Wednesday 24 August 2005

P1
1550-1710 hours

310
Zooplankton, dynamic height and Rossby wave propagation off California
Clarke, Allan¹, Dottori, Marcelo¹, Van Gorder, Stephen¹
1 Florida State University, FL, USA
Author email: clarke@ocean.fsu.edu
Lagged correlation of 50 years (with gaps) of anomalous (i.e., seasonal cycle removed) dynamic height with anomalous coastal sea level in the CalCOFI region off Southern California shows that the anomalous dynamic height signal propagates offshore at a speed of 4 cm/sec. This speed agrees with satellite sea level height estimates found from TOPEX/Jason 1 over the last decade. Both estimates, however, are more than double that expected theoretically even when the effect of the large-scale mean California Current is included. Why is the propagation "too fast"? Along-track satellite mean sea level estimates in the CalCOFI region suggest that the mean sea level has a large zonal scale but oscillates meridionally with an amplitude of a few cm and a comparatively short meridional wavelength of about 300km. By geostrophy, these small meridional sea level oscillations correspond to bands of alternate weak zonal flows ubar and to a northward gradient of vorticity -ubar sub yy that is comparable to beta, the northward gradient of the Coriolis parameter. Theory shows that in the presence of such banded mean flow the interannual variability should propagate westward at approximately double the Rossby wave speed as observed. Theory also suggests that anomalies of the logarithm of zooplankton population should be proportional to anomalous sea level. Consistent with this, interannual variations in ln (zooplankton population) tend to propagate westward across the CalCOFI grid at speeds comparable to long Rossby waves. Lagged correlations suggest that interannual variations in California Current ln (zooplankton) can be predicted from monthly San Diego sea level 6 months in advance with a correlation of over 0.6.

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