Scales of Spatial Variability

The spatial autocorrelation function of velocity at various depths can be computed to deduce the characteristic length scales of the motion in the model. The average first zero crossing is at lags of 250-300 km. The ``integral lengthscale'' of the motion can be obtained from an integral over the small-lag positive fraction of the autocovariance function (following Stammer, 1997). This integral lengthscale is 120 km at 500 meters depth in the autumn, and gradually decreases with the onset of winter. The average integral lengthscale is 95 km at 1000 meters depth, and also decreases by 10 percent as the year progresses. The autocovariance functions were computed from 10-day average velocity fields, which undoubtedly act to smooth the spatial field. Measurements from satellite altimetry reveal that the true lengthscale of the motion is much smaller, somewhere around 40-50 km in the Labrador Sea because of the small Rossby radius of deformation. 10-day model output is insufficient to show such small lengthscales here, but it is also likely that the model does not have some of the high wavenumber variability of the real ocean. The degree of variability present in the model will be addressed later in this report with regard to eddy kinetic energy and sea surface height frequency spectra.