[1] Maps of apparent lateral diffusivity K derived from surface drifters in the Pacific and Atlantic Oceans are analyzed together with mean surface circulation patterns. A remarkable feature of the diffusivity map in the Atlantic was proven to be trans-ocean belts of enhanced K in the thirties latitudes. It was shown that the North Atlantic belt is caused by the meandering and eddy-producing Azores Current, while its counterpart in the South Atlantic results from northwestward and westward drift of warm eddies produced by the Agulhas Retroflection. A puzzling feature of the diffusivity map in the Pacific was a zonally elongated tongue of high K at the center of a subtropical gyre in the Southern Hemisphere beginning from the western boundary. A similar tongue observed at the center of a subtropical gyre of the North Pacific is known to result from baroclinic instability in the seasonal North Subtropical Countercurrent (NSTCC). Both tongues were characterized by a strong and identical seasonal cycle of the eddy kinetic energy (EKE), which persuaded us to suggest an identity for the formation mechanisms that would imply the existence of southern counterpart of NSTCC: the would-be South Subtropical Countercurrent (SSTCC). A seasonal-latitudinal dependence of the mean zonal current and EKE as well as maps of the mean zonal velocity were derived from drifters that provided some evidence in favor of the existence of this SSTCC.

The occurrences of harmful algal blooms (HABs), in terms of frequency and area in the Chinese coastal waters, have been increasing since 1980s and caused considerable economic losses. In the present study, we have analyzed spatial and seasonal characteristics of HAB events in the southern Yellow Sea and East China Sea along Chinese coast from 1933 to 2004. With a total 435 HAB records, the most frequent HAB occurrence area (FHA) is off the Yangtze River mouth and another two FHA areas are located south of the Yangtze River estuary along about isobaths of 30-60 m coastal water in the East China Sea.

[1] The Global Drifter Program/Surface Velocity Program data set is used to derive maps of the lateral diffusivity and Lagrangian scales of velocity, length and time across the whole Pacific. For the lateral diffusivity, the minor principal component of both the Davis' diffusivity tensor and the half growth rate of the single-particle dispersion tensor were calculated in 5°Â 5°bins from drifters for the period 1979-1999. Estimates of the lateral diffusivity, K, obtained by means of the minor principal component approach, are shown to correspond well with other authors' estimates for the Pacific. The highest values of K (2-3 10 4 m 2 /s) are found in the eastern equatorial Pacific, while the lowest ones (2-3 10 3 m 2 /s) are typical for forty-odd degrees in latitude northward of the subpolar fronts in both hemispheres and for the subtropics in the eastern part of the South Pacific. High values of K (about 1 Â 10 4 m 2 /s) are also observed in the Kusoshio/Kuroshio Extension area and in the equatorial Pacific along the whole length of the equator. There are two approximately symmetrical tongues of high K value in the western Pacific centered around 21°N and 24°S, respectively. In general, K has a tendency to increase westward (eastward) in the midlatitudes (equatorial region) and toward the equator in both hemispheres. In the midlatitudes, the Lagrangian length scale L is found to be approximately equal to the firstmode baroclinic radius of deformation, Ri, while the Rossby number defined as Ro = T earth /T sinj, where T is the Lagrangian timescale, T earth is the period of the Earth's rotation, and j is the latitude, is less than unity, implying that the quasigeostrophic mesoscale eddies are the main mechanism for lateral mixing. The lateral diffusivity in the midlatitudes is suggested to be parameterized as K = V 2 Ri, where V 2 is the Lagrangian velocity scale inherent to a mesoscale eddy field. In the low latitudes, L becomes less than Ri, and the condition Ro 1 is no longer valid, which implies the change of the eddycontrolled mechanism of lateral mixing by another mechanism.INDEX TERMS: 4203 Oceanography: General: Analytical modeling; 4568 Oceanography: Physical: Turbulence, diffusion, and mixing processes; KEYWORDS: lateral diffusivity, Lagrangian scales, drifter data Citation: Zhurbas, V., and I. S. Oh, Lateral diffusivity and Lagrangian scales in the Pacific Ocean as derived from drifter data,

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