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ArticleSatellite and in situ salinity : understanding near-surface stratification and subfootprint variability(American Meteorological Society, 2016-08-31) Boutin, Jacqueline ; Chao, Yi ; Asher, William E. ; Delcroix, Thierry ; Drucker, Robert S. ; Drushka, Kyla ; Kolodziejczyk, Nicolas ; Lee, Tong ; Reul, Nicolas ; Reverdin, Gilles ; Schanze, Julian J. ; Soloviev, Alexander ; Yu, Lisan ; Anderson, Jessica ; Brucker, Ludovic ; Dinnat, Emmanuel ; Santos-Garcia, Andrea ; Jones, W. Linwood ; Maes, Christophe ; Meissner, Thomas ; Tang, Wenqing ; Vinogradova, Nadya ; Ward, BrianRemote sensing of salinity using satellite-mounted microwave radiometers provides new perspectives for studying ocean dynamics and the global hydrological cycle. Calibration and validation of these measurements is challenging because satellite and in situ methods measure salinity differently. Microwave radiometers measure the salinity in the top few centimeters of the ocean, whereas most in situ observations are reported below a depth of a few meters. Additionally, satellites measure salinity as a spatial average over an area of about 100 × 100 km2. In contrast, in situ sensors provide pointwise measurements at the location of the sensor. Thus, the presence of vertical gradients in, and horizontal variability of, sea surface salinity complicates comparison of satellite and in situ measurements. This paper synthesizes present knowledge of the magnitude and the processes that contribute to the formation and evolution of vertical and horizontal variability in near-surface salinity. Rainfall, freshwater plumes, and evaporation can generate vertical gradients of salinity, and in some cases these gradients can be large enough to affect validation of satellite measurements. Similarly, mesoscale to submesoscale processes can lead to horizontal variability that can also affect comparisons of satellite data to in situ data. Comparisons between satellite and in situ salinity measurements must take into account both vertical stratification and horizontal variability.
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ArticleEditorial: Oceanobs19: An ocean of opportunity(Frontiers Media, 2019-09-06) Speich, Sabrina ; Lee, Tong ; Muller-Karger, Frank E. ; Lorenzoni, Laura ; Pascual, Ananda ; Jin, Di ; Delory, Eric ; Reverdin, Gilles ; Siddorn, John ; Lewis, Marlon R. ; Marba, Nuria ; Buttigieg, Pier Luigi ; Chiba, Sanae ; Manley, Justin ; Kabo-Bah, Amos Tiereyangn ; Desai, Kruti ; Ackerman, AbbyThe OceanObs conferences are held once every 10 years for the scientific, technical, and operational communities involved in the planning, implementation, and use of ocean observing systems. They serve to communicate progress, promote plans, and to define advances in ocean observing in response to societies' needs. Each conference provides a forum for the community to review the state of the ocean observing science and operations, and to define goals and plans to achieve over the next decade.
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ArticleThe global ocean water cycle in atmospheric reanalysis, satellite, and ocean salinity(American Meteorological Society, 2017-05-02) Yu, Lisan ; Jin, Xiangze ; Josey, Simon A. ; Lee, Tong ; Kumar, Arun ; Wen, Caihong ; Xue, YanThis study provides an assessment of the uncertainty in ocean surface (OS) freshwater budgets and variability using evaporation E and precipitation P from 10 atmospheric reanalyses, two combined satellite-based E − P products, and two observation-based salinity products. Three issues are examined: the uncertainty level in the OS freshwater budget in atmospheric reanalyses, the uncertainty structure and association with the global ocean wet/dry zones, and the potential of salinity in ascribing the uncertainty in E − P. The products agree on the global mean pattern but differ considerably in magnitude. The OS freshwater budgets are 129 ± 10 (8%) cm yr−1 for E, 118 ± 11 (9%) cm yr−1 for P, and 11 ± 4 (36%) cm yr−1 for E − P, where the mean and error represent the ensemble mean and one standard deviation of the ensemble spread. The E − P uncertainty exceeds the uncertainty in E and P by a factor of 4 or more. The large uncertainty is attributed to P in the tropical wet zone. Most reanalyses tend to produce a wider tropical rainband when compared to satellite products, with the exception of two recent reanalyses that implement an observation-based correction for the model-generated P over land. The disparity in the width and the extent of seasonal migrations of the tropical wet zone causes a large spread in P, implying that the tropical moist physics and the realism of tropical rainfall remain a key challenge. Satellite salinity appears feasible to evaluate the fidelity of E − P variability in three tropical areas, where the uncertainty diagnosis has a global indication.
