2014 AGU Fall Meeting

December 15-19, 2014
San Francisco, California

Forty six presentations and posters were featured during four "Ocean Salinity and Water Cycle Variability and Change" sessions at the 2014 American Geophysical Union Fall Meeting. Held on Thursday, December 18th, presentations included science results from the initial 3-year prime mission; an overview of SMOS salinity; details on algorithms, validation and applications of the Aquarius sensor; mixed layer variability and subduction in the SPURS Area; and ocean-to-ocean dissimilarities of salty subtropical surface water.

Program Book
Documents (46)
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A Subtropical North Atlantic Regional Atmospheric Moisture Budget
Bingham, F. and D'Addezio, J. (18-Dec-14). The synergistic effects of evaporation (E), precipitation (P), and Ekman transport make the SPURS (Salinity Processes in the Upper Ocean Regional Study) region in the subtropical North Atlantic (15-30°N, 30-45°W) the ideal location for the world's highest open ocean sea surface salinity. Using the MERRA and ERA-Interim atmospheric reanalyses, we reproduce the mean hydrologic state of the atmosphere over the SPURS region since 1979 and roughly deduce the change in salinity across the meridional domain due solely to interactions between E-P and Ekman transport.

Aquarius Satellite Salinity Measurement Mission Status, and Science Results from the Initial 3-Year Prime Mission
Lagerloef, G. and Kao, H-Y. (18-Dec-14). The Aquarius satellite microwave sensor, launched June 2011 as part of the US-Argentina joint Aquarius/SAC-D mission, commenced observations on 25 August 2011, and completed three years of ocean surface salinity measurements in late August 2014.

Aquarius Sea Surface Salinity in the South Indian Ocean: Revealing Annual-Period Planetary Waves
Menezes, V., Vianna, M., and Phillips, H. (18-Dec-14). In the present work, a thorough analysis of the first 2 years of Aquarius SSS data in the South Indian Ocean is performed together with the Argo and RAMA data. This analysis is focused into 3 questions: How accurately is Aquarius observing the fresh Indonesian Throughflow and the salty subtropical waters? Can Aquarius give a spatial context for interpreting the data measured by the RAMA mooring system, which are highly resolved in time, but very sparse in space? Can westward propagating seasonal signals be observed in the Aquarius SSS fields as recently described in model simulations?

Assessment of the Aquarius Space-borne Sea Surface Salinity Retrievals in Polar Ocean
Dinnat, E., Brucker, L. and Álvarez, I.O.C. (18-Dec-14). Aquarius is a NASA space-borne instrument operating three L-band radiometers. While Aquarius SSS retrievals are performed with a good accuracy in tropical and mid-latitude oceans, a thorough assessment has not been performed in the colder waters of the polar oceans. To assess Aquarius data at high latitudes, we compare them to in-situ measurements from ship cruises.

Assimilation of Satellite Sea Surface Salinity Fields: Validating Ocean Analyses and Identifying Errors in Surface Buoyancy Fluxes
Mehra, A., Nadiga, S., Bayler, E., and Behringer, D. (18-Dec-14). Recently available satellite sea-surface salinity (SSS) fields provide an important new global data stream for assimilation into ocean forecast systems. In this study, we present results from assimilating satellite SSS fields from NASA's Aquarius mission into the National Oceanic and Atmospheric Administration's (NOAA) operational Modular Ocean Model version 4 (MOM4), the oceanic component of NOAA's operational seasonal-interannual Climate Forecast System.

Changes in the Seasonal Cycle of Sea Surface Salinity During the Argo-era (2004-2013)
Reagan, J., Boyer, T., Antonov, J, and Zweng, M. (18-Dec-14). This study attempts to advance our understanding of interannual changes in sea surface salinity by looking at year to year changes in the seasonal cycle over the past decade.

Connections Between a High-Resolution Model and Aquarius Salinity Measurements
Douglass, E. and Richman, J. (18-Dec-14). In a preliminary step toward assimilation of Aquarius data, observed sea surface salinity is compared with modeled sea surface salinity.

Distribution and Seasonal Variation of Halocline in the World Ocean
Ueno, H. and Yasui, K. (18-Dec-14). The distribution and seasonal variation in the halocline in the world ocean were investigated using a simple halocline definition.

Estimating Absolute Salinity in the World
Woosley, R.J., Huang, F., and Millero, F.J. (18-Dec-14). The practical salinity (Sp), which is determined by the relationship of conductivity to the known proportions of the major components of seawater, and reference salinity (SR = (35.16504/35)*Sp), do not account for variations in physical properties such as density and enthalpy. Here, we combine the measurements of previous studies with new measurements for a total of 2,857 conductivity-density measurements covering all of the world's major oceans to derive empirical equations for the effect of silica and total alkalinity on the density and absolute salinity of the global oceans and recommend an equation applicable to most of the world oceans.

