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Since the 1970s, eXpendable BathyThermographs (XBTs) have provided the simplest and most cost-efficient solution for rapid sampling of temperature vs. depth profiles of the upper part of the ocean along ship transects. This manual, compiled by the Ship of Opportunity Program Implementation Panel (SOOPIP) a subgroup of the Global Ocean Observing System (GOOS) Observations Coordination Group (OCG) Ship Observations Team (SOT) together with members of the XBT Science Team, aims to improve the quality assurance of XBT data by establishing best practices for field measurements and promoting their adoption by the global operational and scientific community. The measurement system components include commercially available expendable temperature probes, the launcher, the data acquisition (DAQ) hardware, a Global Navigation Satellite System (GNSS) receiver, an optional satellite transmitter, and a computer with software controls. The measurement platform can be any sea-going vessel with available space for the equipment and operator, and capable of oceanic voyages across the regions of interest. Adoption of a standard methodology in the installation and deployment of the measurement system will lead to data quality improvements with subsequent impact on the computation and understanding of changes in the near surface ocean properties (e.g., heat content), ocean circulation dynamics, and their relationship to climate variability.

The Kuroshio in the Luzon Strait (KLS) has long been a focus of research for its complex ocean dynamics; however, it is poorly understood owing to a lack of long‐term in situ observations. Empirical orthogonal function (EOF) analyses were applied to quarterly expendable bathythermograph data (XBT, with a spatial resolution of 10–20 km in the Kuroshio region and 33 km in the other regions) and sea‐level anomaly (SLA) data, to examine the variations of the KLS. The first EOF modes of water temperature and SLA represent seasonal variations. The volume transport of the KLS referring to a 700 m depth reaches its maximum in warm months (19.4 Sv, July–September) and its minimum in cold months (17 Sv, January–March). This variation is similar to that east of Taiwan but is opposite to that east of Luzon, although the Luzon Strait is only 2° distant from the area east of Luzon. The outflow (1.3 Sv) from the South China Sea (SCS) to the Kuroshio in the warm months and the Kuroshio intrusion into the SCS in the cold months are responsible for this seasonal contrast. The second EOF modes of water temperature and SLA are related to the latitudinal movement of the Kuroshio recirculation on a time scale of 2–24 months. Lag correlation and wavelet analysis demonstrate that this mode is triggered by the westward‐propagating SLA along 21°–24°N and is affected by the downstream propagation of low‐frequency variation (mostly annual to biennial) from the North Equatorial Current bifurcation area. Plain Language Summary: Variations of the Kuroshio in the Luzon Strait (KLS) from 1999 to 2010 were examined by using sea‐level anomaly (SLA) data and long‐term repeated water temperature data observed by expendable bathythermography (XBT, cast by automatic launchers equipped on commercial ships). The decomposition (empirical orthogonal function, EOF) analysis of the two datasets shows that the most dominant components represent seasonal variations. The volume transport of the KLS reaches a maximum in warm months (July–September) and a minimum in cold months (January–March), which is similar to the seasonal variation of the Kuroshio east of Taiwan but is opposite to that east of Luzon. The Kuroshio‐South China Sea (SCS) water exchange is the main cause of the reversed seasonal variation in the Kuroshio transport between the area east of Luzon and the Luzon Strait. The second dominant components represent the latitudinal movement of the Kuroshio recirculation and result from the westward‐propagating SLA along 21°–24°N and the downstream propagation of low‐frequency variation from the area where the North Equatorial Current bifurcates into the Kuroshio and Mindanao Current. This work has implications for the Kuroshio‐SCS water exchange and Kuroshio‐eddy interactions from east of Luzon to the east of Taiwan. Key Points: Variations of the Kuroshio in the Luzon Strait (LS) were examined by analyzing sectional water temperature and sea‐level anomaly dataKuroshio‐South China Sea water exchange contributes to the opposite seasonal variation in volume transport from east of Luzon to the LSWestward propagated eddies along 21°–24°N and variations from the North Equatorial Current bifurcation impact the Kuroshio in the LS [ABSTRACT FROM AUTHOR]