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ArticleIntraseasonal variability of surface salinity in the eastern tropical pacific associated with mesoscale eddies.(American Geophysical Union, 2019-03-28) Hasson, Audrey ; Farrar, J. Thomas ; Boutin, Jacqueline ; Bingham, Frederick ; Lee, TongStrong variability in sea surface salinity (SSS) in the Eastern Tropical Pacific (ETPac) on intraseasonal to interannual timescales was studied using data from the Soil Moisture and Ocean Salinity, Soil Moisture Active Passive, and Aquarius satellite missions. A zonal wave number‐frequency spectral analysis of SSS reveals a dominant timescale of 50–180 days and spatial scale of 8°–20° of longitude with a distinct seasonal cycle and interannual variability. This intraseasonal SSS signal is detailed in the study of 19 individual ETPac eddies over 2010–2016 identified by their sea level anomalies, propagating westward at a speed of about 17 cm/s. ETPac eddies trap and advect water in their core westward up to 40° of longitude away from the coast. The SSS signatures of these eddies, with an average anomaly of 0.5‐pss magnitude difference from ambient values, enable the study of their dynamics and the mixing of their core waters with the surroundings. Three categories of eddies were identified according to the location where they were first tracked: (1) in the Gulf of Tehuantepec, (2) in the Gulf of Papagayo, and (3) in the open ocean near 100°W–12°N. They all traveled westward near 10°N latitude. Category 3 is of particular interest, as eddies seeded in the Gulf of Tehuantepec grew substantially in the vicinity of the Clipperton Fracture Zone rise and in a region where the mean zonal currents have anticyclonic shear. The evolution of the SSS signature associated with the eddies indicates the importance of mixing to their dissipation.
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ArticleThe tropical Atlantic observing system(Frontiers Media, 2019-05-10) Foltz, Gregory R. ; Brandt, Peter ; Richter, Ingo ; Rodriguez-fonseca, Belen ; Hernandez, Fabrice ; Dengler, Marcus ; Rodrigues, Regina ; Schmidt, Jörn Oliver ; Yu, Lisan ; Lefevre, Nathalie ; Cotrim Da Cunha, Leticia ; McPhaden, Michael J. ; Araujo, Moacyr ; Karstensen, Johannes ; Hahn, Johannes ; Martín-Rey, Marta ; Patricola, Christina ; Poli, Paul ; Zuidema, Paquita ; Hummels, Rebecca ; Perez, Renellys ; Hatje, Vanessa ; Luebbecke, Joke ; Polo, Irene ; Lumpkin, Rick ; Bourlès, Bernard ; Asuquo, Francis Emile ; Lehodey, Patrick ; Conchon, Anna ; Chang, Ping ; Dandin, Philippe ; Schmid, Claudia ; Sutton, Adrienne J. ; Giordani, Hervé ; Xue, Yan ; Illig, Serena ; Losada, Teresa ; Grodsky, Semyon A. ; Gasparin, Florent ; Lee, Tong ; Mohino, Elsa ; Nobre, Paulo ; Wanninkhof, Rik ; Keenlyside, Noel S. ; Garcon, Veronique Cameille ; Sanchez-Gomez, Emilia ; Nnamchi, Hyacinth ; Drevillon, Marie ; Storto, Andrea ; Remy, Elisabeth ; Lazar, Alban ; Speich, Sabrina ; Goes, Marlos Pereira ; Dorrington, Tarquin ; Johns, William E. ; Moum, James N. ; Robinson, Carol ; Perruche, Coralie ; de Souza, Ronald Buss ; Gaye, Amadou ; Lopez-Parages, Jorge ; Monerie, Paul-Arthur ; Castellanos, Paola ; Benson, Nsikak U. ; Hounkonnou, Mahouton Norbert ; Trotte Duha, Janice ; Laxenaire, Rémi ; Reul, Nicolashe tropical Atlantic is home to multiple coupled climate variations covering a wide range of timescales and impacting societally relevant phenomena such as continental rainfall, Atlantic hurricane activity, oceanic biological productivity, and atmospheric circulation in the equatorial Pacific. The tropical Atlantic also connects the southern and northern branches of the Atlantic meridional overturning circulation and receives freshwater input from some of