Assessment of seasonal and year-to-year surface salinity signals retrieved from SMOS and Aquarius missions in the Bay of Bengal

ABSTRACT The Bay of Bengal (BoB) exhibits a wide range of sea surface salinity (SSS), with very fresh water induced by heavy monsoonal precipitation and river run-offs to the north, and saltier water to the south. This is a particularly challenging region for the application of satellite-derived SSS measurements because of the potential pollution of the SSS signal by radio frequency interference (RFI) and land-induced contamination in this semi-enclosed basin. The present study validates recent level-3 monthly gridded (1° × 1°) SSS products from Soil Moisture and Ocean Salinity (SMOS) and Aquarius missions to an exhaustive in situ SSS product for the BoB. Current SMOS SSS retrievals do not perform better than existing climatologies. This is in stark contrast to Aquarius, which outperforms SMOS and available SSS climatologies everywhere in the BoB. While SMOS only captures the SSS seasonal evolution in the northern part of the Bay, Aquarius accurately captures the seasonal signal in the entire basin. The Aquarius product is also able to capture SSS non-seasonal anomalies, with an approximate correlation (r) of 0.75 with box-averaged in situ data in the northern, central, and western parts of the Bay. Aquarius can, thus, be confidently used to monitor large-scale year-to-year SSS variations in the BoB.

[1]  Wenqing Tang,et al.  Aquarius geophysical model function and combined active passive algorithm for ocean surface salinity and wind retrieval , 2014 .

[2]  Yann Kerr,et al.  The SMOS Mission: New Tool for Monitoring Key Elements ofthe Global Water Cycle , 2010, Proceedings of the IEEE.

[3]  S. Levitus,et al.  World ocean atlas 2009 , 2010 .

[4]  R. Sivakumar,et al.  Seasonal variability of sea surface salinity and salt budget of the mixed layer of the north Indian Ocean , 2003 .

[5]  S. Basu,et al.  A SEEK filter assimilation of sea surface salinity from Aquarius in an OGCM: Implication for surface dynamics and thermohaline structure , 2014 .

[6]  Ravi S. Nanjundiah,et al.  Indian Ocean sea surface salinity variations in a coupled model , 2009 .

[7]  Raj Kumar,et al.  Assessing Sea Surface Salinity Derived by Aquarius in the Indian Ocean , 2014, IEEE Geoscience and Remote Sensing Letters.

[8]  P. Webster,et al.  The Role of Intraseasonal Variability in the Nature of Asian Monsoon Precipitation , 2007 .

[9]  S. Shenoi,et al.  Differences in heat budgets of the near-surface Arabian Sea and Bay of Bengal: Implications for the summer monsoon , 2002 .

[10]  N. Reul,et al.  SMOS reveals the signature of Indian Ocean Dipole events , 2013, Ocean Dynamics.

[11]  Gary S. E. Lagerloef,et al.  Sea Surface Salinity , 2014, Encyclopedia of Remote Sensing.

[12]  C. Deltel,et al.  A modeling study of the processes of surface salinity seasonal cycle in the Bay of Bengal , 2014 .

[13]  Jacqueline Boutin,et al.  Analyzing the 2010–2011 La Niña signature in the tropical Pacific sea surface salinity using in situ data, SMOS observations, and a numerical simulation , 2014 .

[14]  Jacqueline Boutin,et al.  SMOS salinity in the subtropical North Atlantic salinity maximum: 1. Comparison with Aquarius and in situ salinity , 2014 .

[15]  S. Riser,et al.  The Argo Program : observing the global ocean with profiling floats , 2009 .

[16]  William B. Rossow,et al.  Ganga-Brahmaputra river discharge from Jason-2 radar altimetry: An update to the long-term satellite-derived estimates of continental freshwater forcing flux into the Bay of Bengal , 2012 .

[17]  V. Menezes,et al.  Aquarius sea surface salinity in the South Indian Ocean: Revealing annual‐period planetary waves , 2014 .

