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

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.

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

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

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).

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.

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.

HYCOM

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).

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)

Eric P. Chassignet (echassignet@rsmas.miami.edu) WEB PAGE: http://hycom.rsmas.miami.edu Coordinator: Eric P. Chassignet (echassignet@rsmas.miami.edu)

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 1999-2002 after spin-up) [Hogan, Wallcraft, Chassignet, Hurlburt] NORTH ATLANTIC REGIONAL SIMULATIONS Intra-American (Caribbean) Sea (standard configuration for data assimilation testing) [Townsend, Wallcraft]

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

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)

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

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)

18 degree Mode Water formation

18 degree Mode Water formation

1/12° Atlantic HYCOM Deep Western Boundary Current

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

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

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

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

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 1979-1993 Monthly Mean ECMWF Reanalysis 10 m winds and boundary conditions from the 0.32° North Atlantic HYCOM

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

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

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.

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

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

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

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

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

Hycom Q Movie Gaspar KPP MY2.5 PWP

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]

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

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

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

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

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

Velocity Cross-section Across Luzon Strait Sb-ADCP data versus 1/12° Pacific HYCOM in the upper 300m 120.75°E 18.5-22°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

Velocity Cross-section Along Luzon Strait Sb-ADCP data versus 1/12° Pacific HYCOM in the upper 300m 118.5-124.5°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

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

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

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

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

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

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

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

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.

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.

HYCOM GLOBAL CONFIGURATION

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.

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.

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

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)

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

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

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)

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

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

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.

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

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

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.

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.

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.

Validation Based on current meter moorings available in Faroe Shetland Channel

Exceedence plot from Faroe Bank Channel

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.

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.

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.

How do we define the mean SSH for data assimilation?

OUTREACH - Live Access Server (presentation by A. Srinivasan) http://hycom.rsmas.miami.edu/dataServer/ A web-based ocean current reference site (presentation by A. Mariano and E. Ryan) http://oceancurrents.rsmas.miami.edu