Triangle Trans-Ocean Buoy Network Research Articles

Tropical Ocean Observations for Weather and Climate: A Decadal Overview of the Global Tropical Moored Buoy Array

This paper describes the evolution of the Global Tropical Moored Buoy Array (GTMBA) over the past decade since the last comprehensive and coordinated overview of the Pacific-Atlantic-Indian Ocean system in 2010. GTMBA provides sustained and systematic observations in real time for weather and climate research, forecasting, and assessments. It is maintained through multi-national consortia that support the Tropical Atmosphere Ocean (TAO) Array and the Triangle Trans-Ocean Buoy Network (TRITON) in the Pacific, the Prediction and Research Moored Array in the Tropical Atlantic (PIRATA), and the Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) in the Indian Ocean. Phenomena of interest span a wide range of weather and climate timescales, including tropical cyclones, the Madden-Julian Oscillation, the seasonal cycle, monsoon circulations, El Niño-Southern Oscillation, climate variations on decadal timescales, and trends related to climate change. Recent scientific advances enabled by GTMBA are reviewed along with array design changes that respond to new scientific imperatives and operational exigencies, and future directions are discussed.

Are ocean-moored buoys redundant for prediction of Indian monsoon?

The Tropical Atmosphere Ocean (TAO) and Triangle Trans-Ocean Buoy Network (TRITON) buoys deployed in the tropical Pacific play a significant role in monitoring tropical Pacific conditions such as El-Nino/La-Nina in real-time. Earlier studies have illustrated the importance as well as irrelevance of moored buoy observations towards the prediction of sea surface temperature in the tropical Pacific Ocean. With the advent of Argo floats, have these moored buoy observations become redundant? In the present study, we address this question in the context of Indian summer monsoon rainfall (ISMR) prediction. The extreme monsoon year of 2018 was selected to test the above hypothesis. Without moored buoy observations being assimilated, the oceanic initial conditions and the seasonal forecasts had large oceanic temperature errors and forecasted a normal monsoon instead of a below-normal monsoon during 2018. Therefore, moored buoy observations are essential and should be assimilated to get realistic Pacific sea surface temperature (SST) and accurate ISMR predictions.

Validation of different global data sets for sea surface wind-stress

ABSTRACT Different surface wind-stress products over the global ocean were validated by comparing with in-situ measurements from moored buoys, and by inter-comparing among them. The products are ones constructed from satellite observations by microwave scatterometers and radiometers, and reanalysed ones by data assimilation and numerical models. Comparisons with buoy measurements revealed that the Cross-Calibrated Multi-Platform Version 2 (CCMP v2.0) has the lowest positive bias, the smallest root mean square error (RMSE) and the largest correlation coefficient in this inter-comparison, meaning that the CCMP v2.0 gives the best performance. Inter-comparisons among the different wind-stress products exhibited that the meridional wind-stress data of the National Centre for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) are not different in the subtropical region from those of other ones, and zonal and meridional wind-stress data of the National Centre for Environmental Prediction/Climate Forecast System Reanalysis (NCEP/CFSR) have relatively low values in the westerly region. In the zonal-spectral analysis, we found that the zonal wind-stress/wind-vector data from the Institut Français de Recherche pour la Recherche et l’Exploitation de la Mer (IFREMER) have short wave-like oscillations. Thus, the surface wind and wind-stress data in IFREMER products have been well affected by spatial resolution of background data used in their gridding procedure. We also investigated the spatial characteristics of wind-stress curl fields for the different data sets, and found that there are differences between the CCMP v2.0 and Japanese Ocean Flux Data sets with Use of Remote Sensing Observations Version 3 (J-OFURO3) which are characterized by spike-like features in the equatorial Pacific where there are the Tropical Atmosphere Ocean and the TRIangle Trans-Ocean buoy Network (TAO/TRITON) buoys. These features were spatially correlated with buoy locations, which suggests that the reliability of the CCMP v2.0 products is governed by buoy locations in this region.

