape. Available energy sources
appear able to supply plasma at a high enough rate to keep the field
lines constantly open beyond about 60 RJ. We suggest that
the solar wind interaction with Jupiter may be essentially different
from that with the Earth, with the Jovian magnetosphere opening up to
form a planetary wind.
Title: Plasma Turbulence. (Book Reviews: Plasma Astrophysics)
Authors: Sturrock, Peter A.
Bibcode: 1974Sci...186..626S
Altcode: 1974Sci...186..626K
No abstract at ADS
Title: Spectral Analysis of the Distribution of Quasar Redshifts.
Authors: Knight, J. W.; Sturrock, P. A.
Bibcode: 1974BAAS....6..449K
Altcode:
No abstract at ADS
Title: Two-Fluid Model of the Solar Corona
Authors: Knight, J. W.; Newman, C. E.; Sturrock, P. A.
Bibcode: 1974SoPh...37..183K
Altcode:
A simple model of the lower corona which allows for a possible
difference in the electron and proton temperatures is analyzed. With the
introduction of a phenomenological heating term, temperature and density
profiles are calculated for several different cases. It is found that,
under certain circumstances, the electron and proton temperatures may
differ significantly.
Title: Optical Radiation from the Crab Pulsar
Authors: Sturrock, P. A.; Petrosian, V.; Turk, J. S.
Bibcode: 1974BAAS....6Q.272S
Altcode:
No abstract at ADS
Title: Division of Solar Physics: 1974. Annual report of AAS Division.
Authors: Sturrock, P. A.
Bibcode: 1974BAAS....6..494S
Altcode:
No abstract at ADS
Title: Model of coronal holes.
Authors: Adams, W. M.; Sturrock, P. A.
Bibcode: 1974mch..book.....A
Altcode:
No abstract at ADS
Title: Particle Acceleration in Solar Flares
Authors: Sturrock, P. A.
Bibcode: 1974IAUS...57..437S
Altcode:
A review of observational data supports the proposal that there are two
distinct phases of particle acceleration in solar flares. 'Phase 1' is
associated with the flash phase and is here interpreted as acceleration
during field-line reconnection. 'Phase 2' is associated with type II
and type IV radio bursts, and is ascribed to stochastic acceleration
in the turbulent plasma behind a magnetohydrodynamic shock formed
ahead of an ejected plasmoid.
Title: Solar physics. Plasma physics workshop.
Authors: Baum, P. J.; Beckers, J. M.; Newman, C. E.; Priest, E. R.;
Rosenberg, H.; Smith, D. F.; Sturrock, P. A.; Wentzel, D. G.
Bibcode: 1974sppp.book.....B
Altcode:
No abstract at ADS
Title: Do Pulsars Turn Off?
Authors: Sturrock, P. A.
Bibcode: 1973BAAS....5..426S
Altcode:
No abstract at ADS
Title: Test for Planetary Influences on Solar Activity
Authors: Dingle, L. A.; Van Hoven, G.; Sturrock, P. A.
Bibcode: 1973SoPh...31..243D
Altcode:
A method due to Schuster is used to test the hypothesis that solar
activity is influenced by tides raised in the Sun's atmosphere by
planets. We calculate the distribution in longtitude of over 1000
flares occurring in a 61/2 yr segment of solar cycle 19, referring
the longitude system in turn to the orbital positions of Jupiter and
Venus. The resulting distributions show no evidence for a tidal effect.
Title: Evaluation of Astrophysical Hypotheses
Authors: Sturrock, P. A.
Bibcode: 1973ApJ...182..569S
Altcode:
The aim of this article is to set out a bookkeeping procedure for
formalizing the process of assessing a hypothesis by comparison
of conclusions drawn theoretically from this hypothesis with facts
obtained by reduction of observational data. The formalism used is
that of probability theory. A key role is played by Bayes's rule
representing the inductive process of adjusting a degree of belief
in response to new information. The following model is used. Between
observation and theory is an "interface" which comprises a number of
independent items. Each item comprises a set of mutually exclusive
statements. Probabilities assigned to statements of an item by
reduction of observational data comprise a "fact." Probabilities
assigned to statements of an item by theoretical analysis of a
considered hypothesis represent a "conclusion" drawn from that
hypothesis. Each fact should be free from theoretical bias and each
conclusion free from observational bias. The model requires that one
consider a complete set of mutually exclusive hypotheses. Where this
cannot be done explicitly, it may be achieved by the introduction of a
"null hypothesis or "ignorance hypothesis." "Conclusions" drawn from
this hypothesis are chosen to be maximally noncommittal. Formulae are
derived which show (a) how the probability of each hypothesis should
be adjusted in response to information concerning one item, and (b)
how such estimates concerning more than one item may be combined. The
procedure is illustrated by a "work sheet" showing how a few facts
and conclusions concerning pulsars were combined to appraise the
neutron-star and whitedwarf hypotheses. Subject headings: neutron
stars - pulsars - white dwarf stars
Title: Unexplained Phenomena. (Book Reviews: UFO's--A Scientific
Debate. An AAAS symposium, Boston, Dec. 1969)
Authors: Sturrock, Peter A.
Bibcode: 1973Sci...180..593S
Altcode:
No abstract at ADS
Title: Pulsar Magnetospheres, Braking Index, Polar Caps, and
PERIOD-PULSE-W1DTH Distribution
Authors: Roberts, D. H.; Sturrock, P. A.
