Ravichandran M.

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Moored observations of the surface meteorology and air-sea fluxes in the Northern Bay of Bengal in 2015

2018-12-28 , Weller, Robert A. , Farrar, J. Thomas , Seo, Hyodae , Prend, Channing , Sengupta, Debasis , Lekha, J. Sree , Ravichandran, M. , Venkatesan, Ramasamy

Time series of surface meteorology and air–sea fluxes from the northern Bay of Bengal are analyzed, quantifying annual and seasonal means, variability, and the potential for surface fluxes to contribute significantly to variability in surface temperature and salinity. Strong signals were associated with solar insolation and its modulation by cloud cover, and, in the 5- to 50-day range, with intraseasonal oscillations (ISOs). The northeast (NE) monsoon (DJF) was typically cloud free, with strong latent heat loss and several moderate wind events, and had the only seasonal mean ocean heat loss. The spring intermonsoon (MAM) was cloud free and had light winds and the strongest ocean heating. Strong ISOs and Tropical Cyclone Komen were seen in the southwest (SW) monsoon (JJA), when 65% of the 2.2-m total rain fell, and oceanic mean heating was small. The fall intermonsoon (SON) initially had moderate convective systems and mean ocean heating, with a transition to drier winds and mean ocean heat loss in the last month. Observed surface freshwater flux applied to a layer of the observed thickness produced drops in salinity with timing and magnitude similar to the initial drops in salinity in the summer monsoon, but did not reproduce the salinity variability of the fall intermonsoon. Observed surface heat flux has the potential to cause the temperature trends of the different seasons, but uncertainty in how shortwave radiation is absorbed in the upper ocean limits quantifying the role of surface forcing in the evolution of mixed layer temperature.

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Penetrative radiative flux in the Bay of Bengal

2016-06 , Lotliker, Aneesh , Omand, Melissa M. , Lucas, Andrew J. , Laney, Samuel R. , Mahadevan, Amala , Ravichandran, M.

The Bay of Bengal (BoB), a semi-enclosed basin in the northern Indian Ocean, is a complex region with large freshwater inputs and strong vertical stratification that result in a shallow, spatially variable mixed layer. With the exception of shortwave insolation, the air-sea heat exchange occurs at the sea surface and is vertically redistributed by mixing and advection. Strongly stratified, shallow mixed layers inhibit vertical mixing, and the penetration of solar radiation through the base of the mixed layer can lead to redistribution of upper-ocean heat. This paper compiles observations of hyperspectral downwelling irradiance (Ed) from 67 profiles collected during six research cruises in the BoB that span a broad range of regions and seasons between 2009 and 2014. We report attenuation length scales computed using double and single exponential models and quantify the penetration of radiative flux below the mixed layer depth (Qpen). We then evaluate estimates of Qpen obtained from published chlorophyll-based models and compare them to our observations. We find that the largest penetrative heat flux (up to 40% of the incident Ed) occurs near 16°N where the mixed layers are shallow and the water is optically clear.

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Adrift upon a salinity-stratified sea : a view of upper-ocean processes in the Bay of Bengal during the southwest monsoon

2016-06 , Lucas, Andrew J. , Nash, Jonathan D. , Pinkel, Robert , MacKinnon, Jennifer A. , Tandon, Amit , Mahadevan, Amala , Omand, Melissa M. , Freilich, Mara , Sengupta, Debasis , Ravichandran, M. , Le Boyer, Arnaud

The structure and variability of upper-ocean properties in the Bay of Bengal (BoB) modulate air-sea interactions, which profoundly influence the pattern and intensity of monsoonal precipitation across the Indian subcontinent. In turn, the bay receives a massive amount of freshwater through river input at its boundaries and from heavy local rainfall, leading to a salinity-stratified surface ocean and shallow mixed layers. Small-scale oceanographic processes that drive variability in near-surface BoB waters complicate the tight coupling between ocean and atmosphere implicit in this seasonal feedback. Unraveling these ocean dynamics and their impact on air-sea interactions is critical to improving the forecasting of intraseasonal variability in the southwest monsoon. To that end, we deployed a wave-powered, rapidly profiling system capable of measuring the structure and variability of the upper 100 m of the BoB. The evolution of upper-ocean structure along the trajectory of the instrument’s roughly two-week drift, along with direct estimates of vertical fluxes of salt and heat, permit assessment of the contributions of various phenomena to temporal and spatial variability in the surface mixed layer depth. Further, these observations suggest that the particular “barrier-layer” stratification found in the BoB may decrease the influence of the wind on mixing processes in the interior, thus isolating the upper ocean from the interior below, and tightening its coupling to the atmosphere above.

