Argo Profiling Float Research Articles

Estimating Global Ocean Heat Content Changes in the Upper 1800 m since 1950 and the Influence of Climatology Choice*

AbstractOcean heat content anomalies are analyzed from 1950 to 2011 in five distinct depth layers (0–100, 100–300, 300–700, 700–900, and 900–1800 m). These layers correspond to historic increases in common maximum sampling depths of ocean temperature measurements with time, as different instruments—mechanical bathythermograph (MBT), shallow expendable bathythermograph (XBT), deep XBT, early sometimes shallower Argo profiling floats, and recent Argo floats capable of worldwide sampling to 2000 m—have come into widespread use. This vertical separation of maps allows computation of annual ocean heat content anomalies and their sampling uncertainties back to 1950 while taking account of in situ sampling advances and changing sampling patterns. The 0–100-m layer is measured over 50% of the globe annually starting in 1956, the 100–300-m layer starting in 1967, the 300–700-m layer starting in 1983, and the deepest two layers considered here starting in 2003 and 2004, during the implementation of Argo. Furthermore, global ocean heat uptake estimates since 1950 depend strongly on assumptions made concerning changes in undersampled or unsampled ocean regions. If unsampled areas are assumed to have zero anomalies and are included in the global integrals, the choice of climatological reference from which anomalies are estimated can strongly influence the global integral values and their trend: the sparser the sampling and the bigger the mean difference between climatological and actual values, the larger the influence.

Geostrophic Circulation in the Tropical North Pacific Ocean Based on Argo Profiles

Abstract Absolute geostrophic currents in the North Pacific Ocean are calculated from the newly gridded Argo profiling float data using the P-vector method for the period of 2004–11. The zonal geostrophic currents based on the Argo profile data are found to be stronger than those based on the traditional World Ocean Atlas 2009 (WOA09) data. A westward mean geostrophic flow underneath the North Equatorial Countercurrent is identified using the Argo data, which is evidenced by sporadic direct current measurements and geostrophic calculations in history. This current originates east of the date line and transports more than 4 × 106 m3 s−1 of water westward in the subsurface northwestern tropical Pacific Ocean. The authors name this current the North Equatorial Subsurface Current. The transport in the geostrophic currents is compared with the Sverdrup theory and found to differ significantly in several locations. Analyses have shown that errors of wind stress estimation cannot account for all of the differences. The largest differences are found in the area immediately north and south of the bifurcation latitude of the North Equatorial Current west of the date line and in the recirculation area of the Kuroshio and its extension, where nonlinear activities are vigorous. It is, therefore, suggested that the linear dynamics of the Sverdrup theory is deficient in explaining the geostrophic transport of the tropical northwestern Pacific Ocean.

Intermediate and deep water formation in the Okinawa Trough

Water mass formation in the intermediate and deep layers of the Okinawa Trough is investigated using two distinct data sets: a quasi‐climatological data set of the water properties of the minimum salinity surface produced from Argo float profiles and historical CTD data, and a velocity data set in the Kerama Gap measured by moored current meters during June 2009 to June 2011. The formation process of Okinawa Trough Intermediate Water is explained on the basis of horizontal advection and mixing of North Pacific Intermediate Water (NPIW) and South China Sea Intermediate Water (SCSIW). The salinity‐minimum water intruding into the Okinawa Trough through the channel east of Taiwan is approximately composed of 45% NPIW and 55% SCSIW, while that through the Kerama Gap is 75% NPIW and 25% SCSIW. Salinities of these water masses increase in the Okinawa Trough due to strong diapycnal diffusion; its coefficient is estimated as 6.8–21.5 × 10−4 m2 s−1 based on a simple advection‐diffusion equation. On the other hand, deep water in the Okinawa Trough, below the sill depth of the Kerama Gap (∼1100 m), is ventilated by overflow in the bottom layer of the Kerama Gap down to the deepest layer (∼2000 m) in the southern Okinawa Trough. A simple box model predicts that this bottom overflow (0.18–0.35 Sv) causes strong upwelling (3.8–7.6 × 10−6 m s−1) in the southern Okinawa Trough, which must be maintained by buoyancy gain of the deep water due to strong diapycnal diffusion (4.8–9.5 × 10−4 m2 s−1).

