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UID:20250811T234535EDT-0335F7nVkg@132.216.98.100
DTSTAMP:20250812T034535Z
DESCRIPTION:On quasigeostrophic dynamics near the tropopause\n\nAbstract\n
 \nUnder quasigeostrophic (QG) dynamics\, the presence of a sharp transitio
 n in the stratification profile leads to the formation of comparably sharp
  vertical gradients of buoyancy. When the QG potential vorticity is assume
 d to be confined to the jump region\, as in surface quasigeostrophy (SQG)\
 , the sharp gradients are present initially in the buoyancy field. If smoo
 thly-varying initial conditions are considered instead\, numerical simulat
 ions reveal that jump-scale features nevertheless emerge after a few turno
 ver times. The introduction of this small scale\, h\, characterizing the t
 ropopause implies a larger Froude number\, thereby undermining the validit
 y of the quasigeostrophic approximation. For fixed h\, scale analysis give
 s a characteristic horizontal velocity\, U\, above which not only does QG 
 break down\, but statically unstable conditions also develop. Using typica
 l atmospheric values for the Brunt-Vaisala frequency\, N=0.01 s^-1 and the
  jump width\, h=100 m\, we argue that U must be less than about 1 m/s for 
 static stability to hold (and smaller still for quasigeostrophy to be form
 ally valid). Therefore\, quasigeostrophic dynamics are consistent only wit
 h very weak near-tropopause flows\, and thus can hardly account for the ob
 served wind profiles (e.g. the Nastrom and Gage spectral break).\n
DTSTART:20151111T193000Z
DTEND:20151111T203000Z
LOCATION:Room 934\, Burnside Hall\, CA\, QC\, Montreal\, H3A 0B9\, 805 rue 
 Sherbrooke Ouest
SUMMARY:Student Seminar: Olivier Asselin
URL:/meteo/channels/event/student-seminar-olivier-asse
 lin-255059
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