Brightness variations of the white light corona during the years 1964?67

Hansen, R. T.; García, C.; Hansen, Shirley F.; Loomis, Harold G.

doi:10.1007/bf00146145

Cited by 80 publications

(25 citation statements)

References 9 publications

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“…For such a purpose, one must consider realistic models of the electron density n e and magnetic field B in the corona. Here, we use Hansen's electron density n e model (Hansen et al 1969), which is close to Newkirk's model: …”

Section: Discussionmentioning

confidence: 99%

Polarization and Fragmentation of Solar Type II Radio Bursts

Thejappa

Zlobec

MacDowall

2003

ApJ

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Solar type II radio bursts are the electromagnetic signatures of collisionless shocks propagating radially outward in the solar atmosphere. The Zurich radio spectrograph has detected a fragmented type II burst at high frequencies. The Trieste polarimeter found this event to contain a high degree of left-hand polarization. These observations indicate that (1) the fragmented type II event is probably emitted at the fundamental of the electron plasma frequency f pe as one of the magnetoionic modes, namely, the ordinary (O) mode, (2) the fragmentation is due to fluctuations in the efficiency of linear coupling of Langmuir waves with escaping radiation at sharp density gradients associated with the oncoming shock, and (3) the key role of backscattering Langmuir waves in the direction of the oncoming shock is probably played by one of the saturation mechanisms, such as induced scattering of Langmuir waves on thermal ions or the electrostatic decay instability.

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Section: Discussionmentioning

confidence: 99%

Polarization and Fragmentation of Solar Type II Radio Bursts

Thejappa

Zlobec

MacDowall

2003

ApJ

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“…The low-latitude peak (at ≈Ϫ10Њ) is associated with sunspot activity (Hansen et al 1969). It is evident from the individual pB profiles in Figure 1a that the boundary of polar holes varies in latitude with time.…”

Section: Corona and Solar Interiormentioning

confidence: 92%

“…at ≈‫05ע‬Њ latitude), and the peak in will move with latitude j pB as the average polar hole boundary changes with the solar cycle. The migration of such high-latitude peaks toward the poles from 1965 to 1967 noted by Hansen et al (1969) can thus be largely explained by the shrinking of the polar coronal holes during the rising phase of the solar cycle (Harvey 1996). In addition to the factor of 2 difference in the levels of pB and between polar coronal holes and the quiet Sun, another j pB feature distinguishes these two regions.…”

Section: Corona and Solar Interiormentioning

confidence: 99%

“…INTRODUCTION The growing number of ground-and space-based observations of the Sun (e.g., Hansen et al 1969;Howard & LaBonte 1980;Hathaway et al 1996;Kosovichev & Schou 1997;Schou et al 1998) and of the heliosphere (e.g., Bame et al 1992;McComas et al 2000) has made it possible to explore associations between the corona, the solar interior, and interplanetary space. Such associations provide clues for identifying and understanding the physical processes by which magnetic fields generated in the solar interior make their way through the different layers of the solar atmosphere, shaping the solar wind flow and determining solar activity.…”

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confidence: 99%

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Observed Associations between the Solar Interior, Corona, and Solar Wind

Woo

Armstrong

Habbal

2000

The Astrophysical Journal

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Using polarized brightness (pB) measurements made by the High Altitude Observatory (HAO) Mauna Loa Mk III K-coronameter, we investigate the daily changes of path-integrated density at 1.15 R , . During 1996, when simultaneous pB and helioseismology data were available, we find that the correlation of pB (at zero time lag and 20Њ latitude lag) varies with latitude in the same way that the subsurface differential rotation inferred from helioseismology does. The association is such that bands of higher pB correlation are associated with retrograde subsurface rotation and that lower pB correlation bands are associated with prograde subsurface rotation. We also show that polar coronal holes are distinguished by a nonrecurring longitudinal structure as opposed to a recurring structure in the quiet Sun. In addition, the levels of pB and standard deviation of pB are about j pB half of those of the neighboring quiet Sun. These statistical characteristics of coronal density in polar holes and the quiet Sun were also present in 1993-1994 and are replicated in the statistics of the distant solar wind observed by Ulysses. The association of the density (pB) correlation with subsurface flow (when simultaneous data were available in 1996), together with the association of the latitudinal dependence of the statistical characteristics (average, standard deviation, and autocorrelation function) of the coronal (pB) and solar wind (Ulysses) density (when simultaneous data were available in 1993-1994), suggest a correlated variability of subsurface flow, coronal density, and solar wind density organized by solar latitude.

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“…The increase from minimum to maximum is about a factor of 1.5. Hansen et al (1969) show the rise to the maximum of Cycle 20 from 1964 through 1967 of the polarized Limb Flux (pB) from the High Altitude Observatory (HAO) Mauna Loa Solar Observatory K-Coronameter. Normalized to unity in 1964, the functional dependences of the Limb Flux at four heights from 1.125 R Q to 1.75 R© are nearly identical and equal to the 10.7 cm radio-flux dependence.…”

Section: Solar-cycle Variations Of Fe XIV 5303 Urnmentioning

confidence: 99%

Variations of Coronal Radiations at Optical Wavelengths

Altróck

1994

International Astronomical Union Colloquium

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This paper reviews observations of the variation over long and short time scales of solar coronal flux as observed from ground-based optical observatories. This includes data from Fe X, Fe XIV, Ca XV and the white-light electron corona. The various parameters are compared and contrasted as indicators of global coronal structure and output. The overall envelope of Ca XV minimizes before and during sunspot minimum, begins its slow rise in phase with the solar cycle, but maximizes late with strong 150-day oscillations resulting in values of zero at the local minima. Within the sensitivity of the observations, the increase of the envelope from Cycle minimum to maximum is over a factor of 30. Excluding possible secondary maxima and ignoring strong 150-day oscillations, the general envelope of Fe X appears to indicate a slow decline in intensity following sunspot maximum. Earlier observations indicate a Cycle minimumto-maximum variation of a factor of 2 to 3. Later observations indicate a factor of 4 to 5. The overall picture for Fe XIV indicates that it varies in phase with the sunspot cycle. However, multiple maxima occur. The amplitudes of all observed Cycles are probably approximately equal, and the increase from Cycle minimum to maximum is approximately a factor of 10. The variation of the polarized and unpolarized white light corona is in phase with the sunspot cycle, although it may have a slower decline to minimum than the sunspot number. The increase from Cycle minimum to maximum is a factor of 2 to 3. Notable periodicities seen in the emission-line corona are (approximately) 27, 150, 180, 220 and 340 days and 3.4 years.

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Brightness variations of the white light corona during the years 1964?67

Cited by 80 publications

References 9 publications

Polarization and Fragmentation of Solar Type II Radio Bursts

Polarization and Fragmentation of Solar Type II Radio Bursts

Observed Associations between the Solar Interior, Corona, and Solar Wind

Variations of Coronal Radiations at Optical Wavelengths

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