Fast magnetoacoustic wave trains: from tadpoles to boomerangs | Monthly notices from the Royal Astronomical Society
Fast-propagating, fast magnetoacoustic wave trains guided by field-aligned plasma non-uniformities are confidently observed in the solar corona. Observations at great heights suggest that fast wave trains can travel long distances from the excitation locations. We study the characteristic time signatures of fast dispersive and fully developed magnetoacoustic wave trains in zero-β plasma plates aligned in field in the linear regime. The fast wave trains are excited by an impulsive conductor located in space and propagate along the waveguide as prescribed by the dispersion caused by the waveguide. In slabs with steeper transverse density profiles, the developed wave trains consist of three distinct phases: a long-period quasi-periodic phase with the oscillation period shortening with time, a multi-period (peloton) phase in which distinctly different periods co-exist, and a short-lived periodic Airy phase. The appearance of these phases is attributed to a non-monotonic dependence of the speed of the group of fast waves on the number of parallel waves due to the dispersion of the waveguide, and turns out to be different for the axisymmetric modes (sausage ) and not axisymmetric (kink). In wavelet analysis, this corresponds to the transition from the previously known tadpole shape to a new boomerang shape in the wave train spectrum, with two well-pronounced arms at shorter and longer periods. We describe a specific previously published radio observation of a fast coronal wave train, strongly suggestive of a shift in the wavelet spectrum from a tadpole to a boomerang, largely consistent with our modeling. The applicability of these fast boomerang-shaped wave trains to probe the transverse patterning of coronal waveguide plasma is discussed.
This content is only available in PDF.
© 2021 The author (s) Published by Oxford University Press on behalf of the Royal Astronomical Society