Formation Mechanism of Barrier Layer in the Subtropical Pacific
Katsura, S., Oka, E., and Sato, K. (18-Dec-14). Formation mechanism of barrier layers in the subtropical Pacific was investigated by using Argo profiling float data and shipboard hydrographic section data.

Freshening in the South China Sea during 2012 Revealed By Aquarius and in-Situ Data
Zeng, L., Liu, W.T., Xue, H., Wang, D., and Xing, T. (18-Dec-14). Newly available sea surface salinity (SSS) data from the Aquarius together with in-situ hydrographic data are used to explore the spatial and temporal characteristics of SSS in the South China Sea.

Global River Discharge Variability Revealed by Aquarius and SMOS Sea Surface Salinity
Chandanpurkar, H.A., Reager, J.T., and Famiglietti1, J.S. (18-Dec-14). Sea surface salinity (SSS) is an effective indicator of global freshwater cycle. At the mixed layer, salinity is governed by the net freshwater flux from ocean evaporation (E), precipitation (P), and continental discharge, horizontal advection, and vertical mixing. Here, we use new SSS observations from Aquarius/SAC-D and SMOS, complimented by in situ observations from Argo floats, multiple satellite-based datasets for E and P, and modeled datasets to detect, isolate, and analyze the spatial and temporal patterns of discharge plumes from major rivers in the world.

Improving Aquarius Sea Surface Salinity Estimates in the Southern Ocean: Response Surface Models Link Salinity and Temperature
Mueller, C. and Xie, H. (18-Dec-14). With the Aquarius mission having completed its second full year of acquiring global sea surface salinity measurements, many corrections were accounted for and biases were removed. However, some biases remain, keeping the mission from achieving its goal of ±0.2 psu accuracy for monthly products (150 km pixel size). Uncertainties in the Southern Ocean (among other biases) not only keep the mission from attaining such accuracy globally, but it also forces continued reliance on in situ point data sources. A Python script package is developed to process the Level 2 data for use, allowing users to target specific variables and to prepare ship and buoy data for analysis with the Aquarius data.

Investigating the Physical Basis of Aquarius/SAC-D Salinity Retrievals' Regional SST Bias
Scott, J., Meissner, T., and Wentz, F. (18-Dec-14). Sea-surface temperature (SST) plays an important, and yet to be fully understood, role in sea-surface sailinty (SSS) retrievals. The Version-3 release of Aquarius/SAC-D salinity retrievals applied an empirically derived adjustment to SSS that is a function of SST. This adjustment was derived after noticing regional salinity biases relative to modeled and in situ salinity observations. These SSS biases correlate well with climatological SST maps. While the ΔSSS(SST) adjustment has already been implemented in the ADPS standard processing, there is great value in determining the physical basis of this bias adjustment. Understanding the root causes of this adjustment will enable improved Aquarius's salinity retrievals, as well as ensure that no true SSS-SST correlations or variability are being removed by the adjustment.

Investigating the Possible Mechanisms by Which the Salinity Fronts Form and Grow Under the Pacific Intertropical Convergence Zone
Kao, H-Y. (18-Dec-14). The Pacific Intertropical Convergence Zone (ITCZ) is a zonal band of atmospheric convective instability, clouds and rainfall near the equator. High-resolution sea surface salinity (SSS) measurements from the Aquarius satellite reveals more detail in the band of lower salinity and a sharp front that aligns with the strong ITCZ atmospheric convection.

Is the Tropical Zonal Bias in Aquarius-Argo Salinity Comparisons Due to the Difference in Measurement Depth?
Drucker, R. and Riser, S. (18-Dec-14). We compare Aquarius 3.0 sea surface salinity with Argo upper mixed layer salinities, using both the standard Aquarius level-2 product and the Combined Active Passive (CAP) algorithm.

Isohaline Salinity Budget of the North Atlantic Salinity Maximum
Bryan, F. (18-Dec-14). In this study we analyze the salinity budget of the North Atlantic subtropical salinity maximum region for control volumes bounded by isohaline surfaces.

Lagrangian Modeling of Aquarius Surface Salinity in the Bay of Bengal
Freilich, M. and Mahadevan, A. (18-Dec-14). Monsoonal freshwater runoff into the Bay of Bengal makes it one of the freshest oceans and results in a large spatial gradient in surface salinity (8-10 psu over 8-10 degrees longitude). Our aim is to understand dispersal and mixing of freshwater in the Bay of Bengal, its underlying mechanisms, and the spatial and temporal patterns of variability using Aquarius salinity data.

