2004 LOM Workshop Wednesday 9:00 - 9:20 a.m.
A model study of the South Atlantic Ocean response to an anomalous heat flux forcing
Carlos Lentini, Reindert Haarsma, Edmo Campos, and Rainer Bleck
Instituto Oceanografico da Universidade de Sao Paulo
lentini@io.usp.br
ABSTRACT
An isopycnal coordinate ocean model coupled to an atmospheric model (SPEEDY-MICOM) has been used to investigate the response of this coupled system forced with anomalous heat fluxes on interannual time scales. The main focus of this work is to look for possible oceanic pathways linking the subtropical to the tropical region, as well as the role played by wave processes on propagating such anomalies. The model domain covers the area between 20N-45S and 65W-20E. The coupled model is spun up for the first 20 years before the atmospheric anomalous surface heat forcing is introduced. The ocean model is forced by heat flux anomalies imposed by the atmosphere which have the same spatial pattern of the subtropical South Atlantic dipole (Sterl and Hazeleger, 2003). SPEEDY-MICOM is forced by this dipole for 1 year. After that, the coupled system is free to evolve for the following 20 years. Ensemble means of forced and non-forced experiments are the basis of our results. Preliminary results show that advection by the mean flow and Rossby Wave dynamics are the two main ways of propagating the imposed anomalies away from its origin toward the South American east coast. Thermal subsurface anomalies are advected within the subtropical South Atlantic gyre by the mean flow, reaching the South American east coast in 4-5 years. No clear evidence of subsurface pathways linking the subtropical to the tropical region has been observed, as post-generated subsurface anomalies stayed within the subtropical gyre for the period of study. Westward propagating Rossby Waves not only introduce circulation anomalies to the mean flow, but they also seem to strongly influence the evolution of the intensity and the shape of the subsurface anomalies.
2004 LOM Workshop Wednesday 9:20 - 9:40 a.m.
Investigation of Tropical Atlantic and Pacific variability with SPEEDO: A flexible coupled model for climate studies.
Reindert Haarsma, Wilco Hazeleger, Camiel Severijns, Frank Selten, Andreas Sterl
Royal Netherlands Meteorological Institute (KNMI), P.O. Box 201, 3730 AE De Bilt, The Netherlands
haarsma@knmi.nl
ABSTRACT
A flexible coupled atmosphere/ocean/land model SPEEDO has been developed for climate variability studies. The atmosphere model (SPEEDY, Molteni 2003) is a primitive equation model of intermediate complexity. The horizontal resolution is T30 and it has 7 layers. A simplified physical package makes the model very efficient. It is coupled to a land bucket model. The ocean model is the Miami Isopycnal Coordinate Model (MICOM). For MICOM a user friendly shell has been developed which facilitates the choice and setup of different model configurations. After carefull tuning of cloud and mixing parameters in the ocean the biasses in the Tropical Atlantic and Pacific are strongly reduced. The zonal SST gradients are well represented and the seasonal cycle compares well to observations. First results of the variability in the Tropical Atlantic and Pacific simulated by SPEEDO will be presented. References: Molteni, F., 2003: Atmospheric simulations using a GCM with simplified physical parameterizations. I: model climatology and variability in multi-decadal experiments. Clim. Dyn., 20, 175-191.
2004 LOM Workshop Wednesday 9:40 - 10:00 a.m.
Latitude Dependent Vertical Mixing: OGCM results and the tropical thermocline
VMCanuto, AHoward, YCheng and RLMiller
NASA-GISS
vcanuto@giss.nasa.gov
ABSTRACT
Measurements by Gregg et al.(2003) have shown that the rate of dissipation of internal gravity waves is latitude dependent. The GISS-mixing model is used to transform this information into a latitude dependent momentum, heat and salt diffusivities. A 3D-OGCM is then run. Global avarage T/S profiles are closer to the Lavitus data than those without latitude dependence. The North Atlantic stream function is increased from 19 to 20Sv while the northtward heat transport is reduced from 1.36 to 1.24 Pw. The model also yields a much sharper equatorial thermocline in both Atlantic and Pacific than without the latitude dependence. A sharp equatorial thermocline is a necessary condition for a reliable descripion of the ENSO variations of SST.
2004 LOM Workshop Wednesday 10:00 - 10:20 a.m.
Ocean forecast system for the North Atlantic: sensitivity studies.
Carlos Lozano, Ilya Rivin, D. B. Rao
NCEP
carlos.lozano@noaa.gov
ABSTRACT
A high resolution ocean forecast system for short term forecast in the North Atlantic based on the hybrid ocean model HYCOM is now under development at NCEP. As part of the model validation for the region, sensitivity studies to changes in forcing, geometry and parameterizations will be presented.
