Meridional heat transport in the North Atlantic and the trends of its variations in the second half of the 20th century

The meridional heat transport in the ocean is computed according to the data of zonal sections of the World Ocean Circulation Experiment made in the North Atlantic in 1992–1998. We perform the generalized analysis of the estimates of meridional heat transport obtained by different authors by direct methods on the basis of the data of sections made between 7.5 and 48°N in the second half of the last century. The meridional heat transport averaged over the entire period of observations attains its maximum (1.38 ± 0.19 PW) in the Subtropical Atlantic. The meridional heat transport is characterized by fairly intense seasonal variability. Its maximum (about 1.9 PW) is observed in the Subtropical Atlantic at the end of summer and its minimum (about 0.8 PW) is attained at the end of winter. A significant trend toward the intensification of meridional heat transport is revealed near 36°N in 1959–1993 (from 0.75 to 1.1 PW). This is an indication of the intensification of meridional oceanic circulation in the North Atlantic. Dedicated to the 75th birthday of N. A. Timofeev, Honored Scientist of the Ukraine, Doctor of Geographical Sciences __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 1, pp. 45–58, January–February, 2007.     

Space-and-time variability of the meridional heat transport in the north atlantic

We analyze the space-and-time variability of the meridional heat transport in the North Atlantic. The contribution of various mechanisms to the integral meridional heat transport (MHT) is estimated. The key role played by the drift transport of the Tropical Atlantic in the formation of the meridional oceanic heat transport is confirmed. On the basis of the general analysis of estimations obtained by various authors according to the data accumulated for 1870–2008 and the results of numerical analyses based on the data of NCEP/NCAR reanalysis, we show that the long-term average meridional drift heat (mass) transport attains its maximum values equal to (1.6 ± 0.1) PW [(17.4 ± 1.5) Sv] in the vicinity of 12.5°N in the Tropical Atlantic. The contribution of the heat transport caused by the horizontal Sverdrup circulation to the integral meridional heat transport is maximum in the vicinity of 30° N. On the average, it is equal to ∼ 40%. In the Subtropical Atlantic, the meridional heat transport varies with a period of ∼ 50–70 yr. The minimum value of the integral meridional heat transport was attained in the mid-1960s and its maximum value was at attained at the beginning of the 1990s. The location of the center of Azores pressure maximum makes it possible to conclude that the intensification of the total meridional heat transport in the Subtropical Atlantic on these time scales is accompanied by the displacement of the center of the North Subtropical anticyclonic gyre in the southwest direction.     

Japanese Ocean Flux Data Sets with Use of Remote Sensing Observations (J-OFURO)

We have constructed ocean surface data sets using mainly satellite data and called them Japanese Ocean Flux data sets with Use of Remote sensing Observations (J-OFURO). The data sets include shortwave radiation, longwave radiation, latent heat flux, sensible heat flux, and momentum flux etc. This article introduces J-OFURO and compares it with other global flux data sets such as European Centre for Medium Range Weather Forecasting (ECMWF) and National Center for Environmental Prediction (NCEP) reanalysis data and da Silva et al. (1994). The usual ECMWF data are used for comparison of zonal wind. The comparison is carried out for a meridional profile along the dateline for January and July 1993. Although the overall spatial variation is common for all the products, there is a large difference between them in places. J-OFURO shortwave radiation in July shows larger meridional contrast than other data sets. On the other hand, J-OFURO underestimates longwave radiation flux at low- and mid-latitudes in the Southern Hemisphere. J-OFURO latent heat flux in January overestimates at 10°N–20°N and underestimates at 25°N–40°N. Finally, J-OFURO shows a larger oceanic net heat loss at 10°N–20°N and a smaller loss north of 20°N in January. The data of da Silva et al. in July show small net heat loss around 20°S and large gain around 20°N, while the NCEP reanalysis (NRA) data show the opposite. The da Silva et al. zonal wind speed overestimates at low-latitudes in January, while ECMWF wind data seem to underestimate the easterlies. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of ridges on hydrographic parameters in the Southwest Indian Ocean

