Iwao Ueki

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...

Upper-Ocean Salinity Variability in the Tropical Pacific: Case Study for Quasi-Decadal Shift during the 2000s Using TRITON Buoys and Argo Floats

AbstractUpper-ocean salinity variation in the tropical Pacific is investigated during the 2000s, when Triangle Trans-Ocean Buoy Network (TRITON) buoys and Argo floats were deployed and more salinity data were observed than in previous periods. This study focuses on upper-ocean salinity variability during the warming period of El Nino–Southern Oscillation (ENSO)-like quasi-decadal (QD)-scale sea surface temperature anomalies over the central equatorial Pacific (January 2002–December 2005; hereafter “warm QD phase”). It is shown that strong negative salinity anomalies occur in the western tropical Pacific and the off-equatorial Pacific in the upper ocean at depths less than 80 m, showing a horseshoe-like pattern centered at the western tropical Pacific during the warm QD phase. TRITON mooring buoy data in the western equatorial Pacific show that low-salinity and high-temperature water could be transported eastward from the western equatorial Pacific to the central equatorial Pacific during the warm QD phase...

Data Evaluation for a Newly Developed Slack-Line Mooring Buoy Deployed in the Eastern Indian Ocean

Abstract For the purpose of climate research and forecasting the Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction (RAMA) in the Indian Ocean has been planned. Development of RAMA has been gradually accelerated in recent years as a multinational effort. To promote RAMA the authors have developed a small size buoy system, which uses the slack-line mooring method, intended for the easy handling of maintenance on a relatively small vessel. The authors have also conducted a field experiment of the simultaneous deployment of new slack-line mooring and conventional taut-line mooring in the eastern Indian Ocean. This paper describes the performance of the newly developed buoy system, especially the data consistency against the taut-line mooring system, which is usually used for a tropical moored buoy array. Although the slack-line mooring method has the advantage of downsizing the total mooring system, it also has the disadvantage of having relatively large vertical shifts of ins...

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.

Quasi-2-Day Signals Observed in the Warm Pool Region during TOGA/COARE IOP

During Tropical Ocean and Global Atmosphere (TOGA)/Coupled Ocean and Atmosphere Research Experiment (COARE) Intensive Observing Period (IOP), upward-looking acoustic Doppler current profilers (ADCP) and current meters were moored at two equatorial sites (147°E and 154°E) and two off-equatorial sites (2°N and 2°S, 156°E) in the warm pool region of the western equatorial Pacific. Using current data obtained by these moorings, we have shown that there is a dominant signal with a period of about 2 days from the end of November to the middle of December in 1992, except at the equatorial site on 147°E (Ueki et al., 1998). The energy of this quasi-2-day signal for the meridional current is larger than that for the zonal one and the signal has a high coherence between two off-equatorial sites. In this paper, using band-passed time series of the meridional curerent, we investigated characters of the quasi-2-day signal and attempted to interpret this signal as an equatorially trapped wave. Complex empirical orthogonal function (CEOF) analysis reveals two different phase propagating features between the equatorial and off-equatorial site. One is an upward propagating signal, which is dominant near the surface at two off-equatorial sites, and the other is a downward propagating signal, which is dominant near 200 m at the equatorial site. If one interprets the quasi-2-day signal as an equatorially trapped wave, it is suggested that it cannot be explained as a single wave but can be described as the superimposition of several wave signals. The main part of these signals consists of two signals, one caused by a meteorological forcing and another by another factor in the ocean field.