2004 LOM Workshop Wednesday 10:40 - 11:00 a.m.
A near real-time 1/12 degree Atlantic HYCOM nowcast/forecast system
Ole Martin Smedstad, Bruce Lunde, Harley E. Hurlburt, Alan Wallcraft, Eric Chassignet, Remy Baraille
Planning Systems, Inc., Stennis Space Center, MS 39259, USA
smedstad@nrlssc.navy.mil
ABSTRACT
A 1/12 degree Atlantic Ocean version of the HYbrid Coordinate Ocean Model (HYCOM) is used in a near real-time nowcast/forecast system. The model covers the region between 27S and 70N. 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 (JGR, 1996) technique. A relaxation to the MODAS SST analysis is also a part of the system. The model is currently run once a week to produce the nowcast. The run includes a 14 day forecast. The results from the system can be seen on the HYCOM Consortium web page at http://hycom.rsmas.miami.edu/. The results are compared to observations of frontal locations determined from independent MCSST observations. The frontal analysis is performed at the Naval Oceanographic Office. Independent observations from SeaWifs images are also used in the model-data comparisons. A series of images in the Gulf of Mexico in the summer and fall of 2003 show a very good agreement between the model sea surface height field and the pathway of the chlorophyll. The model results are also routinely compared to available profile data both from XBTs and the permanent PIRATA buoys in the equatorial Atlantic. This system is the first step toward a global 1/12 degree nowcast/forecast system based on HYCOM that is planned for transition to the Naval Oceanographic Office in 2006. The prediction system will provide boundary conditions for higher resolution coastal models. An accurate representation of the oceanographic fields at the open boundaries of a coastal model is important for a successful coastal ocean prediction system. More advanced assimilation techniques are in the process of being implemented/tested with HYCOM, e.g. a multivariate optimal interpolation scheme (MVOI) and the singular evolutive extended Kalman filter (SEEK).
2004 LOM Workshop Wednesday 11:00 - 11:20 a.m.
Ensemble forecasting and the ocean's mesoscale
Arne Melsom
Norwegian Meteorological Institute
arne.melsom@met.no
ABSTRACT
A study using HYCOM has been conducted in order to assess the relative contributions to oceanic variability from (1) the deterministic response to atmospheric forcing and (2) the nondeterministic response due to flow instabilities. Two sets of ensemble simulations have been performed. The sets differ in the horizontal resolution, which were set to 9km (coarse resolution experiment, CRE) and 4.5km (fine resolution experiment, FRE), respectively. CRE and FRE are made up of 8 and 6 ensemble members, respectively. Individual members differ in their initial conditions only. Topics that will be discussed include (i) relations between model resolution and the degree of deterministic variability, (ii) no. of ensemble members and statistical convergence, and (iii) relations between deterministic variability and the magnitude of atmospheric forcing. More information can be found on the project's web site, http://ensemble.met.no
2004 LOM Workshop Wednesday 11:20 - 11:40 a.m.
MULTIVARIATE DATA ASSIMILATION INTO HYCOM USING THE SEEK FILTER : IMPACT STUDIES
David Rozier, Florence Birol, Jean-Michel Brankart, Pierre Brasseur and Jacques Verron
LEGI, Grenoble, France
rozier@hmg.inpg.fr
ABSTRACT
An integrated system for simulation of ocean circulation with data assimilation, has been developed at LEGI, as a result of the European DIADEM/TOPAZ projects. It is based on a 1/3ยบ resolution North and Tropical Atlantic version of the HYCOM model. The assimilation scheme is a reduced-order Kalman filter derived from the Singular Evolutive Extended Kalman (SEEK) methodology. During the TOPAZ project, the SEEK assimilation scheme has been upgraded to incorporate in-situ measurements in addition to surface observations. The system is currently utilised in order to undertake various studies in the context of multivariate assimilation, whilst trying to understand better the mechanisms of assimilation and to pinpoint the current flaws of the methodology. A first set of studies examines the impact of various types of observations (sea-surface salinity data, mean dynamic topography, vertical temperature and salinity in situ profiles) within assimilation experiments. These impact studies illustrate particularly how sensitive the assimilation scheme is to quantitative and qualitative differences in the mean dynamic topography used in conjunction with observed sea-level anomalies. Secondly, experiments based on isolated observations are performed to understand better the assimilation mechanisms, identify any spurious effects such as artificially generated waves over large distances, and accordingly determine improvements of the assimilation method.
