Diffusivities |
||
|
The left hand and right hand panels represent
comparisons of the diffusivities calculated from the 0.1° and 0.28° models with the drifter diffusivities,
respectively. It is clear that on average, the coarser resolution model
reproduces diffusivities that are too low across the entire domain,
especially between 20° and 40°N where the ratios are all less than
one. The only region where diffusivity ratios are close to, or are greater
than one, are in the central part of the domain north of 40° N where the NAC makes its eastward,
displaced northeast turn producing artificially high variability at this
location. In the case of the 0.1° model the diffusivity ratios are generally close to
one. Where ratios are as high as four, the 0.1° standard deviation ellipses shows
unrealistically high variability at those locations. The high zonal 0.1° model and drifter ratios are associated
with the too broad meander envelope of the model GS discussed above, while
the high meridional ratio is at the location of an unrealistic meander
associated with the NAC in the Northwest Corner identified by Smith et al.
(2000).
|
||
|
|
To obtain an understanding of the spread of values of the actual model and drifter time scales, histograms of the diffusivities were constructed for both the meridional and zonal directions. In all cases the 0.1° distributions most closely matched those of the drifters. The drifter diffusivities range from roughly 1-14 x 107 cm2s-1 with most values in the range 1-8 x 107 cm2s-1. The 0.1° diffusivities are similarly distributed except for occurrences of slightly more low diffusivities than in the observed case. The 0.28° distribution is very different in that it is dominated by occurrences of low diffusivities in the range of 1-3 x 107 cm2s-1. |
|
|
|
||
|
|
|
|