the world’s largest rivers. To address these diverse, unique, and interconnected research challenges, a rich network of ocean observations has developed, building on the backbone of the Prediction and Research Moored Array in the Tropical Atlantic (PIRATA). This network has evolved naturally over time and out of necessity in order to address the most important outstanding scientific questions and to improve predictions of tropical Atlantic severe weather and global climate variability and change. The tropical Atlantic observing system is motivated by goals to understand and better predict phenomena such as tropical Atlantic interannual to decadal variability and climate change; multidecadal variability and its links to the meridional overturning circulation; air-sea fluxes of CO2 and their implications for the fate of anthropogenic CO2; the Amazon River plume and its interactions with biogeochemistry, vertical mixing, and hurricanes; the highly productive eastern boundary and equatorial upwelling systems; and oceanic oxygen minimum zones, their impacts on biogeochemical cycles and marine ecosystems, and their feedbacks to climate. Past success of the tropical Atlantic observing system is the result of an international commitment to sustained observations and scientific cooperation, a willingness to evolve with changing research and monitoring needs, and a desire to share data openly with the scientific community and operational centers. The observing system must continue to evolve in order to meet an expanding set of research priorities and operational challenges. This paper discusses the tropical Atlantic observing system, including emerging scientific questions that demand sustained ocean observations, the potential for further integration of the observing system, and the requirements for sustaining and enhancing the tropical Atlantic observing system.
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ArticleLocal and remote forcing of interannual sea‐level variability at Nantucket Island(American Geophysical Union, 2022-06-07) Wang, Ou ; Lee, Tong ; Piecuch, Christopher G. ; Fukumori, Ichiro ; Fenty, Ian ; Frederikse, Thomas ; Menemenlis, Dimitris ; Ponte, Rui M. ; Zhang, HongThe relative contributions of local and remote wind stress and air-sea buoyancy forcing to sea-level variations along the East Coast of the United States are not well quantified, hindering the understanding of sea-level predictability there. Here, we use an adjoint sensitivity analysis together with an Estimating the Circulation and Climate of the Ocean (ECCO) ocean state estimate to establish the causality of interannual variations in Nantucket dynamic sea level. Wind forcing explains 67% of the Nantucket interannual sea-level variance, while wind and buoyancy forcing together explain 97% of the variance. Wind stress contribution is near-local, primarily from the New England shelf northeast of Nantucket. We disprove a previous hypothesis about Labrador Sea wind stress being an important driver of Nantucket sea-level variations. Buoyancy forcing, as important as wind stress in some years, includes local contributions as well as remote contributions from the subpolar North Atlantic that influence Nantucket sea level a few years later. Our rigorous adjoint-based analysis corroborates previous correlation-based studies indicating that sea-level variations in the subpolar gyre and along the United States northeast coast can both be influenced by subpolar buoyancy forcing. Forward perturbation experiments further indicate remote buoyancy forcing affects Nantucket sea level mostly through slow advective processes, although coastally trapped waves can cause rapid Nantucket sea level response within a few weeks.