Temperature and salinity variability at intermediate depths in the western equatorial Pacific revealed by TRITON buoy data

We investigated ocean variability at intermediate depths (300–750 m) in the western equatorial Pacific (WEP) using data from underwater sensors of the Triangle Trans-Ocean Buoy Network (TRITON) buoys. The data were specially processed because high accuracy is necessary for such an application, and we confirmed that sufficient accuracy was achieved. Variability of the temperature and salinity was large in the western boundary regions of the WEP. Seasonal variability is generally dominant at intermediate depths in the WEP; however, intraseasonal variability with period of 30–80 days is not negligible, particularly at 2°N, 138°E, where the New Guinea Coastal Undercurrent retroflects to the east as the Equatorial Undercurrent and/or Northern Subsurface Countercurrent. High correlation is seen between 12-month running means of the Nino 3.4 index anomaly and temperature at 300 and 750 dbar. In other words, the influence of El Nino/Southern Oscillation phenomena reaches to at least a depth of 750 dbar. We found a decreasing trend in salinity at intermediate depths in the WEP: − 0.0032 Practical Salinity Unit (PSU) year−1 at 300 dbar and − 0.00053 PSU year−1 at 750 dbar. This trend is likely associated with the freshening of the North Pacific Intermediate Water and Antarctic Intermediate Water.

The Role of Buoy and Argo Observations in Two SST Analyses in the Global and Tropical Pacific Oceans

Abstract The relative roles of buoy and Argo observations in two sea surface temperature (SST) analyses are studied in the global ocean and tropical Pacific Ocean over 2000–16 using monthly Extended Reconstructed SST version 5 (ERSSTv5) and Daily Optimum Interpolation SST version 2 (DOISST). Experiments show an overall higher impact by buoys than Argo floats over the global oceans and an increasing impact by Argo floats. The impact by Argo floats is generally larger in the Southern Hemisphere than in the Northern Hemisphere. The impact on trends and anomalies of globally averaged SST by either one is small when the other is used. The warming trend over 2000–16 remains significant by including either buoys or Argo floats or both. In the tropical Pacific, the impact by buoys was large over 2000–05 when the number of Argo floats was low, and became smaller over 2010–16 when the number and area coverage of Argo floats increased. The magnitude of El Niño and La Niña events decreases when the observations from buoys, Argo floats, or both are excluded. The impact by the Tropical Atmosphere Ocean (TAO) and Triangle Trans-Ocean Buoy Network (TRITON) is small in normal years and during El Niño events. The impact by TAO/TRITON buoys on La Niña events is small when Argo floats are included in the analysis systems, and large when Argo floats are not included. The reason for the different impact on El Niño and La Niña events is that the drifting buoys are more dispersed from the equatorial Pacific region by stronger trade winds during La Niña events.

Fifteen years progress of the TRITON array in the Western Pacific and Eastern Indian Oceans

The Triangle Trans‐Ocean Buoy Network (TRITON) project by the Japan Agency for Marine-Earth Science and Technology began with deployment in the western tropical Pacific Ocean in 1998 and has shifted to steady, long-term observations since 1999. After on-site inter-comparison with the Autonomous Temperature Line Acquisition System mooring system of the Tropical Atmosphere and Ocean (TAO) array by the National Oceanic and Atmospheric Administration, the TRITON array became the international TAO/TRITON array in 2000 as a key component of the Global Ocean and Climate Observing Systems. The TAO/TRITON array took over from the TAO array, which was developed during the Tropical Ocean and Global Atmosphere program (1985–1994), and replaced the western part of TAO with new additional real-time measurements of salinity and ocean currents. In 2001, two TRITON moorings were deployed in the eastern Indian Ocean for capturing the eastern pole of the Indian Ocean Dipole. From this initiative, the Indian Ocean Observing System (IndOOS) was designed, and the Indian Ocean mooring array (Research Moored Array for Africa–Asian–Australian Monsoon Analysis and Prediction) was developed as a key component of IndOOS. In this paper, 15 years of progress in the TRITON project in the western Pacific and eastern Indian Oceans is reviewed with regards to scientific outcomes, technological development, and collaborations with international and domestic partners. Future directions for sustainable observation in the Pacific and Indian Oceans are also discussed.

