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  • 1985-1989  (116)
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  • 1
    Electronic Resource
    Electronic Resource
    A type IV burst associated with a coronal streamer disruption event (1987)
    Springer
    Solar physics 111 (1987), S. 53-57 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A type IV burst was observed on February 17, 1985 with the Clark Lake Radio Observatory multifrequency radioheliograph operating in the frequency range 20–125 MHz. This burst was associated with a coronal streamer disruption event. From two-dimensional images produced at 50 MHz, we show evidence of a type II burst and a slow moving type IV burst. The observations of the moving type IV burst suggests that a plasmoid containing energetic electrons can result from the disruption of a coronal streamer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00145440
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  • 2
    Electronic Resource
    Electronic Resource
    An eruptive prominence and associated cm-mm emission outside the solar limb (1988)
    Springer
    Solar physics 116 (1988), S. 83-89 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present radio maps at 22 and 44 GHz which show the emission before and after the eruption of a quiescent prominence located at the west limb. The observed radiation following the eruption is not consistent with thermal bremsstrahlung mechanism. It can be interpreted as due to gyrosynchrotron emission of nonthermal electrons. Our observations appear to be similar to the microwave radiation observed in post-flare loops; this radiation is due to nonthermal electrons trapped in the closed magnetic structures formed after the prominence eruption.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00171716
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  • 3
    Electronic Resource
    Electronic Resource
    A study of coronal bright points at 20 cm wavelength (1988)
    Springer
    Solar physics 117 (1988), S. 37-50 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present the results of a study of coronal bright points observed at 20 cm with the VLA on a day when the Sun was exceptionally quiet. Microwave maps of bright points were obtained using data for the entire observing period of 5 hours, as well as for shorter periods of a few minutes. Most bright points, especially those appearing in the full-period maps appear to be associated with small bipolar structures on the photospheric magnetogram. Overlays of bright point (B.P.) maps on the Ca+K picture, show that the brightest part of a B.P. tends to lie on the boundary of a supergranulation network. In general, the bright points exhibit rapid variations in intensity. There is no systematic correlation between the size of a B.P. and its intensity; the apparently slow variation of B.P. emission may have rapid fluctuations superimposed on it.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00148570
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  • 4
    Electronic Resource
    Electronic Resource
    Meterwave observations of a coronal hole (1987)
    Springer
    Solar physics 111 (1987), S. 419-428 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present meterwave maps showing a coronal hole at 30.9, 50.0, and 73.8 MHz using the Clark Lake Radioheliograph in October 1984. The coronal hole seen against the disk at all three frequencies shows interesting similarities to, and significant differences from its optical signatures in He i λl10830 spectroheliograms. Using the model of coronal holes by Dulk et al. (1977) we derive the electron density from the radio observations of the brightness temperature. The discrepancy between the density value derived from the Skylab EUV data and that computed from our radio data is even larger than in Dulk et al. 's comparison at similar and higher frequencies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00148529
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  • 5
    Electronic Resource
    Electronic Resource
    Correlated type III burst emission from distant sources on the Sun (1987)
    Springer
    Solar physics 112 (1987), S. 133-142 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report the observation and interpretation of a correlated type III burst emitted from distant sources on the Sun. The angular separation between the distant sources is as large as 26′ or ∼ 106 km. There was an active region ∼ 30° behind the limb, and it is believed that the type III burst emission originated from activity in this region. The implications of the locations of the correlated sources with regard to the geometry of the magnetic structures involved in the flare process are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00148493
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  • 6
    Electronic Resource
    Electronic Resource
    Clark lake microbursts: On a lower limit to type III burst brightness temperatures (1986)
    Springer
    Solar physics 107 (1986), S. 135-157 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Further observations of solar microbursts by the Clark Lake radioheliograph are reported. The microbursts have properties consistent with weak type III bursts, with the implication that type III's can have brightness temperatures as low as 106 K. We explore the importance of this result. A single model to explain the stronger type III bursts and the weaker microbursts is sought. We show that none of the models for stabilizing the strongest type III electron streams can explain the observed microbursts: these models have threshold levels of Langmuir waves which imply emission (due to spontaneous scattering off ions) with brightness temperatures in excess of those observed. It appears that either some vital physics is still missing from models for type III bursts, or that microbursts should have properties significantly different from those of type III bursts. In the latter case further observations should allow important tests of type III models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00155348
