BEGIN:VCALENDAR
VERSION:2.0
PRODID:www.imperial.ac.uk
BEGIN:VEVENT
UID:616e9cc05f388
DTSTART:20210115T140000Z
SEQUENCE:0
TRANSP:OPAQUE
DTEND:20210115T150000Z
URL:https://www.imperial.ac.uk/events/128464/nonlinear-dynamics-of-forced-b
aroclinic-critical-layers/
LOCATION:United Kingdom
SUMMARY:Nonlinear dynamics of forced baroclinic critical layers
CLASS:PUBLIC
DESCRIPTION:Recently work has revealed that novel vortices in stratified sh
ear flows can replicate themselves through the excitation of critical laye
rs (Marcus et al.\, Phys. Rev. Lett. 2013\, 111(8): 084501). Such vortic
es are referred to ‘zombie vortices\,’ and their replication process i
s suggested to be a promising explanation for the accretion of protoplanet
ary disks. The critical levels that accomplish the self-replication are
‘baroclinic’ critical levels\, located where the Doppler-shifted phase
velocity matches the internal gravity wave velocity. In this talk\, we wi
ll study the dynamics of baroclinic critical layers theoretically via matc
hed asymptotic analysis.\nWe first study the linear and nonlinear evolutio
n of the baroclinic critical layers under a steady forcing. We show that t
he linear critical layer is characterised by secular growth of the wave am
plitude\, and when it becomes nonlinear\, the mean flow distortion of vort
icity is the dominant characteristic. We then show that such a mean-flow d
efect is susceptible to a `secondary instability\,’ which makes the crit
ical layer roll up into billows and has the ability to excite new baroclin
ic critical layers. Our study could provide a theoretical understanding fo
r the self-replicating zombie vortices.
X-ALT-DESC;FMTTYPE=text/html:Recently work has revealed that novel vorti
ces in stratified shear flows can replicate themselves through the excitat
ion of critical layers (Marcus et al.\, Phys. Rev. Lett. 2013\, 111(8):
084501). Such vortices are referred to ‘zombie vortices\,’ and their r
eplication process is suggested to be a promising explanation for the accr
etion of protoplanetary disks. The critical levels that accomplish the sel
f-replication are ‘baroclinic’ critical levels\, located where the Dop
pler-shifted phase velocity matches the internal gravity wave velocity. In
this talk\, we will study the dynamics of baroclinic critical layers theo
retically via matched asymptotic analysis.

\nWe first study the line
ar and nonlinear evolution of the baroclinic critical layers under a stead
y forcing. We show that the linear critical layer is characterised by secu
lar growth of the wave amplitude\, and when it becomes nonlinear\, the mea
n flow distortion of vorticity is the dominant characteristic. We then sho
w that such a mean-flow defect is susceptible to a `secondary instability\
,’ which makes the critical layer roll up into billows and has the abili
ty to excite new baroclinic critical layers. Our study could provide a the
oretical understanding for the self-replicating zombie vortices.

DTSTAMP:20211019T102400Z
END:VEVENT
END:VCALENDAR