Global Ocean Salinity and the Water Cycle Workshop

May 22-26, 2017
Woods Hole, MA

In late May 2017, a five-day workshop was held at the Woods Hole Oceanographic Institution. Oral and poster presentations focused on the following topics: (1) Salinity and the water cycle - trends and variability; (2) Remote sensing of salinity and other water cycle variables; (3) In-situ salinity measurements; (4) Synthesis of salinity measurements (Remote, in-situ, etc.); (5) Salinity process studies; (6) Freshwater discharges from land and ice; (7) Salinity processes in models; and (8) Challenges of future salinity observing, including new techniques and sustainability.

Documents (39)
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Analysis of STS/PAL Float Data in SPURS-2 Study Area
Yang, J., Riser, S., and Asher, W. (24-May-17). In this talk, a preliminary analysis of the Argo and PAL data from the SPURS-2 deployment from Sep. 2016 – April 2017 are presented. In general, the PAL wind speed is consistent with wind speed measured by surface anemometers on the central mooring, while rainfall exhibits strong spatial variability. Salinity and temperature profiles from the 15 floats are presented as well to investigate their correlation with rainfall.

Aquarius Mission Summary and Overview
Lagerloef, G. (22-May-17). Conceived in the late 1990s, and proposed to NASA's Earth System Science Pathfinder (ESSP) Missions program in 2001-2002, the Aquarius mission was selected to resolve missing physical processes that link the water cycle, the climate, and the ocean by measuring sea surface salinity (SSS). The satellite was developed in partnership with Argentina as the joint Aquarius/SACD mission, and included complementary sensors provided by Argentina, Italy, France and Canada.

Climatology of Salinity Fronts in the Tropical Atlantic Ocean
Ruiz-Etcheverry, L., Maximenko, N., and Melnichenko, O. (22-May-17). Marine fronts are narrow boundaries that separate water masses of different properties. These fronts are caused by various forcings and believed to be an important component of the coupled ocean-atmosphere system, particularly in the tropical oceans. In this study, we use three years of sea surface salinity (SSS) observations from Aquarius satellite to investigate the spatial structure and temporal variability of six main frontal SSS features in the tropical Atlantic, their evolution between seasons and differences between individual years.

Dielectric Constant Retrieved from SMOS Multiangular Measurements: the Cardioid Model (Poster)
Boutin, J.J., Vergely, J.L., Waldteufel P., Spurgeon, P., Dinnat, E., and Zhou, Y. (23-May-17). In this poster, we compare information on the dielectric constant retrieved from the angular variation of SMOS brightness temperatures with Klein and Swift (1977) and Meissner and Wentz (2012) models and with interpolated Lang measurements.

Dynamics of the Sea Surface Salinity Maximum Pool in the Indian Ocean
Menezes, V. (23-May-17). Subtropical salinity maximum regions are particularly important because the salty subtropical underwater (STW) is formed by subduction of surface waters in these areas. In all oceans, the STW is transported equatorward from the formation region and are tightly related to the Subtropical-Tropical Cell. In the South Indian Ocean (SIO), the salinity maximum is further poleward (25S-38S) and eastward (60E-120E) compared to those in other oceans, and significantly impacts the circulation of the eastern basin.

Early Results from SPURS-2: Multi-months Timeseries of Salinity, Rain, and Turbulence from Autonomous Gliders
Rainville, L., Drushka K., Eriksen, C., Farrar, T., Shcherbina, A., Thompson, E., Centurioni, L., Hormann, V., Hodges, B., and Schmitt, R. (24-May-17). The SPURS-2 field program aims to understand the structure and variability of upper-ocean salinity in the Eastern Tropical Pacific Ocean over more than one complete annual cycle. Since their deployments in August 2016, Seagliders have resolved salinity, temperature, density, and their lateral gradients, in the top 1000 m of the water column on horizontal scales of 20 km and time scales on the order of the inertial period in the central SPURS-2 region.