Bibcode: 1973ApJ...181..161R
Altcode:
Recent studies indicate that pulsar magnetospheres may contain
nonrelativistic material in amounts sufficient to alter drastically
the magnetic-field configuration. The most important change in the
magnetosphere is to move the boundary between open and closed field
lines from the light cylinder into a region located at r RFB. The
"force-balance radius" RFB is the radius at which the centrifugal
and gravitational forces cancel, and is always much less than the
radius of the light cylinder. We have constructed approximate models
for the magnetic field structure, considering in detail the aligned
and orthogonal cases. If the magnetic field is initially closed (out
to the light cylinder), gas will collect where there is "microscopic
stability." Such locations exist for r > RF3. Most of this region
is "macroscopically unstable" since, when sufficient gas is collected,
the centrifugal force overcomes the magnetic stress and converts close
field lines into open field lines. However, there is a small region
near r = RFB, both microscopically and macroscopically stable, where
gas can collect and remain. Such a magnetospheric structure leads to
a braking index n = 7/3, in good agreement with the observed braking
index of the Crab pulsar. We calculate the polar-cap boundaries,
and the resulting period-pulse-width distribution agrees well with
observational data. It is suggested that the accumulation of gas and
the occurrence of instabijities can explain the timing irregularities
("noise") and glitches observed in the Crab pulsar. Subject headings:
Crab Nebula - gas dynamics - magnetic fields - pulsars - radio radiation
Title: Test for Planetary Influence on Solar Activity
Authors: Dingle, L. A.; van Hoven, G.; Sturrock, P. A.
Bibcode: 1973BAAS....5Q.271D
Altcode:
No abstract at ADS
Title: Mass Flow in Solar Flares
Authors: Sturrock, P. A.
Bibcode: 1973BAAS....5U.280S
Altcode:
No abstract at ADS
Title: A Model for Impulsive Solar X-Ray Bursts
Authors: Petrosian, Vahé; Sturrock, P. A.
Bibcode: 1973BAAS....5Q.278P
Altcode:
No abstract at ADS
Title: Solar Flare Theory
Authors: Sturrock, P. A.
Bibcode: 1973str..conf...63S
Altcode:
No abstract at ADS
Title: Storage and Release of Non-Thermal Energy in the Sun's
Atmosphere
Authors: Sturrock, P. A.
Bibcode: 1973str..conf..275S
Altcode:
No abstract at ADS
Title: Mass Motion in Solar Flares
Authors: Sturrock, P. A.
Bibcode: 1973NASSP.342....3S
Altcode: 1973heps.conf....3S
No abstract at ADS
Title: Magnetosphere Structure and Radiation Methanisms of Pulsars
Authors: Roberts, D. H.; Sturrock, P. A.; Turk, S. J.
Bibcode: 1973NYASA.224..206R
Altcode:
No abstract at ADS
Title: Activity in Galaxies and Quasars
Authors: Sturrock, P. A.; Barnes, C.
Bibcode: 1972ApJ...176...31S
Altcode:
Activity in galaxies and quasars is interpreted in terms of plasma
processes occurring in the magnetosphere of a certain magnetoid
model. This magnetoid comprises a core and an annulus rotating
about a common axis with different angular velocities. The
magnetic field linking the core to the annulus may begin in an
initial current-free state but will be distorted along a sequence
of force-free configurations. After a finite differential rotation,
the force-free configuration has higher energy than a corresponding
open-field configuration. It is conjectured that the transition from
the closed configuration to an open configuration will be effected by
an MHD "eruptive" instability, and that such eruptions lead to high-
velocity clouds of cool gas identified with clouds producing absorption
lines in quasars. The open magnetic-field configuration necessarily
contains current sheets. The magnetic free energy of these current
sheets may be released explosively by the flare mechanism. The ejection
of radio clouds from galaxies and quasars is attributed to "galactic
flares." Current sheets contain mildly relativistic electrons moving
in directions partially transverse to the magnetic field. Synchrotron
radiation from these electrons is held to be responsible for the
nonthermal radiation from quasars and certain galaxies. It is proposed
that minor instabilities of the current sheets are responsible for
fluctuations in the nonthermal luminosity and for small-scale radio
bursts sometimes observed in galaxies and quasars
Title: Force-Free Magnetic-Field Structures and their Role in Solar
Activity
Authors: Barnes, C. W.; Sturrock, P. A.
Bibcode: 1972BAAS....4Q.377B
Altcode:
No abstract at ADS
Title: Force-Free Magnetic-Field Structures and Their Role in Solar
Activity
Authors: Barnes, C. W.; Sturrock, P. A.
Bibcode: 1972ApJ...174..659B
Altcode:
Magnetic-field structures in solar active regions are expected to
be substantially force-free. A method is proposed for calculating
such structures by numencal methods. The method is applied to the
study of the magnetic-field pattern associated with a sunspot of one
polarity surrounded by a magnetic region of opposite polarity when
the sunspot rotates with respect to the surrounding region. Rotation
introduces a toroidal component of magnetic field, and the associated
pressure leads to inflation of the magnetic-field pattern. If the
differential rotation exceeds about 1S0 , the force-free magnetic field
has energy greater than that of an open magnetic-field configuration
with the same photospheric boundary conditions. It is concluded that,
beyond this point, the force-free field structure is metastable and
can be converted into an open field structure by an explosive MHD
instability. The resulting field pattern is then of the form previously
proposed as the site of high-energy solar flares.
