Substantial superb constructions, comparable to zebras, drifting bursts, spikes, and fibers have been reported in the course of the previous a long time of observations of photo voltaic radio bursts. These superb constructions are incessantly related to the wide-band continuum comparable to type-IV bursts, at each metric and decametric wavelengths. They carry essential details about the radiation course of and coronal circumstances.
Earlier research have reported the so-called narrow-band stripes (e.g., Chernov 2008), characterised by a bunch of parallel-drifting stripes with comparatively slim spectral band (i.e., $Delta omega/ omega < 0.1 $). The stripes usually seem in chain, being separated by $sim$<1 s on common and every one lasting for a number of to tens of seconds. They often have unfavorable drift, incessantly accompanied by radiation melancholy (or absorptions) on the low-frequency aspect. A number of mechanisms have been proposed to clarify these options, but the origin of their periodicity and coherence stays elusive.
The Chashan broadband photo voltaic radio spectrometer at meter wavelength (CBSm), an instrument of the Chinese language Meridian Mission-Part II (CMP-II), has excessive frequency-temporal decision (76.29 kHz, 0.84 ms) and sensitivity, making it a number one instrument for detecting superb constructions in photo voltaic radio spectra (Chang et al. 2024). With CBSm knowledge, we recognized a novel spectral superb construction of photo voltaic type-IV burst. The construction is characterised by beaded (or pearl-like) enhancements, alongside a bunch of periodic narrow-banded stripes, termed as “beaded stripes” (see Figures 1 and a pair of). The recurrence time of stripes is $< 1$s (often reaching 8s), usually drifting from excessive to low frequencies and accompanied by absorptions, with trailing stripes showing on the finish of previous ones. The beaded enhancements have a periodicity of $sim$0.1s.
For the periodicity and coherence of those stripes, we proposed the next era mechanism on the premise of the double plasma resonance (DPR) instability, and defined the beaded enhancements by way of modulation by low-frequency magnetohydrodynamic (MHD) waves.
The DPR instability can excite the higher hybrid (UH) waves, within the presence of energetic electrons with unstable velocity distribution features such because the beam-ring, horseshoe, or loss-cone. The UH waves have the most-efficient progress at frequency near $omega_{UH}$ when $omega_{UH} approx sOmega_{ce}$, in overdense plasmas with $omega_{pe}/Omega_{ce} gg 1$ (e.g., Li et al. 2019), the place $s$ is a constructive integer. Temporal variations in plasma density ($n_0$) and/or magnetic area energy ($B_0$) can modulate the values of $omega_{pe}/Omega_{ce}$. As soon as $omega_{pe}/Omega_{ce} $ varies by a unity, i.e., from $s$ to $s+1$ or $s-1$, we’ve excitations of successive UH harmonics of ($s pm 1$) $Omega_{ce}$. These recurring harmonics (together with the variations of $n_0$ and $B_0$) clarify the chained stripes, as schemed in Determine 3. The absorption characteristic corresponds to the unfavorable progress of the UH waves.
We attributed the beaded or pearl-like enhancements to periodic modulations by low-frequency MHD waves with a frequency of $sim$10 Hz. Such modulations differ the background magnetic area and/or plasma density periodically and modulate the UH mode progress price on the similar tempo, resulting in the beaded characteristic.
We demand an elaborate numerical mannequin to guage the expansion charges of the DPR modes and the radiation modes, contemplating temporal variation or inhomogeneous distribution of plasma density or magnetic area energy, in addition to the modulations of low-frequency MHD waves, to attain a greater understanding of the spectral construction.
The examine informs the chance to establish novel spectral superb constructions with devices of excessive sensitivity and spectral-temporal decision, even after a persistent commentary for a number of a long time. In future, we’ll proceed to seek for novel spectral constructions with CBSm.
Determine 1. (a) and (b) CBSm dynamic spectra containing wealthy superb constructions. (c)–(e) Zoom-in views of the chosen areas (black containers in (a) and (b)).
Determine 2. (a) An instance of stripes with an total wavy morphology within the Might 8, 2024 occasion, with beaded construction rising within the center portion. The black traces are fittings of the stripe slopes. (b) Depth profile at 443 MHz (white dashed line in panel (a)). The inset (panel (b1)) exhibits the interval $Delta$t between adjoining peaks.
Determine 3. Schematic diagram for the era of striped chains. (a) Variations of the UH mode frequency as operate of $omega_{pe}/Omega_{ce}$ (t). The shadows characterize the absorptions, and $gamma$ denotes the expansion price. (b) Schematic of chain formation as a result of variations of $omega_{pe}/Omega_{ce}$ (t).
Based mostly on a just lately revealed article: C. Li, Y. Chen, B. Wang, Z. Zhong, B. Tan, Z. Ning, H. Ning, X. Kong, S. Chang, Y. Tang, N. Gai, L. Deng, J. Yan, and F. Yan, A novel superb spectral construction of photo voltaic radio bursts with periodic beaded stripes noticed by CBSm of CMP-II, Sci. China-Phys. Mech. Astron. 68(10), 109611 (2025), DOI: 10.1007/s11433-025-2716-4, https://arxiv.org/abs/2506.06819
Additional information
The CBSm knowledge could be accessed through the web site:
http://47.104.87.104/MWRS/RadioBurstEvent/typeII/typeIIburst_show.html
References
- P. Chernov, 2008, ApJL, 34, 486
- W. Chang, B. Wang, G. Lu, et al., 2024, ApJS, 272, 21
- Li, Y. Chen, X. Kong, et al., 2019, ApJ, 880, 31
*Full checklist of Authors: Chuanyang Li, Yao Chen, Bing Wang, Ze Zhong, Baolin Tan, Zongjun Ning, Hao Ning, Xiangliang Kong, Shuwang Chang, Yanke Tang, Ning Gai, Li Deng, Jingye Yan, and Fabao Yan
