A comparison of He II 304 A and He I 10,830 A spectroheliograms
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Harvey, J. W.↗
Engineering topics
Harvey, J. W.
Publications and source records attributed to Harvey, J. W..
Open magnetic structures on the sun
High-resolution harmonic analysis of the solar magnetic field has been used succesfully to calculate the geometry of open magnetic field lines in the solar corona. Comparison of the loci of open-field-line footpoints with solar X-ray photographs shows that all the coronal holes during two solar rotations are successfully represented, including details of their evolution. Some open magnetic configurations derived in the calculations precede by up to one solar rotation the manifestation of coincident dark areas on the X-ray photographs. The only other areas that contribute open field lines to the corona are separations between active-region loop systems. By varying the radius at which field lines are forced to be open in the calculation, it is possible to reproduce more closely the surface configuration of particular coronal holes. Comparison of the size of X-ray holes with the fraction of the solar surface covered by open field lines leads to the conclusion that a significant part of the area of coronal holes must contain closed magnetic fields. Comparison of open field lines which lie in the equatorial plane of the sun with solar-wind data indicates that eventual high-speed solar-wind streams are associated with those parts of open magnetic structures that diverge the least.
Levine, R. H.↗
Magnetic properties of X-ray bright points
Using high-resolution Kitt Peak National Observatory magnetograms and sequences of simultaneous S-054 soft X-ray solar images, the properties of X-ray bright points (XBP) and ephemeral active regions (ER) are compared. All XBP appear on the magnetograms as bipolar features, except for very recently emerged or old and decayed XBP. The separation of the magnetic bipoles is found to increase with the age of the XBP, with an average emergence growth rate of 2.2 plus or minus 0.4 km per sec. The total magnetic flux in a typical XBP living about 8 hr is found to be about two times ten to the nineteenth power Mx. A proportionality is found between XBP lifetime and total magnetic flux, equivalent to about ten to the twentieth power Mx per day of lifetime.
Golub, L.↗
A pictorial comparison of interplanetary magnetic field polarity, solar wind speed, and geomagnetic disturbance index during the sunspot cycle
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Sheeley, N. R., Jr.↗
Solar sources of the interplanetary magnetic field and solar wind
Open magnetic field lines, those which extend from the solar photosphere to interplanetary space, are traced in the current-free (potential field) approximation using measured photospheric fields as a boundary condition. It is found that (1) only a relatively small fraction of the photospheric area connects via open field lines to the interplanetary magnetic field; (2) those photospheric areas which do contribute open field lines lie beneath coronal holes and within the boundaries of the holes as projected onto the photosphere or else between loop systems of an active region; (3) the interplanetary magnetic field in the plane of the sun's equator, essentially the field in the ecliptic plane, may connect to photospheric regions of high latitude; and (4) the fastest solar wind streams are correlated with those magnetic flux tubes which expand least in cross-sectional area over the distance between the photosphere and the coronal height where the solar wind begins.
Levine, R. H.↗
Coronal holes, solar wind streams, and recurrent geomagnetic disturbances - 1973-1976
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.
Sheeley, N. R., Jr.↗
The calculation of force-free fields from discrete flux distributions
This paper presents particularly simple mathematical formulas for the calculation of force-free fields of constant alpha 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 alpha'. These formulas may be useful in the study of chromospheric magnetic fields by the comparison of high-resolution H-alpha photographs and photospheric magnetograms.
Sheeley, N. R., Jr.↗
A comparison of EUV spectroheliograms and photospheric magnetograms
A comparison of EUV data from an experiment on the OSO-6 satellite with photospheric magnetograms from Kitt Peak National Observatory indicates relationships between the strength of the photospheric magnetic field and density in the overlying corona in quiet and in active regions, distinctly differing from previous notions. In addition, the photospheric field beneath a coronal hole is found to be virtually identical to that beneath normal quiet regions.
Gurman, J. B.↗
Observations of sunspot umbral velocity oscillations.
Review of sunspot umbral velocity measurements obtained free from any cross talk introduced by photospheric and penumbral scattered light by using lines formed only in the sunspot umbrae and showing no Zeeman effect. The maximum peak-to-peak amplitude of the umbral oscillatory velocity component is found to be of the order of 0.5 km per sec.
Bhatnagar, A.↗