El Niño Low Salinity Equatorial Jets
Clarke, A. and Zhang, X. (22-May-17). Fundamental to El Niño dynamics is the eastward movement of the western equatorial Pacific warm/fresh pool edge during El Niño and its westward movement during La Niña. Analysis of TAO/TRITON salinity and temperature measurements, as well as Aquarius sea surface salinity (SSS) and satellite altimetry, show that this zonal movement is mostly controlled by a shallow 23cm/s narrow jet.

Evaluating the Role of Seasonal Freshwater Flux Variability on the Anomalous 2016 Seasonal Freshening of Ocean Surface water in the SPURS-2 Region
Paget, A., Edson, J., and Clayson, C.A. (24-May-17). The upper ocean waters in the SPURS-2 region undergo an annual cycle of seasonal freshening. In particular, the October and November of 2016 are fresher than the previous years, and, even more striking, the salinity values during that period are nearly 1 PSU fresher than the previous years. This freshening is confirmed by Argo floats, the SPURS-2 Buoy, and SMAP observations. The goal of this work is to understand the reasons for this increased freshening in 2016.

Implementation of the Operational Satellite Sea-surface Salnity Data Assimilation at NOAA (Poster)
Bayler, E., Osychny, V., Chawla, A., and Mehra, A. (23-May-17). The assimilation of sea-surface salinity (SSS) data into numerical prediction models serves to extract value from the observations, as well as integrates those observations with other data to produce an optimal output. Sea-surface salinity observations from the European Space Agency’s (ESA) Soil Moisture – Ocean Salinity (SMOS) mission and the National Aeronautics and Space Agency’s (NASA) Soil Moisture Active-Passive mission are now sufficiently mature for assimilation into NOAA’s operational models, in particular the Real-time Ocean Forecast System (RTOFS) and the Global Ocean Data Assimilation System (GODAS), the ocean component of NOAA’s operational Climate Forecast System (CFS).

In Situ Sea Surface Salnity and Temperature Observations from the NCEI Global Thermosalinograph Dataset (NCEI-TSG) (Poster)
Wang, Z., Boyer, T., Biddle, M., Zhang, H-M., and Bayler, E. (23-May-17). The newly developed NCEI Thermosalinograph Dataset (NCEI-TSG) is the world’s most extensive collection of uniformly-formatted, quality-controlled, thermosalinograph (TSG) data available without restriction. TSG data are in-situ high resolution measurements of sea surface salinity (SSS) and temperature (SST) from ships. Measurements of other oceanographic variables, such as oxygen, chlorophyll etc are often measured concurrently with sea surface salinity and temperature and included in the dataset.

Interannual Salinity in the Amazon Plume and Adjacent Areas (Poster)
Grodsky, S. and Carton, J. (23-May-17). The main mode of interannual near surface salinity in the tropical western Atlantic is related to ENSO teleconnections and is produced by changes in precipitation over the ocean and Amazon. The ocean rainfall has an almost immediate impact on underlying salinity in contrast to the land rainfall that leads to a delayed impact related to the hydrology of Amazon system. Due to the need for longer time records to resolve interannual signal, our investigation relies on historical syntheses of in-situ observations mainly focusing on the JAMSTEC analysis. The inferred patterns of variability are compared to those from relatively short AQUARIUS records.

Lagrangian Drifter Observations of Near-surface Circulation and Sea Surface Salinity during SPURS-2
Hormann, V., Centurioni, L., Maximenko, N., and Chao, Y. (24-May-17). To improve understanding of the role of near-surface currents in defining the salinity distribution and location of minimum salinity in the northeastern tropical Pacific, a Lagrangian drifter study with about half the drifters fitted with salinity sensors has been designed as part of the SPURS-2 experiment. First results of the ongoing drifter deployments in the eastern Pacific fresh pool under the ITCZ will be presented, highlighting the observed large spatiotemporal variability in near-surface circulation and sea surface salinity.

