Craig Solodyna - Academia.edu (original) (raw)
Papers by Craig Solodyna
Journal of Geophysical Research, 1975
The properties of directional discontinuities occurring in selected periods of interplanetary mag... more The properties of directional discontinuities occurring in selected periods of interplanetary magnetic field data are investigated. Microscale fluctuations in these selected periods have previously been identified as being predominantly Alfv6nic on time scales ranging from 5 min to a few hours. We argue that the majority of directional discontinuities in such periods are rotational and outwardly propagating.
Geophysical Research Letters, 1976
Geophysical Research Letters publishes short, concise research letters that present scientific ad... more Geophysical Research Letters publishes short, concise research letters that present scientific advances that are likely to have immediate influence on the research of other investigators. GRL letters can focus on a specific discipline or apply broadly to the geophysical science community ...
Solar Physics, 1978
We examine the relationship between coronal hole evolution and solar active regions during the Sk... more We examine the relationship between coronal hole evolution and solar active regions during the Skylab period. We find a tendency for holes to grow or remain stable when the activity nearby, seen as calcium plages and bright regions in X-rays, is predominantly large, long-lived regions. This is consistent with results of previous studies, using somewhat different methods. We also find that there is a significantly higher number of small, short-lived active regions, as indicated by X-ray bright points, in the vicinity of decaying holes than there is near other holes. We interpret this to mean that holes disappear at least in part because they become filled with many small scale, magnetically closed, X-ray emitting features. This interpretation, together with the previously reported observation that the number of X-ray bright points was much larger near solar minimum than it was during the Skylab period, provides a possible explanation for the disappearance of the large, near-equatorial coronal holes at the time of solar minimum.
Narrowband (NB) and wideband (WB) radar signatures are used by the U.S. to improve the fidelity o... more Narrowband (NB) and wideband (WB) radar signatures are used by the U.S. to improve the fidelity of the space catalog. Whereas space surveillance answers the question "Where is it?" using metric information, space object identification (SOI) answers the question "What is it?" using NB and WB radar signatures. NB radar signatures consist of either the radar cross-section (RCS) history or the range-time-intensity (RTI) history of a satellite. NB signatures of simple satellites are analyzed using known RCS scattering formulae to determine size and shape. NB signatures of more complex satellites are automatically compared to databases of signatures of known satellites to properly categorize them. WB radar signatures consist of range-Doppler images. If the motion of the satellite about its center-of-mass is known, range-Doppler images can be properly scaled to obtain accurate shape and size estimates of satellites. By using WB images, analysts can clearly distinguish b...
Bulletin of the American Astronomical Society, Mar 1, 1977
Solar Physics, 1978
A 90 s time resolution study of the soft X-ray emission from three active region loops shows the ... more A 90 s time resolution study of the soft X-ray emission from three active region loops shows the emission to be constant to about two percent over the half hour period of observation. Soft X-ray observations in two wavebands are used to deduce the temperature and density of these loops. The data unambiguously demonstrate that energy is supplied to each loop during the observations. If heating is due to discrete events, the time interval between events is shown to be less than 10 min, which is short relative to the radiative cooling time of the loops.
Bulletin of the American Astronomical Society, Mar 1, 1977
Sol Phys, 1977
Soft X-ray observations confirm that some of the dark gaps seen between interconnecting loops and... more Soft X-ray observations confirm that some of the dark gaps seen between interconnecting loops and inner cores of active regions may be loci of open fields, as it has been predicted by global potential extrapolation of photospheric magnetic fields. It seems that the field lines may open only in a later state of the active region development.
Bulletin of the American Astronomical Society, Mar 1, 1976
Solar Physics, 1978
We have compared sudden shifts in coronal hole boundaries observed by the S-054 X-ray telescope o... more We have compared sudden shifts in coronal hole boundaries observed by the S-054 X-ray telescope on Skylab between May and November, 1973, within 1 day of CMP of the holes, at latitudes-<40 ~ , with the long-term evolution of coronal hole area. We find that large-scale shifts in boundary locations can account for most if not all of the evolution of coronal holes. The temporal and spatial scales of these large-scale changes imply that they are the results of a physical process occurring in the corona. We conclude that coronal holes evolve by magnetic field lines opening when the holes are growing, and by fields closing as the holes shrink.
