Total energy E as the sum of kinetic and available potential energies is co
nsidered here for quasigeostrophic (QG) dynamics. The discrete expression f
or E is derived for the QG model formulation of Marshall and Molteni. While
E is conserved by the nonlinear unforced model equations, an analogous exp
ression in terms of perturbed fields is, in general, not conserved for tang
ent-linearized versions of the model, thereby allowing for growth (or decay
) in this total energy norm. Examples for structures linearly growing optim
ally (i.e., the so-called singular vectors) in terms of either the total en
ergy or just the kinetic energy norm are briefly illustrated and contrasted
. It is argued that E might preferably be used (rather than kinetic energy)
in predictability and data assimilation studies that are based on the QG m
odel considered here.