Mean Structure and Large-Scale Variability of the Subtropical Underwater in the North Atlantic
Qu, T. and Zhang, L. (18-Dec-14). This study investigates the mean property distribution and large scale variability of the high salinity subtropical underwater (STUW) in the North Atlantic, using recently available Argo profiles at observed levels. Our analysis indicates that, once subducted, the STUW spreads in the subtropical North Atlantic as a vertical salinity maximum near 25.5 kg m-3.

Mixed Layer Variability and Subduction in the SPURS Area
Anderson, J. and Riser, S. (18-Dec-14). During the Salinity Processes in the Upper Ocean Regional Study (SPURS) I field campaign a high-density grid of Argo-type profiling floats were deployed surrounding the central mooring. The sixteen (16) floats were deployed in a 4 x 4 array with approximate 0.5 degree spacing and were programed to profile from 2000 meters to the surface every 5 days.

Modeling Skin-Layer Salinity: Focus on Seasonal Variability and Global Means
Song, Y.T., Lee, T., Moon, J-H., Qu, T, and Yueh, S.H. (18-Dec-14). Here, we propose an extended surface salinity layer within a global ocean circulation model to diagnose skin SSS without increasing the computational cost, while allowing comparable solutions with both satellite and Argo salinity at the respective depths within the corresponding uncertainty limits.

Ocean-to-Ocean Dissimilarities of Salty Subtropical Surface Water
Gordon, A. (18-Dec-14). Each ocean basin displays its own 'personality', reflecting its degree of isolation or connectivity to the global ocean, its place in the interocean exchange network and associated ocean overturning circulation systems, as well as regional circulation and air-sea exchange patterns.

Overview of SMOS Salinity
Nicolas, R. (18-Dec-14). In this talk, we will present examples demonstrating how SMOS-derived SSS data are being used to better characterize key land-ocean and atmosphere-ocean interaction processes that occur within the marine hydrological cycle. In particular, we shall illustrate how SMOS and its ocean mapping capability provides observations across the world's largest tropical ocean fresh pool regions and we will discuss intra-seasonal to interannual precipitation impacts as well as large-scale river runoff from the Amazon-Orinoco and Congo rivers and its offshore advection.

Relating River Discharges to Salinity Changes
Xie, X. and Liu, W.T. (18-Dec-14). New river discharge data are brought together with spacebased sea surface salinity measurements by Aquarius and SMOS to demonstrate the role of river discharge in salinity changes near three river mouths: the Mississippi, the Ganges, and the Amazon.

Salinity Exchange through the Quasi-Stationary Jet from the Subtropical to the Subpolar Pacific Ocean
Miyama, T. and Mitsudera, H. (18-Dec-14). It is known that a quasi-stationary jet-like current [referred to as J1 in Isoguchi et al. (2006)] flows along the northern part of the Kuroshio/Oyashio mixed water region in the western Pacific Ocean. Observations (Isoguchi et al. 2006, Wagawa et al. 2014) have shown that the jet transports saline water in the subtropical Pacific Ocean to the subpolar region. To investigate how the subtropical water is transported through the quasi-stationary jet, numerical particle were tracked using a high resolution ocean reanalysis dataset, the Japan Coastal Ocean Predictability Experiment (JCOPE2).

Salinity Variation in the Eastern Tropical Pacific Ocean
Ren, L. and Bayler, E. (18-Dec-14). This study attempts to address the atmospheric and oceanic causes of sub-monthly, monthly, seasonal variability in mixed-layer salinity from observational data sets. The data sets include measurements from the Aquarius sea surface salinity, SMOS sea surface salinity, Argo profiling float data, CMORPH precipitation, OAFlux evaporation and the ocean current measurements from OSCAR.

Salty Anomalies Forced by Central American Gap Winds: Aquarius Observations
Grodsky, S., Carton, J., and Bentamy, A. (18-Dec-14). Although upwelling normally doesn't have direct impact on the sea surface salinity (SSS), we present observational evidence of upwelling-induced SSS patterns off the Pacific Central American coast.