Evaluation of the Tropical Pacific Observing System from the ocean data assimilation perspective

The drastic reduction in the number of observation data from the Tropical Atmospheric Ocean (TAO)/Triangle Trans‐Ocean Buoy Network (TRITON) array since 2012 has given rise to a need to assess the impact of those data in ocean data assimilation (DA) systems. This article provides a review of existing studies evaluating the impacts of data from the TAO/TRITON array and other components of the Tropical Pacific Observing System (TPOS) on current ocean DA systems used for a variety of operational and research applications. It can be considered as background information that can guide the evaluation exercise of TPOS. Temperature data from TAO/TRITON array are assimilated in most ocean DA systems which cover the tropical Pacific in order to constrain the ocean heat content, stratification, and circulation. It is shown that the impacts of observation data depend considerably on the system and application. The presence of model error often makes the results difficult to interpret. Nevertheless there is consensus that the data from TAO/TRITON generally have positive impacts complementary to Argo floats. In the equatorial Pacific, the impacts are generally around the same level or larger than those of Argo. We therefore conclude that, with the current configuration of TPOS, the loss of the TAO/TRITON data is having a significant detrimental impact on many applications based on ocean DA systems. This conclusion needs to be kept under review because the equatorial coverage by Argo is expected to improve in the future.

Evaluation of sea surface temperature and wind speed observed by GCOM-W1/AMSR2 using in situ data and global products

The Global Change Observation Mission (GCOM) 1st-Water (GCOM-W1) satellite, equipped with the Advanced Microwave Scanning Radiometer 2 (AMSR2), was launched on May 18, 2012, by the Japan Aerospace Exploration Agency (JAXA), and began observing on July 3, 2012. In this study, we evaluated the sea surface temperature (SST) and sea surface wind speed (SSW) data from the AMSR2 (ver. 1) standard product, provided by JAXA, by comparison with mooring buoy data or global products. From a comparison of the AMSR2 and Triangle Trans-Ocean Buoy Network (TRITON) data, mean differences of 0.21°C and 0.30m/s, and root mean square (RMS) differences of 0.49°C and 1.25m/s, were inferred for SST and SSW, respectively. During daytime low wind-speed conditions, SSTs from AMSR2 are significantly higher than from TRITON. This implies that SSTs from AMSR2 are strongly affected by diurnal heating. From an intercomparison of global products for the Southern Ocean, the annual-mean SSW from AMSR2 is as much as 1m/s lower than values from other SSW products. Although the SSW data from AMSR2 have a similar accuracy to data from other products, the AMSR2 data have the advantage of fewer missing data compared with other products. Furthermore, we checked for significant differences in annual means by comparing data from WindSat, AMSR2, and AMSR for the Earth Observing System (AMSR-E) provided by JAXA. For the Southern Ocean, we found remarkable differences in the annual-mean values of SST and SSW. SSTs from AMSR2 are lower than from WindSat in regions of strong current in the Northern Hemisphere, and SSTs from AMSR-E JAXA are higher than from WindSat in the same regions. However, the results also suggest a risk of artificial trends in the satellite data if AMSR2, AMSR-E JAXA, and WindSat data are used continuously.

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

Abstract Upper-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 Niño–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. Similar patterns, but with the opposite sign of salinity anomalies, appear in the cold QD phase during January 2007–December 2009 with negative sea surface temperature anomalies over the central equatorial Pacific. It is suggested that effects from zonal salinity advection and precipitation could contribute to the generation of the salinity variations in the western equatorial Pacific for QD phases during the 2000s. On the other hand, the contribution of meridional salinity advection is much less than that of zonal salinity advection. In addition, El Niño Modoki and La Niña events could affect salinity changes for warm and cold QD phases via interannual-scale zonal salinity advection variations in the western equatorial Pacific during the 2000s.