Solar Physics, 1978
ABSTRACT
Journal of Geophysical Research, 1977
We examine the plasma and magnetic field changes occurring across 1359 directional discontinuitie... more We examine the plasma and magnetic field changes occurring across 1359 directional discontinuities taken from interplanetary data spanning almost four solar rotations. The plasma field characteristics of these events exhibit a distinct variation with large-scale solar wind velocity. At low velocities, tangential discontinuities appear to predominate. At higher velocities a substantial and increasing fraction of directional discontinuities exhibits the plasma field properties expected of outwardly propagating rotational discontinuities. The results of Sari (1972, 1975) and of the present study suggest that in the calculation of propagation diffusion coefficients for low-energy cosmic rays, the effects of directional discontinuities should be subtracted from the magnetic fluctuation spectrum during relatively quiet wind conditions. It is not clear that such subtraction is necessary during more disturbed periods.
Solar Physics, 1978
The positions of X-ray coronal transients outside of active regions observed during Skylab were s... more The positions of X-ray coronal transients outside of active regions observed during Skylab were superposed on Ha synoptic charts and coronal hole boundaries for seven solar rotations. We confirmed a detailed spatial association between the transients and neutral lines. We found that most of the transients were related to large-scale changes in coronal hole area and tended to occur on the borders of evolving equatorial hol&s.
Thesis Massachusetts Institute of Technology 1975 Source American Doctoral Dissertations Source Code X1975, 1975
Journal of Geophysical Research, 1974
We have investigated the properties of low-frequency transverse waves in an expanding plasma. The... more We have investigated the properties of low-frequency transverse waves in an expanding plasma. The wave vector k, the background magnetic field B, and the streaming velocity of the plasma V are all assumed to lie along the radial direction. We present expressions for the radial dependence of the amplitude and phase of left and right circularly polarized waves, correct to first order in the wave frequency divided by the proton cyclotron frequency. Differences in the phase velocities of these two circular polarizations result in a Faraday rotation that can be substantial for typical interplanetary conditions near I AU. We also consider the implications of these results for a realistic solar wind model with the interplanetary magnetic field along the spiral direction. Since the formulation of solar wind theory [Parker, 1958] much effort has been directed toward understanding perturbations in the steady coronal expansion. Waves, tangential and rotational discontinuities, turbulence, and shocks are observed perturbations in the steady flow of the solar wind. In particular, Alfv6nic fluctuations with characteristic periods of a few hours and less are a well-known feature of the interplanetary magnetic field [Coleman, 1967, 1968; Unti and Neugebauer, 1968; Belcher et al., 1969; Belcher and Davis, 1971]. Since these waves are observed to propagate away from the sun in the rest frame of the solar wind, it is generally accepted that they are generated close to the sun in regions in which the plasma flow is sub-Alfv6nic. Theoretical work on ray tracing the Alfv6n wave mode into the spiral interplanetary magnetic field [Barnes, 1969; Vi•lk and Alpers, 1973] predicts that near I AU the wave vector k should be essentially radial, the polarization of the waves being perpendicular to the plane formed by the radial direction and the average magnetic field direction. Observationally, there appears to be a small preference for such a polarization [Belcher and Davis, 1971], although the magnitude of the observed effect is at best a factor of 10 less than that predicted. In addition, there is strong observational evidence that k tends to lie along the average field direction at I AU, rather than along the radial direction [Belcher and Davis, 1971; Daily, 1973]. The reason for these discrepancies between observations and theoretical predictions is not well understood. Vi•lk and Alpers [1973] and Daily [1973] speculate that the waves undergo substantial scattering in the interplanetary medium between the sun and the earth. However, as Daily [1973] points out, it is not clear why such scattering would cause the preferential refraction of the wave vector k into directions along magnetic field lines. Barnes and Hollweg [1973] and Vi•lk and Alpers [1973] suggest that nonlinear effects could be dominant in the solar wind, since the observed amplitudes of the Alfv6n waves are comparable to the background field strength. Thus the results of a linearized ray-tracing analysis may be inapplicable. The authors are presently involved in an extensive spectral and cross-spectral analysis of Alfv6nic fluctuations in the solar wind. In the context of this study we have undertaken a limited theoretical investigation of the importance of finite cyclotron effects on the properties of magnetic field fluctuations with spacecraft periods between 15 s and a few minutes.
Solar Physics, 1977
Soft X-ray observations confirm that some of the dark gaps seen between interconnecting loops and... more Soft X-ray observations confirm that some of the dark gaps seen between interconnecting loops and inner cores of active regions may be loci of open fields, as it has been predicted by global potential extrapolation of photospheric magnetic fields. It seems that the field lines may open only in a later state of the active region development.
