This chapter examines the role of barotropic energy conversions in the general circulation. Baroclinic instability is the main source of transient variability in the general circulation. In the later stages of their life cycle, baroclinic waves feed energy into the time-mean zonally averaged flow and planetary-scale low-frequency transients by barotropic exchange processes. The evidence in favor of baroclinic instability/barotropic stability as a conceptual model for interpreting the energetics of large-scale atmospheric motion is based on theoretical analyses, modeling studies, and observational diagnostics. The interactions between the transient eddies and the longitudinally dependent time-mean flow are studied. It is found that the fastest-growing normal mode associated with barotropic instability resembles two observed teleconnection patterns. The normal modes associated with barotropic instability of the time-mean flow are characterized by much lower-frequency oscillatory components than those associated with baroclinic instability. It is observed that the low-frequency fluctuations apparently feed on the time-mean flow, and thereby serve to damp the longitudinally dependent, climatological-mean features at the jet-stream level.
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