Low-Frequency Observations of Transient Quasi-Periodic Radio Emission From the Solar Atmosphere

Abstract

We report low frequency observations of the quasi-periodic, circularly polarized, harmonic type III radio bursts whose associated sunspot active regions were located close to the solar limb. The measured periodicity of the bursts at 80 MHz was ≈ 5.2 s and their average degree of circular polarization (dcp) was ≈ 0.12. We calculated the associated magnetic field B : (1) using the empirical relationship between the dcp and B for the harmonic type III emission, and (2) from the observed quasi-periodicity of the bursts. Both the methods result in B ≈ 4.2 G at the location of the 80 MHz plasma level (radial distance r ≈ 1.3 R ⊙ ) in the active region corona.

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

“…We also used data obtained with the Gauribidanur Radio Interferometric Polarimeter (GRIP; Ramesh et al, 2008). The combined use of the aforementioned imaging, spectral, and polarimetric data helps to understand the radio signatures associated with the corresponding solar activity in a better manner (see, e.g., Sasikumar Raja & Ramesh, 2013). The optical data were obtained in white‐light with the COR1 coronagraph of the Sun‐Earth Connection Coronal and Heliospheric Investigation (SECCHI; Howard et al, 2008) on board the Solar Terrestrial Relationship Observatory‐A (STEREO‐A, https://cor1.gsfc.nasa.gov/).…”

Strength of the Solar Coronal Magnetic Field – A Comparison of Independent Estimates Using Contemporaneous Radio and White-Light Observations

“…Stokes I, alone (Smerd, Sheridan, and Stewart, 1975;Gopalswamy and Kundu, 1990;Bastian et al, 2001;Vršnak et al, 2002;Mancuso et al, 2003;Cho et al, 2007;Kishore et al, 2016) or both the total and circularly polarized intensities, i.e. Stokes I and V (Dulk and Suzuki, 1980;Gary et al, 1985;Ramesh et al, 2010a;Ramesh, Kathiravan, and Narayanan, 2011;Tun and Vourlidas, 2013;Sasikumar Raja and Ramesh, 2013;Hariharan et al, 2014;2016b;Anshu et al, 2017). Note that we have mentioned only Stokes I and V emission here since differential Faraday rotation of the plane of polarization in the solar corona and Earth's ionosphere makes it impossible to observe the linear polarization (represented by Stokes Q and U ) within the typical observing bandwidths of ≈ 100 kHz (see for example Grognard and McLean, 1973.)…”

An Estimate of the Magnetic Field Strength Associated With a Solar Coronal Mass Ejection From Low Frequency Radio Observations

“…That both the CMEs and streamers are primarily density enhancements in the solar atmosphere could be a reason for this; 5) for a similar type IVm burst event explained on the basis of optically thin gyro-synchrotron emission from the mildly relativistic non-thermal electrons in the magnetic field of the associated CME core,Tun & Vourlidas (2013) showed that B ≈ 5 − 15 G at r ≈ 1.7 R ⊙ ; 6) type IVm radio bursts associated with the 'leg' of the corresponding CMEs and generated due to second harmonic plasma emission from the enhanced electron density there indicate that B ≈ 4 G at r ≈ 1.6 R ⊙. Considering that the coronal magnetic field associated with the active regions have a range of values(Dulk & McLean 1978;Ramesh et al 2003Ramesh et al , 2011bSasikumar & Ramesh 2013), the different estimates mentioned above can be regarded as reasonable. With measurements of the coronal magnetic field being very limited, particularly in close association with a CME, the results indicate that contemporaneous whitelight and radio observations of the solar corona close to the Sun (r 2 R ⊙ ) are desirable to understand the CMEs and the associated magnetic field.It is a pleasure to thank the staff of the Gauribidanur observatory for their help in observations, maintenance of the antenna and receiver systems there.…”