Yoshifumi Kuroda

Mismo field experiment in the equatorial Indian Ocean

The Mirai Indian Ocean cruise for the Study of the Madden-Julian oscillation (MJO)-convection Onset (MISMO) was a field experiment that took place in the central equatorial Indian Ocean during October–December 2006, using the research vessel Mirai, a moored buoy array, and landbased sites at the Maldive Islands. The aim of MISMO was to capture atmospheric and oceanic features in the equatorial Indian Ocean when convection in the MJO was initiated. This article describes details of the experiment as well as some selected early results. Intensive observations using Doppler radar, radiosonde, surface meteorological measurements, and other instruments were conducted at 0°, 80.5°E, after deploying an array of surface and subsurface moorings around this site. The Mirai stayed within this buoy array area from 24 October through 25 November. After a period of stationary observations, underway meteorological measurements were continued from the Maldives to the eastern Indian Ocean in early December. All observatio...

Variability of Currents off the Northern Coast of New Guinea

The variability of the New Guinea Coastal Current (NGCC) and New Guinea Coastal Undercurrent (NGCUC) were examined from one year time series of current data from ADCP moorings at 2°S, 142°E and 2.5°S, 142°E. Change in the hydrographic structure induced by monsoonal wind forcing was also examined from hydrographic data along the 142°E covering consecutively two winter seasons and two summer seasons. The westward NGCUC was observed to persist year around. The annual mean depth of the current core was 220 m, the mean speed of the zonal component was 54 cm/s with a standard deviation of 15 cm/s at the 2.5°S site. Velocity fluctuations at 20–30 day period were observed year around. Seasonal reversal of the surface intensified NGCC was clearly observed. In the boreal summer characterized by the southeasterly monsoon, westward currents of over 60 cm/s were dominant in the surface layer. The warm, low-salinity layer thickened at this time and sloped down toward the New Guinea coast from the equator. This surface water accumulation may be caused by onshore Ekman drift at the New Guinea coast, combined with weak Ekman upwelling at the equator. In the boreal winter, an eastward surface current developed to 100 cm/s extending down to 100 m depth in response to the northwesterly monsoonal winds. Coastal upwelling was indicated in this season and the surface water accumulated at the equator due to Ekman convergence. Shipboard ADCP data indicated that the NGCUC intensified in boreal summer as the width and depth of the NGCUC increased.

Drift Characteristics of a Moored Conductivity–Temperature–Depth Sensor and Correction of Salinity Data

Abstract The temperature and conductivity drift (time change of the characteristics) of moored SBE37IM conductivity and temperature (CT) sensors was investigated by pre- and postdeployment calibration of the Triangle TransOcean Buoy Network (TRITON). This buoy network comprises the western portion of the basinwide (Tropical Atmosphere Ocean) TAO/TRITON buoy array, which monitors phenomena such as El Nino and contributes to forecasting climate change. Over the time of deployment the drift of the temperature sensors was very small, within 3 mK of the postdeployment calibration data. The drift of the conductivity sensors was more significant. After 1 yr of mooring, conductivity drift observed in the shallowest layer (1.5–100 m) was positive and 0.010 S m−1 [equivalent to 0.065 (PSS-78) at 30°C and 6 S m−1; here, 1 S is 1 Ω−1] at 6 S m −1 on average. Drift observed in the thermocline layer (125–200 m) was also positive and 0.0053 S m−1 [0.034 (PSS-78)] at 6 S m−1 on average. Conversely, the drift of conductiv...

Observation of internal tides in the East China Sea with an underwater sliding vehicle

Detailed structures of internal tides in the East China Sea were observed during autumn from 1986 to 1989, using an underwater sliding vehicle that can measure temperature, conductivity, and depth continuously, sliding up and down along a faired cable. A variety of structures were observed and are classified with internal Froude numbers of the lowest two modes, which depend on the barotropic tidal current velocities and the phase speeds of internal waves (i.e., stratification). In the central East China Sea, the second-mode waves are most strongly generated at the shelf break and then propagate shoreward onto the East China Sea continental shelf. Since the barotropic tidal current is faster than the phase speed of the second-mode waves on the shelf, the generation mechanism is consistent with conventional models. On the other hand, in the southern East China Sea the lowest-mode response is dominant, although the tidal current velocity is slower than the lowest-mode phase speed. A nonlinear model is proposed for this response.

