Sea level and its horizontal gradient are an expression of oceanic
volume, heat content, and currents. Large-scale currents have
historically been viewed as mostly “baroclinic’, and tides as
“barotropic’, respectively, in the sense of being strongly related
to the oceanic density distribution or not. The purpose of this note
is to give dynamical precision to this distinction and, in the
particular case of the tides, demonstrate the breadth of their
combined barotropic-baroclinic interactions with a realistically
forced, high-resolution simulation of the Pacific Ocean circulation.
While the different tidal sea-level contributions manifest a
horizontal scale separation (\eg more barotropic at larger scales;
more baroclinic surface pressure-gradient force at smaller scales),
there are cross-mode corrections in both at the level of tens of
percent.