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ASIRI : an ocean–atmosphere initiative for Bay of Bengal

2016-11-22 , Wijesekera, Hemantha W. , Shroyer, Emily L. , Tandon, Amit , Ravichandran, M. , Sengupta, Debasis , Jinadasa, S. U. P. , Fernando, Harindra J. S. , Agrawal, Neeraj , Arulananthan, India K. , Bhat, G. S. , Baumgartner, Mark F. , Buckley, Jared , Centurioni, Luca R. , Conry, Patrick , Farrar, J. Thomas , Gordon, Arnold L. , Hormann, Verena , Jarosz, Ewa , Jensen, Tommy G. , Johnston, T. M. Shaun , Lankhorst, Matthias , Lee, Craig M. , Leo, Laura S. , Lozovatsky, Iossif , Lucas, Andrew J. , MacKinnon, Jennifer A. , Mahadevan, Amala , Nash, Jonathan D. , Omand, Melissa M. , Pham, Hieu , Pinkel, Robert , Rainville, Luc , Ramachandran, Sanjiv , Rudnick, Daniel L. , Sarkar, Sutanu , Send, Uwe , Sharma, Rashmi , Simmons, Harper L. , Stafford, Kathleen M. , St. Laurent, Louis C. , Venayagamoorthy, Subhas K. , Venkatesan, Ramasamy , Teague, William J. , Wang, David W. , Waterhouse, Amy F. , Weller, Robert A. , Whalen, Caitlin B.

Air–Sea Interactions in the Northern Indian Ocean (ASIRI) is an international research effort (2013–17) aimed at understanding and quantifying coupled atmosphere–ocean dynamics of the Bay of Bengal (BoB) with relevance to Indian Ocean monsoons. Working collaboratively, more than 20 research institutions are acquiring field observations coupled with operational and high-resolution models to address scientific issues that have stymied the monsoon predictability. ASIRI combines new and mature observational technologies to resolve submesoscale to regional-scale currents and hydrophysical fields. These data reveal BoB’s sharp frontal features, submesoscale variability, low-salinity lenses and filaments, and shallow mixed layers, with relatively weak turbulent mixing. Observed physical features include energetic high-frequency internal waves in the southern BoB, energetic mesoscale and submesoscale features including an intrathermocline eddy in the central BoB, and a high-resolution view of the exchange along the periphery of Sri Lanka, which includes the 100-km-wide East India Coastal Current (EICC) carrying low-salinity water out of the BoB and an adjacent, broad northward flow (∼300 km wide) that carries high-salinity water into BoB during the northeast monsoon. Atmospheric boundary layer (ABL) observations during the decaying phase of the Madden–Julian oscillation (MJO) permit the study of multiscale atmospheric processes associated with non-MJO phenomena and their impacts on the marine boundary layer. Underway analyses that integrate observations and numerical simulations shed light on how air–sea interactions control the ABL and upper-ocean processes.

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Argo data 1999-2019: two million temperature-salinity profiles and subsurface velocity observations from a global array of profiling floats.

