SNAC: A statistical emulator of the north-east Atlantic circulation

Abstract

The three-dimensional statistical emulator SNAC (Statistical North-east Atlantic Circulation) for operational computation of the oceanic circulation in the north-eastern North Atlantic is presented. SNAC was trained with the output of the numerical three-dimensional ocean model HAMSOM (HAMburg Shelf Ocean Model) and determines the most probable circulation from a prescribed transient weather situation. Air pressure distributions derived from a network of eight weather stations (i.e. airports) provide the forcing. The emulator uses the statistical correlation between air pressure differences amongst selected stations and oceanic currents. Horizontal currents and sea surface elevation are computed on a spherical grid with a resolution of 0.25° (zonal) and 0.125° (meridional). Vertically, the water column is resolved by 11 layers. The emulator domain extends from 44° W to 15.75° E, and from 48.5° to 70° N. SNAC is able to reproduce the temporal variability simulated by numerical models on time scales between 2 months and 1 year, though the program runs up to 500 times faster. Optionally, a simple M2 tide model can be integrated into the output. As an alternative to a more complex numerical circulation model, SNAC requires far less atmospheric forcing data and much less computational effort. Presently, SNAC provides circulation fields for a tracer model used in simulating the dispersal of fish larvae around Iceland and on the north-west European continental shelf. It might equally well be used to provide boundary values for regional hydrodynamic ocean models. The program can be downloaded from www.ifm.uni-hamburg.de/~logemann/snac/. © 2003 Elsevier Ltd. All rights reserved.