2004 LOM Workshop Wednesday 11:40 a.m. - 12:00 noon
Development of a monitoring system for the Norwegian coastal zone environment
Nina Winther
Nansen Environmental and Remote Sensing Center
nina.winther@nersc.no
ABSTRACT
As a first step in building up a monitoring system for the Norwegian Coastal Zone Environment, a hindcast modelling system for this area is set up. The model system is a regional high resolution (~4km) model using the Hybrid Coordinate Ocean Model (HYCOM) for the North Sea, Skagerak and Kategat. The regional model receives realistic boundary conditions from larger scale models (the TOPAZ system) and has been run in a hindcast simulation for 1997 and 1998. The model results have been extensively validated using data from ship cruises, and results from this validation work will be presented. The presentation will focus on using HYCOM on a coastal application. This model system has also recently been set up in a forecast mode, producing 10-days forecast once a week. Evaluation of this forecast system will also be presented.
2004 LOM Workshop Wednesday 1:10 - 1:30 p.m.
Performance of mixed layer models in HYCOM on the onset of the 1998 La Nina
BIROL KARA and ALAN WALLCRAFT
NAVAL RESEARCH LAB.
birol@nrlssc.navy.mil
ABSTRACT
The three K-profile vertical mixing models in HYCOM (KPP, Mellor-Yamada level 2.5, and GISS) all perform well enough that it is difficult to choose between them in a typical year or on typical individual events. The onset of the 1998 La Nina is one of the largest short term events (7 degC change is SST over 30 days) on record, and it is certainly the best observed with five equatorial buoys between 180W and 125W and several more at 2S or 2N. It has also proved difficult to replicate with ocean models, and is therefore an excellent test case for HYCOM and its mixed layer submodels. Our standard 26-layer 0.72 degree fully global (Arctic bipolar patch) HYCOM configuration, with KPP, was first spun up from Navy GDEM3 climatology for five years using ECMWF Reanalysis climatological forcing and then extended 1979-2001 using 6-hourly ECMWF forcing. No data assimilation or temperature relaxation was used, but SSS was relaxed to monthly GDEM3 values as a correction to the standard E-P and riverine surface salinity forcing. The June 1995 to December 1998 portion of this simulation was then repeated using Mellor-Yamada and GISS mixed layer submodels to study the El Nino/La Nina cycle. Note that the latitudinal grid size of this model is halved to 0.36 degrees near the equator to better resolve equatorial dynamics. We present the results of comparisons between the three twin simulations and observations for 1996-1998, and in particular for the 1998 La Nina onset in the central equatorial Pacific. The model--data comparisons were also extended to cover the time period from 1996 to 2001. Comparisons with 166 year--long daily SST buoy time series showed that while and KPP and GISS give median median RMS differences of 0.70 degC and 0.76 degC, respectively, MY2.5 gives median RMS difference of 0.85 degC during 1996-2001. TOPICS: e. mixed layer dynamics and mixed layer/layered model interactions h. model/model or model/data comparisons
2004 LOM Workshop Wednesday 1:30 - 1:50 p.m.
Upper ocean response to Hurricane Isabel
Ilya Rivin, Carlos Lozano, Dan Iredell, D. B. Rao
NCEP
ilya.rivin@noaa.gov
ABSTRACT
Oceanic upper layer response to the passage of the Hurricane Isabel is examined using 1/12 degree Mercator HYCOM for the North Atlantic. We employ GISS parameterization for vertical mixing. The model is initialized from the Navy Research Laboratory nowcast for September 2, 2003 and forced by the NCEP Global Forecast System (GFS) analyses. The simulation results are compared with the observed data. The analysis is performed for three time periods: "pre-hurricane" (before hurricane passage), "hurricane", and "relaxation" after the hurricane land fall. Entrainment fluxes, deepening of the ocean mixed layer and currents response to the passing hurricane are analyzed.
2004 LOM Workshop Wednesday 1:50 - 2:10 p.m.
Study of a hurricane induced coastally trapped wave using the HYbrid Coordinate Ocean Model (HYCOM)
E.J. Metzger, L.F. Zamudio, H.E. Hurlburt and P.J. Hogan
Naval Research Lab
metzger@nrlssc.navy.mil
ABSTRACT
The HYbrid Coordinate Ocean Model (HYCOM) has been used to study the propagation of a coastally trapped wave (CTW) along the Mexican west coast and into the Gulf of California (GoC). This wave was generated by Hurricane Juliette in September 2001. It is accurately simulated in a 1/12 degree Pacific basin version of HYCOM forced with winds from the Fleet Numerical Meteorology and Oceanography Center (FNMOC) Navy Operational Global Atmospheric Prediction System. Model-data comparisons of coastal sea level at Manzanillo, Mazatlan, Guaymas, Puerto Penasco and Cabo San Lucas clearly show the propagation of the CTW. Pacific HYCOM accurately simulates the phase of the signal, but the amplitude of the CTW is too weak. Finer resolution (1/25 degree and 1/37.5 degree) versions of nested GoC HYCOM within Pacific HYCOM more accurately simulate the amplitude of the wave suggesting high horizontal resolution is required to resolve this coastal signal. Sensitivity of the CTW to atmospheric hurricane forcing is also investigated by forcing nested GoC HYCOM with FNMOC 27 km resolution Coupled Ocean Atmosphere Prediction System wind stresses.