[18]  Yann Kerr,et al.  Sea Surface Salinity Observations from Space with the SMOS Satellite: A New Means to Monitor the Marine Branch of the Water Cycle , 2014, Surveys in Geophysics.

[19]  Michael J. McPhaden,et al.  Time and space scales for sea surface salinity in the tropical oceans , 2005 .

[20]  D. Shankar,et al.  Hydrography and circulation in the western Bay of Bengal during , 1996 .

[21]  M. R. Ramesh Kumar,et al.  ‘Thermohaline front’ off the east coast of India and its generating mechanism , 2013, Ocean Dynamics.

[22]  M. Lengaigne,et al.  Salinity Measurements Collected by Fishermen Reveal a ``River in the Sea'' Flowing Along the Eastern Coast of India , 2014 .

[23]  Rosemary Morrow,et al.  The French contribution to the voluntary observing ships network of sea surface salinity , 2015 .

[24]  G. Madec,et al.  The upper Bay of Bengal salinity structure in a high-resolution model , 2014 .

[25]  G. Madec,et al.  Influence of upper‐ocean stratification on tropical cyclone‐induced surface cooling in the Bay of Bengal , 2012 .

[26]  V. R. Shamji.  OMNI buoy network in the Bay of Bengal , 2015 .

[27]  Raj Kumar,et al.  Assessment of Satellite-Derived Sea Surface Salinity in the Indian Ocean , 2013, IEEE Geoscience and Remote Sensing Letters.

[28]  Y. Masumoto,et al.  RAMA: The Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction* , 2009 .

[29]  Bulusu Subrahmanyam,et al.  Preliminary SMOS Salinity Measurements and Validation in the Indian Ocean , 2013, IEEE Transactions on Geoscience and Remote Sensing.

[30]  G. V. Reddy,et al.  A new atlas of temperature and salinity for the North Indian Ocean , 2012, Journal of Earth System Science.

[31]  R. Wasson,et al.  Discharge and suspended sediment transport in the Ayeyarwady River, Myanmar: centennial and decadal changes , 2009 .

[32]  Vardis Tsontos,et al.  Aquarius and SMOS detect effects of an extreme Mississippi River flooding event in the Gulf of Mexico , 2013 .

[33]  Simon Yueh,et al.  The Aquarius/SAC-D mission: Designed to meet the salinity remote-sensing challenge , 2008 .

[34]  G. Reverdin,et al.  Near-Surface Salinity as Nature’s Rain Gauge to Detect Human Influence on the Tropical Water Cycle , 2012 .

[35]  Yann Kerr,et al.  ESA's Soil Moisture and Ocean Salinity Mission: Mission Performance and Operations , 2012, IEEE Transactions on Geoscience and Remote Sensing.

[36]  Erratum to: Observed year-to-year sea surface salinity variability in the Bay of Bengal during the 2009–2014 period , 2015, Ocean Dynamics.

[37]  Jacqueline Boutin,et al.  First Assessment of SMOS Data Over Open Ocean: Part II—Sea Surface Salinity , 2012, IEEE Transactions on Geoscience and Remote Sensing.

[38]  Manuel Martín-Neira,et al.  SMOS: The Payload , 2008, IEEE Transactions on Geoscience and Remote Sensing.

[39]  Wenqing Tang,et al.  Uncertainty of Aquarius sea surface salinity retrieved under rainy conditions and its implication on the water cycle study , 2014 .

[40]  Bertrand Chapron,et al.  Overview of the First SMOS Sea Surface Salinity Products. Part I: Quality Assessment for the Second Half of 2010 , 2012, IEEE Transactions on Geoscience and Remote Sensing.

[41]  S. Gorshkov,et al.  World ocean atlas , 1976 .

[42]  Haifeng Zhang,et al.  Assessment of Two SMOS Sea Surface Salinity Level 3 Products Against Argo Upper Salinity Measurements , 2013, IEEE Geoscience and Remote Sensing Letters.

[43]  Bertrand Chapron,et al.  Sea surface salinity structure of the meandering Gulf Stream revealed by SMOS sensor , 2014 .