Measurement of Ocean Surface Turbulence Generated by Rain Using the Controlled Flux Method
Asher, W., Drushka, K., Jessup, A., Thompson, E., and Clark, D. (24-May-17). During the 2016 SPURS-2 field experiment in the eastern equatorial Pacific Ocean, the controlled flux technique (CFT) was used to infer surface turbulence before, during, and after rainstorms. In this paper, preliminary results from the SPURS-2 CFT measurements will be presented to show the effect of rain on turbulence dissipation at the ocean surface. This data will be used along with concurrent measurements of salinity and temperature profiles in the upper meter of the ocean to better understand the generation and evolution of fresh lenses generated by rain.

Measuring SSS with SMOS since 2010: Qualities and Flaws
Boutin, J.J., Reul, N., D'Amico, F., Marchand, S., Tenerelli, J., Vergely, J.L., Hasson, A., Kolodziejczyk, N., Reverdin, G., Supply, A.,Tarot, S., and Vialard, J. (25-May-17). The Soil Moisture and Ocean Salinity (SMOS) mission monitors Sea Surface Salinity (SSS) from space since January 2010. This European Space Agency (ESA) Earth Explorer mission provided the first L-band radiometric observations of the Earth using interferometry. SMOS has demonstrated the feasibility of monitoring SSS and its variability from space with a precision of 0.15-0.3 (in regions free from radio frequency interferences and more than 1000km away from coasts).

Meteorological Quantification of P-E Surface Fluxes during SPURS-2
Edson, J., Graham, R., Paget, A., Clayson, C.A., and Farrar, T. (24-May-17). A comprehensive set of meteorological instrumentation was deployed on the R/V Revelle and 3-m discus buoy during the SPURS-2 experiment in the tropical Eastern Pacific Ocean. These measurements are being used to quantify the amount of precipitation versus evaporation (P–E) that drives a freshwater flux into or out of the upper ocean, respectively.

Multi-platform Lagrangian Observation of Ocean Boundary Layer Shear and Stratification During SPURS-2
Shcherbina, A., Certunioni, L., D'Asaro, E., Hodges, B., Rainville, L., Riser, S., and Volkov, D. (24-May-17). During the first part of SPURS-2 experiment, a cluster of autonomous instruments was deployed for a 100-day 1,800-km coordinated quasi-Lagrangian drift through the North Pacific intertropical convergence zone (ITCZ). The cluster conducted multi-platform observations of the ocean surface boundary layer structure and dynamics in a quasi-Lagrangian frame of reference minimizing the effects of horizontal advection. We will present preliminary results of this coordinated study, focusing on the evolution of upper-ocean stratification and shear in response to storm-induced rainfall and wind bursts.

NASA Salinity Communication and Engagement (Poster)
deCharon, A., Lauter, C., and Taylor, L. (23-May-17). As a NASA pathfinder mission dedicated to public engagement, Aquarius made significant strides in broadening interest in salinity beyond the scientific community. Leveraging the infrastructure and thematic approach developed for Aquarius, new communication and public engagement endeavors are being conducted to align with scientific objectives. Through close coordination and interaction with the science community, these collective efforts will demonstrate how a better understanding of salinity science – and its ties to ocean circulation, climate, and the water cycle – can benefit society.

Near-surface Stratification Effects in the SPURS Field Campaigns
Clayson, C.A., Bogandoff, A., Farrar, T., Edson, J., St. Laurent, L., and Schmitt, R. (24-May-17). This presentation discusses observations and modeling of the upper ocean stratification during the SPURS-1 and SPURS-2 field campaigns, including the variation in stratification seen as a result of diurnal warming, freshwater inputs, or both. The resulting mixing and temporal evolution of the stably stratified upper layers will also be discussed.

