1. A Hybrid Coordinate Ocean Model (HYCOM) For Data-Assimilative
Ocean Modeling
RSMAS
August 19, 2002

2. A multi-institutional effort on the development and evaluation of a data-assimilative hybrid isopycnal-sigma-pressure (generalized coordinate) ocean model (called Hybrid Coordinate Ocean Model or HYCOM.)
The partnering/collaborating organizations are the University of Miami/RSMAS, the Naval Research Laboratory, NOAA/AOML, the Los Alamos National Laboratory, NERSC, LEGI, the Service Hydrographique et Océanographique de la Marine (SHOM), NAVOCEANO, Planning Systems Inc., Orbital Image Corp., and the U.S.Coast Guard.

3. The primary computational goal is the establishment of a global eddy-resolving real-time ocean forecast system with sophisticated data assimilation techniques that can be efficiently executed on massively parallel computers

4. THREE MAJOR COMPONENTS:
The ocean model: the HYbrid Coordinate
Ocean Model (HYCOM)
In-situ and satellite data
3. Data assimilation techniques

5. Background - Rotating and stratified fluids => dominance of
lateral over vertical transport.
- Hence, it is traditional in ocean modeling to orient
the two horizontal coordinates orthogonal to the
local vertical direction as determined by gravity.
- The choice of the vertical coordinate system is the
single most important aspect of an ocean model's
design (DYNAMO, DAMÉE-NAB).
- The practical issues of representation and
parameterization are often directly linked to the
vertical coordinate choice (Griffies et al., 2000).

6. Currently, there are three main vertical coordinates
in use, none of which provides universal utility.
Hence, many developers have been motivated to
pursue research into hybrid approaches.

7. HYCOM
The hybrid coordinate is one that is isopycnal in the open, stratified ocean, but smoothly reverts to a terrain-following coordinate in shallow coastal regions, and to pressure coordinate in the mixed layer and/or unstratified seas.

8. HYCOM

9. HYCOM
The capability of assigning additional coordinate surfaces to the oceanic mixed layer allows for sophisticated closure scheme, such as the K-Profile Parameterization (KPP).

11. HYCOM 2.1 - Add halos for MPI to automatically support periodic
boundaries
- Support nested-domain open boundaries
Fully global (Pan-Am grid)
Alternative mixed layer models (G. Halliwell presentation)
Mellor-Yamada 2.5
Price-Weller-Pinkel
- Orthogonal curvilinear grids
- Single passive tracer
- NetCDF output files
To be released in September 2002
Other numerical developments (M. Iskandarani presentation)

13. Eric P. Chassignet (echassignet@rsmas.miami.edu)
WEB PAGE:
Coordinator:
Eric P. Chassignet

14. NORTH ATLANTIC BASIN-SCALE SIMULATIONS
Based on the CME, DYNAMO and MICOM experience (1˚, 1/3˚ and 1/12˚, respectively)
The CME comparison is completed (sigma-theta,
sigma2, and sigma2 + thermobaricity) [Chassignet
et al., to be submitted]
1/3˚ routine (interannual forcing – 40 years) [Hogan]
1/12˚ in progress (years after spin-up)
[Hogan, Wallcraft, Chassignet, Hurlburt]
NORTH ATLANTIC REGIONAL SIMULATIONS
Intra-American (Caribbean) Sea (standard configuration
for data assimilation testing) [Townsend, Wallcraft]

15. High-resolution 1/12° North Atlantic HYCOM simulation
ECMWF forcing

16. Atlantic Model Configuration
Horizontal grid: 1/12˚ (1678 x 1609 grid points, 6 km spacing on
average)
28°S to 70°N (including the Mediterranean Sea)
26 vertical coordinate surfaces (σ-theta reference)
Bathymetry: Quality controlled ETOPO5
Surface forcing: wind stress, wind speed, heat flux (using bulk
formula), E-P + relaxation to cllimatological surface salinity
River runoff included
Buffer zone: ~3° band along the northern and southern boundaries
with relaxation to monthly climatological T and S (Levitus)