Wavenumber–Frequency Spectra of Inertia–Gravity and Mixed Rossby–Gravity Waves in the Equatorial Pacific Ocean

Abstract In the 1970s and 1980s, there was considerable interest in near-equatorial variability at periods of days to weeks associated with oceanic equatorial inertia–gravity waves and mixed Rossby–gravity waves. At that time, the measurements available for studying these waves were much more limited than today: most of the available observations were from scattered island tide gauges and a handful of short mooring records. More than a decade of the extensive modern data record from the Tropical Atmosphere Ocean (TAO)/Triangle Trans-Ocean Buoy Network (TRITON) mooring array in the Pacific Ocean is used to reexamine the internal-wave climate in the equatorial Pacific, with a focus on interpretation of the zonal-wavenumber/frequency spectrum of surface dynamic height relative to 500 decibars at periods of 3–15 days and zonal wavelengths exceeding 30° of longitude. To facilitate interpretation of the dynamic height spectrum and identification of equatorial wave modes, the spectrum is decomposed into separate spectra associated with dynamic height fluctuations that are symmetric or antisymmetric about the equator. Many equatorial-wave meridional modes can be identified, for both the first and second baroclinic mode. Zonal-wavenumber/frequency spectra of the zonal and meridional wind stress components are also examined. The observed wind stress spectra are used with linear theory of forced equatorial waves to provide a tentative explanation for the zonal-wavenumber extent of the spectral peaks seen in dynamic height. Examination of the cross-equatorial symmetry properties of the wind stress suggests that virtually all of the large-scale equatorial inertia–gravity and mixed Rossby–gravity waves examined may be sensitive to both zonal and meridional wind stress.

Comparison of Oceansat-2 scatterometer winds with buoy observations over the Indian Ocean and the Pacific Ocean

Oceansat-2 scatterometer (OSCAT)-derived winds were compared with in situ observations made by Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction (RAMA) and Triangle Trans-Ocean Buoy Network (TRITON) buoys in the Indian Ocean and the Pacific Ocean, respectively. Root mean square deviation (RMSD) for wind speed is 1.71 m s−1 for the Indian Ocean and 1.92 m s−1 for the Pacific Ocean. The wind speed accuracies are within the mission requirement (<2 m s−1), but the wind direction errors are higher than the mission requirement (>20°). The RMSD values of wind direction are 51.38° and 44.61° for the Indian Ocean and the Pacific Ocean, respectively. OSCAT winds tend to underestimate the buoy value when the wind speeds were low (<4 m s−1) and overestimate the buoy value when the wind speeds were high (>4 m s−1). The wind speed residuals show an increasing trend with the increase of wind speeds. Interestingly, the wind direction residuals decrease with increasing wind speed and deviations of wind directions are conspicuously large for lower wind speeds than for higher wind speeds. OSCAT wind speeds were relatively more accurate for the Indian Ocean than those for the Pacific Ocean.

Observed Ocean Variability in the Mindanao Dome Region

Abstract Ocean variations at semiannual, annual, and interannual time scales in the Mindanao Dome (MD) region of the southern Philippine Sea were examined using data derived from underwater sensors on Triangle Trans-Ocean Buoy Network (TRITON) buoys at 8°N, 137°E; 5°N, 137°E; and 8°N, 130°E. Annual signal dominated above 300-m depth in the MD region. At 5°N, 137°E, saline water exceeding 35 psu was observed at 100–200-m depth from boreal winter to spring, seemingly associated with the meridional migration of the North Equatorial Countercurrent during these seasons. Thermocline ascent, probably related to the MD, was also observed from boreal winter to spring. An important mechanism of the annual variation of the MD at 5°N seems to be the annual variability of local wind, as mentioned in past studies. However, annual variability at 8°N seems to be due to Rossby waves originating west of 150°W rather than to local wind effects. Semiannual variation was also observed, with its amplitude reaching 40%–70% of the annual signal. With regard to interannual variability, ocean variation on the time scale of the El Niño–Southern Oscillation (ENSO) was seen; upper heat content (above 300-m depth) in the Mindanao Dome region decreased during the 2002–03 and 2006–07 El Niño periods and increased between those periods. Increasing upper heat content in this region after 2005 was probably associated with large negative anomalies of Ekman pumping (downwelling) that appeared from 2005 to 2006 east of 150°E and north of 5°N.