Ocean Salinity as a Predictor of Terrestrial Precipitation
Li, L., Schmitt, R., Ummenhofer, C., and Karnauskas, K. (23-May-17). In this presentation, we provide observation-based evidence that springtime salinity in the subtropical North Atlantic can be a very useful predictor of terrestrial precipitation with a one season lead. Specifically, high springtime SSS in the northeastern portion of the subtropical North Atlantic is followed by excessive monsoon precipitation in the African Sahel, whereas high SSS in the western North Atlantic is indicative of extreme summer precipitation in the US Midwest.

Ocean Salinity Stratification during the 2002-2012 Period as Derived from the ISA13 Argo Atlas (Poster)
Maes, C., Kolodziejczyk, N., Prigent, A., and Gaillard, F. (23-May-17). Among the different physical processes contributing to the present climate changes and their impact on the ocean productivity and marine ecosystems, little attention has been paid to the large-scale contributions of stratification changes within the water column. Stratification, which is associated with the density difference between the surface and the deeper layers, characterizes the stability of the water column, and therefore influences the potential for vertical exchange of properties such as nutrients or dissolved oxygen.

Perspectives for Future Enhancement of Spaceborne Salinity Observing Capabilities
Lee, T. (25-May-17). This presentation describes the perspectives for future SSS missions based on community inputs during 2015-2016 to the “2017-2027 Decadal Survey for Earth Science and Applications from Space” organized by the U.S. National Academies. The community inputs recognized three major areas for strengthening spaceborne salinity observing capabilities: (1) improvement of high-latitude SSS accuracy, (2) enhancement of spatial resolution (thereby getting closer to the coasts), and (3) mission continuity. In particular, the need to improve high-latitude satellite SSS stems from the fact that L-band radiometers have poor sensitivity to SSS in cold waters (<5C), and from the importance of high-latitude SSS to deep-water formation, heat and carbon sequestration, and global ocean circulation as well as the related property transports.

Predictability of Tropical Freshwater Lenses due to Convective and Stratiform Rain During SPURS-2
Thompson, E., Drushka, K., Asher, W., Schanze, J., Jessup, A., and Clark, D. (24-May-17). This study seeks to understand the impact of convective and stratiform rainfall on salinity stratification observed during the 2016 SPURS-2 experiment. Previous observational studies have demonstrated a wind-speed-dependent correlation between in-situ salinity stratification and maximum rain rate. However, questions remain about the temporal lag between the maximum rain rate and evolution of the freshwater lens, and how rain intensity impacts the lifetime of a freshwater lens.

Rain-driven Turbulence in the Upper Meter of the Ocean
Drushka, K., Clark, D., Asher, W., Chickadel, C., Jessup, A., Thomson, J., and Thompson, E. (22-May-17). Rain falling on the ocean produces buoyant surface layers of relatively fresh, cool water that are subsequently mixed laterally and vertically into the water column. Because it is difficult to make measurements near the sea surface, relatively little is known about the dynamics of this mixing — and as a result, our understanding of how rainfall affects upper ocean salinity is limited. Here, we consider the response of the upper meter of the ocean using three months of measurements collected during the Friday Harbor Rain Experiment.

Recent Progress in Understanding the Global Water Cycle
Durack, P. (22-May-17). Thanks largely to a boom in measurements and data, the research focus of the oceanic arm of the global water cycle has received considerable attention over the last decade. With the high-frequency measurements provided by salinity measuring satellites, and the sea-going SPURS campaigns, the direct relationship between salinity and rainfall has been further examined. These new assessments have uncovered relationships that occur over very short time and space scales, and which are unresolved by current modeling systems. The presentation will provide an overview of current progress in understanding, and outline some ongoing work aimed at addressing the temporal disconnect between multidecadal and decadal analyses.