Formation and Subduction of North Pacific Tropical Water and Their Interannual Variability

Abstract Formation and subduction of the North Pacific Tropical Water (NPTW), its interannual variability, and its associated mechanisms were investigated by using gridded Argo-profiling float data and various surface flux data in 2003–11. The NPTW has two formation sites in the center of the North Pacific subtropical gyre, corresponding to two regional sea surface salinity maxima. Mixed layer salinity variations in these two NPTW formation sites were found to be significantly different. While seasonal variation was prominent in the eastern formation site, interannual variation was dominant in the western site. The mixed layer salinity variation in the eastern site was controlled mainly by evaporation, precipitation, and entrainment of fresher water below the mixed layer and was closely related to the seasonal variation of the mixed layer depth. In the western site, the effect of entrainment is small due to a small vertical difference in salinity across the mixed layer base, and excess evaporation over precipitation that tended to be balanced by eddy diffusion, whose strength varied interannually in association with the Pacific decadal oscillation. After subduction, denser NPTW that formed in the eastern site dissipated quickly, while the lighter one that formed in the western site was advected westward as far as the Philippine Sea, transmitting the interannual variation of salinity away from its formation region.

Variability of the Heat and Salt Budget in the Subtropical Southeastern Pacific Mixed Layer between 2004 and 2010: Spice Injection Mechanism

Abstract The mixed layer heat and salt budget in the southeastern subtropical Pacific are estimated using 7 years (2004–10) of Argo-profiling float data, surface fluxes, precipitation, surface velocity data, and wind observations and reanalysis. In this region, the mixed layer heat budget is characterized by a strong annual cycle mainly modulated by the shortwave radiation annual cycle. During the austral fall and winter, the shortwave radiation input minimum is overwhelmed by the heat loss mainly because of the latent heat flux. The mixed layer salt budget also presents a strong annual cycle with a minimum of salt content during the late austral winter. In contrast with the heat budget, the salt budget is mainly driven by the unresolved terms computed as the residual of the budget. Among these missing terms, the most likely candidate is the vertical turbulent mixing as a result of convection caused by the heat surface buoyancy loss and the destabilizing vertical gradient of salinity at the base of the mixed layer. This downward flux of salt at the base of the mixed layer could explain the annual spiciness injection and interannual spiciness variability in the permanent thermocline in the southeastern Pacific.

Oxygen dynamics in the Black Sea as seen by Argo profiling floats

Observations collected in the Black Sea from May 2010 until December 2011 from two Argo floats with oxygen sensors demonstrated the potential of the applied technique to deliver high‐quality oxygen data in this oxic/anoxic environment where the oxygen concentration varies from the level of saturation to zero. It was demonstrated that the dynamics of the oxic‐anoxic interface was dominated by vigorous mesoscale processes displacing locally anoxic waters up to about 70 m below the sea surface. Alternatively, oxygenation (ventilation) in the coastal zone penetrated down to about 150–200 m. The range of mesoscale variability, which appeared to reach half of the range of climatic trend during the last 50 years, helped to objectively assess the validity of interpretation of historical data. It was proved that the shift of the suboxic zone from isopycnal depth σt = 16.5 to σt = 15.5 during 1960–2010, interrupted by its deepening between 1990 and 2000, was greater than the possible error limit caused by insufficient sampling of mesoscale variability. Furthermore, profiling floats shed a new light into the seasonal variability of the subsurface oxygen maximum. It was also demonstrated that the assumption of isopycnal alignment of oxygen was coarsely applicable to the suboxic layer in both the coastal and interior part of the Black Sea where the isopycnal mixing revealed large temporal and spatial variability. Therefore, deeper understanding of the dynamics of suboxic zone necessitated continuous basin‐wide sampling.