The seasonal and interannual variability of the Brazil Current (BC) at 22°S is examined using expendable bathythermograph (XBT) transect and satellite altimetry data from 1993 to 2017. The XBT‐based mean absolute geostrophic transport of the BC is estimated as 4.7 ± 1.9 Sv, with additional 0.9 ± 0.9 Sv along the shelf. The strong agreement between the absolute dynamic height and altimetric sea surface height is used in two methods to reconstruct a daily time series of the BC transport since 1993. The altimetry‐based methods can represent well the BC transport seasonal cycle, whereas the XBT‐based estimates are slightly aliased by the strong regional mesoscale variability. At interannual timescales, the BC transport is significantly correlated (r = 0.43) with the wind stress curl in the western half of the basin with a lag of 19 months, which is consistent with baroclinic adjustment timescales. Other sources of variability can be observed in a case study of the summer 2009/2010 event, which was characterized by strong sea surface temperature anomalies of approximately 3 °C. During the event, the BC reached 11 Sv for nearly 3 months, partly driven by an increased coastal upwelling from a cyclonic wind stress anomaly, a standing eddy along the section, and thermosteric anomalies that reached the offshore side of section in February. Heat anomalies were transported southward along the subtropical gyre following the BC path in a period of 2 months, which is consistent with advective timescales. Potential implications for extreme sea level and summer precipitation events in South America are discussed. Plain Language Summary: Two methods were developed to create a 25‐yearlong time series of the Brazil Current (BC) volume transport across 22°S using expendable bathythermograph data and altimetry. The seasonal variability of the BC is out‐of‐phase with the wind stress curl across the basin, suggesting that wave adjustment and local winds control the seasonality. At interannual timescales, the wind stress curl in the western side of the basin and the regional upwelling control the BC variability. In the summer of 2009/2010, the BC transport was 3 times stronger than its mean. The event was characterized by a strong warm sea surface temperature anomaly propagating westward into the region and an associated anticyclonic wind stress anomaly. Results suggest that the BC strengthening was linked to a decreased near‐shore sea level of ~20 cm due to increased coastal upwelling, and an increased offshore sea level of 15 cm influenced by the warm anomaly. Key Points: Seasonal variability of the BC is out‐of‐phase with the Sverdrup transport due to baroclinic adjustmentThe BC transport variability is associated to the wind stress curl in the western part of the basin and coastal upwellingIn the 2009/2010 event, anticyclonic winds lower the coastal sea level, and warm anomalies increase sea level offshore, strengthening the BC [ABSTRACT FROM AUTHOR]

Marine eXpendable Bathythermograph (XBT) launching system is used to launch detecting probes into the ocean quickly and efficiently and has been researched for many years. The probes will measure the ocean parameters of depth and temperature during droppings which make the device with the merits of real-time, fast and wide spreading. The automatic pulling mechanism of probe plug is an important part of XBT automatic launching system which improves the shortcoming of hand-held launch method of XBT probe. This development mentioned a kind of automatic extraction mechanism for probe's plug fixed the probe. The lever is adopted here to magnify the tensile force in order to draw out the plug in limited stroke. That will make sure the full-automatic launching of expendable probes. In tests, the successful dropping rate is over 95% and save time over 50% more than hand-held method which prove the automatic extraction mechanism effect and reliable. The mechanism also can be used into various automatic launchers of expendable probes through a little configuration adjust. Its broad application prospect is viewed. [ABSTRACT FROM AUTHOR]

The T5 expendable bathythermographs reach the greatest depth within the current XBT family. Since the early 1970s, in several areas they have been providing a significant part of available temperature profiles below 1000 m and therefore represent an important resource for ocean climate study. In this paper we present new results from laboratory tests of Sippican T5 and T5/20 probes and analyses of more than 350 XBT–CTD matched pairs from our own field trials and the World Ocean Database (WOD), and we propose an improved fall rate equation (coefficients: A = 6.720 ± 0.025 m s−1, B = 0.001 60 ± 0.000 15 m s−2, Offset = 1.00 ± 0.65 m). Possible influences of probe physical characteristics and initial launch conditions on the probe motion have also been investigated with launching height and probe weight being identified as important factors. Analyses also confirm that fall speed and pure temperature error increase with water temperature, as previously reported for other XBT types. The uncertainties in depth and temperature measurements are then calculated. Finally, a new correction for a global T5 dataset is proposed, with an update of the currently available schemes. [ABSTRACT FROM AUTHOR]

Biases in expendable bathythermograph (XBT) instruments have emerged as a leading uncertainty in reconstructions of historical ocean heat content change and therefore climate change. Corrections for these biases depend on the type of XBT used; however, this is unspecified for 52% of the historical XBT profiles in the World Ocean Database. Here, we use profiles of known XBT type to train a neural network that can classify probe type based on three covariates: profile date, maximum recorded depth, and country of origin. Whereas previous studies have shown an average classification skill of 77%, falling below 50% for some periods, our new algorithm maintains an average skill of 90%, with a minimum of 70%. Our study illustrates the potential for successfully applying machine learning approaches in a wide variety of instrument classification problems in order to promote more homogeneous climate data records. [ABSTRACT FROM AUTHOR]