17. 10 x 16 Equal Ocean Decomposition
Running on Brainerd (ARL)
58,000 CPU hrs/model year on 160 CPUs
770 GB/model year for daily 3-D output
MPI parallelization

18. Sea Surface Temperature
1/12° HYCOM ATLANTIC SIMULATION
~7 km resolution at mid-latitudes
Sea Surface Height
Sea Surface Temperature
Forced by ECMWF 10 m reanalysis monthly climatological wind and thermal fluxes, climatological surface salinity and relaxation to MODAS climatology at the northern and southern boundaries (themohaline component)

21. 18 degree Mode Water formation

22. 18 degree Mode Water formation

23. 1/12° Atlantic HYCOM
Deep Western Boundary Current

24. Denmark Straits Overflow Region
Dickson and Brown
1994 (JGR)
1/12° North Atlantic
HYCOM
layer 20 mean speed
Model transport
sum layers 20-26
ρ > 27.8 (NADW)
4.14
9.36
13.77
5.2
10.7
13.3
Observed transport
from current meters
Denmark Straits Overflow Region

25. Denmark Straits Overflow
Cold fresh water
forms over shelf
in Nordic Seas
and spills over the
Denmark Strait
and entrains more
saline Labrador
Sea water

26. OPEN BOUNDARY CONDITIONS IN HYCOM
No distinction is made between inflow and outflow boundaries
The “well-posed” boundary conditions developed by Browning
and Kreiss (1982) are applied to the barotropic mode, i.e., the
barotropic pressure and velocities are advected into/out of the
domain via characteristics
Relaxation to mass fluxes, interface depths, T, S, and density
is prescribed in a finite-width sponge zone

27. HYCOM Nesting Applied to IAS
[Townsend, Wallcraft]
North Atlantic, 0.32°
North Atlantic, 0.32°
SST
CI = 0.08° C
May 4
Intra-Americas Sea, 0.08°
SST
CI = 0.3° C
Jan 16
SST
CI = 0.08° C
May 4

28. Meridional Velocity, De Soto Canyon, Gulf of Mexico at 29.6N
0.32° North Atlantic HYCOM
Jul 14
0.08° Intra-Americas Sea HYCOM
Jul 14
Forced by Monthly Mean ECMWF Reanalysis 10 m winds and
boundary conditions from the 0.32° North Atlantic HYCOM

29. 0.32° North Atlantic HYCOM
Jan 16
0.08° Intra-Americas Sea HYCOM
Jan 16

30. Atlantic regional modeling
Coastal seas around Florida Bay [Kourafalou]
A nested approach is proposed for a high resolution
HYCOM application around south Florida
(large scale– regional scale– coastal scale)
The regional model will provide boundary conditions for
limited area hydrodynamic, ecosystem and water quality
models in Florida Bay
The simulations will be closely linked to ongoing
observational studies in Florida Bay and adjacent seas

31. The seas adjacent to Florida Bay:
Gulf of Mexico, West Florida Shelf and Florida Straits
(the shaded area marks the regional model domain)
Physical transport processes impose strong hydrodynamic links between Florida Bay and the adjacent coastal seas.
Significant transient inputs can reach Florida Bay from remote regions of the Gulf of Mexico.

32. Recent observational studies provide evidence of transport processes linking south Florida coastal ecosystems

33. A comprehensive, multi-year, interdisciplinary data set is available for model initialization, forcing and validation

34. Atlantic regional modeling
SEED [Jacobs]
Slope To Shelf Energetics And Exchange Dynamics
To understand the mechanisms that transfer properties (energy, mass, momentum, heat, salt, …) across the shelf slope
Focus Area
Gulf of Mexico, Mississippi Bight, west of the DeSoto Canyon

35. Atlantic regional modeling
DIADEM/TOPAZ [Evensen]
Implement and validate a model system for hindcast simulations in the Faroe-Shetland channel
Run the system in a multiyear hindcast simulation to produce current statistics which can be used to derive design criteria for optimal rig-selection and design