The objective of the paper is to use the data collected along two meridional sections (45° E and 57°30′ E) during the austral summer (January–March) 2004 to understand the influence of seabed topography across the Madagascar and Southwest Indian Ridges on hydrographic parameters. The study was supplemented by World Ocean Circulation Experiment (WOCE) Conductivity-Temperature-Depth data collected during February–March 1996 along 30° E, as well as Levitus climatology. A southward shift of 2° latitude (between 45° E and 57°30′ E) was recorded for the two predominant frontal structures, i.e., the Agulhas Return Front and Southern Subtropical Front, which is attributed to the influence of seabed topography on hydrographic parameters. No significant spatial variation of these fronts was noted between the 30° E and 45° E meridional sections. Between latitudes 31° S and 42° S, the temperature and salinity structures show deepening over the ridges. The Antarctic Circumpolar Current core was detected between 40°15′ S and 43° S.     

The three-dimensional structure and seasonal variation of the North Pacific meridional overturning circulation

The three-dimensional structure and the seasonal variation of the North Pacific meridional overturning circulation (NPMOC) are analyzed based on the Simple Ocean Data Assimilation data and Argo profiling float data.The NPMOC displays a multi-cell structure with four cells in the North Pacific altogether.The TC and the STC are a strong clockwise meridional cell in the low latitude ocean and a weaker clockwise meridional cell between 7°N and 18°N,respectively, while the DTC and the subpolar cell are a weaker ...     

Heat fluxes across 7°30′N and 4°30′S in the Atlantic Ocean

Heat fluxes are estimated across transatlantic sections made at 4°30′S and 7°30′N in January–March 1993, following Hall and Bryden (1982. Deep-Sea Research 29, 339–359). Particular care is given to the computation of Ekman volume and heat fluxes, which are assessed both (a) from the windstress data for the period of the cruise and (b) from the comparison between geostrophic and Vessel Mounted Acoustic Doppler Current Profiler (VM-ADCP) velocities. In contrast with previous studies, the two estimates for Ekman fluxes do not converge for either section: (a) (11.5±0.5 Sv; 1.01±0.05 PW) across 7°30′N and (−9.3±1.2 Sv; −0.85±0.12 PW) across 4°30′S when windstress data at the date of the hydrographic stations are used; (b) (6.3±1.1 Sv; 0.56±0.09 PW) across 7°30′N and (−3.4±3.0 Sv; −0.35±0.24 PW) across 4°30′N when the ageostrophic transport above the thermocline is used. The divergence would have been even greater at 4°30′S if the strong ageostrophic signal beneath the thermocline, which brings a transport of (8.4 Sv; 0.82 PW), had been considered. The corresponding total meridional heat fluxes are: (a) 1.40±0.16 PW and (b) 0.95±0.20 PW across 7°30′N, (a) 1.05±0.12 PW and (b) 1.67±0.14 PW (2.39±0.14 PW when the subthermocline ageostrophic transport is taken into account) across 4°30′S.The estimates based on windstress data are compared with the results from an inverse model (Lux and Mercier, 1999) to show the importance of the heat flux due to the deviation of the local depth-averaged potential temperature from its average over the section, which is neglected in the Hall and Bryden (1982. Deep-Sea Research 29, 339–359) method but is not negligible in our computation in which we do not isolate the transport of the western boundary current east of the 200 m isobath; this corrective flux amounts here to −0.19 PW across 7°30′N and 0.33 PW across 4°30′S.The seasonal variability of the meridional heat flux across 7°30′N is studied through the hydrographic data collected during the ETAMBOT 1–2 cruises, which repeated the 7°30′N section west of 35°W in September 1995 and April 1996. When the section is completed east of 35°W with CITHER 1 data and when windstress data are used for the computation of the Ekman transport, the estimates for the meridional heat fluxes are 0.20±0.14 PW in September 1995 and 1.69±0.27 PW in April 1996. The estimates fit well with results from numerical models.     

Variation of the southward interior flow of the North Pacific subtropical gyre,as revealed by a repeat hydrographic survey

Baroclinic variations of the southward flow in the interior region of the North Pacific subtropical gyre are presented with five hydrographic sections from San Francisco to near Japan during 2004–2006. The volume transport averaged temperature of the interior flow, which varies vigorously by a maximum of 0.8°C, is negatively correlated with the transport in the layer of density 24.5–26.5σ _θ, associated with changes in the vertical current structure. Transport variation in this density layer is thus mainly responsible for the thermal impact of the interior flow on the heat transport of the subtropical gyre.     