Sea Surface Salinity Under Rain Cells: SMOS and In-Situ Observations
Boutin, J., Martin, N., Reverdin, G.P., Morisset, S., Yin, X., Centurioni, L., and Reul, N. (18-Dec-14). The Soil Moisture and Ocean Salinity (SMOS) mission monitors sea surface salinity over the global ocean for more than 4.5 years. The objective of this presentation is 1) to analyse the signature of rainfall on SMOS salinity and 2) to validate it. This is a challenging task given that SMOS measures the salinity in the first top centimeter while most in situ measurements of salinity are made at a few meters depth and that other effects than sea surface salinity may affect the radiometric signal, like sea surface roughness modified by rain drops and rain atmospheric effects.

Sea Surface Salinity Variability in the East China Sea Observed by the Aquarius Instrument
Kim, S., Lee, J., de Matthaeis, P., Yueh, S.H., Hong, C., Pang, I., and Lagerloef, G.S.E. (18-Dec-14). This study demonstrates that the spaceborne Aquarius instrument is able to monitor the sea surface salinity variations in the East China Sea, where routine observations are difficult.

Spatial and Temporal Statistics for Validating Aquarius Sea Surface Salinity Measurements With Argo in Situ Observations
Mannshardt, E., Sucic, K., Bingham, F., and Fuentes, M. (18-Dec-15). Salinity is an indicator of the interaction between ocean circulation and the global water cycle, which in turn affects the regulation of the Earth's climate. Due to its fine spatial and temporal coverage, Aquarius presents an ideal measurement system for fully characterizing the distribution and properties of sea surface salinity. This leads to the need for the proper validation of the Aquarius salinity product with independent salinity measurements. Using the first two years of Aquarius 3.0 Level 2 sea surface salinity data we investigate time and space scales of variability and trends.

The Export of Salty Surface Water to Depth in the North Atlantic
Johannes, J. and Busecke, M. (18-Dec-14). Excess evaporation in the subtropics forms a local surface salinity maximum in all subtropical ocean basins. Descent of these waters to depth creates a core layer marked by a subsurface salinity maximum (S-max) spreading towards the equator, an integral part of the lower limb of the meridional subtropical overturning cell. Here we will investigate what governs the evolution of the S-max core layer in the North Atlantic.

The Impact of the Ozone Hole on the Salinity of the Southern Ocean
Solomon, A.I., Polvani, L.M., Abernathey, R.P., and Smith, K.L. (18-Dec-14). Observations have revealed systematic changes in the temperature and salinity of the Southern Ocean since 1960. These trends reflect the evolving exchange of heat and momentum between atmosphere and ocean and are, in part, driven by anthropogenic emissions.

The Relative Influence of Surface Sea Salinity and Temperature on Surface Density Gradient in the Tropical Pacific Ocean
Hasson, A.E.A. and Lee, T. (18-Dec-14). In this study, we use various satellite measurements of sea surface salinity and sea surface temperature to characterize the mean spatial structure and temporal variability of surface density gradients in the tropical Pacific Ocean from 2011 to present.

The Role of Fresh Water and Salt Fluxes in Southern Ocean Deep-Ocean Warming
Young, V., Bulusu, S., and Nyadjro, E.S. (18-Dec-14). Satellite-derived salinity from the Aquarius salinity mission (September, 2011-present) and Simple Ocean Data Assimilation (SODA) Reanalysis (1950-2010) are used to estimate freshwater and salt fluxes. Our results indicate that recent changes in freshwater and salt fluxes are a major component of the deep-ocean warming in the Southern Ocean.

The Role of Ocean Salinity in the Water Cycle Associated With Indian Monsoon
Tang, W., Yueh, S.H., and Liu, W.T. (18-Dec-14). Indian monsoon is one of the most important of all tropical climate systems. Its onset and spatial/temporal variability have strong economic impact and may cause severe human suffering. Using sea surface salinity (SSS) data from Aquarius/SAC-D satellite mission, we study the seasonal and interannual variability of SSS, to identify the potential sources for the monsoon moisture supply.

The Role of Time Scales in Estimating the Relative Importance of Isopycnal and Diapycnal Oceanic Mixing
Schanze, J. and Schmitt, R. (18-Dec-14). Large-scale thermal forcing and freshwater fluxes play an essential role in setting the ocean's temperature and salinity. The ratio of the relative contributions of haline and thermal forcing in the mixed layer is maintained by large-scale surface fluxes, leading to important consequences for mixing in the ocean interior.

The Seasonal Water Cycle over the India Subcontinent Indicated in the Correlated Analysis of Aquarius, GRACE and River Discharge Data
Yueh, S., Tang, W., Fore, A., Hayashi, A., Bindlish, R., Lee, T., and Jackson, T.J. (18-Dec-14). Aquarius is a combined passive/active L-band microwave instrument. Its data have been used to retrieve the sea surface salinity using the Combined Active and Passive algorithm with an accuracy of about 0.1 to 0.2 psu Root-Mean-Square between 40 degrees N and 40 degrees S. In addition to the salinity product, Aquarius radiometer data have been used to produce the surface soil moisture globally. We find that the change of soil moisture over the India subcontinent clearly correlates with the timing of India Monsoon, which produces significant precipitation between June and September, and is consistent with the total land mass change derived from the GRACE mission data.