Title: Pulsar magnetospheres, braking index, polar caps and
period-pulse-width distribution.
Authors: Roberts, D. H.; Sturrock, P. A.
Bibcode: 1972BAAS....4S.414R
Altcode:
No abstract at ADS
Title: The Structure of Pulsar Magnetospheres.
Authors: Roberts, D. H.; Sturrock, P. A.
Bibcode: 1972ApJ...173L..33R
Altcode:
Currents drawn from the neutron-star surface may lead to surface heating
and hence to evaporation. Substantial accumulation of evaporated gas
can occur only in the "force balance" regions where gravitational
and centrifugal forces balance. It is argued that the Y-type neutral
points, separating closed and open field lines, must be at the same
location. For this model, the braking index n = 7/3 and the expected
period-pulse-width distribution and period-age distribution agree well
with observational data. A glitch is interpreted as an instability
leading to the election and/or dumping of accumulated gas.
Title: A Classification of Magnetic Field Configurations Associated
with Solar Flares
Authors: Sturrock, P. A.
Bibcode: 1972SoPh...23..438S
Altcode:
On the assumption that solar flares are due to instabilities which
occur in current sheets in the Sun's atmosphere, one may classify
magnetic-field configurations associated with flares into two types. One
is characterized by `closed' current sheets, magnetic-field lines
adjacent to these sheets beginning and ending at the Sun's surface. The
other is characterized by `open' current sheets, magnetic-field lines
adjacent to these sheets beginning at the Sun's surface but extending
out into interplanetary space. Flares associated with open current
sheets can produce Type III radio bursts and high-energy-particle
events, but flares associated with closed current sheets cannot. The
flare of July 6, 1966 apparently consisted of one flare of each type.
Title: The Braking Index and Period-Pulse Distribution of Pulsars.
Authors: Roberts, D. H.; Sturrock, P. A.
Bibcode: 1972ApJ...172..435R
Altcode:
The braking index n and the period-pulse-width distribution of pulsars
are reinvestigated by relaxing the conventional assumption that Ry =
RL, where Ry is the radius of the neutral points marking the transition
from closed to open field lines, and RL is the radius of the "light
cylinder." This assumption is replaced by the relation Ry = R' flRL",
where R is the radius of the neutron star. It is found that a good
fit to the period-pulse-width distribution can be obtained for in
the range 0.5 < ,; < 0.7. The relation n = I + 2 then gives n
= 2 2 + 0 2 which is in good agreement with values measured for the
Crab pulsar. This model implies that one or two pulsars should show
an interpulse, in agreement with observation (two). This model leads
to new estimates of the surface magnetic field strength B of pulsars,
giving B = 10112 gauss for the Crab pulsar, and indicates that pulsar
magnetospheres are subject to irregular changes associated with
irregularities in period.
Title: Activity in Galaxies and Quasars.
Authors: Sturrock, P. A.
Bibcode: 1972BAAS....4..232S
Altcode:
No abstract at ADS
Title: Periodicity in the Radiofrequency Spectrum of the Pulsar
CP 0328
Authors: Sturrock, P. A.; Antiochos, S.; Switzer, P.; Vallée, J.
Bibcode: 1972ApJ...171L..27S
Altcode:
Long-term averaging of a sequence of wide-band radiofrequency
spectra of CP 0328 reveals a periodicity not apparent in the original
spectra. This may be caused by a mechanism intrinsic to the source,
or by a propagation mechanism distinct from ordinary scintillation.
Title: Magnetic Models of Solar Flares
Authors: Sturrock, P. A.
Bibcode: 1972PrAA...30..163S
Altcode:
No abstract at ADS
Title: On the Possibility of Pulsar Action in Quasars
Authors: Sturrock, P. A.
Bibcode: 1971ApJ...170...85S
Altcode:
A recently proposed theory of pulsars is taken as a basis for evaluating
Morrison's proposal that quasars may be giant pulsars. It is found that
an object with mass 10 g, radius 10 0cm, and magnetic field strength
10 gauss (Morrison's parameters) would not exhibit pulsar activity
but would he an intense source of -rays with luminosity exceeding 10
ergs 5-1 Pulsar activity would occur if the field strength were 101.7
gauss or more, but the lifetime would be only 101 1 years. Most of the
power (>1011 ergs ) would be emitted as -rays. One must conclude, on
the basis of this theory, that quasars are probably not giant pulsars
There seems to be a much stronger similarity between quasars and the
X-ray source Sco X-1 than between quasars and pulsars.
Title: The Period-Age Distribution of Pulsars
Authors: Sturrock, P. A.
Bibcode: 1971ApJ...169L...7S
Altcode:
A recently proposed model of pulsars leads to a constraint on the values
of period T and "age" r [= T(dT/dt)-1] of radio-emitting neutron stars
and a similar constraint for optically emitting neutron stars. These
constraints compare satisfactorily with available data.
Title: Model of Pulsar Magnetospheres.
Authors: Roberts, D. H.; Sturrock, P. A.
Bibcode: 1971BAAS....3R.463R
Altcode:
No abstract at ADS
Title: Maximum Temperatures for Radiation from Plasma Waves
Authors: Smith, D. F.; Sturrock, P. A.