Journal of Geophysical Research, 1975
The properties of directional discontinuities occurring in selected periods of interplanetary mag... more The properties of directional discontinuities occurring in selected periods of interplanetary magnetic field data are investigated. Microscale fluctuations in these selected periods have previously been identified as being predominantly Alfv6nic on time scales ranging from 5 min to a few hours. We argue that the majority of directional discontinuities in such periods are rotational and outwardly propagating.
Geophysical Research Letters, 1976
Geophysical Research Letters publishes short, concise research letters that present scientific ad... more Geophysical Research Letters publishes short, concise research letters that present scientific advances that are likely to have immediate influence on the research of other investigators. GRL letters can focus on a specific discipline or apply broadly to the geophysical science community ...
Solar Physics, 1978
We examine the relationship between coronal hole evolution and solar active regions during the Sk... more We examine the relationship between coronal hole evolution and solar active regions during the Skylab period. We find a tendency for holes to grow or remain stable when the activity nearby, seen as calcium plages and bright regions in X-rays, is predominantly large, long-lived regions. This is consistent with results of previous studies, using somewhat different methods. We also find that there is a significantly higher number of small, short-lived active regions, as indicated by X-ray bright points, in the vicinity of decaying holes than there is near other holes. We interpret this to mean that holes disappear at least in part because they become filled with many small scale, magnetically closed, X-ray emitting features. This interpretation, together with the previously reported observation that the number of X-ray bright points was much larger near solar minimum than it was during the Skylab period, provides a possible explanation for the disappearance of the large, near-equatorial coronal holes at the time of solar minimum.
Narrowband (NB) and wideband (WB) radar signatures are used by the U.S. to improve the fidelity o... more Narrowband (NB) and wideband (WB) radar signatures are used by the U.S. to improve the fidelity of the space catalog. Whereas space surveillance answers the question "Where is it?" using metric information, space object identification (SOI) answers the question "What is it?" using NB and WB radar signatures. NB radar signatures consist of either the radar cross-section (RCS) history or the range-time-intensity (RTI) history of a satellite. NB signatures of simple satellites are analyzed using known RCS scattering formulae to determine size and shape. NB signatures of more complex satellites are automatically compared to databases of signatures of known satellites to properly categorize them. WB radar signatures consist of range-Doppler images. If the motion of the satellite about its center-of-mass is known, range-Doppler images can be properly scaled to obtain accurate shape and size estimates of satellites. By using WB images, analysts can clearly distinguish b...
Bulletin of the American Astronomical Society, Mar 1, 1977
Solar Physics, 1978
A 90 s time resolution study of the soft X-ray emission from three active region loops shows the ... more A 90 s time resolution study of the soft X-ray emission from three active region loops shows the emission to be constant to about two percent over the half hour period of observation. Soft X-ray observations in two wavebands are used to deduce the temperature and density of these loops. The data unambiguously demonstrate that energy is supplied to each loop during the observations. If heating is due to discrete events, the time interval between events is shown to be less than 10 min, which is short relative to the radiative cooling time of the loops.
Bulletin of the American Astronomical Society, Mar 1, 1977
Sol Phys, 1977
Soft X-ray observations confirm that some of the dark gaps seen between interconnecting loops and... more Soft X-ray observations confirm that some of the dark gaps seen between interconnecting loops and inner cores of active regions may be loci of open fields, as it has been predicted by global potential extrapolation of photospheric magnetic fields. It seems that the field lines may open only in a later state of the active region development.
Bulletin of the American Astronomical Society, Mar 1, 1976
Solar Physics, 1978
We have compared sudden shifts in coronal hole boundaries observed by the S-054 X-ray telescope o... more We have compared sudden shifts in coronal hole boundaries observed by the S-054 X-ray telescope on Skylab between May and November, 1973, within 1 day of CMP of the holes, at latitudes-<40 ~ , with the long-term evolution of coronal hole area. We find that large-scale shifts in boundary locations can account for most if not all of the evolution of coronal holes. The temporal and spatial scales of these large-scale changes imply that they are the results of a physical process occurring in the corona. We conclude that coronal holes evolve by magnetic field lines opening when the holes are growing, and by fields closing as the holes shrink.