36. Atlantic regional modeling
Hurricane impact on mixed layer properties
[Jacob, Shay, Halliwell]
Effects of the entrainment closure on the oceanic mixed layer response during a tropical cyclone passage

37. Hycom Q Movie
Gaspar
KPP
MY2.5
PWP

38. PACIFIC BASIN-SCALE SIMULATIONS PACIFIC REGIONAL SIMULATIONS
- 1/12° in progress [Metzger, Hurlburt]
PACIFIC REGIONAL SIMULATIONS
- 1/8° to 1/32° Japan/East Sea [Hogan, Hurlburt]
- 1/32° East Asian Seas [Hogan]

39. PACIFIC MODEL CONFIGURATION
Horizontal grid: 1/12° ( 2294 x 1362 grid points, 6.5 km spacing on average)
20°S to 65.8°N
20 vertical coordinates (σ-theta reference)
Bathymetry: Quality controlled ETOP05
Surface forcing:
wind stress, wind speed, heat flux (using bulk formula),
E-P + relaxation to climatological SSS
• River runoff
• Buffer zone: ~3° band along southern and eastern
boundary with relaxation to monthly climatological T
and S
Closed boundaries along 20°S, in the Indonesian
throughflow region and in the Bering Strait

40. 22 x 13 Equal Area Decomposition (all land tiles discarded)
Running on (MHPCC)
50,000 hrs/model year on 207 CPUs
288 GB/model year for 3-D fields every 3 days
MPI parallelization

41. SSH Snapshot – 17 December
1/12° Pacific HYCOM
SSH Snapshot – 17 December
Forced with climatological HR winds and ECMWF thermal forcing

42. SSH and SST Snapshot – 17 December
1/12° Pacific HYCOM
SSH and SST Snapshot – 17 December
Forced with climatological HR winds and ECMWF thermal forcing

43. Mean Sea Surface Height 1/12° Pacific HYCOM vs. Observations
Qu et al. (2001, JPO)

44. Velocity Cross-section Across Luzon Strait
Sb-ADCP data versus 1/12° Pacific HYCOM in the upper 300m
120.75°E °N
Transport
3.3 Sv
4.4 Sv
Sb-ADCP data from Liang et al. (DSR Part II, in press)
HYCOM is forced with high-frequency HR winds and ECMWF thermal forcing

45. Velocity Cross-section Along Luzon Strait
Sb-ADCP data versus 1/12° Pacific HYCOM in the upper 300m °E
21.0°N
Sb-ADCP data from Liang et al. (DSR Part II, in press)
HYCOM is forced with high-frequency HR winds and ECMWF thermal forcing

46. Impact of Hurricane Julliette (Zamudio, Hurlburt, Metzger)
1/12° Pacific HYCOM
Impact of Hurricane Julliette
(Zamudio, Hurlburt, Metzger)
SST
SSH

47. Plans for JES/EAS Modeling [Hogan, Hurlburt]
1/32° Japan/East Sea (ONR JES DRI)
Branching of Tsushima Warm Current
Nearshore Branch Dynamics
Water mass formation (ESIW)
Model-data comparisons
Impact vertical coordinate configuration
Data assimilation
1/32° East Asian Seas (LINKS)
Ability of HYCOM to robustly simulate shelf (Yellow Sea) and
deep (JES) environment
Branching of Tsushima Warm Current from the Kuroshio
(where, how, etc.)
Interaction of coastal and large-scale currents

48. Japan/East Sea 1/8˚ Surface
1/16˚
Surface
Japan/East Sea
1/8˚
Surface
Japan/East Sea
1/16˚
Deep

50. 1/32° HYCOM East Asian Seas Model
Nested inside 1/8° HYCOM Pacific Basin Model
Boundary conditions via one-way nesting
and 6 hrly ECMWF 10 m atmospheric forcing

53. JES summary JES HYCOM is running with high horizontal grid resolution
and synoptic wind and heat flux forcing
Substantial improvement (especially in separation latitude
of western boundary current) as horizontal grid resolution
increased from 1/8° to 1/32°
Flow over the shelf along the Nearshore Branch
Winter – barotropic – topographic steering
Summer – baroclinic – isopycnal outcropping
HYCOM able to simulate formation and spreading of East Sea
Intermediate Water, most appears to be formed in northern
JES, but some formed locally near Vladivostok

