References

Ocean Science

Ocean Sci.

1812-0792

Copernicus Publications

Göttingen, Germany

10.5194/os-9-183-2013

Sea surface freshening inferred from SMOS and ARGO salinity: impact of rain

Boutin

https://orcid.org/0000-0003-2845-4912

¹ Martin

¹ Reverdin

¹ Yin

¹ Gaillard

CNRS-INSU, UMR7159, LOCEAN/IPSL (CNRS-UPMC-IRD-MNHN), Paris, France

IFREMER, LPO (CNRS-IFREMER-IRD-UBO), Plouzané, France

22 02 2013

9 1 183 192

2013

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The sea surface salinity (SSS) measured from space by the Soil Moisture and Ocean Salinity (SMOS) mission has recently been revisited by the European Space Agency first campaign reprocessing. We show that, with respect to the previous version, biases close to land and ice greatly decrease. The accuracy of SMOS SSS averaged over 10 days, 100 × 100 km<sup>2</sup> in the open ocean and estimated by comparison to ARGO (Array for Real-Time Geostrophic Oceanography) SSS is on the order of 0.3–0.4 in tropical and subtropical regions and 0.5 in a cold region. The averaged negative SSS bias (−0.1) observed in the tropical Pacific Ocean between 5° N and 15° N, relatively to other regions, is suppressed when SMOS observations concomitant with rain events, as detected from SSM/Is (Special Sensor Microwave Imager) rain rates, are removed from the SMOS–ARGO comparisons. The SMOS freshening is linearly correlated to SSM/Is rain rate with a slope estimated to −0.14 mm<sup>−1</sup> h, after correction for rain atmospheric contribution. This tendency is the signature of the temporal SSS variability between the time of SMOS and ARGO measurements linked to rain variability and of the vertical salinity stratification between the first centimeter of the sea surface layer sampled by SMOS and the 5 m depth sampled by ARGO. However, given that the whole set of collocations includes situations with ARGO measurements concomitant with rain events collocated with SMOS measurements under no rain, the mean −0.1 bias and the negative skewness of the statistical distribution of SMOS minus ARGO SSS difference are very likely the mean signature of the vertical salinity stratification. In the future, the analysis of ongoing in situ salinity measurements in the top 50 cm of the sea surface and of Aquarius satellite SSS are expected to provide complementary information about the sea surface salinity stratification.

References 1

Anderson, J. and Riser, S.: Near Surface variability of Temperature and Salinity: Observations from Profiling Floats, Aquarius/SAC-D Science Team Meeting, Buenos Aires, Argentina, 11–13 April 2012, 2012.

Banks, C. J., Gommenginger, C. P., Srokosz, M. A., and Snaith, H. M.: Validating SMOS Ocean Surface Salinity in the Atlantic With Argo and Operational Ocean Model Data, IEEE Trans. Geosci. Remote Sens., 50, 1688–1702, <a href="http://dx.doi.org/10.1109/tgrs.2011.2167340">https://doi.org/10.1109/tgrs.2011.2167340</a>, 2012.

Boutin, J., Waldteufel, P., Martin, N., Caudal, G., and Dinnat, E.: Surface Salinity Retrieved from SMOS Measurements over the Global Ocean: Imprecisions Due to Sea Surface Roughness and Temperature Uncertainties, Journal of Atmospheric and Oceanic Technology, 21, 1432–1447, <a href="http://dx.doi.org/10.1175/1520-0426(2004)021<1432:ssrfsm>2.0.co;2">https://doi.org/10.1175/1520-0426(2004)021<1432:ssrfsm>2.0.co;2</a>, 2004.

Boutin, J., Martin, N., Xiaobin, Y., Font, J., Reul, N., and Spurgeon, P.: First Assessment of SMOS Data Over Open Ocean: Part II – Sea Surface Salinity, IEEE Trans. Geosci. Remote Sens., 50, 1662–1675, <a href="http://dx.doi.org/10.1109/tgrs.2012.2184546">https://doi.org/10.1109/tgrs.2012.2184546</a>, 2012.

