  In this study, we employ and modify the Lorenz energy cycle (LEC) framework
as another way to understand the atmospheric circulation on tidally locked
terrestrial planets. It well describes the atmospheric general circulation in
the perspective of energy transformation, involved with several dynamical
processes. We find that on rapidly rotating, tidally locked terrestrial
planets, mean potential energy (P$_{\rm M}$) and eddy potential energy (P$_{\rm
E}$) are comparable to those on Earth, as they have similar steep meridional
temperature gradients. Mean kinetic energy (K$_{\rm M}$) and eddy kinetic
energy (K$_{\rm E}$) are larger than those on Earth, related to stronger winds.
The two conversion paths, P$_{\rm M}\rightarrow$P$_{\rm E}\rightarrow$K$_{\rm
E}$ and P$_{\rm M}\rightarrow$K$_{\rm M}\rightarrow$K$_{\rm E}$, are both
efficient. The former is associated with strong baroclinic instabilities, and
the latter is associated with Hadley cells. On slowly rotating, tidally locked
terrestrial planets, weak temperature gradients in the free atmosphere and
strong nightside temperature inversion make P$_{\rm M}$ and P$_{\rm E}$ are
much smaller than those on Earth. Meanwhile, large day--night surface
temperature contrast and small rotation rate make the overturning circulation
extend to the globe, so that the main conversion path is P$_{\rm
M}\rightarrow$K$_{\rm M}\rightarrow$K$_{\rm E}$. This study shows that the LEC
analyses improve the understanding of the atmospheric circulation on tidally
locked terrestrial planets.
