A Low-Frequency Radio Spectropolarimeter for Observations of the Solar Corona

Kishore, P.; Ramesh, R.; Kathiravan, C.; Rajalingam, M.

doi:10.1007/s11207-015-0705-0

Cited by 28 publications

(20 citation statements)

References 57 publications

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“…So, even when the Sun is at −23° decl., its elevation for GRAPH would be high (≈53°). For radio spectral data, we used observations with the Gauribidanur LOw‐frequency Solar Spectrograph (GLOSS; Ebenezer et al, 2001, 2007; Hariharan et al, 2016; Kishore et al, 2014), Gauribidanur RAdio Spectro‐Polarimeter (GRASP; Hariharan et al, 2015; Kishore et al, 2015; Sasikumar Raja et al, 2013), and e‐CALLISTO (Benz et al, 2009; Monstein et al, 2007). We also used data obtained with the Gauribidanur Radio Interferometric Polarimeter (GRIP; Ramesh et al, 2008).…”

Section: Observationsmentioning

confidence: 99%

Low‐Frequency Radio Observations of the “Quiet” Corona During the Descending Phase of Sunspot Cycle 24

Ramesh

Kumari

Kathiravan

et al. 2020

Geophysical Research Letters

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We carried out a statistical study of the "quiet" solar corona during the descending phase of the Sunspot Cycle 24 (i.e., January 2015 to May 2019) using data obtained with the Gauribidanur RAdioheliograPH (GRAPH) at 53 and 80 MHz simultaneously. Our results show that the equatorial (east-west) diameters of the solar corona at the above two frequencies shrunk steadily. The decrease was found to be due to a gradual reduction in the coronal electron density (N e). Independent estimates of N e in the equatorial region of the "background" corona using white-light coronagraph observations indicate a decline consistent with our findings.

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Section: Observationsmentioning

confidence: 99%

Low‐Frequency Radio Observations of the “Quiet” Corona During the Descending Phase of Sunspot Cycle 24

Ramesh

Kumari

Kathiravan

et al. 2020

Geophysical Research Letters

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“…Gopalswamy et al, 1994;Tun and Vourlidas, 2013;Kong et al, 2016;Liu et al, 2018). The radioheliograph at Gauribidanur does not have a polarimetric capability itself, but several one-dimensional polarimeters have been installed alongside it (Ramesh et al, 2008;Kishore et al, 2015).…”

Section: Introductionmentioning

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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“…The observations were carried out close to the local meridian transit time of the Sun (≈06:30 UT). For radio spectral data, we used observations with the Gauribidanur LOw-frequency Solar Spectrograph (GLOSS; Ebenezer et al, 2001aEbenezer et al, , 2007Kishore et al, 2014;Hariharan, Ramesh, Kathiravan, Abhilash, & Rajalingam, 2016), Gauribidanur RAdio Spectro-Polarimeter (GRASP, Hariharan et al, 2015;Kishore et al, 2015;Sasikumar Raja et al, 2013), and e-CALLISTO (Benz et al, 2009;Monstein et al, 2007). We also used data obtained with the Gauribidanur Radio Interferometric Polarimeter (GRIP, Ramesh & Sastry, 2005b;Ramesh et al, 2008).…”

Section: Observationsmentioning

confidence: 99%

New Results on the Direct Observations of Thermal Radio Emission from a Solar Coronal Mass Ejection

Ramesh

Kumari

Kathiravan

et al. 2021

Geophysical Research Letters

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Coronal mass ejections (CMEs) are large-scale and energetic eruptions in the solar atmosphere during which ≈ 10 12 -10 16 g of magnetized coronal plasma are ejected into the heliosphere at speeds ranging from ≈ 100 to 3,000 km/s (e.g., Vourlidas et al., 2010). They are mostly observed in whitelight using coronagraphs which use an occulter to block the bright light from the solar photosphere so that structures like CMEs can be observed with better contrast. But the size of the coronagraph occulters to date has always been larger than that of the photosphere. For example, in the Large Angle and Spectrometric Coronagraph C2 (LASCO C2, Brueckner et al., 1995) on board the Solar and Heliospheric Observatory (SOHO), the occulter covers a heliocentric distance (r) of ≈ 2.2 R ⊙ , where R ⊙ is the radius of the photosphere. This prevents observations of the corona present immediately off the solar limb, in addition to the corona above the solar disk. Radio observations are unique in this connection since there is no occulter. The radio emission associated with and/or from the CMEs can be divided into two classes, thermal and nonthermal (e.g., Vourlidas, 2004). In the nonthermal case, type IV radio bursts due to gyrosynchrotron and/or plasma emission from the electrons in the CME (

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A Low-Frequency Radio Spectropolarimeter for Observations of the Solar Corona

Cited by 28 publications

References 57 publications

Low‐Frequency Radio Observations of the “Quiet” Corona During the Descending Phase of Sunspot Cycle 24

Low‐Frequency Radio Observations of the “Quiet” Corona During the Descending Phase of Sunspot Cycle 24

The Low-Frequency Solar Corona in Circular Polarization

New Results on the Direct Observations of Thermal Radio Emission from a Solar Coronal Mass Ejection

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