2020-09-15 , Wong, Annie P. S. , Wijffels, Susan E. , Riser, Stephen C. , Pouliquen, Sylvie , Hosoda, Shigeki , Roemmich, Dean , Gilson, John , Johnson, Gregory C. , Martini, Kim I. , Murphy, David J. , Scanderbeg, Megan , Udaya Bhaskar, T. V. S. , Buck, Justin J. H. , Merceur, Frederic , Carval, Thierry , Maze, Guillaume , Cabanes, Cécile , André, Xavier , Poffa, Noé , Yashayaev, Igor , Barker, Paul M. , Guinehut, Stéphanie , Belbeoch, Mathieu , Ignaszewski, Mark , Baringer, Molly O. , Schmid, Claudia , Lyman, John , McTaggart, Kristene E. , Purkey, Sarah G. , Zilberman, Nathalie , Alkire, Matthew , Swift, Dana , Owens, W. Brechner , Jayne, Steven R. , Hersh, Cora , Robbins, Pelle E. , West-Mack, Deb , Bahr, Frank B. , Yoshida, Sachiko , Sutton, Philip J. H. , Cancouët, Romain , Coatanoan, Christine , Dobbler, Delphine , Garcia Juan, Andrea , Gourrion, Jérôme , Kolodziejczyk, Nicolas , Bernard, Vincent , Bourlès, Bernard , Claustre, Hervé , d’Ortenzio, Fabrizio , Le Reste, Serge , Le Traon, Pierre-Yves , Rannou, Jean-Philippe , Saout-Grit, Carole , Speich, Sabrina , Thierry, Virginie , Verbrugge, Nathalie , Angel-Benavides, Ingrid M. , Klein, Birgit , Notarstefano, Giulio , Poulain, Pierre Marie , Vélez-Belchí, Pedro , Suga, Toshio , Ando, Kentaro , Iwasaska, Naoto , Kobayashi, Taiyo , Masuda, Shuhei , Oka, Eitarou , Sato, Kanako , Nakamura, Tomoaki , Sato, Katsunari , Takatsuki, Yasushi , Yoshida, Takashi , Cowley, Rebecca , Lovell, Jenny L. , Oke, Peter , van Wijk, Esmee , Carse, Fiona , Donnelly, Matthew , Gould, W. John , Gowers, Katie , King, Brian A. , Loch, Stephen G. , Mowat, Mary , Turton, Jon , Pattabhi Rama Rao, Eluri , Ravichandran, M. , Freeland, Howard , Gaboury, Isabelle , Gilbert, Denis , Greenan, Blair J. W. , Ouellet, Mathieu , Ross, Tetjana , Tran, Anh , Dong, Mingmei , Liu, Zenghong , Xu, Jianping , Kang, KiRyong , Jo, HyeongJun , Kim, Sung-Dae , Park, Hyuk-Min

In the past two decades, the Argo Program has collected, processed, and distributed over two million vertical profiles of temperature and salinity from the upper two kilometers of the global ocean. A similar number of subsurface velocity observations near 1,000 dbar have also been collected. This paper recounts the history of the global Argo Program, from its aspiration arising out of the World Ocean Circulation Experiment, to the development and implementation of its instrumentation and telecommunication systems, and the various technical problems encountered. We describe the Argo data system and its quality control procedures, and the gradual changes in the vertical resolution and spatial coverage of Argo data from 1999 to 2019. The accuracies of the float data have been assessed by comparison with high-quality shipboard measurements, and are concluded to be 0.002°C for temperature, 2.4 dbar for pressure, and 0.01 PSS-78 for salinity, after delayed-mode adjustments. Finally, the challenges faced by the vision of an expanding Argo Program beyond 2020 are discussed.

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Seasonal evolution of oceanic upper layer processes in the northern Bay of Bengal following a single Argo float

2019-04-24 , Shee, Abhijit , Sil, Sourav , Gangopadhyay, Avijit , Gawarkiewicz, Glen G. , Ravichandran, M.

Seasonal evolution of the barrier layer (BL) and temperature inversion in the northern Bay of Bengal and their role on the mixed layer temperature (MLT) is examined using observations from a single Argo during December 2013 to July 2017. During fall, low salinity at surface generates BL in this region. It thickens to almost 80 m in winter enhanced by deepening of isothermal layer depth due to remote forcing. During winter, surface cooling lowers near‐surface temperature, and thus, the subsurface BL experiences a significant temperature inversion (~2.5 °C). This temperature inversion diffuses to distribute heat within ML and surface heating begins deep penetration of shortwave radiation through ML during spring. Hence, the ML becomes thermally well stratified, resulting in the warmest MLT. The Monin‐Obukhov length attains its highest value during summer indicating wind dominance in the ML. During spring and fall, upper ocean gains heat allowing buoyancy to dominate over wind mixing.

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A tale of two spicy seas

2016-06 , MacKinnon, Jennifer A. , Nash, Jonathan D. , Alford, Matthew H. , Lucas, Andrew J. , Mickett, John B. , Shroyer, Emily L. , Waterhouse, Amy F. , Tandon, Amit , Sengupta, Debasis , Mahadevan, Amala , Ravichandran, M. , Pinkel, Robert , Rudnick, Daniel L. , Whalen, Caitlin B. , Alberty, Marion S. , Lekha, J. Sree , Fine, Elizabeth C. , Chaudhuri, Dipayan , Wagner, Gregory L.