Bibcode: 1971Ap&SS..12..411S
Altcode:
We derive upper limits to the radiation temperaturesT t(k)
for emission near the fundamental and second harmonic of the electron
plasma frequency in terms of the effective temperature for plasma wavesT
l(k'). We findT t(k)≲(c/(3)1/2
V e)3 T l(k') for emission near the
fundamental which differs from the result of Melrose (1970b) by the
factor in parentheses. This factor can exceed 4×104 in some
plasmas. The conditions under which this limit could be reached are
delinated. For emission near the second harmonicT t(k)≤T
l(k') since the absorption coefficient in this case can
only be positive.
Title: Longitude Distribution of Solar Flares
Authors: Fung, P. C. W.; Sturrock, P. A.; Switzer, P.; Van Hoven, G.
Bibcode: 1971SoPh...18...90F
Altcode:
Statistical tests, based on the maximum-likelihood method, have
been performed on flare series extending over several years. If all
flares in each plage region are taken into account, a rich spectrum
is obtained. If one carries out similar analysis of a `reduced' flare
series, which includes at most one flare from each plage region,
the spectrum is almost devoid of structure, and what structure does
remain is not statistically significant. The inference is that solar
activity does not display genuine rigid-rotation modulation, but that
repeated events from individual centers of activity yield modulation
which may be mistaken for rigid-rotation modulation.
Title: A Model of Pulsars
Authors: Sturrock, P. A.
Bibcode: 1971ApJ...164..529S
Altcode:
The model comprises a rotating neutron star (R 106 cm) with a strong
magnetic field (B 1012 gauss). Magnetic-field lines which reach the
light cylinder are open field lines which connect to the surface
of the star at the "polar caps." Each polar cap contains two zones,
an electron polar zone (EPZ) and a proton polar zone (PPZ) from which
electrons and protons, respectively, stream from the star. Acceleration
of each stream is effected close to the surface of the star. Primary
electrons in the EPZ follow magnetic-field lines; this acceleration
leads to -radiation. It is found that, if the period T is less than 1
sec, these -rays annihilate to produce electron-positron pairs. Steady
flow is then impossible, but flow comprising a sequence of charge
sheets seems possible. These charge sheets produce radio emission. This
may explain why most pulsars have periods shorter than 1 sec. If the
sheets are thin, the spectrum varies as -5/3 and provides a good fit
to the luminosity spectrum of CP 1919. If the sheet has a rectangular
current distribution, the spectrum varies as p '1/3 and provides a
good fit to the radio luminosity spectrum of the Crab pulsar. In each
EPZ of the Crab pulsar, -ray emission and pair creation combine in a
cascade. The resulting flux of electrons and positrons from the star is
of order 1041 . The secondary electrons and positrons radiate by the
synchrotron mechanism to yield a -1I2 spectrum, but the radiation is
self-absorbed in the X-ray part of the spectrum and cannot explain the
optical radiation from the Crab pulsar. The Crab pulsar spins rapidly
enough for pair production to occur at the PPZs also, apparently out
to several times R. In consequence, synchrotron radiation from the
electron-positron flux is self-absorbed at much lower frequencies. It
seems that the optical and X-ray radiation from the Crab pulsar can
be understood quantitatively in this way. The optical, X-ray, and -ray
flux expected from this model of the Crab pulsar can be reconciled with
observation if the rotation axis, dipole axis, and line of sight are
so related that we receive radiation from both PPZs but no radiation
from the EPZs.
Title: Longitude distribution of solar flares.
Authors: Fung, P. C. W.; Sturrock, P. A.; Switzer, P.; van Hoven, G.
Bibcode: 1971SUIPR.393.....F
Altcode:
No abstract at ADS
Title: Particle Flux Associated with Stochastic Processes
Authors: Newman, C. E.; Sturrock, P. A.; Tademaru, E.
Bibcode: 1971Ap&SS..10..102N
Altcode:
The Lagrange expansion, which may be used to derive the Fokker-Planck
equation, is here used to derive the corresponding expression for
the flux of particles subject to a stochastic scattering process. The
coefficients which occur in this expression are, in general, not the
same as the coefficients which occur in the Fokker-Planck equation
itself. In the special case that the particle distribution involves
only one independent variable, the particle flux is determined by the
familiar Fokker-Planck coefficients. Evaluation of particle flux is
of special interest in the study of stochastic acceleration.
Title: Possible High-frequency Modulation of Light from the Crab
Pulsar
Authors: Sturrock, P. A.
Bibcode: 1971Natur.229..186S
Altcode:
ONE of us (P. A. S.) has recently proposed a model of pulsars, the
properties of which were compared with the known radio, optical and
X-ray emission from the Crab pulsar1. We now wish to point
out that the model predicts a high-frequency modulation of the optical,
X-ray and γ-ray radiation which might be detected in the optical part
of the spectrum.
Title: The period-age distribution of pulsars.
Authors: Sturrock, P. A.
Bibcode: 1971SUIPR.427.....S
Altcode:
No abstract at ADS
Title: A Model of Pulsars.
Authors: Sturrock, P. A.
Bibcode: 1970BAAS....2Q.348S
Altcode:
No abstract at ADS
Title: Pulsar Radiation Mechanisms
Authors: Sturrock, P. A.
Bibcode: 1970Natur.227..465S
Altcode:
Gamma rays produced by electrons accelerated in the strong magnetic
fields of neutron stars annihilate to electron-positron pairs. This
leads to a two-stream situation, which results in bunching and coherent
radio emission.
