Development, implementation and evaluation of a data-assimilative ocean forecasting system off the central California coast

Abstract The development and implementation of a real-time ocean forecast system based on the Regional Ocean Modeling System (ROMS) off the coast of central California are described. The ROMS configuration consists of three nested modeling domains with increasing spatial resolutions: the US West coastal ocean at 15-km resolution, the central California coastal ocean at 5 km, and the Monterey Bay region at 1.5 km. All three nested models have 32 vertical sigma (or terrain-following) layers and were integrated in conjunction with a three-dimensional variational data assimilation algorithm (3DVAR) to produce snapshots of the ocean state every 6 h (the reanalysis) and 48-h forecasts once a day. This ROMS forecast system was operated in real time during the field experiment known as the Autonomous Ocean Sampling Network (AOSN-II) in August 2003. After the field experiment, a number of improvements were made to the ROMS forecast system: more data were added in the reanalysis with more careful quality control procedures, improvements were made in the data assimilation scheme, as well as model surface and side boundary conditions. The results from the ROMS reanalysis are presented here. The ROMS reanalysis is first compared with the assimilated data as a consistency check. An evaluation of the ROMS reanalysis against the independent measurements that are not assimilated into the model is then presented. This evaluation shows the mean differences in temperature and salinity between reanalysis and observations to be less than 1 °C and 0.2 psu (practical salinity unit), respectively, with root-mean-square (RMS) differences of less than 1.5 °C and 0.25 psu. Qualitative agreement is found between independent current measurements and the ROMS reanalysis. The agreement is particularly good for the vertically integrated current along the offshore glider tracks: the ROMS reanalysis can realistically reproduce the poleward California Undercurrent. Reasonably good agreement is found in the spatial patterns of the surface current as measured by high-frequency (HF) radars. Preliminary results concerning the ROMS forecast skill and predictability are also presented. Future plans to improve the ROMS forecast system with a particular focus on assimilation of HF radar current measurements are discussed.

[1]  W. Large,et al.  Oceanic vertical mixing: a review and a model with a nonlocal boundary layer parameterization , 1994 .

[2]  Ionel M. Navon,et al.  Optimality of variational data assimilation and its relationship with the Kalman filter and smoother , 2001 .

[3]  Yi Chao,et al.  A high‐resolution surface vector wind product for coastal oceans: Blending satellite scatterometer measurements with regional mesoscale atmospheric model simulations , 2003 .

[4]  Ping Wang,et al.  Parallel Computation of the Regional Ocean Modeling System , 2005, Int. J. High Perform. Comput. Appl..

[5]  Yi Chao,et al.  High-resolution real-time modeling of the marine atmospheric boundary layer in support of the AOSN-II field campaign , 2009 .

[6]  David P. Rogers,et al.  Supercritical Flow Interaction within the Cape Blanco–Cape Mendocino Orographic Complex , 2001 .

[7]  J. Molines,et al.  A sigma-coordinate primitive equation model for studying the circulation in the South Atlantic. Part I: Model configuration with error estimates , 1998 .

[8]  J. McWilliams,et al.  Evaluation and application of the ROMS 1-way embedding procedure to the central california upwelling system , 2006 .

[9]  K. Miyakoda,et al.  One-Way Nested Grid Models: The Interface Conditions and the Numerical Accuracy , 1977 .

[10]  Francisco P. Chavez,et al.  Seasonal fluctuations of temperature, salinity, nitrate, chlorophyll and primary production at station H3/M1 over 1989-1996 in Monterey Bay, California , 2000 .

[11]  A. O'Neill.  Atmospheric Data Assimilation , 2000 .

[12]  Franklin B. Schwing,et al.  Bifurcated flow from an upwelling center: a cold water source for Monterey Bay , 1994 .

[13]  R. Samelson,et al.  Mesoscale Simulation of Supercritical, Subcritical, and Transcritical Flow along Coastal Topography , 1999 .

[14]  Alexander F. Shchepetkin,et al.  Open boundary conditions for long-term integration of regional oceanic models , 2001 .

[15]  W. Large,et al.  Open Ocean Momentum Flux Measurements in Moderate to Strong Winds , 1981 .

[16]  C. C. Eriksen,et al.  Seaglider: a long-range autonomous underwater vehicle for oceanographic research , 2001 .

[17]  Kayo Ide,et al.  A three‐dimensional variational data assimilation scheme for the Regional Ocean Modeling System: Implementation and basic experiments , 2008 .

[18]  Jeffrey D. Paduan,et al.  Remotely sensed surface currents in Monterey Bay from shore-based HF radar (Coastal Ocean Dynamics Application Radar) , 1996 .

[19]  James C. McWilliams,et al.  Upwelling response to coastal wind profiles , 2004 .

[20]  Eric Blayo,et al.  Adaptive Mesh Refinement for Finite-Difference Ocean Models: First Experiments , 1999 .

[21]  Kenneth H. Brink,et al.  The global coastal ocean : regional studies and syntheses , 1998 .

[22]  Ionel M. Navon,et al.  Optimality of variational data assimilation and its relationship with the Kalman filter and smoother , 2001 .

[23]  Alexander F. Shchepetkin,et al.  The regional oceanic modeling system (ROMS): a split-explicit, free-surface, topography-following-coordinate oceanic model , 2005 .

[24]  K. Ide,et al.  A Three-Dimensional Variational Data Assimilation Scheme for the Regional Ocean Modeling System , 2008 .

[25]  J. McWilliams,et al.  A Comparison of Two Vertical-Mixing Schemes in a Pacific Ocean General Circulation Model , 2001 .

[26]  Jorge Nocedal,et al.  On the limited memory BFGS method for large scale optimization , 1989, Math. Program..

[27]  James C. McWilliams,et al.  Equilibrium structure and dynamics of the California Current System , 2003 .

[28]  J. Kondo,et al.  Air-sea bulk transfer coefficients in diabatic conditions , 1975 .

[29]  R. Davis,et al.  The autonomous underwater glider "Spray" , 2001 .

[30]  James C. McWilliams,et al.  The Regional Ocean Modeling System : A Split-Explicit , Free-Surface , Topography-Following-Coordinate Ocean Model , 2022 .

[31]  S. Cohn,et al.  Assessing the Effects of Data Selection with the DAO Physical-Space Statistical Analysis System* , 1998 .

[32]  A. Jazwinski.  Stochastic Processes and Filtering Theory , 1970 .

[33]  William H. Raymond,et al.  A radiation boundary condition for multi‐dimensional flows , 1984 .

[34]  R. Hodur.  The Naval Research Laboratory’s Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) , 1997 .