Upper-ocean turbulent heat fluxes in the Bay of Bengal and the Arctic Ocean drive regional monsoons and sea ice melt, respectively, important issues of societal interest. In both cases, accurate prediction of these heat transports depends on proper representation of the small-scale structure of vertical stratification, which in turn is created by a host of complex submesoscale processes. Though half a world apart and having dramatically different temperatures, there are surprising similarities between the two: both have (1) very fresh surface layers that are largely decoupled from the ocean below by a sharp halocline barrier, (2) evidence of interleaving lateral and vertical gradients that set upper-ocean stratification, and (3) vertical turbulent heat fluxes within the upper ocean that respond sensitively to these structures. However, there are clear differences in each ocean’s horizontal scales of variability, suggesting that despite similar background states, the sharpening and evolution of mesoscale gradients at convergence zones plays out quite differently. Here, we conduct a qualitative and statistical comparison of these two seas, with the goal of bringing to light fundamental underlying dynamics that will hopefully improve the accuracy of forecast models in both parts of the world.

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Introduction to the special issue on the Bay of Bengal : from monsoons to mixing

2016-06 , Mahadevan, Amala , Paluszkiewicz, Theresa , Ravichandran, M. , Sengupta, Debasis , Tandon, Amit

The Bay of Bengal has a surprisingly large influence on the world. It nurtures the South Asian summer monsoon, a tremendous ocean-atmosphere-land phenomenon that delivers freshwater to more than a third of the human population on this planet. During summer, southwesterly winds gather moisture from the ocean and carry it deep inland over the Indian subcontinent, bringing welcome rains to a parched land. During winter, the winds reverse to northeasterly, and the ocean circulation responds by dispersing the terrestrial freshwater runoff concentrated in the northern part of the bay. This freshwater impacts the ocean’s structure, circulation, and biogeochemistry in numerous ways and, through modification of sea surface temperature, feeds back to influence air-sea fluxes. Because the atmosphere obtains its moisture and heat for convection from the ocean, the interplay between ocean and atmosphere is crucial for the development and sustenance of the monsoon.

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A road map to IndOOS-2 better observations of the rapidly warming Indian Ocean

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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Quasi-biweekly mode of the Asian summer monsoon revealed in Bay of Bengal surface observations

2020-11-16 , Lekha, J. Sree , Lucas, Andrew J. , Sukhatme, Jai , Joseph, Jossia K. , Ravichandran, M. , Kumar, N. Suresh , Farrar, J. Thomas , Sengupta, Debasis

Asian summer monsoon has a planetary‐scale, westward propagating “quasi‐biweekly” mode of variability with a 10–25 day period. Six years of moored observations at 18°N, 89.5°E in the north Bay of Bengal (BoB) reveal distinct quasi‐biweekly variability in sea surface salinity (SSS) during summer and autumn, with peak‐to‐peak amplitude of 3–8 psu. This large‐amplitude SSS variability is not due to variations of surface freshwater flux or river runoff. We show from the moored data, satellite SSS, and reanalyses that surface winds associated with the quasi‐biweekly monsoon mode and embedded weather‐scale systems, drive SSS and coastal sea level variability in 2015 summer monsoon. When winds are calm, geostrophic currents associated with mesoscale ocean eddies transport Ganga‐Brahmaputra‐Meghna river water southward to the mooring, salinity falls, and the ocean mixed layer shallows to 1–10 m. During active (cloudy, windy) spells of quasi‐biweekly monsoon mode, directly wind‐forced surface currents carry river water away to the east and north, leading to increased salinity at the moorings, and rise of sea level by 0.1–0.5 m along the eastern and northern boundary of the bay. During July–August 2015, a shallow pool of low‐salinity river water lies in the northeastern bay. The amplitude of a 20‐day oscillation of sea surface temperature (SST) is two times larger within the fresh pool than in the saltier ocean to the west, although surface heat flux is nearly identical in the two regions. This is direct evidence that spatial‐temporal variations of BoB salinity influences sub‐seasonal SST variations, and possibly SST‐mediated monsoon air‐sea interaction.

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What controls seasonal evolution of sea surface temperature in the Bay of Bengal? Mixed layer heat budget analysis using moored buoy observations along 90°E

2016-06 , Thangaprakash, V. P. , Girishkumar, M. S. , Suprit, K. , Kumar, N. Suresh , Chaudhuri, Dipanjan , Dinesh, K. , Kumar, Ashok , Shivaprasad, S. , Ravichandran, M. , Farrar, J. Thomas , Sundar, R. , Weller, Robert A.