Geostrophic meridional transport in tropical Northwest Pacific based on Argo profiles

Absolute geostrophic currents in the North Pacific Ocean were calculated using P-vector method from newly gridded Argo profiling float data collected during 2004-2009. The meridional volume transport of geostrophic currents differed significantly from the classical Sverdrup balance, with differences of 10x10(6)-20x10(6)m(3)/s in the interior tropical Northwest Pacific Ocean. Analyses showed that errors of wind stress estimation could not explain all of the differences. The largest differences were found in the areas immediately north and south of the bifurcation latitude of the North Equatorial Current west of the dateline, and in the recirculation area of the Kuroshio and its extension, where nonlinear eddy activities were robust. Comparison of the geostrophic meridional transport and the wind-driven Sverdrup meridional transport in a high-resolution OFES simulation showed that nonlinear effects of the ocean circulation were the most likely reason for the differences. It is therefore suggested that the linear, steady wind-driven dynamics of the Sverdrup theory cannot completely explain the meridional transport of the interior circulation of the tropical Northwest Pacific Ocean.

Structure and surface properties of eddies in the southeast Pacific Ocean

AbstractA number of studies have posited that coastally generated eddies could cool the southeast Pacific Ocean (SEP) by advecting cool, upwelled waters offshore. We examine this mechanism by characterizing the upper‐ocean properties of mesoscale eddies in the SEP with a variety of observations and by estimating the surface‐layer eddy heat flux divergence with satellite data. Cyclonic and anticyclonic eddies observed during two cruises featured deep positive salinity anomalies along the 26.5 kg m−3isopycnal, indicating that the eddies had likely trapped and transported coastal waters offshore. The cyclonic eddies observed during the cruises were characterized by shoaling isopycnals in the upper 200 m and cool near‐surface temperature anomalies, whereas the upper‐ocean structure of anticyclonic eddies was more variable. Using a variety of large‐scale observations, including Argo float profiles, drifter records, and satellite sea surface temperature fields, we show that, relative to mean conditions, cyclonic eddies are associated with cooler surface temperatures and that anticyclonic eddies are associated with warmer surface temperatures. Within each data set, the mean eddy surface temperature anomalies are small and of approximately equal magnitude but opposite sign. Eddy statistics drawn from satellite altimetry data reveal that cyclonic and anticyclonic eddies occur with similar frequency and have similar average radii in the SEP. A satellite‐based estimate of the surface‐layer eddy heat flux divergence, while large in coastal regions, is small when averaged over the SEP, suggesting that eddies do not substantially contribute to cooling the surface layer of the SEP.

The impact of meso-scale eddies on the Subtropical Mode Water in the western North Pacific

Based on the temperature and salinity from the Argo profiling floats and altimeter-derived geostrophic velocity anomaly (GVA) data in the western North Pacific during 2002–2011, the North Pacific Subtropical Mode Water (NPSTMW) distribution is investigated and cyclonic and anti-cyclonic eddies (CEs and AEs) are constructed to study the influence of their vertical structures on maintaining NPSTMW. Combining eddies identified by the GVA data and Argo profiling float data, it is found that the average NPSTMW thickness of AEs is about 60 dbar, which is thicker than that of CEs. The NPSTMW thicker than 150 dbar in AEs accounts for 18%, whereas that in CEs accounts for only 1%. About 3377 (3517) profiles, which located within one diameter of the nearest CEs (AEs) are used to construct the CE (AE). The composite AE traps low-PV water in the center and with a convex shape in the vertical section. The ‘trapped depth’ of the composite CE (AE) is 300 m (550 m) where the rotational velocity exceeds the transitional velocity. The present study suggests that the anticyclonic eddies are not only likely to form larger amounts of NPSTMW, but also trap more NPSTMW than cyclonic eddies.