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ArticleUnderstanding ENSO diversity(American Meteorological Society, 2015-06) Capotondi, Antonietta ; Wittenberg, Andrew T. ; Newman, Matthew ; Di Lorenzo, Emanuele ; Yu, Jin-Yi ; Braconnot, Pascale ; Cole, Julia ; Dewitte, Boris ; Giese, Benjamin ; Guilyardi, Eric ; Jin, Fei-Fei ; Karnauskas, Kristopher B. ; Kirtman, Benjamin ; Lee, Tong ; Schneider, Niklas ; Xue, Yan ; Yeh, Sang-WookEl Niño–Southern Oscillation (ENSO) is a naturally occurring mode of tropical Pacific variability, with global impacts on society and natural ecosystems. While it has long been known that El Niño events display a diverse range of amplitudes, triggers, spatial patterns, and life cycles, the realization that ENSO’s impacts can be highly sensitive to this event-to-event diversity is driving a renewed interest in the subject. This paper surveys our current state of knowledge of ENSO diversity, identifies key gaps in understanding, and outlines some promising future research directions.
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ArticleClosing the water cycle from observations across scales: where do we stand?(American Meteorological Society, 2021-10-01) Dorigo, Wouter ; Dietrich, Stephan ; Aires, Filipe ; Brocca, Luca ; Carter, Sarah ; Cretaux, Jean-François ; Dunkerley, David ; Enomoto, Hiroyuki ; Forsberg, René ; Güntner, Andreas ; Hegglin, Michaela I. ; Hollmann, Rainer ; Hurst, Dale F. ; Johannessen, Johnny A. ; Kummerow, Christian ; Lee, Tong ; Luojus, Kari ; Looser, Ulrich ; Miralles, Diego ; Pellet, Victor ; Recknagel, Thomas ; Vargas, Claudia Ruz ; Schneider, Udo ; Schoeneich, Philippe ; Schröder, Marc ; Tapper, Nigel ; Vuglinsky, Valery ; Wagner, Wolfgang ; Yu, Lisan ; Zappa, Luca ; Zemp, Michael ; Aich, ValentinLife on Earth vitally depends on the availability of water. Human pressure on freshwater resources is increasing, as is human exposure to weather-related extremes (droughts, storms, floods) caused by climate change. Understanding these changes is pivotal for developing mitigation and adaptation strategies. The Global Climate Observing System (GCOS) defines a suite of essential climate variables (ECVs), many related to the water cycle, required to systematically monitor Earth’s climate system. Since long-term observations of these ECVs are derived from different observation techniques, platforms, instruments, and retrieval algorithms, they often lack the accuracy, completeness, and resolution, to consistently characterize water cycle variability at multiple spatial and temporal scales. Here, we review the capability of ground-based and remotely sensed observations of water cycle ECVs to consistently observe the hydrological cycle. We evaluate the relevant land, atmosphere, and ocean water storages and the fluxes between them, including anthropogenic water use. Particularly, we assess how well they close on multiple temporal and spatial scales. On this basis, we discuss gaps in observation systems and formulate guidelines for future water cycle observation strategies. We conclude that, while long-term water cycle monitoring has greatly advanced in the past, many observational gaps still need to be overcome to close the water budget and enable a comprehensive and consistent assessment across scales. Trends in water cycle components can only be observed with great uncertainty, mainly due to insufficient length and homogeneity. An advanced closure of the water cycle requires improved model–data synthesis capabilities, particularly at regional to local scales.
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ArticleFluxSat: measuring the ocean-atmosphere turbulent exchange of heat and moisture from space(MDPI, 2020-06-03) Gentemann, Chelle L. ; Clayson, Carol A. ; Brown, Shannon ; Lee, Tong ; Parfitt, Rhys ; Farrar, J. Thomas ; Bourassa, Mark A. ; Minnett, Peter J. ; Seo, Hyodae ; Gille, Sarah T. ; Zlotnicki, VictorRecent results using wind and sea surface temperature data from satellites and high-resolution coupled models suggest that mesoscale ocean–atmosphere interactions affect the locations and evolution of storms and seasonal precipitation over continental regions such as the western US and Europe. The processes responsible for this coupling are difficult to verify due to the paucity of accurate air–sea turbulent heat and moisture flux data. These fluxes are currently derived by combining satellite measurements that are not coincident and have differing and relatively low spatial resolutions, introducing sampling errors that are largest in regions with high spatial and temporal variability. Observational errors related to sensor design also contribute to increased uncertainty. Leveraging recent advances in sensor technology, we here describe a satellite mission concept, FluxSat, that aims to simultaneously measure all variables necessary for accurate estimation of ocean–atmosphere turbulent heat and moisture fluxes and capture the effect of oceanic mesoscale forcing. Sensor design is expected to reduce observational errors of the latent and sensible heat fluxes by almost 50%. FluxSat will improve the accuracy of the fluxes at spatial scales critical to understanding the coupled ocean–atmosphere boundary layer system, providing measurements needed to improve weather forecasts and climate model simulations.
