Evaluating the synopticity of the US GLOBEC Georges Bank broad-scale sampling pattern with observational system simulation experiments

A set of observational system simulation experiments (OSSEs) have been designed to assess quantitatively the synopticity of the broad-scale surveys of Georges Bank carried out as part of the US GLOBEC program. The approach uses model simulations that contain realistic spatial and temporal fluctuations of adult females of the planktonic copepod Calanus finmarchicus observed during February and March 1995. Simulations are constructed with two types of assimilation procedures (nudging and the adjoint method), which are used to dynamically interpolate between the two broad-scale surveys taken one month apart. Using these simulations as representations of the real ocean, the model fields are subsampled in space and time along a typical cruise track. These simulated data are then objectively analyzed and the resulting maps compared with “reality” as represented in the original simulation. Results indicate a total error of approximately 50%, which is comprised mostly of simple mapping error (incomplete spatial sampling) and a smaller contribution from space/time smearing. Adjustment of the station positions for displacement by the mean flow reduces the latter error by about half.