Subantarctic mode water in the southeast Pacific: Effect of exchange across the Subantarctic Front

[1] This study considered cross-frontal exchange as a possible mechanism for the observed along-front freshening and cooling between the 27.0 and 27.3 kg m − 3 isopycnals north of the Subantarctic Front (SAF) in the southeast Pacific Ocean. This isopycnal range, which includes the densest Subantarctic Mode Water (SAMW) formed in this region, is mostly below the mixed layer, and so experiences little direct air-sea forcing. Data from two cruises in the southeast Pacific were examined for evidence of cross-frontal exchange; numerous eddies and intrusions containing Polar Frontal Zone (PFZ) water were observed north of the SAF, as well as a fresh surface layer during the summer cruise that was likely due to Ekman transport. These features penetrated north of the SAF, even though the potential vorticity structure of the SAF should have acted as a barrier to exchange. An optimum multiparameter (OMP) analysis incorporating a range of observed properties was used to estimate the cumulative cross-frontal exchange. The OMP analysis revealed an along-front increase in PFZ water fractional content in the region north of the SAF between the 27.1 and 27.3 kg m − 3 isopycnals; the increase was approximately 0.13 for every 15° of longitude. Between the 27.0 and 27.1 kg m − 3 isopycnals, the increase was approximately 0.15 for every 15° of longitude. A simple bulk calculation revealed that this magnitude of cross-frontal exchange could have caused the downstream evolution of SAMW temperature and salinity properties observed by Argo profiling floats.

Observing the bottom density current over a shelf using an Argo profiling float

AbstractPressure, temperature, and salinity data collected during the winter of 2011/2012 by an Argo profiling float over the Adriatic shelf were used to document the dense water formation and subsequent bottom density current (BDC) normally occurring along the shelf slope. The float was advected to the Jabuka Pit and neighboring shallow area (<275 m) after October 2010. The parking depth was set to approximately 150 m, enabling the float to mostly follow the firstOnlineseabed between December 2011 and July 2012. The profiler measured strong spatial‐temporal changes in the BDC thickness (from a few to about 50 m) and the bottom density (between 29.46 and 29.88 kg/m3). These observations show that an Argo float has the capability to observe a bottom density current and suggest that it would be possible to systematically use such floats to investigate these processes on coastal shelves.

The subsurface water in the North Pacific tropical gyre

The subsurface water (22.5–25.5 σθ) in the North Pacific tropical gyre (NPTG; 130°E–150°W, 5°–10°N), addressed as the North Pacific tropical subsurface water (TSSW), features a lateral salinity minimum and vertical salinity maximum in the western and central Pacific Ocean. In this study this water body is investigated using Argo float profiles and Word Ocean Atlas 2009 (WOA09) dataset. Comparing with the North Pacific Tropical water (NPTW), the TSSW is of lower salinity, lower oxygen, higher nutrient concentration, and denser vertical salinity maximum Smax. Subtropical ventilation and local ocean dynamics are both important in setting up its unique characteristics. Our analysis shows that its properties, structure, and seasonal variations are diverse at different longitudes. In the western Pacific, the TSSW is mainly of North Pacific water origin. Its high salinity core is formed by the southward intrusion of the NPTW. Diapycnal mixing with the surface-layer fresh water reduces its salinity and lowers its Smax to denser isopycnals. The TSSW in the western Pacific can be regarded as a diluted portion of the NPTW. In the central Pacific, advection of salty water masses from both hemispheres and westward invasion of the eastern Pacific fresh water are all important in regulating its characteristics. The TSSW in the central Pacific is a mixture of various water sources formed under highly variable flow pattern and intensive mixing. The TSSW should be regarded as an important subsurface water body connecting North/South Pacific thermocline water, although it might not be a water mass by traditional definition.

Comparing Altimetry with Tide Gauges and Argo Profiling Floats for Data Quality Assessment and Mean Sea Level Studies

Altimeter missions have provided accurate measurements of sea surface height since 1992 not only with TOPEX/Poseidon but also with Jason-1, Envisat, and recently Jason-2. The overall quality assessment of altimeter data can be performed by analyzing their internal consistency and the cross-comparison between all missions. In this study, in situ measurements are used as an external, independent reference to enable further quality assessment of the altimeter sea level. The most up-to-date altimeter data are assessed and compared with those from tide gauges and Argo profiling floats. The first focus is on detection of global and regional drifts in altimeter sea surface height compared with in situ measurements. A second point is that the method can assess the impact of new altimeter standards (e.g., orbit solution, instrumental correction, retracking algorithm) thanks to in situ observations. Finally, the study shows how multiple and reliable altimeter products are used to detect potential anomalies in tide gauges. The results demonstrate the close link between these three steps of the method: while the detection of altimeter drifts using in situ measurements is corrected by computing new altimeter standards whose impact can then be estimated, the improved altimeter sea level time series are used as input for controlling the quality of in situ observations.