Title: Possible Radiation Mechanisms for Pulsars
Authors: Sturrock, P. A.
Bibcode: 1970BAAS....2Q.221S
Altcode:
No abstract at ADS
Title: A Model for Extragalactic Radio Sources
Authors: Mills, David M.; Sturrock, Peter A.
Bibcode: 1970BAAS....2S.209M
Altcode:
No abstract at ADS
Title: On the Possibility of Accretion by Quasi-Stellar Sources
Authors: Sturrock, P. A.
Bibcode: 1970ApJ...159L.139S
Altcode:
An estimate of the rate of accretion by a QSO depends upon the
hypotheses on which the calculation is based.
Title: A Model of Extragalactic Radio Sources
Authors: Mills, D. M.; Sturrock, P. A.
Bibcode: 1970ApL.....5..105M
Altcode:
No abstract at ADS
Title: Theoretical study of nonthermal phenomena of astrophysics.
Authors: Sturrock, P. A.
Bibcode: 1970tsnp.book.....S
Altcode:
No abstract at ADS
Title: The Jet of M87 as a Galactic Flare
Authors: Sturrock, P. A.
Bibcode: 1969BAAS....1T.262S
Altcode:
No abstract at ADS
Title: A Statistical Analysis of Flare Events and its Implications
Concerning the Sun's Internal Rotation
Authors: van Hoven, Gerard; Sturrock, P. A.; Switzer, Paul
Bibcode: 1969BAAS....1R.294V
Altcode:
No abstract at ADS
Title: A Mechanism for Pulsar Radio Emission
Authors: Sturrock, P. A.; Moore, R. L.
Bibcode: 1969BAAS....1T.206S
Altcode:
No abstract at ADS
Title: A Model of Quasi-stellar Radio Sources
Authors: Sturrock, P. A.
Bibcode: 1969tsra.conf..147S
Altcode: 1969qhea.conf..147S
No abstract at ADS
Title: Explosions in galaxies and quasars
Authors: Sturrock, P. A.
Bibcode: 1969pia..conf..297S
Altcode:
No abstract at ADS
Title: Proceedings of the Conference on Seyfert Galaxies and Related
Objects: 43: A Mechanism for Quasar Continuum Radiation and its
Possible Application to Seyfert Nuclei
Authors: Sturrock, P. A.; Feldman, P. A.
Bibcode: 1968AJ.....73..910S
Altcode:
No abstract at ADS
Title: Magnetic-Field Structure Associated with Coronal Streamers
Authors: Sturrock, P. A.; Smith, Sheldon M.
Bibcode: 1968SoPh....5...87S
Altcode:
An interesting coronal structure was observed during the solar eclipse
of May 30, 1965. This comprised a series of bright arches centered
approximately on a quiescent prominence. A bright ray originated near
the top of one of the arches and pointed almost radially away from
the photosphere. The ray could be followed for 1.5 solar radii and
was deflected towards a direction parallel to the equatorial plane.
Title: A Mechanism for Continuum Radiation from Quasi-Stellar Radio
Sources with Application to 3c 273B
Authors: Sturrock, P. A.; Feldman, P. A.
Bibcode: 1968ApJ...152L..39S
Altcode:
This mechanism requires a quasi-stellar radio source (QSO) model in
which the central object is magnetically coupled to intergalactic
space. Intergalactic plasma is accreted and flows inward, attaining
supersonic speeds. The kinetic energy of this gas is converted to
(relativistic) electron thermal energy at a collision-free shock
front. The electron energy is rapidly radiated by the synchrotron
process. The quasi-stellar radio source 3C 273B is discussed
quantitatively, and it is shown that the physical character- istics
of the line-emission region and of the meter-wave radio region are
consistent with those proposed for the continuum-emission region
Title: Two-Fluid Model of the Solar Wind
Authors: Hartle, R. E.; Sturrock, P. A.