Coastal upwelling along the north coast of Papua New Guinea and SST cooling over the pacific warm pool: A case study for the 2002/03 El Niño event

We investigate an overlooked mechanism—coastal upwelling—for sea surface temperature (SST) cooling in the western side of the mean location of the Pacific warm pool (WSWP: 5°S–5°N, 140°E–150°E) prior to El Nino onset. We analyze various observed data such as the TRIangle Trans-Ocean buoy Network (TRITON) moored buoy data, Conductivity-Temperature-Depth (CTD) data, satellite data and a hindcast experiment output by a high-resolution ocean general circulation model (OGCM). We focus on the precondition of the 2002/03 El Nino event, for which many datasets are available. Relatively cool water upwelled along the north coast of Papua New Guinea (PNG) during December 2001, prior to the onset of the 2002/03 El Nino event, and then spread out over a wider area to the northeast. Simultaneously, strong west-northerly surface winds occur along the north coast. Heat budget analysis of TRITON buoy data in the WSWP reveals that negative zonal heat advection due to eastward current is the main factor for cooling the mixed layer in the WSWP in contrast to the warming effect of the surface heat flux during the period. This cooling requires a source of colder water to the west. Similar analysis of OGCM outputs also suggests that the upwelled relatively cool water along the PNG north coast, and its northeastward extension to the equatorial region, contributes to cooling of the surface water over the WSWP mainly via negative zonal heat advection. Similar mechanisms are confirmed also for the 1982/83 and 1997/98 El Nino events by analyses of OGCM outputs and historical SST data. The low SST in the WSWP generated a positive zonal SST gradient together with high SST east of the WSWP. It may contribute to enhancement of the westerly surface wind in this region, leading to the onset of the 2002/03 El Nino event.

A New High-Resolution Satellite-Derived Precipitation Dataset for Climate Studies

Abstract The importance of analyzing climate at high spatiotemporal resolution has been emphasized in the recent Intergovernmental Panel on Climate Change (IPCC) report. Several high-resolution analyses of global precipitation have recently been created to meet this need by combining high-quality passive microwave estimates with frequently sampled geosynchronous infrared estimates. A new daily 0.25° analysis has been developed at the Cooperative Institute for Climate Studies (CICS), called the CICS High-Resolution Optimally Interpolated Microwave Precipitation from Satellites (CHOMPS), which is based only on passive microwave satellite estimates. The analysis was developed using all available sensors and the most up-to-date common retrieval scheme. An important advantage of CHOMPS is, therefore, its consistency. The microwave estimates from the different sensors at hourly time scales are combined using optimum interpolation (OI), using estimates of the noise and spatial correlation scales and standardized analysis weights. This technique reduces the random errors while still capturing the tails of the distribution of precipitation and provides estimates of output error based on the noise-to-signal ratio of the inputs. Hourly values are combined to produce a daily average and error estimate. Evaluation of CHOMPS against surface-based observational data, such as the stage IV radar and the Tropical Atmosphere Ocean (TAO)/Triangle Trans-Ocean Buoy Network (TRITON) gauges, indicates that CHOMPS performs well, especially when compared to other high-resolution products. This analysis, therefore, highlights OI as a feasible methodology for the creation of a high-resolution precipitation product. The analysis begins in 1998 and has thus far been continued through 2007, making it a useful dataset to examine intraseasonal variability. When the period of the data becomes long enough, it will prove to be a useful dataset to study longer modes of climate variability.

