The Depiction of Coronal Structure in White-Light Images

Morgan, Huw; Habbal, Shadia Rifai; Woo, Richard

doi:10.1007/s11207-006-0113-6

Cited by 126 publications

(121 citation statements)

References 15 publications

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“…First, the normal radial gradient filtering (NRGF) technique (Morgan et al 2006) was used to filter the background radiation intensity to enhance the structures in the off-limb region. Second, the unsharp-mask technique (MadMax) (Koutchmy & Koutchmy 1989) is applied to reduce the diffuse and strong background radiation in the off-limb region.…”

Section: Data and Analysis Methodsmentioning

confidence: 99%

Observational Evidence for the Causes and Consequences of Chromospheric Reconnection

Yan

Xia

et al. 2015

ApJ

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The chromospheric anemone jets with an inverse "Y" shape are ubiquitous, as revealed by the Solar Optical Telescope observations. These jets are considered to be consequences of chromospheric magnetic reconnections. Although these jets have been studied intensively, the dynamics and their driving causes remain unclear observationally. In this work, we report a case of a chromospheric jet showing complete observational evidencefor the cause and consequence of chromospheric intermittent reconnection. The intermittent eruption of this jet shows two distinct quasi-periods, 50-60 s and 600-700 s. The short-period eruptions may be related to the plasmoidinduced reconnection, and the long-period ones may be interpreted as sequences of cycles of energy storage and release during magnetic reconnections. The observations also reveal Alfvénic waves with a mean period around 88 s and a maximum transverse displacement around 0″ .26. The jet is hosted by a loop moving smoothly with a horizontal speed of ∼0.4 km s −1 . Our results provide observational evidence supporting the magnetic reconnection model of the formation of the chromospheric jets with related products, in which the loop advection drives intermittent magnetic reconnections, and the reconnection outflows carrying plasmoids collide further with the ambient field linesand finally excitewaves and jets.

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Section: Data and Analysis Methodsmentioning

confidence: 99%

Observational Evidence for the Causes and Consequences of Chromospheric Reconnection

Yan

Xia

et al. 2015

ApJ

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“…We take two steps of image processing in order to enhance the spicules for the convenience of further analysis. In the first step, the normal radial gradient filtering (NRGF) technique (Morgan et al 2006) is implemented to filter the background radiation intensity, which fades away gradually along the radius. The purpose of NRGF is to enhance the structures in the off-limb region as compared with the structures on the solar disk.…”

Section: Observations and Data Analysismentioning

confidence: 99%

Upward propagating high-frequency Alfvén waves as identified from dynamic wave-like spicules observed by SOT onHinode

Marsch³

et al. 2009

A&A

102

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Aims. We identify high-frequency Alfvén waves propagating upward in the solar chromosphere and transition region from observation by Solar Optical Telescope (SOT) onboard Hinode. Methods. The spicule shape is enhanced through application of a normal radial gradient filter and an un-sharp mask on the images taken by SOT. The displaced position of the spicule is at each height obtained by tracing the maximum intensity after image processing. The dominant wave period is obtained by the FFT method applied to the time variations of the displaced position at a certain height. The phase speed is estimated with the help of a cross-correlation analysis of two temporal sequences of the displaced positions at two heights along the spicule. Results. We find in four cases that the spicules are modulated by high-frequency (≥0.02 Hz) transverse fluctuations. Such fluctuations are suggested to be Alfvén waves that propagate upward along the spicules with phase speed ranges from 50 to 150 km s −1 . Three of the modulated spicules show clear wave-like shapes with short wavelengths less than 8 Mm. Conclusions. Our work identified directly upward propagation of Alfvén waves in the solar chromosphere and transition region. In addition to the recently reported Alfvén waves with very long wavelength and wave period, we find here four examples of Alfvén waves with shorter wavelengths and periods. These findings shed new light on the wave origin and on coronal and solar-wind heating.

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“…4 an average upB is calculated from many observations made over the course of several weeks (or more than a solar rotation). This average value is almost identical at heights of 2.5−6 R for both solar minimum and maximum.The usefulness of upB as a background for subtraction in coronagraphic image processing (due to its stability, among other reasons) has been noted by Morgan et al (2006).…”

Section: Unpolarized Brightnessmentioning

confidence: 99%

The long-term stability of the visible F corona at heights of 3–6R_\odot

Morgan¹,

Habbal²

2007

A&A

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Context. CMEs can effect the distribution of dust grains in the corona. The brightness of the visible F corona is expected therefore to change as the frequency of CMEs varies with solar cycle. Aims. We search for a variation in the F corona by comparing LASCO C2 observations from solar minimum and maximum.Methods. An established inversion method is used to calculate the visible F corona brightness from LASCO C2 solar minimum observations made during 1996/10. Good agreement is found with the F corona brightness calculated from Skylab observations during 1973/05-1974/02 for heights of 3-6 R . The unpolarized brightness, which is dominated by the unpolarized F corona brightness at these heights, is obtained by subtracting many pairs of polarized brightness images from total brightness images and averaging over a solar rotation. We calculate the unpolarized brightness for both solar activity minimum and maximum. Results. The unpolarized brightness, and therefore the F corona, remain virtually unchanged between solar minimum and maximum at heights above 2.6 R , despite the large change in the shape and activity of the corona. Using a simple density model, it is shown that the small variation in unpolarized brightness seen below 2.6 R can arise from differences in the distribution of electron density, and therefore cannot be attributed to a variation in the F corona. Conclusions. Despite the large rise in frequency of CMEs from solar minimum to maximum, the F coronal brightness, at heights of 3-6 R in the visible, remains very stable.

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The Depiction of Coronal Structure in White-Light Images

Cited by 126 publications

References 15 publications

Observational Evidence for the Causes and Consequences of Chromospheric Reconnection

Observational Evidence for the Causes and Consequences of Chromospheric Reconnection

Upward propagating high-frequency Alfvén waves as identified from dynamic wave-like spicules observed by SOT onHinode

The long-term stability of the visible F corona at heights of 3–6R_\odot

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The Depiction of Coronal Structure in White-Light Images

Cited by 126 publications

References 15 publications

Observational Evidence for the Causes and Consequences of Chromospheric Reconnection

Observational Evidence for the Causes and Consequences of Chromospheric Reconnection

Upward propagating high-frequency Alfvén waves as identified from dynamic wave-like spicules observed by SOT onHinode

The long-term stability of the visible F corona at heights of 3–6R\odot

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The long-term stability of the visible F corona at heights of 3–6R_\odot