Simultaneous temperature and salinity profile measurements are of extreme importance for research; operational oceanography; research and applications that compute content and transport of mass, heat, and freshwater in the ocean; and for determining water mass stratification and mixing rates. Historically, temperature profiles are much more abundant than simultaneous temperature and salinity profiles. Given the importance of concurrent temperature and salinity profiles, several methods have been developed to derive salinity solely based on temperature profile observations, such as expendable bathythermograph (XBT) temperature measurements, for which concurrent salinity observations are typically not available. These empirical methods used to date contain uncertainties as a result of temporal changes in salinity and seasonality in the mixed layer, and are typically regionally based. In this study, a new methodology is proposed to infer salinity in the Atlantic Ocean from the water surface to 2000-m depth, which addresses the seasonality in the upper ocean and makes inferences about longer-term changes in salinity. Our results show that when seasonality is accounted for, the variance of the residuals is reduced in the upper 150 m of the ocean and the dynamic height errors are smaller than 4 cm in the whole study domain. The sensitivity of the meridional heat and freshwater transport to different empirical methods of salinity estimation is studied using the high-density XBT transect across 34.5°S in the South Atlantic Ocean. Results show that accurate salinity estimates are more important on the boundaries, suggesting that temperature–salinity compensation may be also important in those regions. [ABSTRACT FROM AUTHOR]

The difficulty in effectively evaluating sea surface temperature (SST) analyses is finding independent observations, since most available observations have been used in the SST analyses. In this study, the ocean profile measurements [from reverse thermometer, CTD, mechanical bathythermograph (MBT), and XBT] above 5-m depth over 1950–2016 from the World Ocean Database (WOD) are used (data labeled pSSTW). The biases of MBT and XBT are corrected based on currently available algorithms. The bias-corrected pSSTW over 1950–2016 and satellite-based SST from the European Space Agency (ESA) Climate Change Initiative (CCI) over 1992–2010 are used to evaluate commonly available SST analyses. These SST analyses are the Extended Reconstructed SST (ERSST), versions 5, 4, and 3b, the Met Office Hadley Centre Sea Ice and SST dataset (HadISST), and the Japan Meteorological Administration (JMA) Centennial In Situ Observation-Based Estimates of SST version 2.9.2 (COBE-SST2). Our comparisons show that the SST from COBE-SST2 is the closest to pSSTW and CCI in most of the Pacific, Atlantic, and Southern Oceans, which may result from its unique bias correction to ship observations. The SST from ERSST version 5 is more consistent with pSSTW than its previous versions over 1950–2016, and is more consistent with CCI than its previous versions over 1992–2010. The better performance of ERSST version 5 over its previous versions is attributed to its improved bias correction applied to ship observations with a baseline of buoy observations, and is seen in most of the Pacific and Atlantic. [ABSTRACT FROM AUTHOR]

For the first time, a monthly climatology of mixed layer depth (MLD) in the Red Sea has been derived based on temperature profiles. The general pattern of MLD variability is clearly visible in the Red Sea, with deep MLDs during winter and shallow MLDs during summer. Transitional MLDs have been found during the spring and fall. The northern end of the Red Sea experienced deeper mixing and a higher MLD associated with the winter cooling of the high-saline surface waters. Further, the region north of 19° N experienced deep mixed layers, regardless of the season. Wind stress plays a major role in the MLD variability of the southern Red Sea, while net heat flux and evaporation are the dominating factors in the central and northern Red Sea regions. Ocean eddies and Tokar Gap winds significantly alter the MLD structure in the Red Sea. The dynamics associated with the Tokar Gap winds leads to a difference of more than 20m in the average MLD between the north and south of the Tokar axis. [ABSTRACT FROM AUTHOR]

Western boundary currents (WBCs) are highly variable narrow meandering jets, making assessment of their volume transports a complex task. The required high-resolution temporal and spatial measurements are available only at a limited number of sites. In this study a method is developed for improving estimates of the East Australian Current (EAC) mean transport and its low-frequency variability, using complementary modern datasets. The present calculation is a case study that will be extended to other subtropical WBCs. The method developed in this work will reduce uncertainties in estimates of the WBC volume transport and in the interannual mass and heat budgets of the meridional overturning circulations, improving our understanding of the response of WBCs to local and remote forcing on long time scales. High-resolution expendable bathythermograph (HR-XBT) profiles collected along a transect crossing the EAC system near Brisbane, Australia, are merged with coexisting profiles and parking-depth trajectories from Argo floats, and with altimetric sea surface height data. Using HR-XBT/Argo/altimetry data combined with Argo trajectory-based velocities at 1000 m, the 2004–15 mean poleward alongshore transport of the EAC is 19.5 ± 2.0 Sv (1 Sv ≡ 106 m3 s−1) of which 2.5 ± 0.5 Sv recirculate equatorward just offshore of the EAC. These transport estimates are consistent in their mean and variability with concurrent and nearly collocated moored observations at 27°S, and with earlier moored observations along 30°S. Geostrophic transport anomalies in the EAC system, including the EAC recirculation, show a standard deviation of ±3.1 Sv at interannual time scales between 2004 and 2015. [ABSTRACT FROM AUTHOR]

