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A NEAR REAL-TIME 1/12˚ ATLANTIC HYCOM
NOWCAST/FORECAST SYSTEM
Near real-Time and archived results (updated weekly): http://hycom.rsmas.miami.edu
O. M. SMEDSTAD
Planning Systems, Inc., Stennis Space Center, MS 39529, USA
H. E. HURLBURT, A. J. WALLCRAFT, and P. HOGAN
Naval Research Laboratory, Stennis Space Center, MS 39529, USA
E. CHASSIGNET
University of Miami/RSMAS, FL 33149, USA
Abstract
A 1/12° HYbrid Coordinate Ocean Model (HYCOM)
of the Atlantic Ocean north of 28°S is used in a near real-time
nowcast/forecast system. The Modular Ocean Data
Assimilation System (MODAS) sea surface height analysis of
available satellite altimeter data is assimilated into the model.
The surface information is projected in the vertical using the
Cooper and Haines (1996, JGR) technique. The model is
currently run once a week to produce the nowcasts. The run
also includes a 13 day forecast. A web page has been developed
showing the near real-time results from the model. The results
are compared to independent observations of SST, temperature
profiles and frontal locations determined from independent
MCSST observations. The frontal analysis is performed at the
Naval Oceanographic Office (NAVOCEANO). This system is
the first step toward a global 1/12° nowcast/forecast system
based on HYCOM that is planned for transition to the Naval
Oceanographic Office in 2006. More advanced assimilation
techniques will be included in the system as soon as they show
increased model nowcast/forecast skill and the system can run
within the operational time limits.
R. BARAILLE
LEGOS/BRESM, Toulouse, France
The 1/12° Atlantic HYCOM domain
SSH on 21 March 2003
• Horizontal grid: 1/12° (1678 x 1609 grid points, 6.5 km
spacing on average)
• 28°S to 70°N (including the Mediterranean Sea)
• 26 vertical coordinate (σ-theta reference)
• Bathymetry: Quality controlled ETOPO 2.5
• Surface forcing FNMOC
[wind stress, wind speed, heat flux (using bulk formula),
E-P + relaxation to climatological SSS]
• River runoff
• Buffer zones:
3° north and south with relaxation to monthly climatological
T and S (MODAS)
Near real-time run cycle
The model is run once a week, on Friday. The run consists of a 10
day hindcast and a 13 day forecast.
SSH forecast for 31 March 2003
(initialized on 18 March 2003)
13 day forecast
Comparison of SSH to an independent frontal
analysis of MCSST observations
Friday
10 days
Forecast wind and
Analysis wind and
thermal forcing
thermal forcing
Assimilation of MODAS Revert toward
SSH anomaly analysis climatological wind and
thermal forcing after 5 days
Velocity section in the Yucatan Channel
Mean
November/December 2002
August 1999 - June 2000
500
1000
1500
Standard deviation
500
1000
1500
Observations
Mean normal flow in Yucatan Channel. The blue (gray)
shading represents northward (southward) flow. The
Yucatan Current flows to the North above 800 m with
the maximum near the Yucatan coast. Southward flow
into the Caribbean Sea is observed near the surface off
Cuba (Cuban Countercurrent). Deep outflows occur in
both western (Yucatan Undercurrent) and eastern sides
of the Channel, although variability is larger than the
mean.
White/black line is the frontal analysis of MCSST observations
performed at NAVOCEANO. Black line represents data more than
four days old.
Standard deviation of normal velocity. Largest variability
occurs above 300 m, with two maxima, one on the Yucatan
Slope and another on the Cuban Slope. Variability is larger
than the mean flow except for the Yucatan Current.
Vertical temperature and salinity sections in the Gulf of Mexico
From: Abascal, A. J. et al. 2001 AGU Fall Meeting
14 March 2003
Transport sections
HYCOM data assimilation
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HYCOM long term goals for operational prediction
Short term:
▪ .08° fully global ocean prediction system transitioned to
▪ Improve current OI based technique
NAVOCEANO in 2006
• Assimilate satellite data (tracks) directly
• ~7 km mid-latitude resolution
• Improve vertical projection technique using synthetic temperature and
• Include shallow water, minimum depth 10-20m
salinity profiles from MODAS
Long term:
• Bi-polar (PanAm) grid for the Arctic
▪ Reduced Order Information Filter (ROIF, Chin and Mariano,
• Embedded ice model
University of Miami)
▪ Increase to .04° resolution globally and transition to
▪ The Singular Evolutive Extended Kalman filter (SEEK, Pham et al.,
NAVOCEANO by the end of the decade
P. Brasseur, LEGI)
• ~3.5 km mid-latitude resolution
▪ Reduced Order Adaptive Filter (ROAF) - adjoint under development
(R. Baraille)
• Good resolution for coastal model boundary conditions globally
Reference:
• “Baseline” resolution for shelf regions globally
Pham, D.T., J. Verron and M.C. Roubaud, 1998: A singular extended filter
for data assimilation in oceanography. Journal of Marine Systems, 16, 323-340.