Large-Scale Structure of Thermal Fronts in the East Part of the Tropical Atlantic and Their Seasonal Variability

On the basis of the climatic array of hydrological annual and monthly average data on temperature and the data of satellite observations of the surface temperature of the ocean, we refine the annual average structure of the temperature fronts and study their seasonal variability in the east part of the Tropical Atlantic in the meridional sections made along 30, 20, and 10°W, 0°, and 10°E. It is shown that the maximum intensity and seasonal variations are typical of the North Subequatorial and South Tropical Fronts varying with predominant annual period. We revealed a delay of 2–3 months in the attainment of the maximum intensity of the South Tropical and South Subequatorial Fronts in the west-east direction. Various mechanisms specifying the seasonal variability of the surface and subsurface North and South Subequatorial Fronts are discussed. There exists good agreement between the specific features of the seasonal variability of characteristics of the fronts established according to the hydrological and satellite data. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 2, pp. 46–59, March–April, 2005.     

Absolute Volume Transports of the Oyashio Referred to Moored Current Meter Data Crossing the OICE

During November 2000–June 2002, both direct current measurements from deployment of a line of five moorings and repeated CTD observations were conducted along the Oyashio Intensive observation line off Cape Erimo (OICE). All the moorings were installed above the inshore-side slope of the Kuril-Kamchatka Trench. Before calculating the absolute volume transports, we compared vertical velocity differences of relative geostrophic velocities with those of the measured velocities. Since both the vertical velocity differences concerned with the middle three moorings were in good agreement, the flows above the continental slope are considered to be in thermal wind balance. We therefore used the current meter data of these three moorings, selected among all five moorings, to estimate the absolute volume transports of the Oyashio referred to the current meter data. As a result, we estimated that the southwestward absolute volume transports in 0–1000 db are 0.5–12.8 × 10⁶ m³/sec and the largest transport is obtained in winter, January 2001. The Oyashio absolute transports in January 2001, crossing the OICE between 42°N and 41°15′ N from the surface to near the bottom above the continental slope, is estimated to be at least 31 × 10⁶ m³/sec. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characteristics of SSH Anomaly Based on TOPEX/POSEIDON Altimetry and in situ Measured Velocity and Transport of Oyashio on OICE

An observation line along the TOPEX/POSEIDON (T/P) ground track 060 was set to estimate the Oyashio transport. We call this line the OICE (Oyashio Intensive observation line off-Cape Erimo) along which we have been conducting repeated hydrographic observations and maintaining mooring systems. T/P derived sea surface height anomaly (SSHA) was compared with velocity and transport on OICE. Although the decorrelation scale of SSHA was estimated at about 80–110 km in the Oyashio region, the SSHA also contains horizontal, small-scale noise, which was eliminated using a Gaussian filter. In the comparison between the SSHA difference across two selected points and the subsurface velocity measured by a moored Acoustic Doppler Current Profiler (ADCP), the highest correlation (0.92) appeared when the smoothing scale was set at 30 km with the two points as near as possible. For the transport in the Oyashio region, the geostrophic transport between 39°30′ N and 42°N was compared with the SSHA difference across the same two points. In this case the highest correlations (0.79, 0.88 and 0.93) occurred when the smoothing scale was set at 38, 6 and 9 km for reference levels of 1000, 2000 and 3000 db, respectively. The annual mean transport was estimated as 9.46 Sv in the 3000 db reference case. The Oyashio transport time series was derived from the T/P SSHA data, and the transports are smaller than that estimated from the Sverdrup balance in 1994–1996 and larger than that in 1997–2000. This difference is consistent with baroclinic response to wind stress field. This revised version was published online in July 2006 with corrections to the Cover Date.     