Interannual variability in the Mindanao Eddy and its impact on thermohaline structure pattern

The major feature, interannual variability and variation cause of the Mindanao Eddy and its impact on the thermohaline structure are analyzed based on the Argo profiling float data, the history observed data and the SODA data. The analysis results show that the Mindanao Eddy is a permanent cyclonic meso-scale eddy and spreads vertically from about 500 m depth upward do about 50 m depth. In addition to its strong seasonal variability, the Mindanao Eddy displays a remarkable interannual variability associated with ENSO. It strengthens and expands eastward during El Nino while it weakens and retreats westward during La Nina. The interannual variability in the Mindanao Eddy may be caused by the North Equatorial Counter Current, the North Equatorial Current, the Mindanao Current and the Indonesian Through Flow. The eddy variability can have a great influence on the thermohaline structure pattern in the local upper ocean. When the eddy is strong, the cold and low salinity water inside the eddy moves violently upward from deep layer, the thermocline depth greatly shoals, and the subsurface high salinity water largely decreases, with the upper mixed layer becoming thinner, and vice versa.

Assessing the Application of Argo Profiling Float Data to the Study of the Seasonal Variation of the Hydrological Parameters and the Current Field East of Luzon Strait

The seasonal characteristics of water masses, mixed-layer depth and the current field east of Luzon Strait are studied using Argo profiling float data. Based on data from March 2006 to November 2010, the temperature-salinity relation indicates that the seasonal variation of water masses is not obvious, except that the surface temperature is lower and the salinity is higher in spring and winter; the water masses in other layers change little. The seasonal variation of the mixed-layer depth, which is deepest at over 170 m in winter and shallowest at about 25 m in summer, is also discussed. Based on the P-vector method, multi-year seasonal mean Argo data and Levitus data are used to calculate the respective current fields. The surface geostrophic current derived from altimetric data is compared with those computed from Argo data and Levitus data. It is shown that, the current field computed from Argo data, which shows the Kuroshio and eddies clearly, is similar to that obtained from altimetric data, except that the current speed is less in the former case than in the latter one; this may be related to the scarcity and uneven distribution of Argo floats, the subsequent interpolation and extrapolation errors, the shortcomings of the P-vector method, the lack of a barotropic component in the calculation or the altimetry-derived current error associated with the marine geoid, but the resultant current field is much better than that obtained from Levitus data. Moreover, Argo data have an advantage in that they can be used to derive a three-dimensional current field, whereas the altimetric data can only be used to derive the surface current field. The seasonal variations in the vertical current structure and the Kuroshio transport east of Taiwan Island are also discussed; it is found that the thickness of the northward Kuroshio is about 700 m, and the seasonal zonal variation in the main axis of the Kuroshio is obvious. RÉSUMÉ [Traduit par la rédaction] Nous étudions les caractéristiques saisonnières des masses d'eau, la profondeur de la couche de mélange et le champ de courant à l'est du détroit de Luçon à l'aide des données des flotteurs profileurs Argo. D'après les données recueillies entre mars 2006 et novembre 2010, la relation température-salinité indique que la variation saisonnière des masses d'eau n'est pas évidente, sauf que la température de surface est plus basse et la salinité plus élevée au printemps et en hiver; les masses d'eau dans les autres couches changent peu. Nous discutons aussi de la variation saisonnière de la profondeur de la couche de mélange, qui est maximale à plus de 170 m en hiver et minimale à environ 25 m en été. En nous basant sur la méthode des vecteurs P, nous utilisons les données Argo et les données Levitus pluriannuelles de moyennes saisonnières pour calculer les champs de courant respectifs. Nous comparons le courant géostrophique de surface déduit des données altimétriques avec ceux calculés à l'aide des données Argo et des données Levitus. Il apparait que le champ de courant calculé d'après les données Argo, qui montre clairement le Kuroshio et les remous, est semblable à celui obtenu des données altimétriques, sauf que la vitesse du courant est moindre dans le premier cas que dans le dernier; cela peut être lié à la rareté et à la distribution inégale des flotteurs Argo, aux erreurs subséquentes d'interpolation et d'extrapolation, aux faiblesses de la méthode des vecteurs P, au manque d'une composante barotropique dans les calculs ou à l'erreur dans le courant déduit des données altimétriques associée au géoïde marin, mais le champ de courant résultant est bien meilleur que celui obtenu à l'aide des données Levitus. De plus, les données Argo présentent l'avantage de pouvoir être utilisées pour déduire un champ de courant tridimensionnel, alors que les données altimétriques ne permettent que de déduire le champ de courant de surface. Nous discutons aussi des variations saisonnières dans la structure verticale du courant et dans le transport par le Kuroshio à l'est de l’île de Taïwan; nous trouvons que la profondeur du Kuroshio circulant vers le nord est d'environ 700 m et la variation saisonnière zonale dans l'axe principal du Kuroshio est évidente.