The heat flux anomaly (HFa) within Makassar Strait, Indonesia, is investigated using observed velocity time series and El Niño-Southern Oscillation (ENSO)- scaled temperature profiles. Direct measurements of velocity from 40 m to 740 m depth were recorded during 2004-2011 and 2013-2017 during the International Nusantara STratification ANd Transport (INSTANT) and Monitoring Indonesian Throughflow (MITF) programs. The velocity profile is thermocline-intensified, with a velocity maximum near 100 m depth. In situ temperature measurements during 2004-2006 and ship-based CTD profiles collected during these two monitoring campaigns were combined with all available World Ocean Database CTD, ocean station, mechanical bathythermograph, and expendable bathythermograph data collected within Makassar Strait since 1950 to create representative temperature profiles for positive, negative, and neutral phases of ENSO. The Makassar velocity profile displays a stronger (weaker), shallower (deeper) velocity maximum, and a deeper (shallower) thermocline during La Niña (El Niño). Southward Makassar HFa increases rapidly from 2006 to 2008, with a peak of 0.13 PW in 2008 and 2009. Afterward, Makassar HFa slowly decreases to a minimum of -0.25 PW (less southward) during 2015, after which southward heat flux begins to climb again. Variability in depth-integrated volume transport from the surface to 740 m depth explains 57% of HFa variance. However, the total volume transport does not reflect the relative contributions of the warm upper and cool lower layers. Changes in the depth-dependent velocity profile explain 72% of HFa variance, whereas temperature profile variability explains only 28%. The impact of Makassar HFa variability on the Indian Ocean is assessed through comparison with the heat content anomaly (HCa) in an eastern tropical Indian Ocean box (ETIO; 101.5°E-105.5°E, and 9.5°S-15.5°S) using gridded Argo data. The ETIO HCa follows a similar pattern (R = 0.83) when lagged 30 months behind the Makassar HFa. Although well correlated, a notable discrepancy between the two time series is present in the ETIO in 2012/2013, possibly owing to a shift of the ITF from the dominant South Equatorial Current pathway to a southward Leeuwin track. [ABSTRACT FROM AUTHOR]

Biases have been identified in historical expendable bathythermograph (XBT) datasets, which are one of the major sources of uncertainty in the ocean subsurface database. More than 10 correction schemes were proposed; however, their performance has not been collectively evaluated and compared. This study quantifies how well 10 different available schemes can correct the historical XBT data by comparing the corrected XBT data with collocated reference data in both the World Ocean Database (WOD) 2013 and the EN4 dataset. Four different metrics are proposed to quantify their performances. The results indicate CH14 is the best among the currently available methods, and L09/G12/GR10 can be used with some caveats. To test the robustness of the schemes, we further train the CH14 and L09 by using 50% of the XBT--reference data and the schemes are tested by using the remaining data. The results indicate that the two schemes are robust. Moreover, the EN4 andWODcomparison datasets show a systematic difference of XBT error (~0.01°C on a global scale and 0-700m on average). influences of quality control and data processing have been investigated. Additionally, the side-by-side XBT--CTD comparison experiment is used to examine the correction schemes and provides independent high-quality data for the assessment. The schemes that best correct the global datasets do not always perform as well at correcting the side-by-side dataset, and further examination of the discrepancy in performance is still required. Finally, CH14 and L09 result in very similar ocean heat content (OHC) change estimates in the upper 700m since 1966, suggesting the potential of reducing XBT-induced error in OHC estimates. [ABSTRACT FROM AUTHOR]

Time-varying biases in expendable bathythermograph (XBT) instruments have emerged as a key uncertainty in estimates of historical ocean heat content variability and change. One of the challenges in the development of XBT bias corrections is the lack of metadata in ocean profile databases. Approximately 50% of XBT profiles in the World Ocean database(WOD) have no information about manufacturer or probe type. Building on previous research efforts, this paper presents a deterministic algorithm for assigning missing XBT manufacturer and probe type for individual temperature profiles based on 1) the reporting country, 2) the maximum reported depth, and 3) the record date. The criteria used are based on bulk analysis of known XBT profiles in the WOD for the period 1966-2015. A basic skill assessment demonstrates a 77% success rate at correctly assigning manufacturer and probe type for profiles where this information is available. The skill rate is lowest during the early 1990s, which is also a period when metadata information is particularly poor. The results suggest that substantive improvements could be made through further data analysis and that future algorithms may benefit from including a larger number of predictor variables. [ABSTRACT FROM AUTHOR]

