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  • 1975-1979  (32)
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  • 1
    Electronic Resource
    Electronic Resource
    A study of the magnetic and velocity fields in an active region (1976)
    Springer
    Solar physics 47 (1976), S. 233-246 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A time sequence of magnetograms and velocity-grams in the Hα and Fe i 6569 Å lines has been made at a rate of 12 h−1 of McMath Region 10385 from 26 to 29 October, 1969. The 14 flares observed during this period have been studied in relation to the configuration and changes in the magnetic and velocity fields. There was little correlation between flare position and the evolutionary changes in the photospheric magnetic and velocity field, except at large central meridian distances where the velocity observations suggested shearing taking place at flare locations. At central meridian distances 〉 30° we found that flares are located in areas of low line-of-sight photospheric velocity surrounded by higher velocity hills. The one exception to this was the only flare which produced a surge. Blue-shifted velocity changes in the photosphere of 0.3 to 1 km s−1 were observed in localized areas at the times of 8 of 14 flares studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152261
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  • 2
    Electronic Resource
    Electronic Resource
    Motions in solar magnetic tubes (1978)
    Springer
    Solar physics 58 (1978), S. 347-361 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The line-centre magnetogram technique has been used to study velocities at spatial scales ≃5″ in several umbras without interference from light scattered from the surrounding non-magnetic photosphere. In addition, more traditional velocity observations of one sunspot were also analysed. The velocities are highly variable within any spot and from one spot to another. Rms velocities in Hα, b1, 5233 and 5166 Å were typically ±0.6, ±0.20, ±0.10, and ±0.17 km s−1 during present observations, but factors of 2 smaller or larger are not uncommon. In 5166 and 5233 Å these velocities are about two-thirds of those in non-magnetic photospheric regions. In Hα there are umbral intensity variations whose maxima at Δλ = ±0.39 Å occur simultaneously with downward velocity maxima measured at the same Δλ. Intensity maxima at line centre lag by 12 s, demonstrating that there are waves propagating upwards. The corresponding height difference, 60– 70 km at the velocity of sound, requires excitation of Hα at much higher levels in the umbral atmosphere than if in LTE. For about one-quarter of the observations it is possible to match the Hα and 5233 Å waveforms; velocities in the latter lead those in Hα by 27 s on average, also indicating outward wave propagation and, at the velocity of sound, a difference in the mean heights of formation of about 150 km. There is no significant phase difference between the 5166 Å and b1 lines. The velocity spectrum is variable in all lines, but in general has maxima at shorter periods in Hα (∽200 s) than at lower levels. The estimated outward wave flux for the spatial scales studied is ≪3 × 106 erg cm−2 s−1 at the 5233 Å level, much lower than previous estimates and far too low to produce any significant cooling. This conclusion is believed valid for all periods above about 7 s.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00157281
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetic properties of x-ray bright points (1977)
    Springer
    Solar physics 53 (1977), S. 111-121 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using high resolution KPNO magnetograms and sequences of simultaneous S-054 soft X-ray solar images we have compared the properties of X-ray bright points (XBP) and ephemeral active regions (ER). All XBP appear on the magnetograms as bipolar features, except for very newly emerged or old and decayed XBP. We find that the separation of the magnetic bipoles increases with the age of the XBP, with an average emergence growth rate of 2.2 ± 0.4 km s−1. The total magnetic flux in a typical XBP living about 8 hr is found to be ≈ 2 x 1019 Mx. A proportionality is found between XBP lifetime and total magnetic flux, equivalent to ≈ 1020 Mx per day of lifetime.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02260212
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  • 4
    Electronic Resource
    Electronic Resource
    The calculation of force-free fields from discrete flux distributions (1975)
    Springer
    Solar physics 45 (1975), S. 275-290 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper presents particularly simple mathematical formulas for the calculation of force-free fields of constant α from the distribution of discrete sources on a flat surface. The advantage of these formulas lies in their physical simplicity and the fact that they can be easily used in practice to calculate the fields. The disadvantage is that they are limited to fields of ‘sufficiently small α’. These formulas may be useful in the study of chromospheric magnetic fields by the comparison of high-resolution Hα photographs and photospheric magnetograms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00158450
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  • 5
    Electronic Resource
    Electronic Resource
    Coronal holes, solar wind streams, and recurrent geomagnetic disturbances: 1973–1976 (1976)
    Springer
    Solar physics 49 (1976), S. 271-278 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Observations of coronal holes, solar wind streams, and geomagnetic disturbances during 1973–1976 are compared in a 27-day pictorial format which shows their long-term evolution. The results leave little doubt that coronal holes are related to the high-speed streams and their associated recurrent geomagnetic disturbances. In particular, these observations strongly support the hypothesis that coronal holes are the solar origin of the high-speed streams observed in the solar wind near the ecliptic plane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00162451
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  • 6
    Electronic Resource
    Electronic Resource
    Motions in solar magnetic tubes (1978)
    Springer
    Solar physics 59 (1978), S. 49-64 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The method of Giovanelli and Brown (1977) has been used with a variety of spectral lines to study oscillating longitudinal gas velocities inside solar magnetic elements. Oscillations have been found inside all elements observed, the amplitudes increasing with height from typically ±0.27 km s−1 in Fe i 5166 Å (a line of low origin) to ±0.75 km s−1 in Hα. Simultaneous observations in pairs of lines show that a given disturbance occurs later with height, so that disturbances propagate outwards. The period is typically 5 min in all lines originating near or below Mg b1, but is about 3 min in Hα. Simultaneous observations of the gas velocities within the magnetic element and in the immediately-surrounding non-magnetic region often show closely similar behaviour; the amplitudes are almost the same, and the mean phase difference is effectively zero, but there is a large individual variability of the order of ±0.5 min. These results imply that either there is a strong local interaction between outside and inside magnetic tubes, or the disturbances are excited by a common mechanism. The velocities observed inside and immediately outside magnetic elements have the same pattern and amplitudes as those far away from magnetic elements. In particular, the disturbance velocities never exceed about 0.1 of the velocity of sound, suggesting the absence of large-amplitude shock waves anywhere in the magnetic or non-magnetic solar atmosphere between the levels of formation of Fe I 5166 Å and Hα.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00154931