Bowman, K. P., C. R. Homeyer, and D. G. Stone: A comparison of oceanic precipitation estimates in the tropics and subtropics, J. Appl. Meteorol. Climatol., 48, 1335–1344, 2009.

Carval, T., Keeley, B., Takatsuki, Y., Yoshida, T., Loch, S., Schmid, C., Goldsmith, R., Wong, A., McCreadie, R., Thresher, A., and Tran, A.: Argo User's Manual v2.4, IFREMERreference cor-do/dti-mut/02-084, 85, 2012.

Contreras, R. F. and Plant, W. J.: Surface effect of rain on microwave backscatter from the ocean: Measurements and modeling, J. Geophys. Res., 111, C08019, <a href="http://dx.doi.org/10.1029/2005jc003356">https://doi.org/10.1029/2005jc003356</a>, 2006.

Cravatte, S., Delcroix, T., Zhang, D., McPhaden, M. J., and Leloup, J.: Observed freshening and warming of the western Pacific warm pool, Clim. Dyn., 33, 565–589, <a href="http://dx.doi.org/10.1007/s00382-009-0526-7">https://doi.org/10.1007/s00382-009-0526-7</a>, 2009.

Dinnat, E.: De la détermination de la salinité de surface des océans à partir de mesures radiométriques hyperfréquences en bande L, University Paris 6, Paris, 271 pp., 2003.

Durack, P. J., Wijffels, S. E., and Matear, R. J.: Ocean Salinities Reveal Strong Global Water Cycle Intensification During 1950 to 2000, Science, 336, 455–458, <a href="http://dx.doi.org/10.1126/science.1212222">https://doi.org/10.1126/science.1212222</a>, 2012.

Gaillard, F., Autret, E., Thierry, V., Galaup, P., Coatanoan, C., and Loubrieu, T.: Quality Control of Large Argo Datasets, J. Atmos. Ocean. Tech., 26, 337–351, <a href="http://dx.doi.org/10.1175/2008jtecho552.1">https://doi.org/10.1175/2008jtecho552.1</a>, 2009.

Geer, A. J., Bauer, P., and Lopez, P.: Lessons learnt from the operational 1D +4D-Var assimilation of rain- and cloud-affected SSM/I observations at ECMWF, Q. J. R. Meteorol. Soc., 134, 1513–1525, <a href="http://dx.doi.org/10.1002/qj.304">https://doi.org/10.1002/qj.304</a>, 2008.

Gordon, A. L. and Giulivi, C. F.: Sea surface salinity trends over fifty years within the subtropical north Atlantic, Oceanogr., 21, 20–29, <a href="http://dx.doi.org/10.5670/oceanog.2008.64">https://doi.org/10.5670/oceanog.2008.64</a>, 2008.

Guimbard, S., Gourrion, J., Portabella, M., Turiel, A., Gabarro, C., and Font, J.: SMOS Semi-Empirical Ocean Forward Model Adjustment, IEEE Trans. Geosci. Remote Sens., 50, 1676–1687, <a href="http://dx.doi.org/10.1109/tgrs.2012.2188410">https://doi.org/10.1109/tgrs.2012.2188410</a>, 2012.

Hénocq, C., Boutin, J., Reverdin, G., Petitcolin, F., Arnault, S., and Lattes, P.: Vertical Variability of Near-Surface Salinity in the Tropics: Consequences for L-Band Radiometer Calibration and Validation, J. Atmos. Ocean. Tech., 27, 192–209, <a href="http://dx.doi.org/10.1175/2009jtecho670.1">https://doi.org/10.1175/2009jtecho670.1</a>, 2010.