Observed and CAM3 GCM Sea Surface Wind Speed Distributions: Characterization, Comparison, and Bias Reduction

Abstract Climatological surface wind speed probability density functions (PDFs) estimated from observations are characterized and used to evaluate, for the first time, contemporaneous wind PDFs predicted by a GCM. The observations include NASA’s global Quick Scatterometer (QuikSCAT) dataset, the NCEP/Department of Energy Global Reanalysis 2 (NCEP-2) 6-hourly reanalysis, and the Tropical Atmosphere Ocean (TAO)/Triangle Trans-Ocean Buoy Network (TRITON) moored buoy data, all from 2000 to 2005. Wind speed mean, 90th percentile, standard deviation, and Weibull shape parameter climatologies are constructed from these data. New features that emerge from the analysis include the identification of a stationary pattern to the wind speed variance in the equatorial Pacific. Interestingly, a distinct wind speed shape anomaly migrates with the ITCZ across this stationary background. The GCM despite its coarser spatial and temporal resolution predicts wind speed PDFs in general agreement with observations. Relative to QuikSCAT, the NCAR Community Atmosphere Model, version 3 (CAM3) GCM has a globally averaged positive mean wind speed bias of about 0.2 m s−1 originating primarily within the trades and Southern Hemisphere storm track. Global standard deviation biases are largest in the winter hemisphere storm tracks. The largest shape biases occur along the equatorial peripheries of the Northern Hemisphere and southern Indian Ocean anticyclones. Year-round negative shape and mean wind speed biases persist along the ITCZ. The GCM’s overactive tropical convection and slight subtropical anticyclone displacement contribute to positive mean speed, standard deviation, and shape trade biases. Surface heat and energy fluxes depend nonlinearly on wind speed magnitude, are sensitive to the tails of the wind distribution, and hence vary significantly on spatiotemporal scales not resolved by GCMs. Limited computing resources force the use of coarse-resolution GCMs, which do not resolve finer-scale wind speed fluctuations. Rather, surface fluxes are determined from the mean wind speed computed by averaging spatially and temporally over subgrid-scale features. Some surface flux routines account for gustiness during low mean winds resulting from thermally driven convection. The authors hypothesize that GCMs systematically underestimate surface momentum flux nonlinearities and that this biases surface wind predictions most in regions of strong winds with high variability. To test this, climate simulations that account for surface fluxes due to subgrid-scale GCM winds are performed. This significantly improves climatological surface wind speed statistics, particularly in the Southern Hemisphere storm track, consistent with the hypothesis. These wind speed improvements can be attributed to a reduction in GCM sea level pressure biases throughout the globe.

In-situ diurnal sea surface temperature variations and near-surface thermal structure in the tropical hot event of the Indo-Pacific warm pool

Diurnal Sea Surface Temperature (SST) variations and the near-surface thermal structure of the tropical hot event (HE) have been investigated using advanced in-situ equatorial observations with hourly temporal resolution. The information on the HE area defined by the satellite cloud-free SSTs is used to sample the in-situ observations. The in-situ SSTs sampled for the HE conditions show that a maximum (minimum) SST has a histogram mode at 30.8°C (29.0°C), and frequently appears at 15:00 (07:00) local time. The amplitude of the diurnal SST variation (DSST) is defined by the difference between the maximum and minimum SSTs. The mean DSST during HEs is greater than 0.5°C, and has a maximum of about 0.75°C at the HE peak. The time series of mean DSST gradually increases (rapidly decreases) before (after) the peak. The satellite SST has a systematic positive bias against the corresponding daytime SST measured by the Triangle Trans-Ocean buoy Network. This bias is enhanced under conditions of large in-situ DSST. One-dimensional numerical model simulation suggests that the systematic bias is caused by the sharp vertical temperature gradient in the surface layer of HE. The near-surface thermal structure is generated by conditions of high insolation and low wind speed, which is the typical HE condition.