Upper ocean variability in the Bay of Bengal during the tropical cyclones Nargis and Laila

Upper ocean variability at different stages in the evolution of the tropical cyclones Nargis and Laila is evaluated over the Bay of Bengal (BoB) during May 2008 and May 2010 respectively. Nargis initially developed on 24 April 2008; intensified twice on 27–28 April and 1 May, and eventually made landfall at Myanmar on 2 May 2008. Laila developed over the western BoB in May 2010 and moved westward towards the east coast of India. Data from the Argo Profiling floats, the Research Moored Array for African–Asian–Australian Monsoon Analysis and prediction (RAMA), and various satellite products are analyzed to evaluate upper ocean variability due to Nargis and Laila. The analysis reveals pre-conditioning of the central BoB prior to Nargis with warm (>30°C) Sea Surface Temperature (SST), low (<33psu) Sea Surface Salinity (SSS) and shallow (<30m) mixed layer depths during March–April 2008. Enhanced ocean response to the right of the storm track due to Nargis includes a large SST drop by ∼1.76°C, SSS increase up to 0.74psu, mixed layer deepening of 32m, shoaling of the 26°C isotherm by 36m and high net heat loss at the sea surface. During Nargis, strong inertial currents (up to 0.9ms−1) were generated to the right of storm track as measured at a RAMA buoy located at 15°N, 90°E, producing strong turbulent mixing that lead to the deepening of mixed layer. This mixing facilitated entrainment of cold waters from as deep as 75m and, together with net heat loss at sea surface and cyclone-induced subsurface upwelling, contributed to the observed SST cooling in the wake of the storm. A similar upper ocean response occurs during Laila, though it was a significantly weaker storm than Nargis.

Relationship of maximum tropical cyclone intensity to sea surface temperature and tropical cyclone heat potential in the North Pacific Ocean

We investigated whether the maximum intensity of tropical cyclones (TC) in the North Pacific Ocean depends on sea surface temperature (SST) and tropical cyclone heat potential (TCHP). The study used reanalysis data sets for both the oceans and atmosphere: daily, 10‐day, and monthly oceanic data sets; six‐hour and monthly atmospheric data sets; and a daily satellite SST data set, for the July‐to‐October season from 2002 to 2005. For each TC, we summed TCHP from the time of genesis to the time of first reaching a minimum central pressure (MCP), to obtain an accumulated TCHP. In a linear regression analysis, the relationship between maximum TC intensity and accumulated TCHP differed between the eastern and western Pacific: high values of accumulated TCHP were needed before a TC attained a certain MCP in the western Pacific. In addition, the background convective available potential energy (CAPE) value was nearly four times larger in the western Pacific than in the eastern Pacific. The static stability was also 6.5% lower, the inertial stability 29.7% higher, and the size of tropical cyclones 38.2% larger in the western Pacific than in the eastern Pacific. The result indicated a deeper Rossby penetration depth and stronger TC in the western Pacific. Finally, we validated the TCHP values derived from three oceanic reanalysis data sets by using Argo profiling float observations. We found that use of only the daily data can reproduce the cooling effect of a passage of a TC, which caused a decrease in the TCHP values.