The Time-Variable Position of the Antarctic Circumpolar Current Salinity Fronts from Aquarius Data
Volkov, D., Dong, S., and Goni, G.J. (18-Dec-14). As part of the validation of the Aquarius data and a demonstration of its capabilities and utility for oceanographic studies, we use along-track Aquarius data for the determination of the Antarctic Circumpolar Current sea surface salinity fronts between Africa and Antarctica.

Three Years of Aquarius Salinity Measurements: Algorithm, Validation and Applications
Meissner, T., Wentz, F., Le Vine, D., and Lagerloef, G. (18-Dec-14). This presentation reports the status of the Aquarius salinity retrieval algorithm highlighting the advances that have been made for and since the Version 3 release.

To What Extent Aquarius' Sampling Pattern Affects the Estimated Amplitude of Tropical Instability Waves?
Lee, T. (18-Dec-14). Tropical instability waves (TIWs) are important to ocean dynamics, air-sea interaction, and biogeochemistry. Measurements of sea surface salinity (SSS) from the Aquarius/SAC-D and SMOS missions have demonstrated their capabilities to detect TIWs both in the Pacific and the Atlantic Oceans. The accuracy of satellite SSS in representing TIW amplitudes has strong implication to the assimilation of these data in ocean models.

Upper Ocean Salinity Stratification in the Tropics as Derived from the Buoyancy Frequency N2
Maes, C. and O'Kane, T. (18-Dec-14). The present study aims to isolate the specific role of the salinity stratification in the layers above the main pycnocline by taking into account the respective thermal and saline dependencies in the Brunt-Vaisala frequency, N2.

Upper Water Structure and Mixed Layer Depth in Sub-Tropical Waters: The Seats Station in the Northern South China Sea
Tai, J.H. and Wong, G.T.F. (18-Dec-14). 702 CTD profiles were collected in the subtropical northern South China Sea at and in the vicinity of the SouthEast Asian Time-series Study (SEATS) station (18.2°N, 115.8°E) between 17.5 and 18.5°N and 115.3 and 116.3°E in 64 cruises in 1997 to 2013. The hydrographic structure of the upper water above the permanent thermocline may be classified into 4 principal types: (a) classic type (an almost isopycnic upper water); (b) stepwise type (with one or more small but significant step-increases in σθ in the upper water); (c) graded type (an approximately constant depth gradient in a monotonic increase in σθ in the upper water); and (d) mixed type (a combination of the stepwise and graded types).

Validation of SMOS With Malaspina Surface Drifter Data
Ballabrera, J., Turiel, A., Salvador, J., Fernández, P., and Font, J. (18-Dec-14). To fill the bridge between the skin depth (one cm penetration depth) of the satellite measurements and the uppermost reliable measures (between 5 and 10 meters below the surface) from the Argo floats, a new generation of surface drifters has been designed and deployed in various oceans of the world. Here the drifters deployed during Malaspina Campaign, and their impact in the validation of the various SMOS prodcts, are described.

Variability of the Tropical Atlantic and Pacific SSS Minimum Zones in the Last Three Decades and Their Relations to the ITCZ and NECC
Delcroix, T.C., Tchilibou, M.L., Alory, G., Reverdin, G.P., and Arnault, S. (18-Dec-14). This study focuses on the time-space variability of the low Sea Surface Salinity waters located from the West to the East within about 2°N-12°N in the Atlantic and Pacific oceans.

Water Cycle Amplification Inferred from Broadening of the Ocean's Salinity Distribution
Zikal, J.D., Skliris, N., Nurser, G., Blaker, A., and Marsh, R. (18-Dec-14). The water cycle leaves an imprint on ocean salinity through evaporation and precipitation. It has been proposed that observed changes in salinity could be used to infer changes in the water cycle. Here salinity is characterized by the distribution of water masses in salinity coordinates.

Where to Look for Recent Decadal Ocean Temperature and Salinity Changes: a CMIP Model Density Analysis
Guilyardi, E., Durack, P., and Gleckler, P. (18-Dec-14). In this study, we use global climate models (from the CMIP5 and CMIP3 model suites) and a number of available observational analyses to investigate the global and regional distribution of temperature and salinity changes in neutral density space.