Salinity Remote Sensing from SMAP
Meissner, T., Wentz, F., Manaster, A., and Lee, T. (25-May-17). Remote Sensing System’s (RSS) SMAP Version 2 sea surface salinity (SSS) data have been released on September 13, 2016. The release contains a Level 2 swath product and Level 3 maps of 8-day running averages and monthly averages. Our talk discusses the major steps of the SMAP salinity retrieval algorithm, including updates and improvements from the Version 1 (BETA release).

Small-scale Temperature Variability Affected by Rain Events During SPURS-2
Chickadel, C., Drushka, K., Asher, W., Thompson, E., Gaube, P., and Jessup, A. (24-May-17). High-resolution thermal imagery captured from a shipboard infrared camera during the SPURS 2 experiment shows development of small-scale skin temperature variability. These centimeter to meter wavelength features are typically elongate and linear, similar to classic Langmuir cells.

SMAP Sea Surface Salinity Retrieval Algorithm
Fore, A., Yueh, S., Tang, W., and Hayashi, A. (25-May-17). The Soil Moisture Active Passive (SMAP) mission was launched January 31st, 2015. It is designed to measure the soil moisture over land using a combined active / passive L-band system. Due to the Aquarius mission, L-band model functions for ocean winds and salinity are already mature and may be directly applied to the SMAP mission. In contrast to Aquarius, the higher resolution and scanning geometry of SMAP allows for wide-swath ocean winds and salinities to be retrieved. In this talk we present the SMAP Sea Surface Salinity (SSS) dataset and algorithm.

SMOS Pilot-Mission Exploitation Platform (Pi-MEP): Project Overview
Sabia, R., Mecklenburg, S., Reul, N., Guimbard, S., and Laur, H. (25-May-17). The recent SMOS Pilot-Mission Exploitation Platform (Pi-MEP) project principal objective will be to perform a systematic assessment of SMOS SSS data quality (at L2, L3 & L4) by systematically compare each product with relevant in situ data (ARGO, TSG, moorings, drifters...). In this talk, the current state of the initial phase of the Pi-MEP project regarding the collected datasets, visualization and extraction tools and a non-exhaustive list of oceanographic process studies will be presented.

SPURS-2 Data Management – Status and Plans
Bingham, F. and Li, Z. (24-May-17). A short presentation on the data management efforts associated with SPURS-2.

Surface Freshening and Salinification – Decadal Fluctuations Versus Secular Trends
Vinogradova, N., Buckley, M., Piecuch, C., and Ponte, R. (22-May-17). In recent decades, noticeable decadal salinity trends have emerged at the ocean surface, reflecting the changes in the ocean water cycle, strength of the ocean circulation, and changes in the ocean transports of salt. A number of potential causes for the observed changes have been suggested, including those related to anthropogenic aerosol forcing as well as natural climate fluctuations. Here we explore how the recent decadal salinity trends fit into the long-term picture, focusing on those ocean regions where the decadal changes oppose the long-term trends.

Surface Layer Salinity Balance at the SPURS-1 Central Mooring
Farrar, T., Rainville, L., Plueddemann, A., Kessler, B., Lee, C., Hodges, B., Schmitt, R., Riser, S., Edson, J., Eriksen, C., and Fratantoni, D. (24-May-17). The Salinity Processes Upper-ocean Regional Study (SPURS) was a field campaign focused on understanding the physical processes affecting the evolution of upper-ocean salinity in the region of climatological maximum sea surface salinity (SSS) in the subtropical North Atlantic. An upper-ocean salinity budget provides a useful framework for guiding progress toward that goal.

Synergistic Use of Satellite and In Situ Observations for Production of New, Multi-platform Salinity Estimates for Climate Research
Vinogradova, N., Ponte, R., Fukumori, I., and Wang, O. (25-May-17). The modern salinity observing system includes an expansive network of in situ and space-borne measurements. Reconciling salinity estimates from these different platforms into a coherent picture is one of the objectives of the NASA Ocean Salinity Science Team and the Satellite & In Situ Salinity (SISS) working group. Here we introduce a new salinity estimate based on the synthesis of information from various sources over the 1992-2015 period.

