Varieties of submesoscale dynamics in the south-west Pacific.
Varieties of submesoscale dynamics in the south-west Pacific.
Abstract:
The large-scale circulation in the topographically complex south-west Pacific region con-
sists of an equatorward western boundary current along the coast of Papua New Guinea and
western Solomon sea, the equatorial currents to the north and east of the Solomon islands,
and the multiple jet-like zonal currents generated by the numerous islands to the south in the
Coral Sea. Employing a hierarchy of nested, realistic ocean modeling experiments in ROMS,
with horizontal resolutions as fine as 500m, we examine the dynamics of submesoscales in
this region. We construct spatial maps of statistics of the surface divergence (δ), vortic-
ity (ζ)), buoyancy gradient (∇b) and the frontogenetic tendency (Tadv ), to identify areas of
active submesoscales and their seasonal variability. More specifically, such areas are charac-
terized by high variance of δ, ζ, ∇b and Tadv and a corresponding high negative skewness
in surface divergence, since frontogenesis is a downwelling-dominant physical process. Such
areas include sites in and around the Solomon Sea, with eddy generation through separa-
tion of bottom-drag generated shear layers, the Coral Sea open ocean mixed-layer submesoscale ‘soup’
generated through baroclinic instability and frontogenesis, and lastly, Equatorial fronts that
we believe are hitherto unobserved and thought to be largely absent on theoretical grounds
requiring the presence of background rotation in frontogenesis. While the Coral Sea subme-
soscale soup peaks in the (Southern hemisphere) winter, Equatorial frontal activity shows
a summer-spring maximum. The dynamics of frontogenesis is particularly complex in the
Solomon Sea where topographically generated eddies interact with mixed-layer buoyancy
gradients, that are in turn controlled by interplay of the warm equatorial currents to the
north, the cooler Coral sea intrusions from the south and rather significantly, the strong
and highly seasonal rainfall patterns and the corresponding freshwater input. A concomi-
tant analysis of the energy inter-conversion between eddy and mean potential and kinetic
energies is used to supplement the statistical results.
sists of an equatorward western boundary current along the coast of Papua New Guinea and
western Solomon sea, the equatorial currents to the north and east of the Solomon islands,
and the multiple jet-like zonal currents generated by the numerous islands to the south in the
Coral Sea. Employing a hierarchy of nested, realistic ocean modeling experiments in ROMS,
with horizontal resolutions as fine as 500m, we examine the dynamics of submesoscales in
this region. We construct spatial maps of statistics of the surface divergence (δ), vortic-
ity (ζ)), buoyancy gradient (∇b) and the frontogenetic tendency (Tadv ), to identify areas of
active submesoscales and their seasonal variability. More specifically, such areas are charac-
terized by high variance of δ, ζ, ∇b and Tadv and a corresponding high negative skewness
in surface divergence, since frontogenesis is a downwelling-dominant physical process. Such
areas include sites in and around the Solomon Sea, with eddy generation through separa-
tion of bottom-drag generated shear layers, the Coral Sea open ocean mixed-layer submesoscale ‘soup’
generated through baroclinic instability and frontogenesis, and lastly, Equatorial fronts that
we believe are hitherto unobserved and thought to be largely absent on theoretical grounds
requiring the presence of background rotation in frontogenesis. While the Coral Sea subme-
soscale soup peaks in the (Southern hemisphere) winter, Equatorial frontal activity shows
a summer-spring maximum. The dynamics of frontogenesis is particularly complex in the
Solomon Sea where topographically generated eddies interact with mixed-layer buoyancy
gradients, that are in turn controlled by interplay of the warm equatorial currents to the
north, the cooler Coral sea intrusions from the south and rather significantly, the strong
and highly seasonal rainfall patterns and the corresponding freshwater input. A concomi-
tant analysis of the energy inter-conversion between eddy and mean potential and kinetic
energies is used to supplement the statistical results.