Meridional mass and energy fluxes in the vicinity of the Arctic border

The air exchange between the Arctic and midlatitude regions is one of the processes forming the climate of the whole Northern Hemisphere. Analysis of the wind regime in the vicinity of the Arctic border (70° N) at the boundary between the 20th and 21st (1997–2004) centuries showed significant changes in the conditions of a meridional air transport between the Arctic and midlatitude regions as compared to the previous years (1960–1990). In this study, the wind fluxes of mass and heat (internal) and kinetic energies are estimated without consideration for turbulent and convective processes. The importance of spatial, seasonal, and interannual variations in wind velocity and air temperature in the formation of these fluxes is analyzed. It is shown that, during the period 1997–2004, an advective transport of energy from the northern latitudes occurred in the lower 6-km tropospheric layer at 70° N latitude over almost a whole year. Only in spring (April) did the wind fluxes bring heat energy from the south. The total amount of both heat and kinetic energies transported from the Arctic region in this way during a year is comparable to the mean amount of these energies contained in the whole atmosphere over the area bounded by 70° N latitude. The current spatial and temporal distributions of wind velocity and meridional mass and energy fluxes, which are presented in this study, may serve as additional information for interpreting data obtained from different on-site measurements in Arctic regions.     

西北太平洋137°E断面海流的纬向体积输送

利用日本气象厅1967－1989年间沿137°E断面观测到的水文和海流资料，计算了该断面上1°S－34°N的纬向体积输送。纬向体积输送的明显特点是复强冬弱，无论是多年平均的还是个别年份的，不管是东向输送分量还是西向输送分量，该特征都是非常明显的。净输送量有非常大的年际变化，70年代以向西输送为主，80年代则以向东输送为主，峰值出现在ElNio事件前后，二者有一定的关系。     

Meridional heat transport determined with expandable bathythermographs—Part II: South Atlantic transport

Fourteen temperature sections collected between July 2002 and May 2006 are analyzed to obtain estimates of the meridional heat transport variability of the South Atlantic Ocean. The methodology proposed in Part I is used to calculate the heat transport from temperature data obtained from high-density XBT profiles taken along transects from Cape Town, South Africa to Buenos Aires, Argentina. Salinity is estimated from Argo profiles and CTD casts for each XBT temperature observation using statistical relationships between temperature, latitude, longitude, and salinity computed along constant-depth surfaces. Full-depth temperature/salinity profiles are obtained by extending the profiles to the bottom of the ocean using deep climatological data. The meridional transport is then determined by using the standard geostrophic method, applying NCEP-derived Ekman transports, and requiring that salt flux through the Bering Straits be conserved. The results from the analysis indicate a mean meridional heat transport of 0.54 PW (PW=10¹⁵ W) with a standard deviation of 0.11 PW. The geostrophic component of the heat flux has a marked annual cycle following the variability of the Brazil Malvinas Confluence Front, and the geostrophic annual cycle is 180° out of phase with the annual cycle observed in the Ekman fluxes. As a result, the total heat flux shows significant interannual variability with only a small annual cycle. Uncertainties due to different wind products and locations of the sections are independent of the methodology used.     

Balance of Volume Transports between Horizontal Circulation and Meridional Overturn in the North Pacific Subarctic Region

Horizontal and meridional volume transports on timescales from intra-seasonal to interannual in the North Pacific subarctic region were investigated using a reanalysis dataset for 1993–2001 that was constructed from an assimilation of the TOPEX altimeter and in situ data into an eddy-permitting North Pacific ocean general circulation model. The barotropic flow is excited along east of the Emperor Seamounts by the western intensification dynamics. The volume transport of this flow compensates for that across the interior region east of the Seamounts below the summit depth of the Seamounts. The Oyashio, which is also considered as a compensation flow for the transport in the whole interior region, includes baroclinic as well as barotropic components. Baroclinic transports in the whole interior region exceed those in the western boundary region in the upper (200–1000 m) and lower (2000–5000 m) layers, and the total transport is northward (southward) in the upper (lower) layer. These excesses of the baroclinic transport are balanced by a vertical transport of the meridional overturn. The meridional overturn has a complementary relation to the basin-scale baroclinic circulation in the North Pacific subactic region. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interdecadal Variation of the Transition Zone Chlorophyll Front: A Physical-Biological Model Simulation between 1960 and 1990

