[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.

[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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Numerous conductivity‐temperature‐depth data obtained in the Arctic basins are analyzed to describe structural features of intrusive layering. Special attention is paid to large intrusions (vertical scale of 40–100 m) observed in upper, intermediate and deep layers (depth ranges of 150–200, 200–600 and 600–1000 m, respectively). The analysis of the intrusions is accompanied by descriptions of the frontal zones where the layering was observed. Based on observations detailed estimates of frontal zone parameters are presented. Vertical profiles of temperature and salinity are found to have a well‐defined “sawtooth” or “cog” shape, displaying a sequence of relatively thick, weak gradient layers, where temperature and salinity are decreasing with depth, interleaved with relatively thin, high‐gradient sublayers, where temperature and salinity are increasing with depth. Some hypotheses about causes responsible for cog structure existence are discussed. Intrusions with high‐amplitude anomalies in the vertical profiles of temperature and salinity are shown to be present at baroclinic fronts. Based on models of interleaving and data analysis the apparent vertical and lateral diffusivity in the frontal zones of the upper and deep ocean layers are estimated, and the slope of unstable modes relative to the isopycnals is examined at the baroclinic front in the situation when both temperature and salinity are stably stratified.

Abstract. To examine processes controlling the entrainment of ambient water into the Denmark Strait overflow (DSO) plume / gravity current, measurements of turbulent dissipation rate were carried out by a quasi-free-falling (tethered) microstructure profiler (MSP). The MSP was specifically designed to collect data on dissipation-scale turbulence and fine thermohaline stratification in an ocean layer located as deep as 3500 m. The task was to perform microstructure measurements in the DSO plume in the lower 300 m depth interval including the bottom mixed layer and the interfacial layer below the non-turbulent ambient water. The MSP was attached to a Rosette water sampler rack equipped with a SeaBird CTDO and an RD Instruments lowered acoustic Doppler current profiler (LADCP). At a chosen depth, the MSP was remotely released from the rack to perform measurements in a quasi-free-falling mode.Using the measured vertical profiles of dissipation, the entrainment rate as well as the bottom and interfacial stresses in the DSO plume were estimated at a location 200 km downstream of the sill at depths up to 1771 m. Dissipation-derived estimates of entrainment were found to be much smaller than bulk estimates of entrainment calculated from the downstream change of the mean properties in the plume, suggesting the lateral stirring due to mesoscale eddies rather than diapycnal mixing as the main contributor to entrainment. Dissipation-derived bottom stress estimates are argued to be roughly one third the magnitude of those derived from log velocity profiles. In the interfacial layer, the Ozmidov scale calculated from turbulence dissipation rate and buoyancy frequency was found to be linearly proportional to the overturning scale extracted from conventional CTD data (the Thorpe scale), with a proportionality constant of 0.76, and a correlation coefficient of 0.77.