In Situ Observations of Madden–Julian Oscillation Mixed Layer Dynamics in the Indian and Western Pacific Oceans

Abstract The boreal winter response of the ocean mixed layer to the Madden–Julian oscillation (MJO) in the Indo-Pacific region is determined using in situ observations from the Argo profiling float dataset. Composite averages over numerous events reveal that the MJO forces systematic variations in mixed layer depth and temperature throughout the domain. Strong MJO mixed layer depth anomalies (&amp;gt;15 m peak to peak) are observed in the central Indian Ocean and in the far western Pacific Ocean. The strongest mixed layer temperature variations (&amp;gt;0.6°C peak to peak) are found in the central Indian Ocean and in the region between northwest Australia and Java. A heat budget analysis is used to evaluate which processes are responsible for mixed layer temperature variations at MJO time scales. Though uncertainties in the heat budget are on the same order as the temperature trend, the analysis nonetheless demonstrates that mixed layer temperature variations associated with the canonical MJO are driven largely by anomalous net surface heat flux. Net heat flux is dominated by anomalies in shortwave and latent heat fluxes, the relative importance of which varies between active and suppressed MJO conditions. Additionally, rapid deepening of the mixed layer in the central Indian Ocean during the onset of active MJO conditions induces significant basin-wide entrainment cooling. In the central equatorial Indian Ocean, MJO-induced variations in mixed layer depth can modulate net surface heat flux, and therefore mixed layer temperature variations, by up to ~40%. This highlights the importance of correctly representing intraseasonal mixed layer depth variations in climate models in order to accurately simulate mixed layer temperature, and thus air–sea interaction, associated with the MJO.

Decadal seesaw of the Central and Subtropical Mode Water formation associated with the Kuroshio Extension variability

Available Argo profiling float data from 2002 to 2011 were analyzed to examine the effect of the Kuroshio Extension (KE) current system variability on the formation of the Central Mode Water. Just north of the upstream portion of the KE at 140–152°E, formation of a lighter variety of the Central Mode Water in winter was active during the unstable period of the upstream KE in 2006–2009 and was reduced when the upstream KE was in the stable period of 2002–2005 and 2010–2011. This decadal formation variability is out of phase with that of the Subtropical Mode Water just south of the KE.

Drift in Salinity Data from Argo Profiling Floats in the Sea of Japan*

Abstract In drift analysis of salinity sensors, one major problem is the difficulty in delineating sensor drift from water mass changes. In the present study, a new method is proposed for finding sensor drift that is free from water mass changes. The efficiency of this new method in finding out possible drift in the Argo salinity is demonstrated in the Sea of Japan (SOJ) by using the “near-linear” subsurface salinity structure of the SOJ. The new method is based on the time–space decorrelation scale. The salinity difference between two neighboring observations within the time–space decorrelation scale (SALD) is used to find out possible drift. Neighboring observations within the time–space decorrelation scale are referred to as matchups. The SALD derived from matchups between Argo floats and shipboard CTD observations from the SOJ shows linear drift. Although all four selected floats (5 yr completed) from the SOJ show linear drift (&amp;lt;0.001 PSS yr−1), the drift alone is not so significant to affect the objective of the Argo program in understanding climate variability. In the SOJ, SALD identified salinity error other than drift in good quality data that are flagged by the Argo delayed-mode quality control (ADMQC) method. Therefore, SALD could be used as an effective additional tool in the Argo data quality control. To examine the applicability of SALD in open ocean regions, in addition to confined basins such as SOJ, SALD was applied successfully to detect salinity error in Argo data from the subtropical North Pacific (SNP).