  In this letter, we report the outcome of a spatial energy budget performed
for the linear convective instability of the plane incompressible mixing layer
within the inviscid framework. We find that, as the critical condition for the
onset of absolute instability is approached, the integrated pressure-transport
term becomes increasingly more prominent as compared to the integrated
production term and it dominates the energy budget completely at the critical
condition. This implies that, near the threshold of absolute instability, the
growth of disturbances is almost entirely due to the pressure transport
mechanism (rather than the production mechanism), which is a striking result.
The part of the pressure-transport term that represents the work done by the
fluctuating pressure forces is seen to be primarily responsible for the
observed shift in the energy balance. These results can help us better
understand the physical processes causing absolute instability in a mixing
layer. In particular, the redistribution of disturbance energy in streamwise
direction by fluctuating pressure, which is "non-local" in character for
incompressible flows, seems to play a key role in this respect.
