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Decameter hectometric (DH; 1–14 MHz) type IV radio bursts are produced by flare-accelerated electrons trapped in postflare loops or the moving magnetic structures associated with the coronal mass ejections (CMEs). From a space weather perspective, it is important to systematically compile these bursts, explore their spectrotemporal characteristics, and study the associated CMEs. We present a comprehensive catalog of DH type IV bursts observed by the Radio and Plasma Wave Investigation instruments on board the Wind and Solar TErrestrial RElations Observatory spacecraft covering the period of white-light CME observations by the Large Angle and Spectrometric Coronagraph on board the Solar and Heliospheric Observatory mission between 1996 November and 2023 May. The catalog has 139 bursts, of which 73% are associated with a fast (>900 km s ^−1 ) and wide (>60°) CME, with a mean CME speed of 1301 km s ^−1 . All DH type IV bursts are white-light CME-associated, with 78% of the events associated with halo CMEs. The CME source latitudes are within ±45°. Seventy-seven events had multiple-vantage-point observations from different spacecraft, letting us explore the impact of the line of sight on the dynamic spectra. For 48 of the 77 events, there were good data from at least two spacecraft. We find that, unless occulted by nearby plasma structures, a type IV burst is best viewed when observed within a ±60° line of sight. Also, bursts with a duration above 120 minutes have source longitudes within ±60°. Our inferences confirm the inherent directivity in the type IV emission. Additionally, the catalog forms a Sun-as-a-star DH type IV burst database.

We report spectral and polarimeter observations of two weak, low-frequency (≈85–60 MHz) solar coronal type II radio bursts that occurred on 2020 May 29 within a time interval ≈2 minutes. The bursts had fine structures, and were due to harmonic plasma emission. Our analysis indicates that the magnetohydrodynamic shocks responsible for the first and second type II bursts were generated by the leading edge (LE) of an extreme-ultraviolet flux rope/coronal mass ejection (CME) and interaction of its flank with a neighboring coronal structure, respectively. The CME deflected from the radial direction by ≈25° during propagation in the near-Sun corona. The estimated power spectral density and magnetic field strength ( B ) near the location of the first burst at heliocentric distance r ≈ 1.35 R _⊙ are ≈2 × 10 ^−3 W ^2 m and ≈1.8 G, respectively. The corresponding values for the second burst at the same r are ≈10 ^−3 W ^2 m and ≈0.9 G. The significant spatial scales of the coronal turbulence at the location of the two type II bursts are ≈62–1 Mm. Our conclusions from the present work are that the turbulence and magnetic field strength in the coronal region near the CME LE are higher compared to the corresponding values close to its flank. The derived estimates of the two parameters correspond to the same r for both the CME LE and its flank, with a delay of ≈2 minutes for the latter.

The Zeeman effect has been routinely used to image and quantify the solar photospheric magnetic field (B). Such a direct measuring technique is not yet available for the corona (Lin et al. 2004). Since almost all transient nonthermal radio emissions from the corona are either partially or fully circularly polarized, observing their polarization signatures over broad frequency ranges would be of help to estimate B as a function of heliocentric height. This article aims to describe the design and development of a Cross-polarized Log-Periodic Dipole Antenna (CLPDA), an integral part of a radio spectro-polarimeter, which works in the 50–500 MHz frequency-range and to explain the tests that were carried out to characterize it. The above frequency range corresponds to a heliocentric height range ≈1.03 < r < 2.5 R _⊙ ( R _⊙ = photospheric radius ), wherein the numerous coronal nonthermal transients associated with space-weather effects are observed to originate. The CLPDA is used to determine the strength and sense of polarization of the received radio signal. The uncertainty involved in the determination depends on the polarization-isolation (PI) between the two orthogonal components of a CLPDA. Some of the recent advancements made in the antenna design concepts at high frequencies (∼GHz) were adopted to reduce the PI at low frequencies (∼MHz). Throughout the above frequency range, the CLPDA has a gain, return loss, and PI of ≈6.6 dBi, ≲−10 dB, and ≲−27 dB, respectively. The average PI of the CLPDA varies from −30 to −24 dB over an azimuthal angle range 0° to ±45° within which the observations are performed regularly.

We report a solar coronal split-band type II radio burst that was observed on 2016 March 16 with the Gauribidanur Radio Spectro-Polarimeter in the frequency range ≈90–50 MHz, and the Gauribidanur RadioheliograPH at two discrete frequencies, viz. 80 and 53.3 MHz. Observations around the same epoch in extreme ultraviolet (EUV) and white light show that the above burst was associated with a flux-rope structure and a coronal mass ejection (CME), respectively. The combined height–time plot generated using EUV, radio, and white-light data suggests that the different observed features (i.e., the flux rope, type II burst, and the CME) are all closely associated. We constructed an empirical model for the coronal electron density distribution (Ne(r), where r is the heliocentric distance) from the above set of observations themselves and used it to estimate the coronal magnetic field strength (B) over the range of r values in which the respective events were observed. The B values are consistent with each other. They vary as B(r) = 2.61 × r−2.21 G in the range r ≈ 1.1–2.2R⊙. As far as we know, similar direct estimates of B in the near-Sun corona without assuming a model for Ne(r), and by combining cotemporal set of observations in two different regions (radio and white-light) of the electromagnetic spectrum, have rarely been reported. Further, the present work is a novel attempt where the characteristics of a propagating EUV flux-rope structure, considered to be the signature of a CME close to the Sun, have been used to estimate B(r) in the corresponding distance range. [ABSTRACT FROM AUTHOR]

We report observations of the high frequency type II radio burst (≈430–30 MHz) that occurred in the solar corona on 2015 November 4. The drift rate of the burst, estimated close to the start frequency of its fundamental component (≈215 MHz), is unusually high (≈2 MHz s−1). Our analysis shows that the estimated speed of the magnetohydrodynamic shock driver of the burst varies with time. The peak speed and acceleration are very large, and , respectively. There is spatio-temporal correlation between the type II burst and the associated coronal mass ejection (CME) in the whitelight and extreme-ultraviolet images. The time profile of the shock speed and the light curve of the associated soft X-ray flare correlate well. These results indicate that in the present case, (i) the magnetohydrodynamic shock responsible for the high frequency coronal type II burst is driven by the CME and (ii) the time profile of the type II burst shock speed represents the near-Sun kinematics of the CME. [ABSTRACT FROM AUTHOR]