Bibcode: 1968ApJ...151.1155H
Altcode:
This theoretical study of the solar wind takes account of the fact
that the collisional energy-exchange rate between electrons and
protons is sufficiently slow that the electrons and protons can
have quite dif- ferent temperatures. The basic equations comprise a
continuity equation, an equation of motion, and two heat equations,
one for each species-electrons and protons. Each heat equation
takes account of thermal conductivity in that species and energy
exchange with the other species. In order to determine the region of
applicability of these fluid-type equations, the electron-electron,
and proton-proton energy/ momentum relaxation rates are compared with
the local expansion rate. These comparisons indicate that, for the
model investigated, the use of fluid equations is justifiable out to
about 1O~ Ro. The conditions imposed on the solution of these coupled
equations are that the electron (or proton) density and the electron and
proton temperatures should have specified values at the "base" (inner
boundary) of the model, that there should be a subsonic-supersonic flow
transition, and that the electron and proton temperatures should tend to
zero as the heliocentric radius tends to infinity. The effects of solar
rotation, viscosity, non-thermal heat sources (e.g., wave dissipation),
and magnetic field are neglect- ed, and the flow pattern is required
to be steady and spherically symmetrical These requirements appear
to determine the model uniquely. The equations are solved numerically
using iterative procedures It is found that a good fit to the Blackwell
model of the electron density of the outer corona is ob- tained,
over the range 2-20 Ro, for the following choice of number density n
(electrons or protons), electron temperature Te, and proton temperature
T~ at the base, the radius of which is taken to be Ro: no = 3 X 1O~
cm3, T60 = T~0 = 2 X 106 ° K. If the base is regarded as being 2
Ro (the radius at which agreement with the Blackwell model begins),
the values would be no = 1.5 X 106 cm3; Te0 1 5 X 106 ° K, T~0 = 1.2
X 106 ° K. This model has the following values for these variables
and for the velocity v at Earth's orbit: ~E = 15 cm3, VE 250 km sec',
TeE = 3 5 X 10~ °K, T~E = 4 4 X 1O~ ° K. These results for ~B, VE,
TPE fit most nearly the observed characteristics of the solar wind
at geomagneti- cally quiet times, although the density is somewhat
high, the velocity is somewhat low, and the proton temperature is
quite low. It is believed that the discrepancy between this model
and Blackwell data between the base of the corona and 2 Ro is to be
attributed to coronal heating, and that departures of the solar-wind
charac- teristics near Earth from those of this model are also to
be attributed to heating by a flux of non-thermal energy; additional
heating inside the radius at which the flow becomes supersonic, which is
at 7.1 Ro, will produce primarily an increase in solar-wind velocity,
whereas additional heating outside 7.1 Ro will produce primarily an
increase in solar-wind temperature. Data are presented which show
the effect upon the characteristics of this model at Earth's orbit
of a change in density or in electron or proton temperature at the
base. The density increases sharply with the base electron temperature,
even more sharply with the base proton temperature, and approximately
linearly with the base density. The velocity varies almost linearly
with the base electron temperature, and is insensitive to the other
base quantities The proton temperature varies approximately linearly
with the base density and electron temperature, but increases sharply
with the base proton temperature The electron temperature increases
with the base electron temperature but varies inversely with the base
density and proton temperature; these variations are not stron
Title: Buchbesprechungen über: Plasma Astrophysics,
(Ed. P. A. STURROCK) (Ref. E. RICHTER)
Authors: Sturrock, P. A.
Bibcode: 1968ZA.....68..421S
Altcode:
No abstract at ADS
Title: A Model of Solar Flares.
Authors: Sturrock, P. A.
Bibcode: 1968AJS....73Q..79S
Altcode:
Stanford University.-A model of solar flares is proposed in which
the preflare state comprises a bipolar magnetic-field structure
associated with a bipolar photospheric magnetic region. At low heights
the magnetic lines are closed and the field is force-free but not
necessarily current-free; energy stored in this region is derived from
photospheric motion. At greater heights, the magnetic lines extend out
from the sun to form a bipolar flux tube containing a "sheet pinch" ;
energy stored in this region is derived from the non thermal energy flux
which heats the sun's atmosphere. Such a sheet pinch is probably the
core of a coronal streamer. The flare is identified with a progressive
reconnection of magnetic field by the tearing-mode instability to
release the excess magnetic energy associated with the electric
currents. This process in the closed-field region would begin at the
photo- spheric neutral line and work outwards across successive magnetic
shells, giving rise to an optical flare with familiar characteristics
but not to a radio or particle event. This stage may be slow or
rapid. When the reconnection process reaches the open magnetic lines,
there may be a rapid (in about 1 sec) acceleration of electrons,
which can produce a type III radio burst, since the sheet pinch will
have a scale of order 10~ cm if its thickeuss is set by the resistive
diffusion rate. Subsequent reconnection, producing further high-energy
events, may proceed rapidly (102 sec) by the Petschek mechanism if the
turbulent state set up by the instability permits diffusion at the Bohm
rate. The decay phase of the optical flare (10~ sec) may be attributed
to slow heating of the chromosphere by thermal conduction from coronal
gas heated by the flare to 1070K or more. Research sponsored by Air
Force Office of Scientific Research, Office of Aerospace Research,
United States Air Force Contract AF-49(638)-1321.
Title: A Model of Solar Flares
Authors: Sturrock, P. A.
Bibcode: 1968IAUS...35..471S
Altcode:
No abstract at ADS
Title: Magnetic Field Structure Associated with Coronal Streamers.
Authors: Sturrock, P. A.; Smith, S. M.
Bibcode: 1968AJS....73R..79S
Altcode:
An interesting coronal structure was observed during the solar eclipse
of 30 May 1965. This comprised a series of bright arches centered
approximately on a quiescent prominence. A bright ray originated
near the top of one of the arches and pointed almost radially away
from the photosphere. The ray could be followed 1.5 solar radii from
the arch top, and was deflected toward a direction parallel to the
equatorial plane. By comparing the photographs with Fraunhofer maps
and magnetograms, the following interpretation of the structure was
obtained: The prominence lies above the neutral line of an extended
bipolar magnetic region. The bright arches coincide with flux
tubes arising from small photospheric regions of enhanced magnetic
field strength. The ray represents a projection view of a region of
enhanced plasma density in the neighborhood of a current sheet which
separates two flux tubes of opposite polarity. The ray is interpreted
as a cornonal streamer, and it is suggested that all streamers are
related to current sheets. This work was supported in part by the Air
Force Office of Scientific Research, U. S. Air Force under Contract
AF 49(638)-1321, and in part by NASA, Ames Research Center.
Title: Solar Oblateness and Magnetic Field
Authors: Sturrock, P. A.; Gilvarry, J. J.
Bibcode: 1967Natur.216.1280S
Altcode:
It has been suggested that the observed Solar oblateness may be caused
by a gravitational quadrupole moment. The answer may not be so simple,
however, because of magnetic stress and differential rotation between
the radiation layer and the core.
