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DESCRIPTION: \n\nStudent Seminar Series\n\nDepartment of Atmospheric & Ocea
 nic Sciences\n\npresents\n\na talk by\n\nTsz Kin (Eric) Lai\n	PhD student\n
 \nBarotropic Instability across the Moat and Inner Eyewall Decay of Tropic
 al Cyclone\n\nThe eyewall of a tropical cyclone (TC) is the region having 
 the most intense winds and rainfall within the TC. It is frequently observ
 ed that the strongest TCs develop a secondary eyewall outside the primary 
 eyewall with an annular moat region separating the two eyewalls. Generally
 \, a double-eyewall TC undergoes an eyewall replacement cycle such that th
 e inner eyewall gradually dissipates while the outer eyewall strengthens a
 nd contracts.\n\nRadar imagery of some double-eyewall TCs shows that the i
 nner eyewalls become elliptical prior to their dissipation. According to p
 revious 2D idealised studies\, this feature indicates that a barotropic in
 stability across the moat (a.k.a. type-2 barotropic instability) may play 
 a role. To further investigate the mechanism for dissipation\, a WRF simul
 ation of Hurricane Wilma (2005) is performed. The analyses reveal the occu
 rrence of a type-2 instability\, which led to the elliptical elongation of
  the inner eyewall\, and the associated wavenumber-2 radial flow. A time s
 eries analysis of the inner core circulation indicates the weakening of th
 e inner eyewall\, largely due to the wavenumber-2 radial flow pattern.\n\n
 To further examine the physics of inner eyewall decay\, idealised 3D numer
 ical experiments are performed. In the moist full physics run\, the simula
 ted vortex reproduces the type-2 instability and the wavenumber-2 radial f
 low pattern as in the Wilma simulation. The evolution of the absolute angu
 lar momentum (AAM) demonstrates that the region of negative radial transpo
 rt of AAM located at and near the inner eyewall starts to significantly en
 large after the ellipticity of the whole vortex becomes prominent. The AAM
  budget calculation after the excitation of the type-2 instability indicat
 es a significant intensification in the outward eddy radial advection of A
 AM resulting in the total radial AAM advection becoming negative in the la
 ter stage of the instability. The budget calculation also shows that the n
 egative total radial advection of AAM contributes the most to the inner ey
 ewall decay except in the boundary layer where frictional effects dominate
 . Another dry no-physics idealised experiment is conducted and the result 
 shows that the type-2 instability alone is able to weaken the inner eyewal
 l with non-negligible effect. Taking together\, these two idealised experi
 ments suggest that the type-2 instability can accelerate the decay of the 
 inner eyewall in concert with the cut-off effect of the boundary layer.\n
 \nWednesday Feb 12/ 2.30 PM/ Room 934 Burnside Hall\n\n \n
DTSTART:20200212T193000Z
DTEND:20200212T203000Z
LOCATION:Room 934\, Burnside Hall\, CA\, QC\, Montreal\, H3A 0B9\, 805 rue 
 Sherbrooke Ouest
SUMMARY:Barotropic Instability across the Moat and Inner Eyewall Decay of T
 ropical Cyclone
URL:https://www.mcgill.ca/meteo/channels/event/barotropic-instability-acros
 s-moat-and-inner-eyewall-decay-tropical-cyclone-320254
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