The dynamic data transmission technology of an expendable current profiler is proposed in this paper. Two parallel varnished wires are employed as the data transmission medium. By testing the transmission properties of the varnished wires, a baseband transmission system is studied and designed. An optocoupler is used as the physical layer for data transmission. The data transmission protocol is modified and optimized in accordance with the RS232 protocol, and the Manchester code is superimposed. According to the results of indoor and marine tests, the data transmission distance of the designed system, which employed a 0.1-mm-diameter varnished wire, extends to 2 km with high accuracy for data transmission, exhibiting excellent performance. Moreover, this data transmission technology could be used for other expendable marine-environment parametric measuring instruments such as an expendable bathythermograph and expendable conductivity temperature depth profiler. [ABSTRACT FROM PUBLISHER]

The Yellow Sea Bottom Cold Water (YSBCW) is a large cold water mass lying in the deep part of the Yellow Sea during the warm season. We acquired multichannel seismic (MCS) data using an air gun source to image the structure of the YSBCW. The MCS data recorded reflections from sea water. The recognition of these reflections was confirmed by finite-difference seismic modeling in the frequency-domain. The seismic section from MCS data enabled discrimination of water masses distinctly separated by reflecting horizons. The structure of the water masses is fairly consistent with temperature-depth variations obtained using expandable bathythermograph (XBT) casts. The YSBCW is imaged as the lowermost water mass, maximally 40 m thick, that extends as a lens-like form along the sea bottom under the warm mixed layer. The correlation of XBT measurements and the seismic section indicates a rapid decrease in temperature from around 11 to 8 °C in the uppermost part of the YSBCW. A transition zone between the mixed layer and the underlying YSBCW is also defined. This transition zone has fairly uniform thickness of 14-18 m and marks an interval of rapid temperature drop, indicating vigorous thermal mixing. Our study demonstrates that MCS profiling is a useful and reliable tool for imaging fine structures in the shallow Yellow Sea. [ABSTRACT FROM AUTHOR]

Expendable bathythermograph (XBT) data provide one of the longest available records of upper-ocean temperature. However, temperature and depth biases in XBT data adversely affect estimates of long-term trends of ocean heat content and, to a lesser extent, estimates of volume and heat transport in the ocean. Several corrections have been proposed to overcome historical biases in XBT data, which rely on constantly monitoring these biases. This paper provides an analysis of data collected during three recent hydrographic cruises that utilized different types of probes, and examines methods to reduce temperature and depth biases by improving the thermistor calibration and reducing the mass variability of the XBT probes. The results obtained show that the use of individual thermistor calibration in XBT probes is the most effective calibration to decrease the thermal bias, improving the mean thermal bias to less than 0.02°C and its tolerance from 0.1° to 0.03°C. The temperature variance of probes with screened thermistors is significantly reduced by approximately 60% in comparison to standard probes. On the other hand, probes with a tighter weight tolerance did not show statistically significant reductions in the spread of depth biases, possibly because of the small sample size or the sensitivity of the depth accuracy to other causes affecting the analysis. [ABSTRACT FROM AUTHOR]

Generation and propagation processes of upper-ocean heat content (OHC) in the North Pacific are investigated using oceanic subsurface observations and an eddy-resolving ocean general circulation model hindcast simulation. OHC anomalies are decomposed into physically distinct dynamical components (OHC ρ) due to temperature anomalies that are associated with density anomalies and spiciness components (OHC χ) due to temperature anomalies that are density compensating with salinity. Analysis of the observational and model data consistently shows that both dynamical and spiciness components contribute to interannual-decadal OHC variability, with the former (latter) component dominating in the subtropical (subpolar) North Pacific. OHC ρ variability represents heaving of thermocline, propagates westward, and intensifies along the Kuroshio Extension, consistent with jet-trapped Rossby waves, while OHC χ variability propagates eastward along the subarctic frontal zone, suggesting advection by mean eastward currents. OHC χ variability tightly corresponds in space to horizontal mean spiciness gradients. Meanwhile, area-averaged OHC χ anomalies in the western subarctic frontal zone closely correspond in time to meridional shifts of the subarctic frontal zone. Regression coefficient of the OHC χ time series on the frontal displacement anomalies quantitatively agree with the area-averaged mean spiciness gradient in the region, and suggest that OHC χ is generated via frontal variability in the subarctic frontal zone. [ABSTRACT FROM AUTHOR]

