New Results from the Spectral Observations of Solar Coronal Type II Radio Bursts

2022

ApJ

Self Cite

Using temporal observations of circular polarized harmonic plasma emission from a split-band type II solar radio burst at 80 MHz, we separately estimated the coronal magnetic field strengths (B) associated with the lower (L) and upper (U) frequency bands of the burst. The corresponding Stokes I and V data were obtained with the polarimeter operating at the above frequency in the Gauribidanur observatory. The burst was associated with a flare/coronal mass ejection on the solar disk. Simultaneous spectral observations with the spectrograph there in the frequency range 80–35 MHz helped to establish that the observed polarized emission was from the harmonic component of the burst. The B values corresponding to the polarized emission from the L and U bands at 80 MHz are B L ≈ 1.2 G and B U ≈ 2.4 G, respectively. The different values of B for the observed harmonic emission at the same frequency (80 MHz) from the two bands imply unambiguously that the corresponding fundamental emission at 40 MHz must have originated at different spatial locations. Two-dimensional radio imaging observations of the burst with the radioheliograph in the same observatory at 80 MHz indicate the same. As comparatively higher B is expected behind a propagating shock due to compression as well as the corresponding coronal regions being closer to the Sun, our results indicate that the sources of L- and U-band emission should be located ahead of and behind the associated coronal shock, respectively. These are useful to understand the pre- and postshock corona as well as locations of electron acceleration in a propagating shock.

Section: Observationssupporting

confidence: 78%

Polarization Observations of a Split-band Type II Radio Burst from the Solar Corona

2022

ApJ

Self Cite

“…Its measurement position angle (MPA) and angular width were ≈63°and ≈37°, respectively. 6 The narrow bandwidth of the type II bursts is reasonably consistent with the latter (see, e.g., Ramesh et al 2022a). The MPA of the LE was ≈75°at r ≈ 5.8 R e .…”

Section: Observationssupporting

confidence: 61%

“…The occurrence of such events are attributed to either two successive flares or two successive CMEs or a flare and CME, or leading edge (LE) and flank of a CME (Mancuso & Raymond 2004;Shanmugaraju et al 2005;Subramanian & Ebenezer 2006;Cho et al 2008Cho et al , 2011Hariharan et al 2015;Lv et al 2017, Koval et al 2021. The CME driven type II bursts could occur at locations along the front of the shock wherever appropriate conditions for electron acceleration are satisfied (Knock & Cairns 2005;Jebaraj et al 2021;Kouloumvakos et al 2021;Ramesh et al 2022a). Statistical study using two-dimensional imaging observations of coronal type II bursts observed near the solar limb by Ramesh et al (2012a) indicate that they are located within the angular range 46°from the central position angle of the LE of the associated CMEs.…”

Section: Introductionmentioning

confidence: 99%

Solar Coronal Density Turbulence and Magnetic Field Strength at the Source Regions of Two Successive Metric Type II Radio Bursts

Kumari

2023

ApJ

Self Cite

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 W2m and ≈1.8 G, respectively. The corresponding values for the second burst at the same r are ≈10−3 W2m 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 average instantaneous bandwidth of the type II burst in Figure 1, estimated from its F-component, is ≈10 MHz. This indicates that the angular width of the associated CME should be ≈250° ( Ramesh et al 2022). The latter is in good agreement with the CME observations mentioned above.…”

Section: Observationsmentioning

confidence: 93%

Circular Polarization Observations of Type II Solar Radio Bursts and the Coronal Magnetic Field

Chellasamy

2022

ApJ

Self Cite

It is well known that magnetic field strength (B) in the solar corona can be calculated using the Alfvén Mach number (M A ) and Alfvén speed (v A ) of the magnetohydrodynamic shock waves associated with coronal type II radio bursts. We show that observations of weak circularly polarized emission associated with the harmonic component of the type II bursts provide independent and consistent estimates of B. For the coronal type II burst observed on 2021 October 9, we obtained B ≈1.5 G and ≈1.9 G at a heliocentric distance (r) of ≈1.8 R ⊙, using the above two techniques, respectively.