Temporal Variability in Surface Eddy Mixing
Busecke, J., Gordon, A., and Abernathey, R. (24-May-17). Lateral mixing by mesoscale eddies is widely recognized as a crucial mechanism for the global ocean circulation and the associated heat/salt/tracer transports. The Salinity in the Upper Ocean Processes Study (SPURS) confirmed the importance of eddy mixing for the surface salinity fields even in the center of the subtropical gyre of the North Atlantic. We focus on the global salinity maxima due to their role as indicators of global changes in the hydrological cycle as well as providing the source water masses for the shallow overturning circulation.

The Southern Hemisphere Subtropical SSS-max Regimes
Gordon, A.L. (22-May-17). The salty subtropical regimes of the world ocean display significant differences. Evaporation alone is not sufficient to explain the spatial and temporal characteristics of the salty subtropical regimes, the wind also shapes sea surface salinity maximum (SSS-max), both at seasonal and inter annual time scales. However, even the combination of regional air-sea water flux and the wind stress is insufficient to fully explain the SSS-max patterns.

The Vertical Structure of Eddy Freshwater Transport Inferred from Satellite Observations and Argo Profile Data
Melnichenko, O., Amores, A., Hacker, P., Maximenko, N., and Potemra, J. (25-May-17). Satellite observations and Argo profile data are used to investigate the vertical structure of meridional eddy freshwater transport in the interiors of the subtropical gyres. To overcome limitations arising from the relative sparseness of in-situ profile data, an eddy composite analysis is utilized; namely, the mean vertical structure of mesoscale eddies and their transport properties are evaluated by synthesizing all available data in the framework of the eddy tracking technique.

Tools, Services and Support of NASA Salinity Mission Data Archival and Distribution through the PO.DAAC (Poster)
Tsontos, V., Vazquez, J., and Lee, T. (23-May-17). The Physical Oceanography Distributed Active Center (PO.DAAC) serves as the designated NASA repository and distribution node for all Aquarius/SAC-D and SMAP sea surface salinity (SSS) mission data products in close collaboration with the projects. Here we report on the status of these data holdings at PO.DAAC, and the range of data services and access tools that we provide in support of NASA salinity.

Upper Ocean Variability during the SPURS-2 Field Campaign under the ITCZ
Sprintall, J. (24-May-17). A major goal as part of the SPURS-2 field campaign is to understand the characteristics and variability of the upper ocean salinity stratification in the vicinity of the ITCZ and identify the main mechanisms that are responsible for this variability. Our contribution focused on the “mesoscale” box (10-300 km) spatial scale, undertaking upper ocean stratification and velocity measurements that will help provide some regional context for the nested small-scale and single-point moored measurements.

Verifying Aquarius Calibration Drift Using In Situ Data
Lagerloef, G. (22-May-17). Key Aquarius science objectives were to (1) map the mean SSS field, (2) measure the annual SSS cycle, and (3) document interannual variations, within a three-year minimum duration. This presentation addresses objectives (2) and (3) by analyzing the radiometer calibration drift on these time scales using co-located in situ data.

Wave Gliders in SPURS-2
Hodges, B., Schmitt; R., Levang, S., Fratantoni, D., and Shcherbina, A. (24-May-17). Three Wave Gliders were deployed in August 2016 to commence sampling for SPURS-2. They measure temperature and salinity at 2-minute intervals at depths of 30 cm and 6.5 m, and return the data in real time via satellite link. Additional temperature observations at 30-second intervals are made at other depths, the shallowest being 10 cm. Together with measurements of wind speed, these observations begin to form a picture of the formation conditions, size, frequency, duration, and seasonality in the SPURS-2 study area of the shallow "fresh puddles" which form when rain falls on a calm ocean surface.