2004 LOM Workshop Wednesday 2:10 - 2:25 p.m.
1/12 degree, Sigma-0 North Atlantic HYCOM Development
Tamara Townsend, Harley Hurlburt, Alan Wallcraft, Patrick Hogan
Naval Research Laboratory
townsend@nrlssc.navy.mil
ABSTRACT
Results from recent 1/12 degree, sigma-0 North Atlantic HYCOM experiments will be presented. These primarily involve elimination of the previously reported noise at this resolution in the weakly-stratified subpolar region. However, the results of additional developments will also be illuminated.
2004 LOM Workshop Wednesday 2:25 - 2:40 p.m.
North Atlantic simulations with HYCOM in sigma-2* coordinates.
Z. Garraffo, E. Chassignet, G. Halliwell, L. Smith, H. Hurlburt, A. Wallcraft, T. Townsend
U. Miami. RSMAS/MPO
zgarraffo@rsmas.miami.edu
ABSTRACT
Several 1/3 degree HYCOM North Atlantic sigma-2* simulations were performed, with the objective of selecting the best cases to be realized at 1/12 degree resolution. Differences among the 1/3 degree cases are in the z-level spacing and stretching factors, in hybgen parameters, and in the advection scheme. The first results of a 1/12 sigma-2* simulation will also be discussed.
2004 LOM Workshop Wednesday 2:40 - 3:00 p.m.
Sensitivity studies using HYCOM nested regional models
Patrick Hogan, Luis Zamudio, Alan Wallcraft
Naval Research Laboratory
hogan@nrlssc.navy.mil
ABSTRACT
HYCOM has been configured for several regional areas to investigate sensitivity to nesting parameters and ocean dynamics. Boundary conditions for the regional models are provided by high resolution (1/12 degree) basin-scale Pacific and Atlantic HYCOM simulations. An exact boundary condition is used for the barotropic mode and relaxation to temperature, salinity, pressure, and velocity (optionally) are used for the baroclinic mode. The nested regions include the Gulf of California, the Gulf of Mexico, the Mississippi Bight region, and the East Asian Seas region. Each region is characterized by unique processes and dynamics which are impacted by the accuracy of the open boundary conditions. Several 1/12 to 1/12 degree Gulf of California simulations have been used to investigate the sensitivity to several nesting parameters, such as updating frequency, the width of the buffer zone, the e-folding time within the buffer zone, and relative importance of the baroclinic and barotropic modes. A 0.08 to 0.027 degree (3x) nested Gulf of Mexico simulation is used to investigate the coastal circulation in the northern Gulf of Mexico, with emphasis on deep ocean - coastal exchange processes.
2004 LOM Workshop Wednesday 3:20 - 3:40 p.m.
South Florida Regional HYCOM nested simulations
Villy Kourafalou, Roland Balotro, Alan Wallcraft and Tammy Townsend
University of Miami/RSMAS
villy@rsmas.miami.edu
ABSTRACT
The South Florida regional HYCOM model is an implementation of HYCOM around South Florida, from approximately 22.50N to 270N and from 790W to 840W, thus covering Florida Bay, the Florida Keys, the Florida Straits and parts of the southwest and southeast Florida shelf areas including the Dry Tortugas. The regional model has been nested (a) within the North and Equatorial Atlantic Ocean basin (NA) HYCOM and (b) within the Intra-American Seas (IAS) HYCOM. The minimum depth has been configured to 5m, with a 1m coastline. The simulations have been forced with perpetual year atmospheric forcing (monthly mean winds with 6-hour anomalies). River inputs have been specified for two west Florida shelf rivers: Shark River and Caloosahatchee River; the influence of low-salinity waters of Mississippi River origin are evident during summer. The shallow depths along the Florida Keys Reef Tract allow the propagation of eddies along the Florida Current front; enhanced eddy activity (as compared to the larger scale models) is also observed south of the Florida Current front. The regional model simulations reveal a wind-driven southeastward flow that is present in the Florida Straits along the Florida Keys shelf; this flow agrees well with drifter trajectories and with wind-driven events recorded in moored current meters. Movies of tracer dispersion help elucidate the pathways of passive tracers along and across the Florida Straits.
