Time Scales

Abstract

Introduction

Model Descriptions

Surface Drifters

Numerical Trajectories

Eulerian Statistics

• Mean Velocity Vectors
• MKE
• Ellipses
• EKE
• James test

Lagrangian Statistics

• Diffusivities
• Time Scales
• Length Scales

Summary

Appendix A

Appendix B

Acronyms

References

Acknowledgements

Forum

Comparisons of the 0.1° and 0.28° model time scales with the drifter time scales show that the coarser model produces scales that are too long relative to the drifter scales. A statistical t-test was used to show that the domain-averaged 0.28° model time scale was statistically different from the domain-averaged observed scale at the 95% confidence level, in both the zonal and meridional directions. The observed mean time scales are 3.7 d and 2.7 d in the meridional and zonal directions, respectively, while the corresponding model values are 6.3 d and 4.3 d, respectively. In the case of the 0.1° model, the mean zonal time scale was not statistically different from the observed mean zonal scale although the mean meridional scales did differ.

The observed mean time scales are 3.6 d and 2.6 d in the zonal and meridional directions, respectively, while the corresponding model values are 3.9 d and 3.2 d, respectively. The slight difference in the observed scale is due to limiting the statistics to bins where both the model and the data have 400 or more observations. A visual inspection of the zonal ratios suggest that the values are close to one over much of the domain with a couple of outliers which are biasing the statistics. In all, the 0.1° scales are more realistic than those produced by the 0.28° model.

The drifter time scales cover a range of 1 to 7 days with the majority in the range of 1-4 days. The 0.1° scales range from 1-9 days, however like the observations most of the scales are in the 1-4 day range. For both the model and the observations, a typical time scale is about 2 to 4 days. The 0.28° scales range from 1-10 days however the time scales are more evenly spread over this entire range with some bunching occurring between 3 and 5 days.