A dynamic data transmission technology for expendable current profilers (XCPs) is proposed in this paper. Two parallel varnished wires are employed as the data transmission medium. By testing the transmission properties of the varnished wires, a baseband transmission system is studied and designed. Modified low-voltage differential signaling (LVDS) is adopted as the physical layer for data transmission. The data transmission protocol is modified and optimized in accordance with the RS-232 protocol and the Manchester code is superimposed. According to the results of indoor and marine tests, the data transmission distance of the designed system, which employs a 0.1mm diameter varnished wire, extends to 2 km with high efficiency and accuracy for data transmission, exhibiting excellent performance. Moreover, this data transmission technology could be used for other expendable marine-environment parametric measuring instruments such as an expendable bathythermograph and an expendable conductivity temperature depth profiler. [ABSTRACT FROM AUTHOR]

The early 21st century experienced a transition in global ocean observing systems from the expendable bathythermograph (XBT) to the Argo. There has been a decrease in XBT observations, and a significant increase in Argo profiling floats in the global ocean. However, numerical XBT observation evaluations during this transition period have been under presented. This study investigates the XBT use effects on the global ocean observing systems using a coupled data assimilation model developed by the Geophysical Fluid Dynamics Laboratory (GFDL). Results show that the inclusion of XBT data significantly increases the accuracy of heat content and sea level change estimations during the pre-Argo period. During the Argo period, the amount of heat content correction by XBT assimilation is significantly weakened, especially in the upper ocean. However, it remains in the deeper oceans below 700 m depths, which is the residual effects of assimilating XBT data with the pre-Argo period. This study also confirms that although XBT only provides temperature observations mostly in the upper 700 m of the northern hemisphere, it can affect both the temperature and salinity fields of data assimilation systems, especially in the deep and southern oceans, which is also supported by the significant change in steric height. [ABSTRACT FROM AUTHOR]

Applying segment-wise altimetry-based gravest empirical mode method to expendable bathythermograph temperature, Argo salinity, and altimetric sea surface height data in March, June, and November from San Francisco to near Japan (30 N, 145 E) via Honolulu, we estimated the component of the heat transport variation caused by change in the southward interior geostrophic flow of the North Pacific subtropical gyre in the top 700 m layer during 1993-2012. The volume transport-weighted temperature ( T ) is strongly dependent on the season. The anomaly of T from the mean seasonal variation, whose standard deviation is 0.14C, was revealed to be caused mainly by change in the volume transport in a potential density layer of 25.0−25.5 σ . The anomaly of T was observed to vary on a decadal or shorter, i.e., quasi-decadal (QD), timescale. The QD-scale variation of T had peaks in 1998 and 2007, equivalent to the reduction in the net heat transport by 6 and 10 TW, respectively, approximately 1 year before those of sea surface temperature (SST) in the warm pool region, east of the Philippines. This suggests that variation in T affects the warm pool SST through modification of the heat balance owing to the entrainment of southward transported water into the mixed layer. [ABSTRACT FROM AUTHOR]

Expendable bathythermograph (XBT) data were the major component of the ocean temperature profile observations from the late 1960s through the early 2000s, and XBTs still continue to provide critical data to monitor surface and subsurface currents, meridional heat transport, and ocean heat content. Systematic errors have been identified in the XBT data, some of which originate from computing the depth in the profile using a theoretically and experimentally derived fall-rate equation (FRE). After in-depth studies of these biases and discussions held in several workshops dedicated to discussing XBT biases, the XBT science community met at the Fourth XBT Science Workshop and concluded that XBT biases consist of 1) errors in depth values due to the inadequacy of the probe motion description done by standard FRE and 2) independent pure temperature biases. The depth error and temperature bias are temperature dependent and may depend on the data acquisition and recording system. In addition, the depth bias also includes an offset term. Some biases affecting the XBT-derived temperature profiles vary with manufacturer/probe type and have been shown to be time dependent. Best practices for historical XBT data corrections, recommendations for future collection of metadata to accompany XBT data, impact of XBT biases on scientific applications, and challenges encountered are presented in this manuscript. Analysis of XBT data shows that, despite the existence of these biases, historical XBT data without bias corrections are still suitable for many scientific applications, and that bias-corrected data can be used for climate research. [ABSTRACT FROM AUTHOR]

