Very Large Array and SOHO Observations of Type I Noise Storms, Large-Scale Loops and Magnetic Restructuring in the Corona

Willson, R. F.

doi:10.1007/s11207-005-1104-8

Cited by 11 publications

(8 citation statements)

References 23 publications

(7 reference statements)

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“…The authors postulated that addition of new material to the corona in the aftermath of a CME leads to reorganization of the local coronal magnetic field, a necessary precondition for the onset of noise storm (Benz & Wentzel 1981;Spicer et al 1981). Similar radio observations in the post-CME period were recently reported by Willson (2005) also through high angular resolution observations with the Very Large Array (VLA). Using the same kind of radio data, Habbal et al (1996) had earlier shown that a type I radio noise storm is limited to the site of a CME despite the existence of a number of active regions on the disk.…”

Section: Introductionsupporting

confidence: 85%

“…In doing this, we selected only those CME events with central position angle located inside an angular span of ‫54ע‬Њ with respect to the noise storm. We introduced the latter condition because (1) the average width of CMEs observed during the period under study was in the range 47Њ-61Њ (Yashiro et al 2004); (2) CMEs are generally accompanied by a reconfiguration of the magnetic field over extensive regions of the solar atmosphere which in many cases exceeds the CME size (Fainshtein et al 1998;Chertok et al 2001); (3) activity occurring in association with magnetic field changes in the solar atmosphere can be noticed even at an angular distance of ∼30Њ away (Bruzek 1952 (4) the location of a radio noise storm can be close to the footpoint of a CME (Lantos et al 1981;Willson 2005). Figure 1 shows the result of our work.…”

Section: Resultsmentioning

confidence: 99%

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The Post-Coronal Mass Ejection Solar Atmosphere and Radio Noise Storm Activity

Kathiravan

Ramesh

Nataraj

2007

ApJ

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We carried out a statistical study of solar radio noise storms whose onset was in the aftermath of coronal mass ejections (CMEs) that occurred during 1997-2004, the first half of present solar cycle 23. The work is an attempt to understand the post-CME corona through observations of noise storms since the latter are considered to be closely related to structural changes there. The radio events were taken as the starting point for our study, and details about start time and location were available for 340 of them. We imposed the following conditions to verify the association between the above two phenomena: (1) the noise storm must have occurred ≤24 hr from the onset of a CME and (2) the central position angle of the CME must be located inside an angular span of ‫54ע‬Њ with respect to the noise storm. We found that 196/340 noise storms were associated with CMEs. More interestingly, the time interval between CME liftoff and noise storm onset in all the above cases was ≤13 hr. We suggest that this represents the upper bound of the timescale over which coronal magnetic field reorganization had taken place in the aftermath of the aforementioned 196 noise storm associated CMEs. We also found that for a particular CME, the above temporal cutoff depends on its kinetic energy. Overall, it varies inversely with the logarithm of CME kinetic energy.

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Section: Introductionsupporting

confidence: 85%

Section: Resultsmentioning

confidence: 99%

The Post-Coronal Mass Ejection Solar Atmosphere and Radio Noise Storm Activity

Kathiravan

Ramesh

Nataraj

2007

ApJ

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“…Despite decades of study, there are a number of unanswered questions about the nature of Type I bursts. Not all active regions that are productive at other wavelengths produce noise storms, and the non-radio signatures are often scant (Willson, 2005;Iwai et al, 2012;Li et al, 2017), unlike Type II and III bursts, which have obvious associations with CMEs and flares (Cairns et al, 2003;Reid and Ratcliffe, 2014). There is general agreement that both the burst and continuum components of noise storms are produced by plasma emission, largely due to their often high circular polarizations (Aschwanden, 1986;Mugundhan et al, 2018), but what accelerates the electrons is still debated.…”

Section: Active Region Noise Storm Sourcesmentioning

confidence: 99%

The Low-Frequency Solar Corona in Circular Polarization

et al. 2019

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We present spectropolarimetric imaging observations of the solar corona at low frequencies (80 -240 MHz) using the Murchison Widefield Array (MWA). These images are the first of their kind, and we introduce an algorithm to mitigate an instrumental artefact by which the total intensity signal contaminates the polarimetric images due to calibration errors. We then survey the range of circular polarization (Stokes V ) features detected in over 100 observing runs near solar maximum during quiescent periods. First, we detect around 700 compact polarized sources across our dataset with polarization fractions ranging from less than 0.5 % to nearly 100 %. These sources exhibit a positive correlation between polarization fraction and total intensity, and we interpret them as a continuum of plasma emission noise storm (Type I burst) continua sources associated with active regions. Second, we report a characteristic "bullseye" structure observed for many low-latitude coronal holes in which a central polarized component is surrounded by a ring of the opposite sense. The central component does not match the sign expected from thermal bremsstrahlung emission, and we speculate that propagation effects or an alternative emission mechanism may be responsible. Third, we show that the large-scale polarimetric structure at our lowest frequencies is reasonably well-correlated with the line-of-sight (LOS) magnetic field component inferred from a global potential field source surface (PFSS) model. The boundaries between opposite circular polarization signs are generally aligned with polarity inversion lines in the model at a height roughly corresponding to that of the radio limb. This is not true at our highest frequencies, however, where the LOS magnetic field direction and polarization sign are often not straightforwardly correlated.

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“…They are associated with active regions, but not directly with flares (for reviews, see Elgarøy 1977;Kai et al 1985;Klein 1998). Noise storm observations were presented by, e.g., Krucker et al (1995) and Malik & Mercier (1996), and their relationship to evolving magnetic structures in the solar atmosphere was discussed in Stewart et al (1986), Raulin & Klein (1994), Bentley et al (2000), and Willson (2005).…”

Section: Introductionmentioning

confidence: 99%

A single picture for solar coronal outflows and radio noise storms

Zanna¹,

Aulanier

Klein

et al. 2011

A&A

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We propose a unified interpretation for persistent coronal outflows and metric radio noise storms, two phenomena typically observed in association with quiescent solar active regions. Our interpretation is based on multi-wavelength observations of two such regions as they crossed the meridian in May and July 2007. For both regions, we observe a persistent pattern of blue-shifted coronal emission in high-temperature lines with Hinode/EIS, and a radio noise storm with the Nançay Radioheliograph. The observations are supplemented by potential and linear force-free extrapolations of the photospheric magnetic field over large computational boxes, and by a detailed analysis of the coronal magnetic field topology. We find true separatrices in the coronal field and null points high in the corona, which are preferential locations for magnetic reconnection and electron acceleration. We suggest that the continuous growth of active regions maintains a steady reconnection across the separatrices at the null point. This interchange reconnection occurs between closed, high-density loops in the core of the active region and neighbouring open, low-density flux tubes. Thus, the reconnection creates strong pressure imbalances which are the main drivers of plasma upflows. Furthermore, the acceleration of low-energy electrons in the interchange reconnection region sustains the radio noise storm in the closed loop areas, as well as weak type III emission along the open field lines. For both active regions studied, we find a remarkable agreement between the observed places of persistent coronal outflows and radio noise storms with their locations as predicted by our interpretation.

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Very Large Array and SOHO Observations of Type I Noise Storms, Large-Scale Loops and Magnetic Restructuring in the Corona

Cited by 11 publications

References 23 publications

The Post-Coronal Mass Ejection Solar Atmosphere and Radio Noise Storm Activity

The Post-Coronal Mass Ejection Solar Atmosphere and Radio Noise Storm Activity

The Low-Frequency Solar Corona in Circular Polarization

A single picture for solar coronal outflows and radio noise storms

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