Lee, S., and I. M. Held, 1993: Baroclinic wave packets in models
and observations. Journal of the Atmospheric Sciences, 50(10),
1413-1428.
Abstract: Coherent baroclinic wave packets are present in the Southern
Hemisphere, most clearly in the summer season. These coherent packets are
also found in a hierarchy of models of nonlinear baroclinic instability
- a two-layer quasigeostrophic (QG) model on a beta-plane, a two-level
primitive equation (PE) model, and a general circulation model. The flows
are chaotic, but the packet itself can remain remarkably coherent, despite
the complex evolution of the flow within the packet. In both QG and PE
models, the packets become more robust as the supercriticality of the flow
is reduced. In both models and the observations, the packets move with
a group velocity that is greater than the phase speed of the individual
disturbances, so that these disturbances exhibit downstream development.
The structure of the baroclinic waves in the packet as a function of longitude
resembles the life cycles of sinusoidal baroclinic waves as a function
of time. More than one packet can exist in the domain at the same time.
In the QG model, the number of packets increases in a systematic way as
the length of the channel increases.