A very large portion of the historical information on ocean temperatures has been measured using expendable bathythermograph (XBT) devices. For decades, these devices provided the majority of global information. It is, therefore, important to quantify their accuracy and identify biases in this important historical dataset. Here, calculations are made of the influence of water temperature on the rate of descent of the XBT devices into the ocean waters. In colder regions, the larger viscosity of the water is expected to cause a greater drag force on the device, which would slow the descent. It was found through computational fluid dynamic models that the impact of temperature and viscosity on the probe descent is approximately 2.2% for water temperatures that range from 0° to 27°C. Probe-specific temperature-dependent fall rate equations were applied to 269 collocated XBT/conductivity-temperature-depth (CTD) measurements from two different research cruises. It was found that the probe-specific descent equations were an improvement over the uncorrected method. Next, in an effort to automate the process, the fall rate coefficients were related to the topmost measured temperature in the water column. With this relationship, comparisons were made between the probe-specific descent calculations and 2937 high-resolution XBT-CTD pairs. It was found that again, the new methodology outperformed the standard fall rate equation. The new method was also compared with an independent correction method that was previously published. It was found that both new methods were improvements upon the industry-standard fall rate calculation. Subsequent calculations using the top-100-m water temperature were performed and were found to be statistically insignificant compared to the proposed simplified method. [ABSTRACT FROM AUTHOR]

Expendable bathythermographs (XBTs) are probes widely used to monitor global ocean heat content, variability of ocean currents, and meridional heat transports. In the XBT temperature profile, the depth is estimated from the time of descent in the water using a fall-rate equation. There are two main errors in these profiles: temperature and depth errors. The reduction of error in the estimates of the depth allows a corresponding reduction in the errors in the computations in which XBTs are used. Two experiments were carried out to study the effect of the deployment height on the depth estimates of Deep Blue XBT probes. During these experiments, XBTs were deployed from different heights. The motion of the probes after entering the water was analyzed to determine the position and the velocity of the probes as a function of time, which was compared to that obtained using the Hanawa et al. fall-rate equation. Results showed a difference or offset between the experimentally observed depths and those derived from Hanawa et al. This offset was found to be linked to the deployment height. To eliminate the offset in the fall-rate equation for XBTs deployed from different heights, a methodology is proposed here based on the initial velocities of the probes in the water (or deployment height). Results indicate that the depth estimates in the profiles need to be corrected for an offset, which in addition to having a launch height dependence is time dependent during the first 1.5 s of descent of the probe in the water, and constant after that. [ABSTRACT FROM AUTHOR]

The development and application of a regional ocean data assimilation system are among the aims of the Global Ocean Data Assimilation Experiment. The ocean data assimilation system in the regions including the Indian and West Pacific oceans is an endeavor motivated by this goal. In this study, we describe the system in detail. Moreover, the reanalysis in the joint area of Asia, the Indian Ocean, and the western Pacific Ocean (hereafter AIPOcean) constructed using multi-year model integration with data assimilation is used to test the performance of this system. The ocean model is an eddy-resolving, hybrid coordinate ocean model. Various types of observations including in-situ temperature and salinity profiles (mechanical bathythermograph, expendable bathythermograph, Array for Real-time Geostrophic Oceanography, Tropical Atmosphere Ocean Array, conductivity-temperature-depth, station data), remotely-sensed sea surface temperature, and altimetry sea level anomalies, are assimilated into the reanalysis via the ensemble optimal interpolation method. An ensemble of model states sampled from a long-term integration is allowed to change with season, rather than remaining stationary. The estimated background error covariance matrix may reasonably reflect the seasonality and anisotropy. We evaluate the performance of AIPOcean during the period 1993-2006 by comparisons with independent observations, and some reanalysis products. We show that AIPOcean reduces the errors of subsurface temperature and salinity, and reproduces mesoscale eddies. In contrast to ECCO and SODA products, AIPOcean captures the interannual variability and linear trend of sea level anomalies very well. AIPOcean also shows a good consistency with tide gauges. [ABSTRACT FROM AUTHOR]

In the present work, nine years of altimetry data are analyzed in combination with sea surface temperature and ocean color images in order to track Brazil Current eddies generated at Cape São Tomé, Brazil. Direct evidences are presented that at least six eddies detach from the main current during this period giving rise to isolated rings. Two rings move southward, bordering the current, while four migrate northward, and translate in the direction of the Tubarão Bight. These rings eventually reach the bight, leading to a cyclonic circulation in that region that is analogous, at surface levels, to what would be observed during formation of the Vitória Eddy. For one ring, the observations are complemented by in situ measurements: a Lagrangian surface drifter, an expandable bathythermograph section during the ring formation at Cape São Tomé, and acoustic Doppler current profiler data during the ring formation and inside the bight. The cyclonic circulation within the bight in this occasion reaches levels much deeper than those previously reported for locally-generated eddies. These results indicate that properties of shelf and slope waters near Cape São Tomé can be carried upstream the Brazil Current, eventually influencing the coastal waters further north, with possible ecological and environmental implications. [ABSTRACT FROM AUTHOR]

