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<p>Type II solar radio bursts are commonly associated with shocks generated by coronal mass ejections (CMEs), where plasma waves are excited by magnetohydrodynamic (MHD) processes and converted into radio waves at the local plasma frequency or its harmonics. However, there are instances where type II bursts occur in the absence of whitelight CMEs. We analysed one such metric type II radio burst observed on 2 November 2023, characterized by split band features and fundamental-harmonic lanes. Notably, no CME was detected with space-based coronagraphs during this event. However, an intense M1.6 class flare was observed just before the type II burst and an extreme ultraviolet (EUV) disturbance was observed expanding into surrounding regions. The absence of any whitelight CME seen in any coronagraph field of view, even though the EUV shock had a moderate speed of <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\approx }500\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>≈</mo> <mn>500</mn> </mrow> </math></EquationSource> </InlineEquation>&#xa0;km s<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(^{-1}\)</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow /> <mrow /> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </mmultiscripts> </math></EquationSource> </InlineEquation>, which was close to the shock speed derived from radio observations. These observations indicate that the shock in the inner corona was most likely driven by the EUV ejecta seen in the lower corona, but the ejecta did not survive as a CME in the coronagraph field of view.</p>

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A type II solar radio burst without a coronal mass ejection association

  • 期刊论文

  • 发表日期：

    2025年12月12日

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  • ANSHU KUMARI,
  • NAT GOPALSWAMY

摘要

Type II solar radio bursts are commonly associated with shocks generated by coronal mass ejections (CMEs), where plasma waves are excited by magnetohydrodynamic (MHD) processes and converted into radio waves at the local plasma frequency or its harmonics. However, there are instances where type II bursts occur in the absence of whitelight CMEs. We analysed one such metric type II radio burst observed on 2 November 2023, characterized by split band features and fundamental-harmonic lanes. Notably, no CME was detected with space-based coronagraphs during this event. However, an intense M1.6 class flare was observed just before the type II burst and an extreme ultraviolet (EUV) disturbance was observed expanding into surrounding regions. The absence of any whitelight CME seen in any coronagraph field of view, even though the EUV shock had a moderate speed of \({\approx }500\) ≈ 500  km s \(^{-1}\) - 1 , which was close to the shock speed derived from radio observations. These observations indicate that the shock in the inner corona was most likely driven by the EUV ejecta seen in the lower corona, but the ejecta did not survive as a CME in the coronagraph field of view.