A suite of shipboard and satellite observations are analyzed and synthesized to investigate the threedimensional structure of clouds and influences from sea surface temperature fronts over the western North Pacific. Sharp transitions are observed across the Kuroshio Extension (KE) front in the marine atmospheric boundary layer (MABL) and its clouds. The ocean's influence appears to extend beyond the MABL, with higher cloud tops in altitude along the KE front than the surroundings.In winter, intense turbulent heat release from the ocean takes place on the southern flank of the KE front, where the cloud top penetrates above the MABL and reaches the midtroposphere. In this band of high cloud tops, frequent lightning activity is observed. The results of this study suggest a sea level pressure mechanism for which the temperature gradient in the MABL induces strong surface wind convergence on the southern flank of the KE front, deepening the clouds there.In early summer, sea fog frequently occurs on the northern flank of the subtropical KE and subarctic fronts under southerly warm advection that suppresses surface heat flux and stabilizes the surface atmosphere. Sea fog is infrequently observed over the KE front even under southerly conditions, as the warm ocean current weakens atmospheric stratification and promotes vertical mixing. The KE front produces a narrow band of surface wind convergence, helping support a broad band of upward motion at 700 hPa that is associated with the eastward extension of the baiu rainband from Japan in June-July.

An array of seven inverted echo sounders was moored along and across the Kuroshio in the East China Sea for more than one year. The data from this array show evidence of energetic meanders with periods of 7, 11, and 16 days. The respective phase velocities of these meanders are 28, 20, and 17 km day Ϫ1 downstream. The 7-and 16-day waves are intermittent, but the 11-day waves are present throughout the deployment. The instability responsible for these waves is investigated with a spectral numerical model applied to a background state representing the Kuroshio in this region. The fastest-growing instability from the model has e-folding growth time of 2 days, period of 12 days, and phase velocity of 18 km day Ϫ1 downstream. It appears to be a close representation of the 11-day wave seen in the observational data. Such a model has been previously used to represent meanders in the Gulf Stream at similar latitudes off the east coast of the United States. The Kuroshio meanders have approximately half the phase velocity and twice the period of the Gulf Stream meanders. To investigate the reasons for these differences, the flow and topography of the model background state were varied. The slower phase velocity and longer period of the Kuroshio meanders appear to be consequences of the deeper shelf and lower transport, with a modifying effect due to the difference in cross-shelf positioning of the current core (more over-the-shelf in the case of the Kuroshio).

Abstract. In 1993-1995, we carried out observations of the Kuroshio south of Japan, including direct current measurements and repeated hydrographic surveys along a satellite track of the TOPEX/POSEIDON altimeter. The velocity field of the Kuroshio is determined by geostrophic calculation using the repeated hydrographic survey data, referenced to velocities observed at mid and abyssal depths. The volume transport of the Kuroshio is estimated from this velocity field. The estimated transports of the Kuroshio have a high correlation with sea-surface height differences across the Kuroshio. Having this relationship and using the altimeter data, we obtained a time series of the Kuroshio transport over seven years at ten-day intervals. The Kuroshio transport, excluding contributions by local recirculations, is estimated to be 42 x 10 6 m3/sec on average. The correlation between sea-surface height difference and transport provides a practical method of long-term monitoring of the Kuroshio transport using satellite altimetry.

[1] Kuroshio velocity structure and transport in the East China Sea (ECS) were investigated as part of a 23-month study using inverted echo sounders and acoustic Doppler current profilers (ADCPs) along the regularly sampled PN-line. Flow toward the northeast is concentrated near the continental shelf with the mean surface velocity maximum located 30 km offshore from the shelf break (taken as the 170 m isobath). There are two regions of southwestward flow: a deep countercurrent over the continental slope beneath the Kuroshio axis and a recirculation offshore which extends throughout the whole water column. There is a bimodal distribution to the depth of maximum velocity with occurrence peaks at the surface and 210 dbar. When the maximum velocity is located within the top 80 m of the water column, it ranges between 0.36 m/s and 2.02 m/s; when the maximum velocity is deeper than 80 m, it ranges between 0.31 m/s and 1.11 m/s. The 13-month mean net absolute transport of the Kuroshio in the ECS is 18.5 ± 0.8 Sv (standard deviation, s = 4.0 Sv). The mean positive and negative portions of this net flow are 24.0 ± 0.9 Sv and À5.4 ± 0.3 Sv, respectively.

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a b s t r a c tData from the Kuroshio Extension Observatory (KEO) surface mooring are used to analyze the balance of processes affecting the upper ocean heat content and surface mixed layer temperature variations in the Recirculation Gyre (RG) south of the Kuroshio Extension (KE). Cold and dry air blowing across the KE and its warm RG during winter cause very large heat fluxes out of the ocean that result in the erosion of the seasonal thermocline in the RG. Some of this heat is replenished through horizontal heat advection, which may enable the seasonal thermocline to begin restratifying while the net surface heat flux is still acting to cool the upper ocean. Once the surface heat flux begins warming the ocean, restratification occurs rapidly due to the low thermal inertia of the shallow mixed layer depth. Enhanced diffusive mixing below the mixed layer tends to transfer some of the mixed layer heat downward, eroding and potentially modifying sequestered subtropical mode water and even the deeper waters of the main thermocline during winter. Diffusivity at the base of the mixed layer, estimated from the residual of the mixed layer temperature balance, is roughly 3 Â 10 À 4 m 2 /s during the summer and up to two orders of magnitude larger during winter. The enhanced diffusivities appear to be due to large inertial shear generated by wind events associated with winter storms and summer tropical cyclones. The diffusivity's seasonality is likely due to seasonal variations in stratification just below the mixed layer depth, which is large during the summer when the seasonal thermocline is fully developed and low during the winter when the mixed layer extends to the top of the thermocline.Published by Elsevier Ltd.

Horizontal patterns and meander motions of the Kuroshio paths in the northern Okinawa Trough between the continental slope and the Tokara Strait are investigated using surface drifter buoy trajectory data, NOAA sea surface temperature (SST) measurements, and shipboard acoustic Doppler current profiler (ADCP) current observations. Temporal variations are also examined by spectral analyses of 1‐year moored velocity/temperature records along the continental slope near 28.8°–30.5°N and of the Kuroshio position time series in the Tokara Strait. Drifter buoy trajectories show that the Kuroshio paths in the northern Okinawa Trough are quasibimodal in character consisting of the northern paths and southern ones, which are associated with anticyclonic and cyclonic Kuroshio circulations, respectively. The Kuroshio position time series show that the northern paths tend to be persistent and intermittently undergo transition to southern paths at periods of 1–3 months. Moored current variations in the slope area and the Kuroshio path variations in the Tokara Strait are highly coherent near a period of 34 days due to the meander motions resulting from the transitions between the northern and southern paths. Successive NOAA SST images and shipboard ADCP current fields show that the transition from the northern path to the southern one is associated with a spatially growing cyclonic eddy, which is initially generated from a downstream‐propagating frontal meander with wavelength of about 200 km. When the cyclonic eddy grows into the scale of the northern Okinawa Trough (about 200‐km E–W, 250‐km N–S), the Kuroshio path changes from the northern path to the southern one.