The interdecadal climate variability affects marine ecosystems in both the subtropical and subarctic gyres, consequently the position of the Transition Zone Chlorophyll Front (TZCF). A three-dimensional physical-biological model has been used to study interdecadal variation of the TZCF using a retrospective analysis of a 30-year (1960–1990) model simulation. The physical-biological model is forced with the monthly mean heat flux and surface wind stress from the COADS. The modeled winter mixed layer depth (MLD) shows the largest increase between 30°N and 40°N in the central North Pacific, with a value of 40–60% higher during 1979–90 relative to 1964–75 values. The winter Ekman pumping velocity difference between 1979–90 and 1964–75 shows the largest increase located between 30°N and 45°N in the central and eastern North Pacific. The modeled winter surface nitrate difference between 1979–90 and 1964–75 shows increase in the latitudinal band between 30°N and 45°N from the west to the east (135°E–135°W), the modeled nitrate concentration is about 10 to 50% higher during the period of 1979–90 relative to 1964–75 values depending upon locations. The increase in the winter surface nitrate concentration during 1979-90 is caused by a combination of the winter MLD increase and the winter Ekman pumping enhancement. The modeled nitrate concentration increase after 1976–77 enhances primary productivity in the central North Pacific. Enhanced primary productivity after the 1976–77 climatic shift contributes higher phytoplankton biomass and therefore elevates chlorophyll level in the central North Pacific. Increase in the modeled chlorophyll expand the chlorophyll transitional zone and push the TZCF equatorward. This revised version was published online in August 2006 with corrections to the Cover Date.     

Short-term variabilities of upper ocean current in the warm pool region during TOGA/COARE IOP

Oceanic current data in the warm pool region of the western equatorial Pacific measured by upward-looking moored Acoustic Doppler Current Profilers at two equatorial sites (147°E and 154°E) and two off-equatorial sites (2°N and 2°S, 156°E) during TOGA/COARE Intensive Observing Period (IOP) from November 1992 to February 1993 are used to examine short-term variabilities in the upper layer above 160–240 m. In time series of the zonal and meridional currents in many layers, spectral peaks are found at periods around 2 days and 4 days in addition to high energies in a period range longer than 10 days. The signal with the period of about 2 days has significantly high energies at all sites, and its magnitude is higher for the meridional current than for the zonal one. This signal is especially active in the first half of IOP from November to December in 1992. In this period, the quasi-2-day signal in the current field is coherent between northern (2°N) and southern (2°S) stations, but it has no evident relationship with that in the surface wind field around the stations. The quasi-4-day signal with the period of about 4 days has highest energies in layers above 160 m at the southern station, and is coherent between northern and southern stations. Besides, the signal at the station of 2°S has a significantly high coherence with that in the wind at the southern station, suggesting that it is a local phenomenon.     

Meridional energy flux in the Arctic from data of the radiosonde archive IGRA

The meridional energy transport into high latitudes of the Northern Hemisphere is an important climate-forming factor in the Arctic. This work presents the results of calculating the meridional energy flux across 70° N based on the Integrated Global Radiosonde Archive (IGRA) data from the radio sounding of the atmosphere. The long-term mean energy flux over the period 1992–2007 in the layer from the Earth’s surface to 30 hPa is 70.6 W m^?2. The fraction of the sensible heat flux is 23.2 W m^?2, i.e., 33% of the total energy flux; the fraction of the latent heat flux is 28.0 W m^?2 (40% of the total energy flux); the fraction of the potential energy is 20.0 W m^?2 (27%); and the fraction of the kinetic energy is 0.53 W m^?2, i.e., less than 1% of the total energy flux. The vertical structure of the flux shows that the main energy transport into the Arctic takes place in the middle troposphere-lower stratosphere layer, whereas the energy is transported mainly out of the Arctic in the lower troposphere, which agrees well with the schematic notion about the polar circulation cell. The spatial structure of the flux shows that the key regions with a positive (directed into the Arctic) energy flux are located in the vicinity of 160° E (the northwestern part of Eurasia, Pacific sector) and 50° W (Greenland sector). The regions with a negative (directed out of the Arctic) energy flux are located near 120° W (Canadian Arctic Archipelago) and from 20° E to 90° E (Atlantic sector). In the period from 1992 to 2007, the meridional energy transport into the Arctic weakened by ?0.26 W m^?2 yr^?1. The changes were mutually correlated; namely, positive and negative energy fluxes weakened in amplitude, almost without changing their locations.     