54. INDIAN OCEAN REGIONAL SIMULATIONS
Arabian Sea model configuration [Baraille]
(34°E-76°E) ; (10°N-30.3°N)
16/20 layers, 1/4° horizontal resolution
Initial condition extracted from the global MICOM model (Bleck)
Bimonthly relaxation fields extracted from the global MICOM model
applied at the south boundary, in the Gulf of Aden and in the Gulf of
Oman
4-year integration with monthly-averaged ECMWF forcing fields
Integration since 01/01/2000 with high frequency forcing (6 hours)
Assimilation of altimetry since 11/01/2001
(mean SSH provided by O. M. Smedstad)
INDIAN OCEAN REGIONAL SIMULATIONS

55. 10 day forecast 01/31/2001 Sea Surface Height Sea Surface Temperature
Density field at 20N

56. GLOBAL SIMULATIONS HYCOM/MICOM comparison (100-year simulation)
for quasi-global domain (northern boundary at 65° N)
at 2° resolution. [“An oceanic general circulation model
framed in hybrid isopycnic-cartesian coordinates” by
R. Bleck (available on web site)]
Fully global in progress: target resolution 1.4° for
reanalysis [D. Bi, R. Bleck, A. Wallcraft].
GODAE intensive period: 1/12° in North Atlantic and
North Pacific, .72° elsewhere.
- 1/12° everywhere in 2005.

57. HYCOM GLOBAL CONFIGURATION
A Mercator mesh of resolution 2ºx2º (cos(φ)) is used south of 60ºN. At this latitude, the Mercator projection smoothly transitions to a bipolar projection with poles over Canada and Siberia, but without grid singularity over the ocean area.

58. HYCOM GLOBAL CONFIGURATION

59. HYCOM GLOBAL CONFIGURATION
HYCOM global version (GLBx2.00) represents the ocean by 26 layers vertically, using σ0 (potential density referenced to the sea surface) as vertical coordinate in the ocean interior. However, coordinate surfaces level off to become constant-depth surface wherever the isopycnals they follow outcrop at the sea surface.
This figure shows a snap shot of the layers along the 20ºW meridian.

60. HYCOM GLOBAL CONFIGURATION
Experimental Design
Surface forcing: COADS monthly atmospheric climatology, including wind stresses, wind speed, solar radiation, net radiation, moisture, etc.. No fresh water flux (E-P) is applied. In stead, the sea surface salinity is relaxed to Levitus climatology.
Initialization: the model ocean is initialized with the Levitus climatology, i.e., monthly salinity and temperature.
Sea ice: Energy load.
Mixed layer: KPP
Integration duration: 38 years.

61. HYCOM GLOBAL CONFIGURATION
Surface features
Sea Surface Height
(annual mean and seasonal cycle)
Mixed layer thickness
Surface heat flux
Sea ice concentration

62. HYCOM GLOBAL CONFIGURATION
Water mass properties
Surface distribution:
SST (annual mean and seasonal cycle)
SSS (annual mean and seasonal cycle)
SSD (annual mean and seasonal cycle)
Vertical structure (zonal average)
Temperature (annual mean and seasonal cycle)
Salinity (annual mean and seasonal cycle)
Stratification (annual mean and seasonal cycle)

63. HYCOM GLOBAL CONFIGURATION
Horizontal currents
Mixed Layer Velocity
Annual mean and Seasonal cycle
Horzontal currents at 1000m depth

64. HIERARCHY OF DATA ASSIMILATION TECHNIQUES
The main source of data is provided by altimetry
(see presentation by Thacker/Lee for in-situ data assimilation)
Altimetry gives an estimation of the surface circulation