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  • 7
    Electronic Resource
    Electronic Resource
    A comparison of He ii 304 Å and He i 10 830 Å spectroheliograms (1977)
    Springer
    Solar physics 54 (1977), S. 343-351 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Spectroheliograms were obtained simultaneously in the He ii 304 Å emission line and the He i 10 830 Å absorption line with an angular resolution of approximately 5″. A negative print of the 304 Å image is matched with a positive print of the 10 830 Å image so that corresponding features of the chromospheric network (including active regions) appear identical in the two images. Differences between these images include the facts that: (1) Disk filaments and limb darkening are strongly visible in the 10 830 Å positive image, but they are weakly visible (as lightenings) in the 304 Å negative image. (2) The contrast between the chromospheric network and the network cell centers is much greater in the 10 830 Å image than in the 304 Å negative image. These results provide constraints on models of helium line formation in various types of solar features.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00159924
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  • 8
    Electronic Resource
    Electronic Resource
    Ephemeral active regions in 1970 and 1973 (1975)
    Springer
    Solar physics 40 (1975), S. 87-102 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A study of ephemeral active regions (ER) identified on good quality full-disk magnetograms reveals: (1) On the average 373 and 179 ER were present on the Sun in 1970 and 1973 respectively. The number varies with the solar cycle. (2) The median lifetime of ER depends on observation quality and selection rules but is estimated as about 12 hr for our data. (3) The latitude distribution is very broad but not uniform. The distribution peaks near the equator and shows variations similar to distributions of large active regions. (4) The longitude distribution is essentially homogeneous. (5) The spatial orientation of ER is almost random. In 1973 there is a hint of an excess of new cycle orientations at high latitudes. A comparison of parameters of ER and regular active regions suggests that ER are the small-scale end of a broad spectrum of active regions. The role of ER in the light of present theories of solar activity is investigated but is not yet clear. Heating of the chromosphere and corona may be significantly affected by ER.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00183154
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  • 9
    Electronic Resource
    Electronic Resource
    Coronal holes, solar wind streams, and geomagnetic activity during the new sunspot cycle (1978)
    Springer
    Solar physics 59 (1978), S. 159-173 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have extended our previous study of coronal holes, solar wind streams, and geomagnetic disturbances from the declining phase (1973–1975) of sunspot cycle 20 through sunspot minimum (1976) into the rising phase (1977) of cycle 21. Using daily He I 10830 Å spectroheliograms and photospheric magnetograms, we found the following results: (1) As the magnetic field patterns changed, the solar atmosphere evolved from a structure having a few, large, long-lived, low-latitude coronal holes to one having numerous small, short-lived, high-latitude holes (in addition to the polar holes which persisted throughout this 5-year interval). (2) The high-latitude holes recurred with a synodic rotation period of 28–29 days instead of the 27-day period already known to be characteristic of low-latitude holes. (3) During 1976–1977 many coronal holes were intrinsically ‘weak’ in the sense that their average intensities did not differ greatly from the intensity of their surroundings. Such low-contrast holes were rare during 1973–1975. An updated Bartels display of the occurrence of holes, wind speed, and geomagnetic activity summarizes the evolution of their characteristics and interrelations as the sunspot cycle has progressed. Long-lived, low-latitude holes have become rare but remain terrestrially effective. The more common high-latitude holes are effective only when the Earth lies at a relatively high heliographic latitude in the same solar hemisphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00154939
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  • 10
    Electronic Resource
    Electronic Resource
    A pictorial comparison of interplanetary magnetic field polarity, solar wind speed, and geomagnetic disturbance index during the sunspot cycle (1977)
    Springer
    Solar physics 52 (1977), S. 485-495 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Observations of interplanetary magnetic field polarity, solar wind speed, and geomagnetic disturbance index (C9) during the years 1962–1975 are compared in a 27-day pictorial format that emphasizes their associated variations during the sunspot cycle. This display accentuates graphically several recently reported features of solar wind streams including the fact that the streams were faster, wider, and longer-lived during 1962–1964 and 1973–1975 in the declining phase of the sunspot cycle than during intervening years (Bame et al., 1976; Gosling et al., 1976). The display reveals strikingly that these high-speed streams were associated with the major, recurrent patterns of geomagnetic activity that are characteristic of the declining phase of the sunspot cycle. Finally, the display shows that during 1962–1975 the association between long-lived solar wind streams and recurrent geomagnetic disturbances was modulated by the annual variation (Burch, 1973) of the response of the geomagnetic field to solar wind conditions. The phase of this annual variation depends on the polarity of the interplanetary magnetic field in the sense that negative sectors of the interplanetary field have their greatest geomagnetic effect in northern hemisphere spring, and positive sectors have their greatest effect in the fall. During 1965–1972 when the solar wind streams were relatively slow (500 km s-1), the annual variation strongly influenced the visibility of the corresponding geomagnetic disturbance patterns.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00149663
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