Formation, Distribution and Volume Transport of the North Pacific Intermediate Water Studied by Repeat Hydrographic Observations

In order to examine the formation, distribution and transport of North Pacific Intermediate Water (NPIW), repeated hydrographic observations along several lines in the western North Pacific were carried out in the period from 1996 to 2001. NPIW formation can be described as follows: (1) Oyashio water extends south of the Subarctic Boundary and meets Kuroshio water in intermediate layers; (2) active mixing between Oyashio and Kuroshio waters occurs in intermediate layers; (3) the mixing of Oyashio and Kuroshio waters and salinity minimum formation around the potential density of 26.8σ_θ proceed to the east. It is found that Kuroshio water flows eastward even in the region north of 40°N across the 165°E line, showing that Kuroshio water extends north of the Subarctic Boundary. Volume transports of Oyashio and Kuroshio components (relative to 2000 dbar) integrated in the potential density range of 26.6–27.4σθ along the Kuroshio Extension across 152°E–165°E are estimated to be 7–8 Sv (10⁶ m³s⁻¹) and 9–10 Sv, respectively, which is consistent with recent work. This revised version was published online in July 2006 with corrections to the Cover Date.     

Study of the Kuroshio/Ryukyu Current system based on satellite-altimeter and <Emphasis Type="Italic">in situ</Emphasis> measurements

Data from satellite altimeters and from a 13-month deployment of in situ instruments are used to determine an empirical relationship between sea-level anomaly difference (SLA) across the Kuroshio in the East China Sea (ECS-Kuroshio) and net transport near 28°N. Applying this relationship to the altimeter data, we obtain a 12-year time series of ECS-Kuroshio transport crossing the C-line (KT). The resulting mean transport is 18.7 ± 0.2 Sv with 1.8 Sv standard deviation. This KT is compared with a similarly-determined time series of net Ryukyu Current transport crossing the O-line near 26°N southeast of Okinawa (RT). Their mean sum (24 Sv) is less than the mean predicted Sverdrup transport. These KT and RT mean-flow estimates form a consistent pattern with historical estimates of other mean flows in the East China Sea/Philippine Basin region. While mean KT is larger than mean RT by a factor of 3.5, the amplitude of the KT annual cycle is only half that of RT. At the 95% confidence level the transports are coherent at periods of about 2 years and 100–200 days, with RT leading KT by about 60 days in each case. At the annual period, the transports are coherent at the 90% confidence level with KT leading RT by 4–5 months. While the bulk of the Kuroshio enters the ECS through the channel between Taiwan and Yonaguni-jima, analysis of satellite altimetry maps, together with the transport time series, indicates that the effect of mesoscale eddies is transmitted to the ECS via the Kerama Gap southwest of Okinawa. Once the effect of these eddies is felt by the ECS-Kuroshio at 28°N, it is advected rapidly to the Tokara Strait.     

Variability of Upper Ocean Heat Balance in the Shikoku Basin during the Ocean Mixed Layer Experiment (OMLET)

The heat balance of the surface layer in the vicinity of the former Ocean Weather Station “Tango” (OWS-T; 29°N, 135°E), where a large amount of heat is transported by the Kuroshio and transferred to the atmosphere, was studied by during Ocean Mixed Layer Experiment (OMLET) as an oceanographic component of the Japanese World Climate Research Program (1987–1991). Temperature and velocity in the upper ocean measured using a surface moored buoy system deployed by the Ocean Research Institute, the University of Tokyo, in total 668 days of four time series namely the periods of April 1988–November 1988 (OMELET-88), August 1989–February 1990 (OMLET-89), April 1990–September 1990 (OMLET-901) and September 1990–January 1991 (OMLET-902). We have analyzed the moored buoy data of the upper 100 m for the latter three time series (OMLET-89, -901 and -902) and here we discuss the heat balance of the upper 100 m, in combination with surface heat flux and oceanographic data provided by the Japan Meteorological Agency. A large fluctuation of oceanic heat convergence/divergence of 200–300 W/m² in amplitude with predominant period of 20–30 days occurred in the first half of OMLET-89 period, which was just the early stage in the formation process of a large meander path of the Kuroshio. A large amount of heat convergence of 71 and 79 W/m² on average was detected in observation period of OMLET-89 and -901, respectively. During OMLET-902, relatively small heat convergence of 13 W/m² was obtained. It is suggested that these variations of oceanic heat convergence in this region were closely related to the fluctuation of the Kuroshio axis to the south of Japan. This revised version was published online in July 2006 with corrections to the Cover Date.