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ArticleEvolving the physical global ocean observing system for research and application services through international coordination(Frontiers Media, 2019-08-06) Sloyan, Bernadette M. ; Wilkin, John L. ; Hill, Katherine Louise ; Chidichimo, Maria Paz ; Cronin, Meghan F. ; Johannessen, Johnny A. ; Karstensen, Johannes ; Krug, Marjolaine ; Lee, Tong ; Oka, Eitarou ; Palmer, Matthew D. ; Rabe, Benjamin ; Speich, Sabrina ; von Schuckmann, Karina ; Weller, Robert A. ; Yu, WeidongClimate change and variability are major societal challenges, and the ocean is an integral part of this complex and variable system. Key to the understanding of the ocean’s role in the Earth’s climate system is the study of ocean and sea-ice physical processes, including its interactions with the atmosphere, cryosphere, land, and biosphere. These processes include those linked to ocean circulation; the storage and redistribution of heat, carbon, salt and other water properties; and air-sea exchanges of heat, momentum, freshwater, carbon, and other gasses. Measurements of ocean physics variables are fundamental to reliable earth prediction systems for a range of applications and users. In addition, knowledge of the physical environment is fundamental to growing understanding of the ocean’s biogeochemistry and biological/ecosystem variability and function. Through the progress from OceanObs’99 to OceanObs’09, the ocean observing system has evolved from a platform centric perspective to an integrated observing system. The challenge now is for the observing system to evolve to respond to an increasingly diverse end user group. The Ocean Observations Physics and Climate panel (OOPC), formed in 1995, has undertaken many activities that led to observing system-related agreements. Here, OOPC will explore the opportunities and challenges for the development of a fit-for-purpose, sustained and prioritized ocean observing system, focusing on physical variables that maximize support for fundamental research, climate monitoring, forecasting on different timescales, and society. OOPC recommendations are guided by the Framework for Ocean Observing which emphasizes identifying user requirements by considering time and space scales of the Essential Ocean Variables. This approach provides a framework for reviewing the adequacy of the observing system, looking for synergies in delivering an integrated observing system for a range of applications and focusing innovation in areas where existing technologies do not meet these requirements.
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ArticleA road map to IndOOS-2 better observations of the rapidly warming Indian Ocean(American Meteorological Society, 2020-11-01) Beal, Lisa M. ; Vialard, Jérôme ; Roxy, Mathew Koll ; Li, Jing ; Andres, Magdalena ; Annamalai, Hariharasubramanian ; Feng, Ming ; Han, Weiqing ; Hood, Raleigh R. ; Lee, Tong ; Lengaigne, Matthieu ; Lumpkin, Rick ; Masumoto, Yukio ; McPhaden, Michael J. ; Ravichandran, M. ; Shinoda, Toshiaki ; Sloyan, Bernadette M. ; Strutton, Peter G. ; Subramanian, Aneesh C. ; Tozuka, Tomoki ; Ummenhofer, Caroline C. ; Unnikrishnan, Shankaran Alakkat ; Wiggert, Jerry D. ; Yu, Lisan ; Cheng, Lijing ; Desbruyères, Damien G. ; Parvathi, V.The Indian Ocean Observing System (IndOOS), established in 2006, is a multinational network of sustained oceanic measurements that underpin understanding and forecasting of weather and climate for the Indian Ocean region and beyond. Almost one-third of humanity lives around the Indian Ocean, many in countries dependent on fisheries and rain-fed agriculture that are vulnerable to climate variability and extremes. The Indian Ocean alone has absorbed a quarter of the global oceanic heat uptake over the last two decades and the fate of this heat and its impact on future change is unknown. Climate models project accelerating sea level rise, more frequent extremes in monsoon rainfall, and decreasing oceanic productivity. In view of these new scientific challenges, a 3-yr international review of the IndOOS by more than 60 scientific experts now highlights the need for an enhanced observing network that can better meet societal challenges, and provide more reliable forecasts. Here we present core findings from this review, including the need for 1) chemical, biological, and ecosystem measurements alongside physical parameters; 2) expansion into the western tropics to improve understanding of the monsoon circulation; 3) better-resolved upper ocean processes to improve understanding of air–sea coupling and yield better subseasonal to seasonal predictions; and 4) expansion into key coastal regions and the deep ocean to better constrain the basinwide energy budget. These goals will require new agreements and partnerships with and among Indian Ocean rim countries, creating opportunities for them to enhance their monitoring and forecasting capacity as part of IndOOS-2.