During the Dynamics of Madden-Julian Oscillation (DYNAMO) Experiment in 2011, airborne expendable conductivity-temperature-depth (AXCTD) probes and airborne expendable bathythermographs (AXBTs) were deployed using NOAA's WP-3D Orion aircraft over the southern tropical Indian Ocean. From initial analysis of the AXCTD data, about 95% of profiles exhibit double mixed layer structures. The presence of a mixed layer from some of these profiles were erroneous and were introduced because of the AXCTD processing software not being able to correctly identify the starting point of the probe descent. This work reveals the impact of these errors in data processing and presents an objective method to remove such erroneous data from the profiles using spectrograms from raw audio files. Reconstructed AXCTD/AXBT profiles are compared with collocated shipborne conductivity-temperature-depth (CTD) and expendable bathythermograph (XBT) profiles and are found to be in good agreement. [ABSTRACT FROM AUTHOR]

The impact of the assimilation of ocean observations on reducing global Hybrid Coordinate Ocean Model (HYCOM) 48-h forecast errors is presented. The assessment uses an adjoint-based data impact procedure that characterizes the forecast impact of every observation assimilated, and it allows the observation impacts to be partitioned by data type, geographic region, and vertical level. The impact cost function is the difference between HYCOM 48- and 72-h forecast errors computed for temperature and salinity at all model levels and grid points. It is shown that routine assimilation of large numbers of observations consistently reduces global HYCOM 48-h forecast errors for both temperature and salinity. The largest error reduction is due to the assimilation of temperature and salinity profiles from the tropical fixed mooring arrays, followed by Argo, expendable bathythermograph (XBT), and animal sensor data. On a per-observation basis, the most important global observing system is Argo. The beneficial impact of assimilating Argo temperature and salinity profiles extends to all depths sampled, with salinity impacts maximum at the surface and temperature impacts showing a subsurface maximum in the 100-200-m-depth range. The reduced impact of near-surface Argo temperature profile levels is due to the vertical covariances in the assimilation that extend the influence of the large number of sea surface temperature (SST) observations to the base of the mixed layer. Application of the adjoint-based data impact system to identify a data quality problem in a geostationary satellite SST observing system is also provided. [ABSTRACT FROM AUTHOR]

Systematic biases in historical expendable bathythermograph (XBT) data are examined using two datasets: 4151 XBT-CTD side-by-side pairs from 1967 to 2011 and 218 653 global-scale XBT-CTD pairs (within one month and 1°) extracted from the World Ocean Database 2009 ( WOD09) from 1966 to 2010. Using the side-by-side dataset, it was found that both the pure thermal bias and the XBT fall rate (from which the depth of observation is calculated) increase with water temperature. Correlations between the terminal velocity A and deceleration B terms of the fall-rate equation (FRE) and between A and the offset from the surface terms are obtained, with A as the dominant term in XBT fall-rate behavior. To quantify the time variation of the XBT fall-rate and pure temperature biases, global-scale XBT-CTD pairs are used. Based on the results from the two datasets, a new correction scheme for historical XBT data is proposed for nine independent probe-type groups. The scheme includes corrections for both temperature and depth records, which are all variable with calendar year, water temperature, and probe type. The results confirm those found in previous studies: a slowing in fall rate during the 1970s and 2000s and the large pure thermal biases during 1970-85. The performance of nine different correction schemes is compared. After the proposed corrections are applied to the XBT data in the WOD09 dataset, global ocean heat content from 1967 to 2010 is reestimated. [ABSTRACT FROM AUTHOR]

Ocean 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. [ABSTRACT FROM AUTHOR]

Abstract: Mathematical modeling, absent simplifying assumptions and coupled with numerical simulation, has been implemented to determine the motions and forces experienced by a sphere penetrating a water surface from an air space above the surface. The model and simulation are validated by comparisons with extensive experimental data and with trends from approximate analyses. Although the present work adds to the understanding and quantification of the sphere as an entry object, its major contribution is model development and validation to enable investigation of water entry of objects of practical utility such as the expendable bathythermograph (XBT). The XBT device is widely used in the determination of temperature distributions in large water bodies such as oceans. The measured temperature distributions are, in turn, used to determine the thermal energy content of oceans. During the course of the numerical simulations, parametric variations were made of the sphere velocity, surface tension, flow regime (laminar or turbulent), and Reynolds number. The drag-coefficient results were found to be independent of these quantities. This outcome indicates that momentum transfer from the sphere to the adjacent liquid is responsible for the drag force and that friction is a secondary issue. [Copyright &y& Elsevier]