Continuous time-series measurements of near surface meteorological and ocean variables obtained from Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) moorings at 15°N, 90°E; 12°N, 90°E; and 8°N, 90°E and an Ocean Moored buoy Network for Northern Indian Ocean (OMNI) mooring at 18°N, 90°E are used to improve understanding of air-sea interaction processes and mixed layer (ML) temperature variability in the Bay of Bengal (BoB) at seasonal time scales. Consistent with earlier studies, this analysis reveals that net surface heat flux primarily controls the ML heat balance. The penetrative component of shortwave radiation plays a crucial role in the ML heat budget in the BoB, especially during the spring warming phase when the ML is thin. During winter and summer, vertical processes contribute significantly to the ML heat budget. During winter, the presence of a strong barrier layer and a temperature inversion (warmer water below the ML) leads to warming of the ML by entrainment of warm subsurface water into the ML. During summer, the barrier layer is relatively weak, and the ML is warmer than the underlying water (i.e., no temperature inversion); hence, the entrainment cools the mixed layer. The contribution of horizontal advection to the ML heat budget is greatest during winter when it serves to warm the upper ocean. In general, the residual term in the ML heat budget equation is quite large during the ML cooling phase compared to the warming phase when the contribution from vertical heat flux is small.

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RAMA : the Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction

2009-04 , McPhaden, Michael J. , Meyers, G. , Ando, Kentaro , Masumoto, Yukio , Murty, V. S. N. , Ravichandran, M. , Syamsudin, F. , Vialard, Jérôme , Yu, Lisan , Yu, W.

The Indian Ocean is unique among the three tropical ocean basins in that it is blocked at 25°N by the Asian landmass. Seasonal heating and cooling of the land sets the stage for dramatic monsoon wind reversals, strong ocean–atmosphere interactions, and intense seasonal rains over the Indian subcontinent, Southeast Asia, East Africa, and Australia. Recurrence of these monsoon rains is critical to agricultural production that supports a third of the world's population. The Indian Ocean also remotely influences the evolution of El Niño–Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), North American weather, and hurricane activity. Despite its importance in the regional and global climate system though, the Indian Ocean is the most poorly observed and least well understood of the three tropical oceans. This article describes the Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction (RAMA), a new observational network designed to address outstanding scientific questions related to Indian Ocean variability and the monsoons. RAMA is a multinationally supported element of the Indian Ocean Observing System (IndOOS), a combination of complementary satellite and in situ measurement platforms for climate research and forecasting. The article discusses the scientific rationale, design criteria, and implementation of the array. Initial RAMA data are presented to illustrate how they contribute to improved documentation and understanding of phenomena in the region. Applications of the data for societal benefit are also described.

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Supplement to RAMA : the Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction

2009-04 , McPhaden, Michael J. , Meyers, G. , Ando, Kentaro , Masumoto, Yukio , Murty, V. S. N. , Ravichandran, M. , Syamsudin, F. , Vialard, Jérôme , Yu, Lisan , Yu, W.

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Technological advancements in observing the upper ccean in the Bay of Bengal : education and capacity building

2016-06 , Tandon, Amit , D'Asaro, Eric A. , Stafford, Kathleen M. , Sengupta, Debasis , Ravichandran, M. , Baumgartner, Mark F. , Venkatesan, Ramasamy , Paluszkiewicz, Theresa

Because the monsoon strongly affects India, there is a clear need for indigenous expertise in advancing the science that underlies monsoon prediction. The safety of marine transport in the tropics relies on accurate atmospheric and ocean environment predictions on weekly and longer time scales in the Indian Ocean. This need to better forecast the monsoon motivates the United States to advance basic research and support training of early career US scientists in tropical oceanography. Earlier Indian field campaigns and modeling studies indicated that an improved understanding of the interactions between the upper ocean and the atmosphere in the Bay of Bengal at finer spatial and temporal scales could lead to improved intraseasonal monsoon forecasts. The joint US Air-Sea Interactions Regional Initiative (ASIRI) and the Indian Ocean Mixing and Monsoon (OMM) program studied these interactions, resulting in scientific advances described by articles in this special issue of Oceanography. In addition to these scientific advances, and while also developing long-lasting collaborations and building indigenous Indian capability, a key component of these programs is training early career scientists from India and the United States. Training has been focusing on fine-scale and mixing studies of the upper ocean, air-sea interactions, and marine mammal research. Advanced methods in instrumentation, autonomous robotic platforms, experimental design, data analysis, and modeling have been emphasized. Students and scientists from India and the United States at all levels have been participating in joint cruises on Indian and US research vessels and in training participants in modern tools and methods at summer schools, at focused research workshops, and during research visits. Such activities are building new indigenous capability in India, training a new cadre of US scientists well versed in monsoon air-sea interaction, and forging strong links between Indian and US oceanographic institutions.

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A sustained ocean observing system in the Indian Ocean for climate related scientific knowledge and societal needs

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, Weidong

The 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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