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ArticleCompounding impact of severe weather events fuels marine heatwave in the coastal ocean(Nature Research, 2020-09-22) Dzwonkowski, Brian ; Coogan, Jeffrey ; Fournier, Séverine ; Lockridge, Grant R. ; Park, Kyeong ; Lee, TongExposure to extreme events is a major concern in coastal regions where growing human populations and stressed natural ecosystems are at significant risk to such phenomena. However, the complex sequence of processes that transform an event from notable to extreme can be challenging to identify and hence, limit forecast abilities. Here, we show an extreme heat content event (i.e., a marine heatwave) in coastal waters of the northern Gulf of Mexico resulted from compounding effects of a tropical storm followed by an atmospheric heatwave. This newly identified process of generating extreme ocean temperatures occurred prior to landfall of Hurricane Michael during October of 2018 and, as critical contributor to storm intensity, likely contributed to the subsequent extreme hurricane. This pattern of compounding processes will also exacerbate other environmental problems in temperature-sensitive ecosystems (e.g., coral bleaching, hypoxia) and is expected to have expanding impacts under global warming predictions.
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ArticleInfluence of nonseasonal river discharge on sea surface salinity and height(American Geophysical Union, 2022-01-18) Chandanpurkar, Hrishikesh A. ; Lee, Tong ; Wang, Xiaochun ; Zhang, Hong ; Fournier, Séverine ; Fenty, Ian ; Fukumori, Ichiro ; Menemenlis, Dimitris ; Piecuch, Christopher G. ; Reager, John T. ; Wang, Ou ; Worden, JohnRiver discharge influences ocean dynamics and biogeochemistry. Due to the lack of a systematic, up-to-date global measurement network for river discharge, global ocean models typically use seasonal discharge climatology as forcing. This compromises the simulated nonseasonal variation (the deviation from seasonal climatology) of the ocean near river plumes and undermines their usefulness for interdisciplinary research. Recently, a reanalysis-based daily varying global discharge data set was developed, providing the first opportunity to quantify nonseasonal discharge effects on global ocean models. Here we use this data set to force a global ocean model for the 1992–2017 period. We contrast this experiment with another experiment (with identical atmospheric forcings) forced by seasonal climatology from the same discharge data set to isolate nonseasonal discharge effects, focusing on sea surface salinity (SSS) and sea surface height (SSH). Near major river mouths, nonseasonal discharge causes standard deviations in SSS (SSH) of 1.3–3 practical salinity unit (1–2.7 cm). The inclusion of nonseasonal discharge results in notable improvement of model SSS against satellite SSS near most of the tropical-to-midlatitude river mouths and minor improvement of model SSH against satellite or in-situ SSH near some of the river mouths. SSH changes associated with nonseasonal discharge can be explained by salinity effects on halosteric height and estimated accurately through the associated SSS changes. A recent theory predicting river discharge impact on SSH is found to perform reasonably well overall but underestimates the impact on SSH around the global ocean and has limited skill when applied to rivers near the equator and in the Arctic Ocean.
