COMPARISONS OF MESOSCALE VARIABILITY IN THE SEMTNER-CHERVIN 1 4-DEGREES MODEL, THE LOS-ALAMOS PARALLEL OCEAN PROGRAM 1/6-DEGREES MODEL, ANDTOPEX/POSEIDON DATA/

Measures of mesoscale variability in the Semtner-Chervin 1/4 degrees a nd the Los Alamos Parallel Ocean Program (POP) 1/6 degrees models were compared with those obtained from TOPEX/POSEIDON (T/P) data. The obje ctives of these comparisons were two-fold: the first was to validate t he models using altimetry as a measure of the variability of the real ocean, and the second was to evaluate the effect of increased model re solution/decreased horizontal friction. Mesoscale root-mean-square (rm s) sea surface height (SSH), eddy kinetic energies, and length scales were used to quantify the mesoscale variability. Results showed that t he models reproduced the distribution and much of the magnitude of thi s variability associated with the major current systems; however, in t he oceans' interiors the magnitude was underrepresented. The 1/6 degre es and 1/4 degrees models were found to explain about 60% and 50% of t he global T/P variability, respectively. Estimates of eddy kinetic ene rgy (and rms velocities) from T/P and the models were compared, demons trating that the models were less energetic than the T/P fields, Indep endent comparisons were made with lagrangian drifters in the Pacific b asin. Excellent agreement was found between the total POP velocity fie lds and the drifter data in the tropics, where the T/P geostrophic val ues were too high due to error amplification by the 1/f factor. In the midlatitudes, the drifter values exceeded those derived from the tota l model velocities; the T/P results lay between the two. Differences a re attributed to the drifter analysis choices and possible residual no ise in the altimetry data. The effect of increased resolution/decrease d friction was best seen in the length scales where the POP scales agr eed more closely with the T/P values than with the 1/4 degrees model. The distribution and magnitude of the POP length scales were generally in agreement with the T/P values between 10 degrees and 40 degrees. N ear the equator, discrepancies were due to the long equatorial and ins tability waves, whose long wavelengths were too great to be resolved b y the the combination of noise in the altimeter slopes, and the partic ular definition of length scale chosen.