Coronal rotation during solar cycle 20

Parker, G. D.; Hansen, R. T.; Hansen, Shirley F.

doi:10.1007/bf00153432

Cited by 34 publications

(25 citation statements)

References 25 publications

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“…Hansen et al (1969), from the analysis of white-light data acquired in 1967 near solar minimum conditions, found a rigid rotation rate for heights ranging from 1.1 to 2 R . Parker et al (1982), with similar observations obtained during solar cycle 20, reported instead a general increase with height in the coronal rotation rate between 1.1 and 1.5 R at low latitudes. During the solar minimum activity of cycle 23, Lewis et al (1999), using white-light data from the Large Angle and Spectrometric Coronagraph (LASCO; Brueckner et al 1995) C2 and C3 telescopes aboard SOHO, found a nearly constant rotation rate for heights ranging from 2.5 to 15 R .…”

Section: Introductionsupporting

confidence: 90%

“…As already commented by Parker et al (1982), the observed variations in the rotation rate may reflect changes at a deeper level below the solar photosphere. If the tracers of the coronal rotation observed by UVCS/SOHO were rooted at some depth beneath the surface in the upper layers of the convection zone of the Sun (say, above ∼0.90 R ), they should somehow reflect, maybe amplified by some factor, the variations in rotation rate found there.…”

Section: Comparison Between Coronal and Subphotospheric Rotation Ratessupporting

confidence: 55%

“…The ACF technique has been extensively applied in studies of coronal rotation (e.g., Parker et al 1982;Fisher & Sime 1984;Parker 1986;Sime et al 1989;Lewis et al 1999;Lewis & Simnett 2001;Vats et al 2001;Giordano & Mancuso 2008;Chandra et al 2009). As in Mancuso & Giordano (2011), we considered one-year time series because they represent a satisfactory compromise between time resolution, accuracy, and request of stationarity.…”

Section: Observations and Data Analysismentioning

confidence: 99%

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Coronal equatorial rotation during solar cycle 23: radial variation and connections with helioseismology

Mancuso

Giordano

2012

A&A

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Time-series observations of the O vi 1032 Å spectral line intensity provided by the UltraViolet Coronagraph Spectrometer (UVCS) telescope aboard the Solar and Heliospheric Observatory (SOHO) spacecraft have been analyzed to establish the rotational characteristics of the equatorial solar corona as a function of height and time during solar cycle 23. Overall, the coronal rotation period is observed to vary considerably from 1996 to 2006, with episodes of sudden acceleration and deceleration. On average, the rotation period in the equatorial corona tends to increase radially by ∼0.2 days/R from 1.6 to 3.0 R . An anticorrelation throughout the solar cycle is observed between the radial gradients in the inner corona ( < ∼ 2.2 R ), where the magnetic pressure dominates and the plasma is more rigidly connected, and the outer corona ( > ∼ 2.4 R ), where the field lines open up. Around the equator, the extended corona is found to rotate faster than the underlying photosphere, but its rotation rate is comparable to that estimated within the subphotospheric layers in the outer 5% of the Sun. Moreover, a striking significant positive correlation (r = 0.629 at the 0.99 R level) has been discovered between the variations in the residual rotation rates of the coronal and subphotospheric equatorial plasma, at least down to 0.95 R . This correlation suggests that the observed variations in the coronal rotation rate reflect the dynamic changes inferred within the near-surface shear layer, where the tracer structures responsible for the observed coronal emission are thus most probably anchored. These results raise the possibility that the plasma in the upper layers of the solar convection zone, at least around the equator, may be tightly connected to the plasma in the extended corona and that the deeper layers in the Sun might thus directly influence the dynamic evolution of the solar wind.