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ArticleRevisiting the global patterns of seasonal cycle in sea surface salinity(American Geophysical Union, 2021-03-17) Yu, Lisan ; Bingham, Frederick ; Lee, Tong ; Dinnat, Emmanuel ; Fournier, Séverine ; Melnichenko, Oleg ; Tang, Wenqing ; Yueh, Simon H.Argo profiling floats and L-band passive microwave remote sensing have significantly improved the global sampling of sea surface salinity (SSS) in the past 15 years, allowing the study of the range of SSS seasonal variability using concurrent satellite and in situ platforms. Here, harmonic analysis was applied to four 0.25° satellite products and two 1° in situ products between 2016 and 2018 to determine seasonal harmonic patterns. The 0.25° World Ocean Atlas (WOA) version 2018 was referenced to help assess the harmonic patterns from a long-term perspective based on the 3-year period. The results show that annual harmonic is the most characteristic signal of the seasonal cycle, and semiannual harmonic is important in regions influenced by monsoon and major rivers. The percentage of the observed variance that can be explained by harmonic modes varies with products, with values ranging between 50% and 72% for annual harmonic and between 15% and 19% for semiannual harmonic. The large spread in the explained variance by the annual harmonic reflects the large disparity in nonseasonal variance (or noise) in the different products. Satellite products are capable of capturing sharp SSS features on meso- and frontal scales and the patterns agree well with the WOA 2018. These products are, however, subject to the impacts of radiometric noises and are algorithm dependent. The coarser-resolution in situ products may underrepresent the full range of high-frequency small scale SSS variability when data record is short, which may have enlarged the explained SSS variance by the annual harmonic.
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ArticleAdequacy of the ocean observation system for quantifying regional heat and freshwater storage and change(Frontiers Media, 2019-08-29) Palmer, Matthew D. ; Durack, Paul J. ; Chidichimo, Maria Paz ; Church, John A. ; Cravatte, Sophie ; Hill, Katherine Louise ; Johannessen, Johnny A. ; Karstensen, Johannes ; Lee, Tong ; Legler, David ; Mazloff, Matthew R. ; Oka, Eitarou ; Purkey, Sarah G. ; Rabe, Benjamin ; Sallee, Jean-Baptiste ; Sloyan, Bernadette M. ; Speich, Sabrina ; von Schuckmann, Karina ; Willis, Josh ; Wijffels, Susan E.Considerable advances in the global ocean observing system over the last two decades offers an opportunity to provide more quantitative information on changes in heat and freshwater storage. Variations in these storage terms can arise through internal variability and also the response of the ocean to anthropogenic climate change. Disentangling these competing influences on the regional patterns of change and elucidating their governing processes remains an outstanding scientific challenge. This challenge is compounded by instrumental and sampling uncertainties. The combined use of ocean observations and model simulations is the most viable method to assess the forced signal from noise and ascertain the primary drivers of variability and change. Moreover, this approach offers the potential for improved seasonal-to-decadal predictions and the possibility to develop powerful multi-variate constraints on climate model future projections. Regional heat storage changes dominate the steric contribution to sea level rise over most of the ocean and are vital to understanding both global and regional heat budgets. Variations in regional freshwater storage are particularly relevant to our understanding of changes in the hydrological cycle and can potentially be used to verify local ocean mass addition from terrestrial and cryospheric systems associated with contemporary sea level rise. This White Paper will examine the ability of the current ocean observing system to quantify changes in regional heat and freshwater storage. In particular we will seek to answer the question: What time and space scales are currently resolved in different regions of the global oceans? In light of some of the key scientific questions, we will discuss the requirements for measurement accuracy, sampling, and coverage as well as the synergies that can be leveraged by more comprehensively analyzing the multi-variable arrays provided by the integrated observing system.