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  • 7
    Electronic Resource
    Electronic Resource
    Coronal bright points at 6 cm wavelength (1987)
    Springer
    Solar physics 108 (1987), S. 99-111 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report the results of the first observations of solar coronal bright points at 6 cm wavelength using the Very Large Array (VLA), with a spatial resolution of ∼ 1″.2. The maximum brightness temperature of the sources observed is ≈ 3 × 104 K with a mean value of ≈ 1 × 104 K (above the quiet Sun value). The lifetime of most sources is between 5 and 20 min. The average diameter of the sources is about 5–15″ arc. The sources are gaussian-like near the footpoint of miniature loops and they appear in groups. The observations indicate that significant fluctuations in the brightness temperature (sometimes quasi-periodic) and in the spatial extents of these sources can occur over periods of a few minutes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152080
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  • 8
    Electronic Resource
    Electronic Resource
    Large-scale structure of the sun's corona from radio observations using the Clark Lake Radioheliograph (1987)
    Springer
    Solar physics 108 (1987), S. 113-129 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present meterwave maps of the solar corona made with the Clark Lake Radioheliograph at 30.9, 50, and 73.8 MHz for one solar rotation. We compare and contrast them with optical data: 10830 Å maps, white-light coronagraph images (SOLWIND and Mauna Loa K coronameter) and forbidden line scans. Most of the sources in the radio maps persist for two days or more, and appear to rotate approximately with the solar rate. A coronal hole seen against the disk at all three frequencies shows interesting similarities and significant differences with the optical signatures of the hole. Elongated features of the 50 MHz corona correspond rather well to the azimuthal position of white light streamers seen in SOLWIND images. Synoptic charts made from the radio maps show overall similarities to synoptic charts constructed from (limb) coronagraph data. Some of the differences may result from the different weightings given by the radio and optical data to density and temperature, or by the different sensitivities to non-radial geometries. We show that the combined use of meter wave and optical images provide considerable new insights into the three-dimensional structure of the low to middle corona.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152081
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  • 9
    Electronic Resource
    Electronic Resource
    A new microwave/X-ray diagnostic for the thermal phase of solar flares (1986)
    Springer
    Solar physics 105 (1986), S. 87-99 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have observed 10 solar bursts during the thermal phase using the Haystack radio telescope at 22 GHz. We show that these high frequency flux observations, when compared with soft X-ray band fluxes, give useful information about the temperature profile in the flare loops. The microwave and X-ray band fluxes provide determinations of the maximum loop temperature, the total emission measure, and the index δ of the differential emission measure (q(T)/T = cTδ−1). The special case of an isothermal loop (δ = ∞) has been considered previously by Thomas et al. (1985), and we confirm their diagnostic calculations for the GOES X-ray bands, but find that the flare loops we observed departed significantly from the isothermal regime. Our results (δ = 1–3.5) imply that, during the late phases of flares, condensation cooling (δ ≈ 3.5) competes with radiative cooling (δ ≈ 1.5). Further, our results appear to be in good agreement with previous deductions from XUV rocket spectra (δ ≈ 2–3).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00156379
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  • 10
    Electronic Resource
    Electronic Resource
    Simultaneous microwave observations of solar flares at 6 and 20 cm wavelengths using the VLA (1985)
    Springer
    Solar physics 97 (1985), S. 345-361 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using the Very Large Array, solar burst observations have been carried out simultaneously at 6 and 20 cm. Structural changes and preheating have been observed in the flaring regions on time scales of minutes to tens of minutes before the onset of the burst impulsive phase. The 6 cm burst sources are located close to the neutral line, or near the legs of a flaring loop. The 20 cm burst sources show complex and extended structures spatially separated from both the preburst emission and the gradual decay phase of the burst. We interpret the observations in terms of a two-component flare model (bulk heating as well as acceleration of particles) and derive the physical parameters of the burst sources.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00165994
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