AOSN-II August 2003
The ESSE forecast for August 13, 0000 GMT was initialized from an error nowcast for August 11, 0000 GMT. The background ocean field on August 11, 0000 GMT is a HOPS forecast simulation which assimilates all calibrated data up to 1300 GMT on August 10.
The dominant 263 eigenvectors of the error covariance estimate for August 11, 0000 GMT (computed during the night, extending the 52 members issued during the day yesterday) was utilized to perturb the ocean fields on August 11, 0000 GMT. 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 2-day forecast simulations, each forced by forecast COAMPS atmospheric fluxes, was then carried out. Presently, 56 of such forecast simulations are utilized to forecast the uncertainties on August 13, 0000 GMT (August 12, 5PM PDT).
| 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) | |||
| 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) | |||
U and V velocities are the two components of the internal velocity (i.e. total velocity - vertically averaged velocity) along the domain coordinate system (zonal is 29.4 degrees northeast from a latitude, meridional is 29.4 degrees northwest from a longitude)
Compared to yesterday's forecast (for Aug 12 GMT00), focusing on the Monterey Bay region, the main point is that errors have been advected by the flow and have grown in three-dimensions (errors are larger in part because the uncertainty nowcast has more correct amplitudes than the historical error IC used yesterday). The stronger winds have increased the uncertainty amplitudes at 30m depth, especially south of the mouth of Monterey Bay (near Pt Sur) where the upwelling-driven and wind-driven currents are forecast to be the strongest. The amplitudes of the internal velocity and barotropic transport streamfunction uncertainties reflect these properties. The effect of the vertically-averaged cyclonic circulation over Monterey Bay remains visible in the error fields but the center of this cyclone has shifted southward. The uncertainties are thus now much larger near Pt Sur.
For the full domain, the above main point still holds. The salinity error field is especially interesting because in the upper-layers, it closely follows the meanders of the main coastal current along the Californian coast. These meanders results from a combination of internal and wind-forced effects. In addition, we start to see an error growth at the southern boundary (see temperature). The surface flow is mainly southward there and strong, driven in a large part by the local winds. This implies that the data from the Pt Sur is being "flushed out of the domain" and the uncertainties thus increase. Errors there are also larger due to the numerical open-boundary conditions.