AOSN-II August 2003

ESSE Uncertainty Forecasts

ESSE uncertainty initialization and forecast procedure

The ESSE forecast for September 5, 0000 GMT was initialized from an error nowcast for September 3, 0000 GMT. The background ocean field on September 3, 0000 GMT is a HOPS forecast simulation which assimilates all available and calibrated data up to September 2, 10GMT.

The dominant 400 eigenvectors of the posterior error covariance estimate for September 3, 0000GMT were utilized to perturb the ocean fields. 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 forecast simulations, each forced by forecast COAMPS atmospheric fluxes issued on September 2, was then carried out.

A total of 323 perturbed forecasts were issued. These 323 ensemble members are then utilized to compute the standard deviations shown in the Table below.

Error Subspace Statistical Estimation (ESSE) Results
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)

Analyses of ESSE Results

Dynamics and uncertainties. In Monterey Bay, the cyclonic circulation, in accord with the saltier and cooler upwelled waters previously advected in the center of the Bay, is forecast to move southward and somewhat intensify. This is partly due to the inflows of warm and fresh waters in the southwestern portion of the Bay, just west and north of the Monterey Bay Peninsula, which accentuate the cyclonic-favorable pressure gradient. Focusing on errors, the recent assimilation of several R/V Martin surveys and returning SIO-WHOI gliders has reduced uncertainties in the Monterey Bay region. However, the effects of the cyclonic circulation, e.g. see quasi-circular patterns in the T-errors at 0m, and of the inflow of warm and fresh waters, e.g. see higher uncertainties west and north of the Monterey Bay Peninsula in T and S at 30m, are visible.

For the full-domain, the filament of upwelled waters out off Pt-Sur and Monterey Bay Peninsula is forecast to pinch off a cyclonic eddy. This leads to locally higher uncertainties in the T, S, u, v and Psi fields (e.g. at 0-10m, see T and S errors, and u and v errors on north-south and east-west sides of the eddy, respectively) In the upper-layers, the meanders, strength and position of the coastal current are also related to the regions of higher uncertainties. At 100-200m depths, the different branches of the northward flowing California-Under-Current strongly influence the uncertainty fields.

Adaptive sampling recommendations

  • The remaining gliders should focus on the center of the Bay and on the inflows just offshore from the Monterey Bay Peninsula.



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