MMM SEMINAR NCAR
The coupling of balanced
motions and gravity waves in baroclinic instability
Riwal Plougonven
NCAR/MMM
Jets and fronts are important sources of gravity waves, yet the dynamical mechanisms responsible for these waves are still poorly understood. Standard asymptotic approaches based on the timescale separation between balanced motions and gravity waves do not capture how these two types of motions can couple.
We have investigated the spatial coupling of balanced motions and gravity waves through the analysis of the normal modes of a constant vertical shear with no upper boundary. In the quasi-geostrophic approximation, the normal modes are balanced (Eady) edge waves; within the linearized primitive equations, they are unstable modes which exhibit both a balanced behavior (near the ground) and a gravity-wave like behavior (aloft). The transition from balanced motions to gravity wave occurs in the region of the inertial critical layer, and can be simply understood from consideration of the Lagrangian timescales involved. The amplitude of the gravity waves can be obtained analytically
and it is shown to be exponentially small in Rossby number, confirming expectations from previous studies.
The relevance of this spatial coupling in more realistic flows is presently investigated in idealized simulations of baroclinic instability using the WRF model. Preliminary results from this ongoing work will be presented.
Thursday, July 22 2004, 3:30
PM
NCAR-Foothills
Laboratory
3450 Mitchell Lane
Bldg 2, Rm 1022,
Auditorium