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Section: Introductionsupporting

confidence: 90%

Section: Comparison Between Coronal and Subphotospheric Rotation Ratessupporting

confidence: 55%

Section: Observations and Data Analysismentioning

confidence: 99%

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Coronal equatorial rotation during solar cycle 23: radial variation and connections with helioseismology

Mancuso

Giordano

2012

A&A

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“…This technique has been extensively applied in previous studies of coronal rotation (e.g., Parker et al 1982;Sime et al 1989;Lewis et al 1999). The autocorrelation function (ACF) measures the degree of linear correlation between a time series and the same time series delayed or lagged by a number of days.…”

Section: Period Determination By Autocorrelation Techniquementioning

confidence: 98%

Coronal Rotation at Solar Minimum from UV Observations

Giordano

Mancuso

2008

Astrophysical Journal

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The observations of the UVCS SOHO instrument from 1996 May to 1997 May have been analyzed to reconstruct intensity time series of the O vi 1032 8 and H i Ly 1216 8 spectral lines at different coronal heliolatitudes from 1.5 to 3.0 R from Sun center. At solar minimum, some features persist for several rotations, thus allowing analysis of the UV emission as time series modulated at the period of the solar rotation. We find evidence of coronal differential rotation, which significantly differs from that of the photospheric plasma. The estimated equatorial synodic rotation period of the corona at 1.5 R is 27:48 AE 0:10 days. The study of the latitudinal variation shows that the UV corona decelerates toward the photospheric rates from the equator up to the poleward boundary of the midlatitude streamers, reaching a peak of 28:16 AE 0:20 days around +30 from the equator at 1.5 R , while a less evident peak is observed in the northern hemisphere. This result suggests a real north-south rotational asymmetry as a consequence of different activity and weak coupling between the magnetic fields of the two hemispheres. The study of the radial rotation profiles shows that the corona is rotating almost rigidly with height, but we find an abrupt increase by about half a day between 2.3 and 2.5 R . The larger gradients of the rotation rates are localized at the boundaries between open and closed field lines, suggesting that in these regions the differential rotation might be a source of magnetic stress and, consequently, of energy release.

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“…For example, by using CHs as tracers (Wagner 1975(Wagner , 1976Timothy & Krieger 1975;Bohlin 1977) and large-scale coronal structures (Hansen et al 1969;Parker et al 1982;Fisher & Sime 1984;Hoeksema 1984;Wang et al 1988;Weber et al 1999;Weber & Sturrock 2002), previous studies show that the corona rotates rigidly, while other studies (Shelke & Pande 1985;Obridko & Shelting 1989;Navarro-Peralta & Sanchez-Ibarra 1994;Insley et al 1995) indicate differential rotation. In addition to using CHs as tracers, X-ray bright points (Chandra et al 2010;Kariyappa 2008;Hara 2009), coronal bright points (Karachik et al 2006;Brajša et al 2004;Wöhl et al 2010), and SOHO/LASCO images have been used for the computation of rotation rates and yield a differentially rotating corona.…”

Section: Introductionmentioning

confidence: 99%

Rotation Rates of Coronal Holes and Their Probable Anchoring Depths

Hiremath

Hegde

2013

ApJ

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From 2001From -2008, we use full-disk, SOHO/EIT 195 Å calibrated images to determine latitudinal and day-to-day variations of the rotation rates of coronal holes (CHs). We estimate the weighted average of heliographic coordinates such as latitude and longitude from the central meridian on the observed solar disk. For different latitude zones between 40• north and 40• south, we compute rotation rates and find that, irrespective of their area, the number of days observed on the solar disk, and their latitudes, CHs rotate rigidly. Combined for all the latitude zones, we also find that CHs rotate rigidly during their evolution history. In addition, for all latitude zones, CHs follow a rigid body rotation law during their first appearance. Interestingly, the average first rotation rate (∼438 nHz) of CHs, computed from their first appearance on the solar disk, matches the rotation rate of the solar interior only below the tachocline.

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Coronal rotation during solar cycle 20

Cited by 34 publications

References 25 publications

Coronal equatorial rotation during solar cycle 23: radial variation and connections with helioseismology

Coronal equatorial rotation during solar cycle 23: radial variation and connections with helioseismology

Coronal Rotation at Solar Minimum from UV Observations

Rotation Rates of Coronal Holes and Their Probable Anchoring Depths

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