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ArticleA sustained ocean observing system in the Indian Ocean for climate related scientific knowledge and societal needs(Frontiers Media, 2019-06-28) Hermes, Juliet ; Masumoto, Yukio ; Beal, Lisa M. ; Roxy, Mathew Koll ; Vialard, Jérôme ; Andres, Magdalena ; Annamalai, Hariharasubramanian ; Behera, Swadhin ; D’Adamo, Nick ; Doi, Takeshi ; Feng, Ming ; Han, Weiqing ; Hardman-Mountford, Nick ; Hendon, Harry ; Hood, Raleigh R. ; Kido, Shoichiro ; Lee, Craig M. ; Lee, Tong ; Lengaigne, Matthieu ; Li, Jing ; Lumpkin, Rick ; Navaneeth, K. N. ; Milligan, Ben ; McPhaden, Michael J. ; Ravichandran, M. ; Shinoda, Toshiaki ; Singh, Arvind ; Sloyan, Bernadette M. ; Strutton, Peter G. ; Subramanian, Aneesh C. ; Thurston, Sidney ; Tozuka, Tomoki ; Ummenhofer, Caroline C. ; Unnikrishnan, Shankaran Alakkat ; Venkatesan, Ramasamy ; Wang, Dongxiao ; Wiggert, Jerry D. ; Yu, Lisan ; Yu, WeidongThe Indian Ocean is warming faster than any of the global oceans and its climate is uniquely driven by the presence of a landmass at low latitudes, which causes monsoonal winds and reversing currents. The food, water, and energy security in the Indian Ocean rim countries and islands are intrinsically tied to its climate, with marine environmental goods and services, as well as trade within the basin, underpinning their economies. Hence, there are a range of societal needs for Indian Ocean observation arising from the influence of regional phenomena and climate change on, for instance, marine ecosystems, monsoon rains, and sea-level. The Indian Ocean Observing System (IndOOS), is a sustained observing system that monitors basin-scale ocean-atmosphere conditions, while providing flexibility in terms of emerging technologies and scientificand societal needs, and a framework for more regional and coastal monitoring. This paper reviews the societal and scientific motivations, current status, and future directions of IndOOS, while also discussing the need for enhanced coastal, shelf, and regional observations. The challenges of sustainability and implementation are also addressed, including capacity building, best practices, and integration of resources. The utility of IndOOS ultimately depends on the identification of, and engagement with, end-users and decision-makers and on the practical accessibility and transparency of data for a range of products and for decision-making processes. Therefore we highlight current progress, issues and challenges related to end user engagement with IndOOS, as well as the needs of the data assimilation and modeling communities. Knowledge of the status of the Indian Ocean climate and ecosystems and predictability of its future, depends on a wide range of socio-economic and environmental data, a significant part of which is provided by IndOOS.
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PreprintHeat and freshwater changes in the Indian Ocean region(Nature Research, 2021-07-20) Ummenhofer, Caroline C. ; Murty, Sujata A. ; Sprintall, Janet ; Lee, Tong ; Abram, Nerilie J.Across the Indo-Pacific region, rapid increases in surface temperatures, ocean heat content and concomitant hydrological changes have implications for sea level rise, ocean circulation and regional freshwater availability. In this Review, we synthesize evidence from multiple data sources to elucidate whether the observed heat and freshwater changes in the Indian Ocean represent an intensification of the hydrological cycle, as expected in a warming world. At the basin scale, twentieth century warming trends can be unequivocally attributed to human-induced climate change. Changes since 1980, however, appear dominated by multi-decadal variability associated with the Interdecadal Pacific oscillation, manifested as shifts in the Walker circulation and a corresponding reorganization of the Indo-Pacific heat and freshwater balance. Such variability, coupled with regional-scale trends, a short observational record and climate model uncertainties, makes it difficult to assess whether contemporary changes represent an anthropogenically forced transformation of the hydrological cycle. Future work must, therefore, focus on maintaining and expanding observing systems of remotely sensed and in situ observations, as well as extending and integrating coral proxy networks. Improved climate model simulations of the Maritime Continent region and its intricate exchange between the Pacific and Indian oceans are further necessary to quantify and attribute Indo-Pacific hydrological changes.