Hilburn, K. A. and F. J. Wentz: Intercalibrated passive microwave rain products from the Unified Microwave Ocean Retrieval Algorithm (UMORA), J. Appl. Meteorol. Climatol., 47, 778–794, 2008.

Kainulainen, J., Colliander, A., Closa, J., Martin-Neira, M., Oliva, R., Buenadicha, G., Rubiales Alcaine, P., Hakkarainen, A., and Hallikainen, M. T.: Radiometric Performance of the SMOS Reference Radiometers – Assessment After One Year of Operation, IEEE Trans. Geosci. Remote Sens., 50, 1367–1383, <a href="http://dx.doi.org/10.1109/tgrs.2011.2177273">https://doi.org/10.1109/tgrs.2011.2177273</a>, 2012.

Kerr, Y. H., Waldteufel, P., Wigneron, J. P., Delwart, S., Cabot, F., Boutin, J., Escorihuela, M. J., Font, J., Reul, N., Gruhier, C., Juglea, S. E., Drinkwater, M. R., Hahne, A., Martin-Neira, M., and Mecklenburg, S.: The SMOS Mission: New Tool for Monitoring Key Elements ofthe Global Water Cycle, Proceedings of the IEEE, 98, 666–687, <a href="http://dx.doi.org/10.1109/jproc.2010.2043032">https://doi.org/10.1109/jproc.2010.2043032</a>, 2010.

Lagerloef, G., Boutin, J., Chao, Y., Delcroix, T., Font, J., Niiler, P., Reul, N., Riser, S., Schmitt, R., Stammer, D., and Wentz, F.: Resolving the Global Surface Salinity Field and Variations by Blending Satellite and In Situ Observations, Oceanobs'09: Sustained Ocean Observations and Information for Society Venise, Italy, 21–25 September 2009, ESA Publication WPP-306, <a href="http://dx.doi.org/10.5270/OceanObs09.cwp.51">https://doi.org/10.5270/OceanObs09.cwp.51</a>, 2010.

Mecklenburg, S., Drusch, M., Kerr, Y. H., Font, J., Martin-Neira, M., Delwart, S., Buenadicha, G., Reul, N., Daganzo-Eusebio, E., Oliva, R., and Crapolicchio, R.: ESA's Soil Moisture and Ocean Salinity Mission: Mission Performance and Operations, IEEE Trans. Geosci. Remote Sens., 50, 1354–1366, <a href="http://dx.doi.org/10.1109/tgrs.2012.2187666">https://doi.org/10.1109/tgrs.2012.2187666</a>, 2012.

Peichl, M., Wittmann, V., Anterrieu, E., Picard, B., Skou, N., and Solbjerg, S.: Scientific inputs for the SMOS Level 1 Processor development, Final report for ESA contract No. 10508/02/NL/GS, DLR, Munich, 2004.

Portabella, M., Stoffelen, A., Lin, W., Turiel, A., Verhoef, A., Verspeek, J., and Ballabrera-Poy, J.: Rain Effects on ASCATRetrieved Winds: Toward an Improved Quality Control, IEEE Trans. Geosci. Remote Sens., 50, 2495–2506, <a href="http://dx.doi.org/10.1109/tgrs.2012.2185933">https://doi.org/10.1109/tgrs.2012.2185933</a>, 2012.

Reul, N., Tenerelli, J., Boutin, J., Chapron, B., Paul, F., Brion, E., Gaillard, F., and Archer, O.: Overview of the First SMOS Sea Surface Salinity Products, Part 1: Quality Assessment for the Second Half of 2010, IEEE Trans. Geosci. Remote Sens., 50, 1636–1647, <a href="http://dx.doi.org/10.1109/tgrs.2012.2188408">https://doi.org/10.1109/tgrs.2012.2188408</a>, 2012.

Reverdin, G., Morisset, S., Boutin, J., and Martin, N.: Rain-induced variability of near sea-surface T and S from drifter data, J. Geophys. Res., 117, C02032, <a href="http://dx.doi.org/10.1029/2011jc007549">https://doi.org/10.1029/2011jc007549</a>, 2012.