Title: Galactic flares: a plasma-physics interpretation of explosions
in radio galaxies and quasi-stellar objects
Authors: Sturrock, P. A.
Bibcode: 1967AJ.....72Q.322S
Altcode:
No abstract at ADS
Title: Model of the High-Energy Phase of Solar Flares
Authors: Sturrock, P. A.
Bibcode: 1966Natur.211..695S
Altcode:
No abstract at ADS
Title: A Model of Quasi-Stellar Radio Sources
Authors: Sturrock, P. A.
Bibcode: 1966Natur.211..697S
Altcode:
No abstract at ADS
Title: Two-Fluid Model of the Solar Wind
Authors: Sturrock, P. A.; Hartle, R. E.
Bibcode: 1966PhRvL..16..628S
Altcode:
No abstract at ADS
Title: Wave Motion and the Structure of the Solar Chromosphere
Authors: Sturrock, P. A.
Bibcode: 1966IAUTB..12..561S
Altcode:
No abstract at ADS
Title: A New Model of Solar Flares
Authors: Sturrock, P. A.; Coppi, B.
Bibcode: 1966ApJ...143....3S
Altcode:
Observational data concerning solar flares are reviewed briefly in
order to list the salient requirements of a model of solar flares. The
requirements of a theory of the flash phase are discussed in more
detail, and previous flare theories are reviewed to determine the
extent to which they meet these requirements. It is submitted that
no theory meets enough of the requirements to be acceptable. A new
model is proposed in which the preflare state consists of a mass of
gas supported by a sheared magnetic field. This field configuration
is likely to be met in the neighborhood of a fault line, across which
there has been a shear displacement of the photosphere, since such a
fault line tends to coincide with the dividing line between regions of
opposite magnetic polarity. Such a configuration of gas and magnetic
field is believed to be responsible for quiescent prominences, but
the energy released in a flare is believed to come from lower parts
of such a system, involving stronger fields and greater mass. This
model there- fore explains the close relationship between flares and
quiescent filaments. The flash phase of a solar flare is identified
with a gravitational resistive instability of the above plasma-field
configuration. It is shown that the rise time of this instability is
sufficiently rapid to explain the very rapid development of the flash
phase. The instability tends to break up the plasma into filaments with
dimensions of a kilometer or less, in agreement with certain inferences
which have been drawn from flare spectra. The development of fine-scale
structure provides conditions for subsequent slower release of stored
energy; this subsequent release is identified with the main or decay
phase of flares. The flash-phase instability develops high current
parallel to the magnetic field, which must be driven by an electric
field parallel to the magnetic field. This permits one to identify
the acceleration process in solar flares as runaway acceleration,
and it is shown that this interpretation enables one to explain the
observed energies of protons produced by solar flares. There is a
brief discussion of the possibility of interpreting certain secondary
flare phenomena, such as surges and loop prominences, by means of the
proposed model.
Title: A New Model for Solar Filaments.
Authors: Sturrock, P. A.; Woodbury, E.
Bibcode: 1965AJ.....70..694S
Altcode:
Filaments are known to run along the "neutral line" which divides
regions of the photo sphere of opposite magnetic polarity. However,
this characteristic alone does not account for the properties of
filaments. It is suggested that filaments (quiescent prominences)
result from slippage of the photo sphere, and that such slippage
occurs preferentially along a neutral line. The resulting magnetic
field will not be current-free but if the amount of gas supported is
not too large, it will be nearly force-free. A relaxation method has
been devised for computing force- free magnetic field configurations and
used to calculate the structure of a model filament. It is found that,
for heights smaller than the slip distance, the magnetic field lines'
rise almost vertically, run nearly parallel to the slip line almost
horizontally, and then descend almost vertically. Such a field
configuration is well suited for supporting a mass of gas. The
shape of the suspended gas would then simulate the "sheet" or
"veil"-like structure of a filament. It is also clear that such a
structure permits flow of gas parallel to the neutral line. This
interpretation of a filament provided a mechanism for supplying the
dense gas supported by the magnetic field, since slippage tends to
raise magnetic- field lines and so to raise the gas in which the field
lines are embedded. The relationship between filaments and flares may
be understood by identifying the pre-flare state of a recent flare
model (Sturrock, P. A., and Coppi, B., "A New Model of Solar Flares,"
Stanford University Rept. SUPR 6, April 1965) with a massive filament
(or part of a filament) in the low chromosphere. Work supported by
the U. S. Air Force Office of Scientific Research.
Title: Shock Waves in the Solar Wind and Geomagnetic Storms
Authors: Sturrock, P. A.; Spreiter, J. R.
Bibcode: 1965JGR....70.5345S
Altcode:
Certain geomagnetic storms exhibit, in addition to the usual initial
sudden positive impulse, a subsequent sudden negative impulse. The
former is normally ascribed to a shock wave in the interplanetary
medium, and it has recently been suggested that the latter may be
ascribed to a reverse shock convected away from the sun by the solar
wind. If the velocity of efflux of gas from a source is supersonic
(with respect to the source), if the velocity is instantaneously
increased, and if certain subsidiary conditions are met, a pair of
shock waves will be produced which propagate away from the source. The
`fast' shock propagates away from the contact surface in the ambient
gas (which was ejected from the source before the change in efflux
velocity); the `slow' shock propagates away from the contact surface
in the driver gas but has an outward velocity when this velocity is
measured relative to the source. This problem (which may be identified
with a classical problem considered by Riemann) is discussed in its
relation to the production of pairs of shock waves by the enhanced solar
wind produced by a solar flare. The equations giving the relationship
between the velocities of the shock waves and those of the ambient and
driver gases become very simple in the strong-shock approximation. It is
shown that the propagation times of the positive and negative impulses
of the July 11, 1959, magnetic storm may be explained satisfactorily
on the basis of this theory.
