Fibre structure of decametric type II radio bursts as a manifestation of emission propagation effects in a disturbed near-solar plasma
This paper addresses the fine structure of solar decametric type II radio bursts in the form of drifting narrowband fibres on the dynamic spectrum. Observations show that this structure appears in those events where there is a coronal mass ejection (CME) traveling in the near-solar space ahead o...
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2009-10-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/27/3933/2009/angeo-27-3933-2009.pdf |
| Summary: | This paper addresses the fine structure of solar decametric type II
radio bursts in the form of drifting narrowband fibres on the
dynamic spectrum. Observations show that this structure appears in
those events where there is a coronal mass ejection (CME) traveling
in the near-solar space ahead of the shock wave responsible for the
radio burst. The diversity in observed morphology of fibres and
values of their parameters implies that the fibres may be caused by
different formation mechanisms. The burst emission propagates
through extremely inhomogeneous plasma of the CME, so one possible
mechanism can be related to radio propagation effects. I suggest
that the fibres in some events represent traces of radio emission
caustics, which are formed due to regular refraction of radio waves on the large-scale
inhomogeneous structure of the CME front. To
support this hypothesis, I have modeled the propagation of radio
waves through inhomogeneous plasma of the CME, taking into
consideration the presence of electron density fluctuations in it.
The calculations, which are based on the Monte Carlo technique,
indicate that, in particular, the emission of the fibres should be
harmonic. Moreover, the mechanism under consideration suggests that
in solar observations from two different points in space, the
observed sets of fibres can be shifted in frequency with respect to
one another or can have a different structure. This potentially can
be used for identifying fibres caused by the propagation effects. |
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| ISSN: | 0992-7689 1432-0576 |