Phenomenon of Alfvénic Vortex Shedding

2019

Phys. Rev. Lett.

Vortex shedding is an oscillating flow that is commonly observed in fluids due to the presence of a blunt body in a flowing medium. Numerical simulations have shown that the phenomenon of vortex shedding could also develop in the magnetohydrodynamic (MHD) domain. The dimensionless Strouhal number, the ratio of the blunt body diameter to the product of the period of vortex shedding and the speed of a flowing medium, is a robust indicator for vortex shedding, and, generally of the order of 0.2 for a wide range of Reynolds number. Using an observation from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we report a wavelike or oscillating plasma flow propagating upward against the Sun's gravitational force. A newly formed shrinking loop in the post-flare region possibly generates the oscillation of the upflow in the wake of the hot and dense loop through vortex shedding. The computed Strouhal number is consistent with the prediction from previous MHD simulations. Our observation suggests the possibility of vortex shedding in the solar corona.

supporting

confidence: 88%

mentioning

confidence: 44%

mentioning

confidence: 99%

See 1 more Smart Citation

Evidence for Vortex Shedding in the Sun’s Hot Corona

Samanta

2019

Phys. Rev. Lett.

“…(41)). This model could explain the selectivity in the excitation of the loops oscillations (only those whose natural kink frequency matches the vortex shedding frequency are excited) and the initial growth of the oscillation amplitude, detected in some cases Gruszecki et al 2010). However, observational confirmation of this mechanism is still absent.…”

Section: Excitation Of Kink Oscillations Of Solar Coronal Loopsmentioning

confidence: 99%

Magnetohydrodynamic Oscillations in the Solar Corona and Earth’s Magnetosphere: Towards Consolidated Understanding

Пилипенко

Heilig³

et al. 2016

Space Sci Rev

Self Cite

188

128

Magnetohydrodynamic (MHD) oscillatory processes in different plasma systems, such as the corona of the Sun and the Earth's magnetosphere show interesting similarities and differences, which so far received little attention and remain underexploited. The successful commissioning within the past ten years of SDO, Hinode, STEREO and THEMIS spacecraft, in combination with matured analysis of data from earlier spacecraft (Wind, SOHO, ACE, Cluster, TRACE and RHESSI) makes it very timely to survey the breadth of observations giving evidence for MHD oscillatory processes in solar and space plasmas, and state-of-the-art theoretical modelling. The paper reviews several important topics, such as Alfvénic resonances and mode conversion; MHD waveguides, such as the magnetotail, coronal loops, coronal streamers; mechanisms for periodicities produced in energy releases during substorms and solar flares, possibility of Alfvénic resonators along open field lines; possible drivers of MHD waves; diagnostics of plasmas with MHD waves; interaction of MHD waves with partly-ionised boundaries (ionosphere and chromosphere). The review is mainly oriented to specialists in magnetospheric physics and solar physics, but not familiar with specifics of the adjacent research fields.

“…In this case, a small displacement of the loop footpoint is magnified by the "sensitivity" of the equilibrium magnetic topology to a small perturbation (Schrijver & Brown 2000;Schrijver et al 2002;White et al 2013). The apparent association of kink oscillation events with the phenomenon of coronal EUV dimming led to the development of a mechanism based on the resonant excitation of the oscillations by the aerodynamic drag force caused by periodic shedding of Alfvénic vortices Gruszecki et al 2010). Another mechanism based upon the presence of field-aligned electric currents in loops, causing their inductive interaction, was developed in Khodachenko et al (2009).…”

Section: Introductionmentioning

confidence: 99%

Excitation of kink oscillations of coronal loops: statistical study

Zimovets

2015

A&A

Self Cite

121

128

Context. Solar flares are often accompanied by kink (transverse) oscillations of coronal loops. Despite intensive study of these oscillations in recent years, the mechanisms that excite them are still not known. Aims. We aim to clarify the excitation mechanisms for these kink oscillations of coronal loops. Methods. We analysed 58 kink-oscillation events observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) during its first four years (2010)(2011)(2012)(2013)(2014) with the use of the JHelioviewer. Association of these oscillation events with flares, lower coronal (r 1.4 R ) eruptions and plasma ejections, coronal mass ejections (CMEs), and coronal Type-II radio bursts is studied. Results. We find that 44 of these 58 oscillation events (76%) were associated with CMEs observed in the white light emission. Moreover, 57 events (98%) were accompanied by lower coronal eruptions/ejections (LCEs) observed in the extreme-ultraviolet band in the parental active regions. In the remaining event an LCE was not clearly seen, but it was definitely associated with a CME too. The main observational finding is that the kink oscillations were excited by the deviation of loops from their equilibria by a nearby LCE in 55 events (95%). In three remaining events, it was difficult to reliably determine the cause of the oscillations because of limitations in the observational data. We also found that 53 events (91%) were associated with flares. In five remaining events, the parental active regions were behind the limb and we could not directly see flare sites. It indicates that there is a close relationship between these two kinds of solar activity. However, the estimated speeds of a hypothetical driver of kink oscillations by flares were found to be lower than 500 km s −1 in 80% of the cases. Such low speeds do not favour the association of the oscillation excitation with a shock wave, as usually assumed. That only 23 (40%) of the oscillation events were found to be associated with coronal Type-II radio bursts also goes against the shock wave mechanism for the excitation of kink oscillations.Conclusions. The statistical analysis shows that the most probable mechanism for exciting the kink oscillations of coronal loops is the deviation of loops from their equilibrium by nearby eruptions or plasma ejections rather than a blast shock wave ignited by a flare.