65. HIERARCHY OF DATA ASSIMILATION TECHNIQUES
- Optimal Interpolation with vertical projection either by
using isopycnal modes or Cooper-Haines (NRL, SHOM,
RSMAS)
- Ensemble Kalman Filter (EKF) (NERSC)
- Single Evolutive Extended Kalman (SEEK Filter) (LEGI)
- Reduced Order Adaptive Filter [ROAF] (SHOM)
- Reduced Order Information Filter [ROIF] (RSMAS)

66. Present assimilation system
- 1/3° Atlantic version of HYCOM
Assimilation of the Modular Ocean Data Assimilation
System (MODAS) optimal interpolated SSH anomalies
from satellite altimetry
Vertical projection of the surface observations by
Cooper-Haines
- Running in near real-time

67. 1/3° Atlantic HYCOM SSH 20 November 2000
Assimilation of MODAS SSH
analyzed fields
NO ASSIMILATION
Independent frontal analysis of IR observations performed at the
Naval Oceanographic Office overlaid. White line shows the part
of the front being observed within the last 4 days. Black line
shows the part of the front older than 4 days

68. 1/3° Atlantic HYCOM SSH 30 July 2001
Independent frontal analysis of IR observations performed at the
Naval Oceanographic Office overlaid. White line shows the part of the front being observed within the last 4 days. Black line shows the part of the front older than 4 days.

69. Sea-surface temperature forecast Sea-surface height forecast
Current European project: TOPAZ Towards an Operational Prediction system for the North Atlantic and european coastal Zones Real-time experiment based on EnKF (NERSC) and SEEK (LEGI)
Sea-surface temperature forecast
November 21st, 2001
Sea-surface height forecast
November 21st, 2001

70. TOPAZ: project participants
NERSC:
Coordination
HYCOM model system
EnKF with HYCOM and ecosystem model
Assimilation of ice parameters
Nested model applications
LEGI:
In situ data assimilation
SEEK with HYCOM and ecosystem model
Impact studies

71. The large scale model grid used for providing boundary conditions for the regional North Sea model.
Note increased grid resolution in the Gulf Stream extension and the Nordic Seas. The inclusion of the
Arctic and the South Atlantic is necessary to avoid effects of improper specification of boundary conditions.

72. The large scale model grid used for providing boundary conditions for the regional North Sea model.
Note increased grid resolution in the Gulf Stream extension and the Nordic Seas. The inclusion of the
Arctic and the South Atlantic is necessary to avoid effects of improper specification of boundary conditions.

73. The large scale model grid used for providing boundary conditions for the regional North Sea model.
Note increased grid resolution in the Gulf Stream extension and the Nordic Seas. The inclusion of the
Arctic and the South Atlantic is necessary to avoid effects of improper specification of boundary conditions.

74. Validation Based on current meter moorings available in Faroe Shetland Channel

75. Exceedence plot from Faroe Bank Channel

76. Deliverables Total of 9146 grid points One hour time resolution
Velocity, temp., saln., layer depth, wind and SLH
32.6 Gigabytes per year
Database is accessed online on the Internet
Database with model diagnostics
The large scale model grid used for providing boundary conditions for the regional North Sea model.
Note increased grid resolution in the Gulf Stream extension and the Nordic Seas. The inclusion of the
Arctic and the South Atlantic is necessary to avoid effects of improper specification of boundary conditions.

77. Adaptive Filter with HYCOM
(development started on 09/17/2001, R. Baraille)
Development of the tangent linear model is finished
We check the validity of the Taylor formula to determine the window where the approximation is valid, depending on the size of the initial perturbation. This work is completed by the definition of a set of variables (not necessarily the HYCOM variables) which can vary linearily with time. This problem is adressed because hybgen is highly non linear.
The adiabtic adjoint of HYCOM is under developement.

78. The Reduced Order Information Filter (ROIF)
[Chin and Mariano]
The horizontal (cross-) covariance functions of SSH and velocities in an extended information filter are parameterized assecond-order spatial Markov Random Fields. A vertical projection scheme is used to correct lower-layer thicknesses and velocities.

79. How do we define the mean SSH for data assimilation?

87. OUTREACH - Live Access Server (presentation by A. Srinivasan)
A web-based ocean current reference site (presentation by A. Mariano and E. Ryan)