Radius variations over a solar cycle

Selhorst, C. L.; Silva, A. V. R.; Costa, J. E. R.

doi:10.1051/0004-6361:20034382

Cited by 28 publications

(32 citation statements)

References 13 publications

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“…Moreover, the SSC is a 2-D model that takes into account the solar spherical curvature in order to study the solar radius and the limb brightening at 17 GHz. This model yields a radius of ∼970 at 1 AU which is about 5 smaller than the mean observed value (Selhorst et al 2004). As for the limb brightening, we obtained 36% of center-to-limb variation, which is compatible with the larger values detected at the solar poles.…”

Section: Introductionsupporting

confidence: 80%

What determines the radio polar brightening?

Selhorst

Silva

Costa

2005

A&A

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Abstract. In order to explain the bright patches of emission near the poles of 17 GHz solar maps, we have applied a previously developed atmospheric model based on radio observations. This 2-D model, which includes spicules, yields results in good agreement with brightness temperature values at the disk center, radius, and limb brightening 17 GHz observations at equatorial and intermediate regions. Nevertheless, the intensity of discrete bright patches observed near the poles in 17 GHz maps (as bright as 40% over the quiet Sun), can only be explained by holes in the spicule forest. These regions without spicules probably reflect the presence of polar faculae, which inhibit the appearance of spicules. Moreover, the absence of spicules over faculae explains the anti-correlation between the mean polar limb brightening and the solar cycle, because the polar faculae are known be anti-correlated with the solar cycle. Results from the model with spicule-less regions showed that: 1) for bare regions of the same size (5 • ), the limb brightening increases with the pole proximity; 2) larger regions yield more intense limb brightening; 3) the average height of the spicules greatly influences the solar radius; 4) the maximum excess brightness temperature of 40% is in very good agreement with the polar limb observations above bright patches.

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Section: Introductionsupporting

confidence: 80%

What determines the radio polar brightening?

Selhorst

Silva

Costa

2005

A&A

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“…This result resembles that of the solar poles, however, it is somewhat larger than the brightening observed at equatorial (∼15%) and intermediate (∼10%) regions (see Selhorst et al 2003). -The solar radius obtained from the model was (∼970 ), which is at least 5 smaller than the mean observed value (Selhorst et al 2004). …”

Section: Discussionmentioning

confidence: 64%

“…The limb brightening width of 34 , that is the distance where the intensity is half the maximum value of the excess above quiet Sun, is also much smaller than that measured from 17 GHz maps, which is on average 66 ± 16 arcsec (Selhorst et al 2003). As for the radius determined after the convolution, the measured value of 970 from this simulation is at least 5 smaller than the mean solar radius measured from 17 GHz maps (Selhorst et al 2004). Before convolution, a radius of 966.5 was measured, increasing the discrepancy with observations even more.…”

Section: Comparison With 17 Ghz Limb Observationsmentioning

confidence: 57%

Solar atmospheric model with spicules applied to radio observation

Selhorst¹,

Silva

Costa³

2005

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Abstract. An atmospheric model was constructed in order to reproduce quantitatively the observations at 17 GHz from Nobeyama Radio Heliograph, namely the brightness temperature at disk center (from 1.4 to 400 GHz), center-to-limb brightening distribution, and radius derived from 17 GHz solar maps. The two dimensional solar atmospheric model, that takes into account the curvature of the Sun, includes spicules, which physical characteristics (such as size, temperature, density, position, and inclination angle) were randomly attributed. After the interferometer instrumental response is taken into account, the results showed than an atmospheric model without spicules produces 36% of limb brightening, approximately the value observed at the solar poles. However, the inferred solar radius from the model (970 ) was 6 smaller than the mean value derived from the solar maps. An improvement of the model is made by including spicules. Results from this upgraded model showed that depending on their physical parameters, limb brightening and solar radius values are obtained in agreement with the radio observations (except for polar regions).

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“…Similarly, Djafer et al (2008b) applied a new analysis techniques to the same data of SDS experiment and showed that the solar radius increased from 1992 to 1996 by about 197 milliarcseconds (mas), namely 0.05 arcsec/year) at the opposite phase with sunspot cycle. Selhorst et al (2004) reported the analysis results of solar radius determination for more than 3800 maps at 17 GHz from the Nobeyama Radioheliograph (NoRH) over a solar cycle (1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003). They found a correlation of 0.88 for 3820 maps with sunspot numbers, whereas an anti-correlation of −0.64 with sunspot numbers was present in the case where only the polar limb coordinates were taken into account in the polar radius determination.…”

Section: Resultsmentioning

confidence: 99%

Comparison of long-term trend of solar radius with sunspot activity and flare index

Kılıç

Golbasi

2011

Astrophys Space Sci

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Results are presented from a study of solar radius measurements taken with the solar astrolabe at the TUBITAK National Observatory (TUG) over seven years, 2001-2007. The data series with standard deviation of 0.35 arcsec shows the long-term variational trend with 0.04 arcsec/year. On the other hand, the data series of solar radius are compared with the data of sunspot activity and H -α flare index for the same period. Over the seven year trend, we have found significant linear anti-correlations between the solar radius and other indicators such as sunspot numbers, sunspot areas, and H -α flare index. While the solar radius displays the strongest anti-correlation (−0.7676) with sunspot numbers, it shows a significant anti-correlation of −0.6365 with sunspot areas. But, the anti-correlation between the solar radius and H -α flare index is found to be −0.4975, slightly lower than others. In addition, we computed Hurst exponent of the data sets ranging between 0.7214 and 0.7996, exhibiting the persistent behavior for the long term trend. In the light of the strong correlations with high significance, we may suggest that there are a causal relationship between the solar radius and solar time series such as sunspot activity and H -α flare index.

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Radius variations over a solar cycle

Cited by 28 publications

References 13 publications

What determines the radio polar brightening?

What determines the radio polar brightening?

Solar atmospheric model with spicules applied to radio observation

Comparison of long-term trend of solar radius with sunspot activity and flare index

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