Soloviev, A. and Lukas, R.: Observation of Spatial Variability of Diurnal Thermocline and Rain-Formed Halocline in the Western Pacific Warm Pool, J. Phys. Oceanogr., 26, 2529–2538, <a href="http://dx.doi.org/10.1175/1520-0485(1996)026<2529:oosvod>2.0.CO;2">https://doi.org/10.1175/1520-0485(1996)026<2529:oosvod>2.0.CO;2</a>, 1996.

Soloviev, A. and Lukas, R.: Observation of large diurnal warming events in the near-surface layer of the western equatorial Pacific warm pool, Deep-Sea Res. Pt. I, 44, 1055–1076, <a href="http://dx.doi.org/10.1016/s0967-0637(96)00124-0">https://doi.org/10.1016/s0967-0637(96)00124-0</a>, 1997.

Terray, L., Corre, L., Cravatte, S., Delcroix, T., Reverdin, G., and Ribes, A.: Near-Surface Salinity as Nature's Rain Gauge to Detect Human Influence on the Tropical Water Cycle, J. Climate, 25, 958–977, <a href="http://dx.doi.org/10.1175/jcli-d-10-05025.1">https://doi.org/10.1175/jcli-d-10-05025.1</a>, 2011.

Ulaby, F. T., Moore, R. K., and Fung, A. K.: Microwave Remote Sensing – Active and Passive: Vol 1: Microwave Remote Sensing Fundamentals and Radiometry, ARTECH House, Norwood, MA 02062, 456 pp., 1981.

UNESCO: The international system of units (SI) in oceanography, UNESCO Technical Papers No. 45, IAPSO Pub. Sci. No. 32, Paris, France, 1985.

Vialard, J., Duvel, J. P., McPhaden, M. J., Bouruet-Aubertot, P., Ward, B., Key, E., Bourras, D., Weller, R., Minnett, P., Weill, A., Cassou, C., Eymard, L., Fristedt, T., Basdevant, C., Dandonneau, Y., Duteil, O., Izumo, T., de Boyer Montégut, C., Masson, S., Marsac, F., Menkes, C., and Kennan, S.: Cirene: Air-Sea Interactions in the Seychelles – Chagos Thermocline Ridge Region, Bull. Am. Meteorol. Soc., 90, 45–61, <a href="http://dx.doi.org/10.1175/2008bams2499.1">https://doi.org/10.1175/2008bams2499.1</a>, 2009.

Ward, B., Wanninkhof, R., Minnett, P. J., and Head, M. J.: SkinDeEP: A Profiling Instrument for Upper-Decameter Sea Surface Measurements, J. Atmos. Ocean. Tech., 21, 207–222, <a href="http://dx.doi.org/10.1175/1520-0426(2004)021<0207:sapifu>2.0.CO;2">https://doi.org/10.1175/1520-0426(2004)021<0207:sapifu>2.0.CO;2</a>, 2004.

Wentz, F. J.: The Effect of Clouds and Rain on the Aquarius Salinity Retrieval, Remote Sensing System Technical Memorandum 3031805, Santa Rosa, California, 2005.

Yin, X., Boutin, J., Martin, N., and Spurgeon, P.: Optimization of L-Band Sea Surface Emissivity Models Deduced From SMOS Data, IEEE Trans. Geosci. Remote Sens., 50, 1414–1426, \href{http://dx.doi.org/10.1109/tgrs.2012.2184547} https://doi.org/10.1109/tgrs.2012.2184547, 2012.

Zhang, Y. and Zhang, X.: Ocean haline skin layer and turbulent surface convections, J. Geophys. Res., 117, C04017, <a href="http://dx.doi.org/10.1029/2011jc007464">https://doi.org/10.1029/2011jc007464</a>, 2012.