Semiannual variability in temperature and salinity observed by Triangle Trans‐Ocean Buoy Network (TRITON) buoys in the eastern tropical Indian Ocean

The time series of temperature and salinity obtained by Triangle Trans‐Ocean Buoy Network buoys in the eastern Indian Ocean was used to investigate the characteristics of their variations and possible mechanisms of the semiannual ocean variability. Spectral analysis indicates that the dominant temperature signals in the surface layer and below the thermocline have intraseasonal and semiannual timescales, respectively. The semiannual isotherm deepening in the thermocline appears clearly during the monsoon transition periods, and indicates the vertical phase shift below the thermocline. The characteristic speed of the wave estimated from the vertical phase shift corresponds to a value between the characteristic speeds of the second and third baroclinic modes. The correlation between the zonal surface wind stress on the equator and the depth of 20°C isotherm variation shows that the forcing region of the semiannual isotherm variation is located around 68°E to 78°E longitude. The estimation of characteristic speed from the lag between these variations also shows a value between the second and third vertical‐mode gravity waves. The salinity variations also indicate that the intraseasonal and semiannual signals are dominant in the surface layer and the thermocline, respectively. The appearance of salty water around the upper thermocline lags the subsurface zonal current variation by about 45 days on the semiannual timescale, suggesting the advection of salty water by the subsurface currents along the equator. There is a possibility that the contact between the subsurface salty water and surface fresh water results in the formation of a barrier layer in the eastern basin.

A monthly mean dataset of global oceanic temperature and salinity derived from Argo float observations

We produced a global monthly dataset of temperature and salinity using data from Argo floats, Triangle Trans-Ocean Buoy Network (TRITON), and available conductivity-temperature-depth (CTD) casts. The Argo project started from 2000, and the number of floats is increasing yearly throughout the global ocean. The Argo floats observe pressure, temperature and salinity from the sea surface down to 2000 dbar and enable the production of monthly global datasets of temperature and salinity. We have created Grid Point Value of the Monthly Objective Analysis using Argo float data (MOAA GPV) that contains optimally interpolated temperature and salinity values at selected standard pressure levels on a 1˚ grid in the global ocean. The dataset is freely available on the Argo website of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) at http://www.jamstec.go.jp/ARGO/J_ARGOe.html.

Ocean variability North of New Guinea derived from TRITON buoy data

We investigated variability in the ocean surface-subsurface layer north of New Guinea using Triangle Trans-Ocean Buoy Network (TRITON) buoys at 2°N, 138°E and 0°N, 138°E during the period from October 1999 to July 2004. Both North and South Pacific waters were observed below the subsurface at these stations. The variability in the subsurface waters was particularly high at 2°N, 138°E. Clear interannual variability occurred near the surface; the water type differed before and after onset of the 2002–03 El Nino. Before summer 2001, water that appeared to be advected from the central equatorial Pacific occupied the near surface layer. After autumn 2001, waters advected by the New Guinea Coastal Current were observed near the surface. Intraseasonal and seasonal variations were also observed below the subsurface. With regard to seasonal variability, the salinity of the subsurface saline water, the South Pacific Tropical Water, was generally high during the boreal summer-autumn, when the New Guinea Coastal Undercurrent was strong. Intraseasonal fluctuations on a scale of 20 to 60 days were also seen and may have been associated with intrinsic oceanic variability, such as ocean eddies, near the stations. Ocean variability in the thermocline layer between 100 and 200 m greatly affects the surface dynamic height variability; water variability before 2001 and variability in the pycnocline depth after 2002 are important factors affecting the thermocline.

Sub-seasonal variance of surface meteorological parameters in buoy observations and reanalyses

[1] Tropical Atmosphere Ocean (TAO)/Triangle Trans-Ocean Buoy Network (TRITON) and Eastern Pacific Investigation of Climate (EPIC) moorings across the equatorial Pacific are used to evaluate the mean climate and sub-seasonal variance in surface meteorological variables in the NCEP/NCAR, NCEP/DOE, and ERA40 reanalyses. This study focuses on the June–November time period when tropical storms are most frequent in the region. For the mean fields, the reanalysis surface products compare better with the moorings than the 1000 hPa products. In contrast, the variance in the 1000 hPa ERA40 state variables is in best agreement with the mooring variance. As long as these disparities exist, air-sea interaction studies and our ability to drive ocean models with observed fluxes will be limited.