AOSN-II August 2003

Uncertainties were initialized for August 11, GMT00, using the ESSE initialization approach. The background ocean field on August 11, GMT00 is based on a HOPS forecast simulation which assimilates all calibrated data up to 1PM on August 9.

The observed field variables are mostly temperature (T) and salinity (S), and the T and S data collected from August 2 to August 9 are used to initialize uncertainties. The differences between these data and the background simulation are utilized to compute multivariate T and S vertical empirical functions (EOFs). To obtain three-dimensional EOFs for T and S, the vertical EOFs are combined with horizontal eigenmodes. These horizontal eigenmodes were computed based on a "Mexican hat" (second derivative of a Gaussian) covariance function, whose parameters were set to 5km decorrelation (decay) scale (km) and 12.5km zero crossing. To compute the non-observed velocity uncertainties, the background field is pertubed with each three-dimensional EOFs for T and S, and the momentum equations are then numerical integrated until adjustment. The result is an ensemble of adjusted velocity anomalies. The singular value decomposition of normalized T, S, u and v anomalies is then computed to lead a complete error subspace (dominant error singular vectors/EOFS). Presently, 500 three-dimensional, multivariate singular vectors are retained to determine the initial error subspace.

To forecast uncertainties for August 12, the fields on August 11 are perturbed using a random combination of the 200 dominant T, S, u and v initial singular vectors, weighted by their eigenvalues. A white noise of an amplitude proportional to the estimated absolute and relative errors in the observations is added to this random combination, in part to represent the errors truncated by the error subspace. An ensemble of 1-day forecast simulations, each forced by forecast COAMPS atmospheric fluxes, is then carried out. Presently, 52 of such forecast simulations are utilized to forecast the uncertainties on August 12.

Full Domain | |||

Temperature | Salinity | U velocity component | V velocity component |

Monterey Bay Zoom | |||

Temperature | Salinity | U velocity component | V velocity component |

Barotropic Streamfunction (including Monterey Bay) |

Focusing on the Monterey Bay zoom, there are some instabilities forecast near the mouth of the Bay.

Focusing on the full domain, the East-West temperature and salinity fronts, and the corresponding meandering of the plumes, are the reasons for the local high temperature and salinity error patterns.