This energy cycle is not reflective of the fundamental properties found in the atmosphere.
Given the assumptions we have made, (quasi-geosrophic flow, etc) we can only use this as
a general approximation. However, we have seen in class that this is a good first order
approximation for instability in the mid latitudes. The figure below, taken from Holton,
shows the cycle graphically.
Starting with the top left box: Mean heating at the equator and cooling at the poles generates
mean PE. A small portion of the mean PE is also transferred to the Southern Hemisphere
(represented by B(P)). The meridional gradient of zonal mean PE then leads to baroclinic
instability which results in the transport of heat to the poles.
These baroclinic eddies transform the mean PE into eddy PE. Clouds and precipitation in
the atmosphere result in a positive contribution by the eddy heating term (R ) to the eddy
PE; in a cloudless system this term would be negative.
The vertical component of the eddy motions also transform a portion of the eddy PE to eddy
KE. Eddy momentum is lost through frictional dissipation and the remaining energy is used
to maintain the mean KE.
Eddy KE is the primary source for mean KE. Mean frictional dissipation is minimal in the
system and contributes to the lost of mean KE. In the mid latitudes a small amount of KE
is converted back to PE. However, for the tropics, symmetric overturning results in mean PE
becoming mean KE.