Decameter Wavelength Observations of an Absorption Burst from the Sun and Its Association with an X2.0/3B Flare and the Onset of a “Halo” Coronal Mass Ejection

Abstract

We report a transient intensity reduction/absorption burst observed at decameter wavelengths in close temporal association with an X2.0/3B flare near the disk center and the onset of a "halo" coronal mass ejection. The observed bandwidth of the burst was about 10 MHz. The size of the absorption region was estimated to be ≈28,000 km.

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

“…Each 1‐D brightness distribution obtained as mentioned above was reproduced using an iterative multi‐Gaussian least squares curve fitting technique as described in Ramesh et al (2006). The minimum width of each Gaussian profile was limited to 1 ′ , the smallest source size reported at frequencies <100 MHz (Kathiravan et al, 2011; Mugundhan et al, 2016, 2018; Ramesh & Ebenezer, 2001; Ramesh & Sastry, 2000; Ramesh et al, 1999a, 2012). The typical discrete thermal sources in the above frequency range are mostly the radio counterparts of large‐scale structures like the coronal streamers and/or coronal holes.…”

High Angular Resolution Radio Observations of a Coronal Mass Ejection Source Region at Low Frequencies During a Solar Eclipse

“…The estimated T b based on the above source size is ≈3 × 10 9 K. Using the above value of T b , we calculated the coronal magnetic field near the radio source region, and it is ≈70 mG. With the noise storms closely associated with CMEs and also usually circularly polarized, similar high angular resolution studies particularly in both total and circularly polarized intensity, are expected to be useful in understanding the CMEs close to the Sun where white light observations and magnetic field measurements are currently difficult. We would like to add here that although the smallest observed source size is ≈1 in the present case, it is possible that the observable limiting size of discrete radio sources in the solar corona, particularly frequencies 100 MHz, could be smaller still (McConnell 1983;Ramesh & Ebenezer 2001). The fact that the observed T b (≈3 × 10 9 K) in the present case is less than the predicted maximum T b (≈10 10 K) for the noise storm continuum based on theoretical calculations (Thejappa 1991) supports this argument.…”

Short‐Lived Absorptive Type III–like Microwave Bursts as a Signature of Fragmented Electron Injections

“…Absorptive events have been frequently observed superposed on solar type IV/II radio bursts from the dekametric to microwave ranges (Boischot et al 1959;Wild et al 1963;Slottje 1972;Kai 1973;Fokker 1982;Gopalswamy et al 1983;Fleishman et al 1994;Klassen 1996;Ramesh & Ebenezer 2001;Konovalenko et al 2007). Sometimes their observational characteristics resemble those of type IIIYlike bursts, and they are also called ''fast-drift absorption bursts'' (Zaitsev & Stepanov 1975) and ''shadow type III bursts'' ( Kai 1973;Melrose 1974aMelrose , 1974b.…”

“…Klassen regarded this as a signature of propagating bidirectional electron beams. Several mechanisms have been proposed to explain these peculiar absorptive events, including screening effects (Fokker 1982), wave-wave interactions ( Melrose 1974a( Melrose , 1974bGopalswamy et al 1983;Ramesh & Ebenezer 2001), and new injections of electron beams to ''quench'' the loss-cone instability, which is responsible for the type IV continuum (Zaitsev & Stepanov 1975;Benz & Kuijpers 1976;Fleishman et al 1994).…”

“…However, as discussed in Melrose (1974b), this approach is based on the important assumption that the electron beams responsible for the absorptive type IIIYlike bursts should generate ion sound turbulence themselves, which has still not yet been testified. This mechanism was then used by some authors to interpret a number of absorptive observations in the dekameter frequency range (Gopalswamy et al 1983;Ramesh & Ebenezer 2001) by introducing shock waves to generate the required ion sound turbulence, but the drifting feature could not be easily explained in this way either.…”