2004 LOM Workshop Wednesday 3:40 - 4:00 p.m.
Vertical Circulation Patterns Near the Florida Keys/Florida Bay Region
Jorge F. Willemsen, George Halliwell
RSMAS
jorge@rsmas.miami.edu
ABSTRACT
The development of float advection programs for HYCOM has had the interesting side effect of providing a capability to compute and diagnose the vertical velocity (w). We discuss the application of the extraction of w in a nested Keys/Bay domain supplied by Alan Wallcraft. Preliminary results show the presence of transient organized upwelling/downwelling cells as the Gulf Stream approaches the Florida Straits. The temporal and spatial variability will be demonstrated through a series of pictures. The numerical values are not unreasonable for the region.
2004 LOM Workshop Wednesday 4:00 - 4:20 p.m.
Initial Results From West Florida Shelf Simulations
George Halliwell
MPO/RSMAS, University of Miami
ghalliwell@rsmas.miami.edu
ABSTRACT
Simulatons of the West Florida Shelf at a horizontal resolution of 1/24 degrees and driven by high-frequency atmospheric forcing are performed to test the sensitivity of HYCOM coastal ocean simulations to vertical mixing and vertical coordinate choices, and also to evaluate the HYCOM nesting algorithm. The vertical mixing choices evaluated include the KPP, NASA/GISS, and Mellor-Yamada submodels. The vertical coordinate choices evaluated include pure sigma coordinates over the entire shelf versus p and isopycnic coordinates over the middle and outer shelf.
2004 LOM Workshop Wednesday 4:20 - 4:40 p.m.
Study of the Slopewater current from MICOM high resolution simulation outputs.
Angelique Haza, Arthur Mariano, Mike Chin, Donald Olson
RSMAS/ University of Miami
ahaza@rsmas.miami.edu
ABSTRACT
The Gulf Stream-Slopewater system is analyzed from four year-outputs of MICOM high-resolution simulations of the North Atlantic, forced by the ECMWF 6 hourly winds. The code was able to reproduce an eastward surface current in the Slope water region, with characteristics similar to the Slopewater Jet measured from hydrographic surveys. The mean path of the Slope current coincides with the sharp temperature and salinity surface fronts separating the Shelf waters from the Slope waters. Its mean transport doubles from 7-9 Sv downstream of the NESC, to 19 Sv south of the Grand Banks. A Taylor column effect of the NESC appears to be the main mechanism captured by the numerical model to account for the strong upper ocean-topographic coupling, resulting in a Gulf Stream bifurcation downstream of the chain and transport increase of the Slopewater current. The coherence and path of this current are maintained by the combination of the western intensification, and the vertical velocity shear of the DWBC, which acts as a barrier. Statistical analysis of the variability shows that the Slope Jet's path and transport are influenced by lateral shift and feeding of the Gulf Stream shortly downstream of the NESC, with 9 month and 1 year periodicities, while near the Grand Banks, the currents are regrouped and accelerated in this zone of convergence, and the SJ only varies in intensity. Mean flow and EOF analyses show good agreement with the latest observations on the Slopewater current, including a coupling in intensity of the Slope Jet with the DWBC and Labrador current.
2004 LOM Workshop Wednesday 4:40 - 5:00 p.m.
Simulation of oceanic carbon sequestration via iron fertilization or direct injection
Rainer Bleck
Los Alamos National Lab
bleck@lanl.gov
ABSTRACT
As part of the international effort to retard climate change due to fossil fuel burning, the U.S. Dept. of Energy is exploring ways to remove carbon dioxide from the atmosphere. Among the technologies proposed to date are two that involve the ocean. One proposal is to inject either liquefied or solidified CO2 into the deep ocean. The second is to increase the air-sea CO2 flux by encouraging phytoplankton growth in regions where the latter is limited by lack of iron. The long-term effectiveness and environmental ramifications of the two approaches are being studied by numerical simulation. Time-averaged isopycnic mass fluxes extracted from two circulation models available in Los Alamos, HYCOM and POP, are being used to simulate the dispersion of liquefied CO2 in the world ocean on 100- to 1000-year time scales. A biogeochemistry model developed to simulate iron fertilization in an eddy-resolving version of POP is being ported to HYCOM to assess the likelihood (based on experiments conducted in parallel in both models) that large-scale, sustained iron fertilization will have a long-term net "drawdown" effect on atmospheric CO2. The project is in its initial phase; hence, only preliminary results will be shown.