Transcript Japan/East Sea Hybrid Coordinate Ocean Model (HYCOM)

Japan/East Sea Hybrid Coordinate Ocean Model (HYCOM)
Patrick J. Hogan and Harley E. Hurlburt
Naval Research Laboratory, Code 7323, Stennis Space Center, MS, 39529-5004, USA
[email protected]
Impact of resolution on deep and surface circulation
Zonal and meridonal cross sections of temperature
1/8° surface layer mean
speed and currents
Abstract: HYCOM is a generalized (hybrid isopycnal/sigma/z) vertical coordinate
ocean circulation model. It is isopycnal in the open stratified ocean, but reverts to
a terrain-following coordinate in shallow coastal regions, and to z-level coordinates
near the surface in the mixed layer. This generalized vertical coordinate approach
is dynamic in space and time via the layered continuity equation, and permits the
existence of zero thickness layers. Hence HYCOM allows for an accurate
transition between deep and shallow water, historically a difficult problem for
ocean models. It also allows high vertical resolution where it is most needed, over
the shelf and in the mixed layer. The isopycnal coordinate reduces the need for
high vertical resolution in deep water.
JES-HYCOM is funded by the Office of Naval Research. HYCOM development is
also funded by the National Ocean Partnership Program (NOPP) in a collaborative
effort with the University of Miami (E. Chassignet), Los Alamos National Laboratory
(R. Bleck), and the University of Minnesota (M. Okeefe). The long term goals of the
project are to make HYCOM a state of the art community ocean model with data
assimilation capability which can (1) be used in a wide range of ocean-related
research, (2) be used in a next generation eddy-resolving global ocean prediction
system, and (3) be coupled to a variety of other models, including atmospheric, ice,
and biological.
1/16° surface layer mean
speed and currents
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1/8° winter
1/8° deep layer mean
speed and currents
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1/16° deep layer mean
speed and currents
• Generalized vertical coordinate ocean model
• includes realistic coastline geometry and bottom topography, including the
shelf
• forced by ECMWF 10 m reanalysis monthly climatological (1979-1993) wind
and atmospheric forcing
• K-Profile Parameterization (KPP) mixed layer (or K/T as an option)
• vertical resolution: 15 layers
• 2 Sv barotropic throughflow
• bimonthly relaxation to temperature and interface depth at the straits
• bimonthly relaxation to MODAS SST and SSS
• currently no assimilation of oceanic data
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1/8° summer
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1/16° winter
JES-HYCOM characteristics:
The impact of increasing the horizontal grid resolution on the mesoscale circulation
dynamics has been demonstrated by Hogan and Hurlburt (2000) with the NRL
Layered Ocean Model (NLOM). These results, although preliminary in nature, also
show the impact of grid resolution on mean flow patterns. In particular, the surface
circulation near Vladivostok reverses from anticyclonic at 1/8° to cyclonic at 1/16°,
which is supported by most observations. Another benefit of increased resolution is
the ability to resolve the bottom topography. This is clearly illustrated by the
appearance of the sigma levels over the shelf region just east of the Noto Peninsula.
Future plans for HYCOM include forcing with high frequency atmospheric forcing
and assimilation of observed oceanic data.
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1/16° summer
Cross sections of temperature from the 1/8° (left) and 1/16° (right) HYCOM model during winter (top) and summer (bottom). During the
summer, the mixed layer is maintained at 12 m. During the winter, the mixed layer is diagnostically determined (0.2 sigma-t from the
surface). Vertical resolution in the mixed layer is maintained via z-levels during the winter, when densities are colder than “target” densities.
These z-levels revert to isopycnals during the summer. The impact of resolving the bottom topography is clearly illustrated by the
appearance of the sigma levels over the shelf region in zonal section from the 1/16° simulation during winter.
These panels show the impact of increased horizontal grid resolution. At 1/8° there is unrealistic anticyclonic
surface flow near Vladivostok (top left) . At 1/16° (top right) this flow is cyclonic as observed. The corresponding
deep flow (Layer 11, the 27.10 isopycnal) patterns are shown below. The deep flow at 1/16° is in general agreement
with recent current meter measurements by Takematsu (1999).