A comparison of buoy meteorological systems

Funding was provided by the National Oceanic and Atmospheric Administration under Grant Number NA96GPO429.

Variability and Linkages of New Guinea Coastal Undercurrent and Lower Equatorial Intermediate Current

Abstract Velocity at depths of 700–800 m was measured between September 1998 and October 2002 at 2.5°S, 142°E off the New Guinea coast and at 0°, 138°E to examine the New Guinea Coastal Undercurrent (NGCUC) and the current on the equator carrying Antarctic Intermediate Water (AAIW). Velocity characteristics before November 1999 were markedly different from those after November 1999. The typical state occurred during the second period: the intermediate NGCUC and the Lower Equatorial Intermediate Current (LEIC) varied markedly with an annual cycle in opposite phases. In austral winter, the NGCUC flowed west-northwestward strongly (14 cm s−1, 285°T), especially in May–July during which the LEIC disappeared and eddylike equatorial variations with periods of 20–60 days were significant. In austral summer, the LEIC flowed westward strongly (12 cm s−1, 270°T), especially in October–December, whereas the NGCUC reversed its direction repeatedly to flow east-southeastward in November–February. Thus, the intermediat...

Two Modes of Salinity and Temperature Variation in the Surface Layer of the Pacific Warm Pool

The characteristics of temperature and salinity variation in the Pacific warm pool were investigated using Empirical Orthogonal Function (EOF) analysis on one years temperature and salinity data in the surface layer (0–50 m) obtained from the Triangle Trans-Ocean Buoy Network (TRITON) buoy array. Two dominant modes of surface temperature and salinity variation were found. One is a positive correlation mode where temperature and salinity were scattered almost parallel to isopycnal lines in a T-S diagram, which has little effect on the density field. The other is a negative correlation mode where temperature and salinity were distributed across isopycnal lines, which has a substantial impact on the density field. In particular, we found that the negative correlation mode at 5°N, 156°E was predominant on a seasonal time scale and contributed to the surface dynamic height variation, and therefore to surface geostrophic current.

Hydrographic profiling across the East China sea shelf edge by an underwater sliding vehicle with CTD sensors

Temperature, salinity and density structures were observed on Sept. 23 and 24, 1986 at one vertical section across the East China Sea shelf edge by an advanced type of towed vehicle with CTD sensors which was developed by the Japan Marine Science and Technology Center. The vehicle was towed at a speed of 2.5 m s−1 down to 150 m depth and at intervals of 170–500 m width. The observed profile was 50 km long on Sept. 23 and 70 km long on Sept. 24 along the cross-shelf section. An on-ship acoustic Doppler current profiler was simultaneously used to measure current velocities at depths of 20, 50 and 100 m. Interesting features were noticed. Firstly, there was a vertical displacement of pycnoclines at the lower edge of the surface mixed layer accompanied by vertical inversion of the salinity and temperature in the vicinity of the shelf edge. Pycnoclines were displaced upward by 12 m toward the outer edge on Sept. 23 and by 20 m on Sept. 24. On Sept. 23, the salinity inversion took place in a layer 20 m thick and 8 km wide, whereas the temperature inversion took place in a layer 8 m thick and 1.5 km wide. These vertical inversions were probably generated by vertical shear of tidal currents which was observed by the Doppler current profiler. These results throw light on understanding the vertical mixing process of stratified water on the continental shelf edge. Secondly, an intrusion of the shelf water into the Kuroshio water was observed along pycnoclines below the surface mixed layer 60 to 70 m deep in the Kuroshio region outer break. The measurement was successful in showing a horizontal mixing process of the shelf water and the Kuroshio water which could not be found out by standard CTD observations.