Solar Physics, 1978
ABSTRACT
Journal of Geophysical Research, 1977
We examine the plasma and magnetic field changes occurring across 1359 directional discontinuitie... more We examine the plasma and magnetic field changes occurring across 1359 directional discontinuities taken from interplanetary data spanning almost four solar rotations. The plasma field characteristics of these events exhibit a distinct variation with large-scale solar wind velocity. At low velocities, tangential discontinuities appear to predominate. At higher velocities a substantial and increasing fraction of directional discontinuities exhibits the plasma field properties expected of outwardly propagating rotational discontinuities. The results of Sari (1972, 1975) and of the present study suggest that in the calculation of propagation diffusion coefficients for low-energy cosmic rays, the effects of directional discontinuities should be subtracted from the magnetic fluctuation spectrum during relatively quiet wind conditions. It is not clear that such subtraction is necessary during more disturbed periods.
Solar Physics, 1978
The positions of X-ray coronal transients outside of active regions observed during Skylab were s... more The positions of X-ray coronal transients outside of active regions observed during Skylab were superposed on Ha synoptic charts and coronal hole boundaries for seven solar rotations. We confirmed a detailed spatial association between the transients and neutral lines. We found that most of the transients were related to large-scale changes in coronal hole area and tended to occur on the borders of evolving equatorial hol&s.
Thesis Massachusetts Institute of Technology 1975 Source American Doctoral Dissertations Source Code X1975, 1975
Journal of Geophysical Research, 1974
We have investigated the properties of low-frequency transverse waves in an expanding plasma. The... more We have investigated the properties of low-frequency transverse waves in an expanding plasma. The wave vector k, the background magnetic field B, and the streaming velocity of the plasma V are all assumed to lie along the radial direction. We present expressions for the radial dependence of the amplitude and phase of left and right circularly polarized waves, correct to first order in the wave frequency divided by the proton cyclotron frequency. Differences in the phase velocities of these two circular polarizations result in a Faraday rotation that can be substantial for typical interplanetary conditions near I AU. We also consider the implications of these results for a realistic solar wind model with the interplanetary magnetic field along the spiral direction. Since the formulation of solar wind theory [Parker, 1958] much effort has been directed toward understanding perturbations in the steady coronal expansion. Waves, tangential and rotational discontinuities, turbulence, and shocks are observed perturbations in the steady flow of the solar wind. In particular, Alfv6nic fluctuations with characteristic periods of a few hours and less are a well-known feature of the interplanetary magnetic field [Coleman, 1967, 1968; Unti and Neugebauer, 1968; Belcher et al., 1969; Belcher and Davis, 1971]. Since these waves are observed to propagate away from the sun in the rest frame of the solar wind, it is generally accepted that they are generated close to the sun in regions in which the plasma flow is sub-Alfv6nic. Theoretical work on ray tracing the Alfv6n wave mode into the spiral interplanetary magnetic field [Barnes, 1969; Vi•lk and Alpers, 1973] predicts that near I AU the wave vector k should be essentially radial, the polarization of the waves being perpendicular to the plane formed by the radial direction and the average magnetic field direction. Observationally, there appears to be a small preference for such a polarization [Belcher and Davis, 1971], although the magnitude of the observed effect is at best a factor of 10 less than that predicted. In addition, there is strong observational evidence that k tends to lie along the average field direction at I AU, rather than along the radial direction [Belcher and Davis, 1971; Daily, 1973]. The reason for these discrepancies between observations and theoretical predictions is not well understood. Vi•lk and Alpers [1973] and Daily [1973] speculate that the waves undergo substantial scattering in the interplanetary medium between the sun and the earth. However, as Daily [1973] points out, it is not clear why such scattering would cause the preferential refraction of the wave vector k into directions along magnetic field lines. Barnes and Hollweg [1973] and Vi•lk and Alpers [1973] suggest that nonlinear effects could be dominant in the solar wind, since the observed amplitudes of the Alfv6n waves are comparable to the background field strength. Thus the results of a linearized ray-tracing analysis may be inapplicable. The authors are presently involved in an extensive spectral and cross-spectral analysis of Alfv6nic fluctuations in the solar wind. In the context of this study we have undertaken a limited theoretical investigation of the importance of finite cyclotron effects on the properties of magnetic field fluctuations with spacecraft periods between 15 s and a few minutes.
Solar Physics, 1977
Soft X-ray observations confirm that some of the dark gaps seen between interconnecting loops and... more Soft X-ray observations confirm that some of the dark gaps seen between interconnecting loops and inner cores of active regions may be loci of open fields, as it has been predicted by global potential extrapolation of photospheric magnetic fields. It seems that the field lines may open only in a later state of the active region development.