80,450 research outputs found
Homoclinic bifurcations in low-Prandtl-number Rayleigh-B\'{e}nard convection with uniform rotation
We present results of direct numerical simulations on homoclinic gluing and
ungluing bifurcations in low-Prandtl-number ()
Rayleigh-B\'{e}nard system rotating slowly and uniformly about a vertical axis.
We have performed simulations with \textit{stress-free} top and bottom
boundaries for several values of Taylor number () near the
instability onset. We observe a single homoclinic ungluing bifurcation, marked
by the spontaneous breaking of a larger limit cycle into two limit cycles with
the variation of the reduced Rayleigh number for smaller values of . A pair of homoclinic bifurcations, instead of one bifurcation, is
observed with variation of for slightly higher values of () in the same fluid dynamical system. The variation of the bifurcation
threshold with is also investigated. We have also constructed a
low-dimensional model which qualitatively captures the dynamics of the system
near the homoclinic bifurcations for low rotation rates. The model is used to
study the unfolding of bifurcations and the variation of the homoclinic
bifurcation threshold with .Comment: 6 pages, 7 figures, 1 tabl
Eruption of a plasma blob, associated M-class flare, and large-scale EUV wave observed by SDO
We present a multiwavelength study of the formation and ejection of a plasma
blob and associated EUV waves in AR NOAA 11176, observed by SDO/AIA and STEREO
on 25 March 2011. SDO/AIA images clearly show the formation and ejection of a
plasma blob from the lower solar atmosphere at ~9 min prior to the onset of the
M1.0 flare. This onset of the M-class flare happened at the site of the blob
formation, while the blob was rising in a parabolic path with an average speed
of ~300 km/s. The blob also showed twisting and de-twisting motion in the lower
corona, and the blob speed varied from ~10-540 km/s. The faster and slower EUV
wavefronts were observed in front of the plasma blob during its impulsive
acceleration phase. The faster EUV wave propagated with a speed of ~785 to 1020
km/s, whereas the slower wavefront speed varied in between ~245 and 465 km/s.
The timing and speed of the faster wave match the shock speed estimated from
the drift rate of the associated type II radio burst. The faster wave
experiences a reflection by the nearby AR NOAA 11177. In addition, secondary
waves were observed (only in the 171 \AA channel), when the primary fast wave
and plasma blob impacted the funnel-shaped coronal loops. The HMI magnetograms
revealed the continuous emergence of new magnetic flux along with shear flows
at the site of the blob formation. It is inferred that the emergence of twisted
magnetic fields in the form of arch-filaments/"anemone-type" loops is the
likely cause for the plasma blob formation and associated eruption along with
the triggering of M-class flare. Furthermore, the faster EUV wave formed ahead
of the blob shows the signature of fast-mode MHD wave, whereas the slower wave
seems to be generated by the field line compression by the plasma blob. The
secondary wave trains originated from the funnel-shaped loops are probably the
fast magnetoacoustic waves.Comment: A&A (in press), 22 pages, 13 figure
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