Title: Galactic Flares and Quasi-Steller Radio Sources
Authors: Sturrock, P. A.
Bibcode: 1965Natur.205..861S
Altcode:
No abstract at ADS
Title: Galactic Flares and Quasistellar Radio sources
Authors: Sturrock, P. A.
Bibcode: 1965AJ.....70R.331S
Altcode:
There is a strong similarity between explosions which occur on
a galactic scale, and give rise to extragalactic radio sources,
and solar flares. The possibility is therefore examined that the
solar flare mechanism might occur on a galactic scale. The preflare
state would comprise a large self-gravitating mass of gas which is
prevented from collapsing by a trapped magnetic field. This hypothesis
is examined in particular for the quasi- stellar radio source 3C273. The
"galactic flare" is the explosion which gave rise to the ejection of
the cloud 3C273A from the quasistellar object 3C273B. Consideration of
the energy requirements and observed optical periodicity leads one to
assign to the B component a mass of 10~~ g, a "radius" of 1017.8 cm
and a mean magnetic field of 104.2 G. It appears that such an object
could form by condensation from normal intergalactic gas if there
is a large-scale intergalactic magnetic field of strength about 10-~
G. It appears furthermore that such a flare would accelerate protons
to energies in excess of 1018 eV so that cosmic-ray particles may
originate in galactic flares.
Title: A New Model of Solar Flares.
Authors: Sturrock, P. A.; Coppi, B.
Bibcode: 1965AJ.....70S.331S
Altcode:
A review of observational data concerning solar flares, including in
particular data concerning homologous flares, leads to a statement of
the principal requirements to be met by a flare model. It is submitted
that earlier theories do not meet these requirements. A new model
of solar flares is proposed in which the pre-flare state consists
of a heavy mass of gas partially supported by a compressed magnetic
field. Such a configuration is likely to form in those parts of the
low chromosphere of a center of activity for which the magnetic
field is nearly horizontal and for which the radius of curvature
is directed upwards. The pre-flare state may have its origin in gas
circulation due either to photo spheric temperature differences at
a center of activity or to the nonthermal (acoustic) energy flux,
or to a small vertical (upward) displacement of the magnetic field
configuration. The instability appropriate to this configuration, to
be identified with the flash phase of solar flares, is a gravitational
resistive instability. This instability is sufficiently rapid, and it
develops electric fields of sufficient magnitude to explain observed
particle acceleration in solar flares. The instability also causes the
plasma-field configuration to break up into fine filaments, in agreement
with observations. This finescale structure effects a decoupling of
the plasma and magnetic fields, permitting the overlying mass of gas
to sink to the photosphere and the compressed magnetic field to relax
to a force-free state; energy released in this phase corresponds to
the main part of the light curve of a flare.
Title: A New Model of Solar Flares
Authors: Sturrock, P. A.; Coppi, B.
Bibcode: 1964Natur.204...61S
Altcode:
THE extensive observational results and theoretical investigations
of solar flares have recently been compiled in refs. 1 and 2. Most
models of solar flares have assumed that the only reasonable mechanism
for energy storage is that of magnetic field. Parker3 has
recently criticized these theories and shown, in particular, that they
do not explain the rapidity (102 sec) of the flash phase.
Title: Structure of the Solar Chromosphere
Authors: Sturrock, P. A.
Bibcode: 1964Natur.203..285S
Altcode:
THE suggestion of Biermann1 and Schwarzschild2,
that the radially increasing temperature of the solar atmosphere
is to be ascribed to propagation of non-thermal energy, such as
acoustic waves, is now generally accepted. The effect of magnetic
field, and the possibility that the energy-carrying waves are
of a magnetohydrodynamic character rather than acoustic, has been
considered seriously3. However, the fact that the density
and temperature of the chromosphere are significantly affected by
magnetic field only when the field attains the strength (~ 50 gauss)
which is found only in localized regions (plages) on the Sun's surface
indicates that magnetic field is not of primary significance. Hence
one may attempt to understand the energy propagation and its effects on
the assumption that one can ignore the magnetic field and so consider
only acoustic waves.
Title: Type III Solar Radio Bursts
Authors: Sturrock, P. A.
Bibcode: 1964NASSP..50..357S
Altcode: 1964psf..conf..357S
No abstract at ADS
Title: Spectral Characteristics of Type II Solar Radio Bursts
Authors: Sturrock, P. A.
Bibcode: 1961Natur.192...58S
Altcode:
IT has been, recognized for some time that Type II solar radio
bursts are due to the excitation of plasma oscillations in
the solar corona by some exciting agency which moves through the
corona. Roberts1, in reviewing observations and theories of
these phenomena, leaves unexplained two salient characteristics: (1)
the appearance of radiation at the fundamental and second harmonic at
comparable powers and the lack of radiation at all higher harmonics;
(2) the frequent splitting of each of these two `lines' into a pair
of lines, the fractional splitting of each of these two pairs being
the same, typically a few per cent.