Ocean Science www.ocean-sci.net 1812-0784 1812-0792 5 3 2009 10.5194/os-5-379-2009 http://www.ocean-sci.net/5/379/2009/ http://www.ocean-sci.net/5/379/2009/os-5-379-2009.html http://www.ocean-sci.net/5/379/2009/os-5-379-2009.pdf 379 387 2009-09-28 On the porosity of barrier layers J. Mignot juliette.mignot@locean-ipsl.upmc.fr C. de Boyer Montégut M. Tomczak IPSL/LOCEAN, UPMC/CNRS/IRD/MNHN, Paris, France Laboratoire d'Océanographie Spatiale, IFREMER, centre de Brest, France School of Chemistry, Physics and Earth Sciences, Flinders University of South Australia, Adelaide, Australia Barrier layers are defined as the layer between the pycnocline and the thermocline when the latter are different as a result of salinity stratification. We present a revisited 2-degree resolution global climatology of monthly mean oceanic Barrier Layer (BL) thickness first proposed by de Boyer Montégut et al. (2007). In addition to using an extended data set, we present a modified computation method that addresses the observed porosity of BLs. We name porosity the fact that barrier layers distribution can, in some areas, be very uneven regarding the space and time scales that are considered. This implies an intermittent alteration of air-sea exchanges by the BL. Therefore, it may have important consequences for the climatic impact of BLs. Differences between the two computation methods are small for robust BLs that are formed by large-scale processes. However, the former approach can significantly underestimate the thickness of short and/or localized barrier layers. This is especially the case for barrier layers formed by mesoscale mechanisms (under the intertropical convergence zone for example and along western boundary currents) and equatorward of the sea surface salinity subtropical maxima. Complete characterisation of regional BL dynamics therefore requires a description of the robustness of BL distribution to assess the overall impact of BLs on the process of heat exchange between the ocean interior and the atmosphere. Boyer, T. P., Antonov, J. I., Garcia, H. E., Johnson, D. R., Locarnini, R. A., Mishonov, A. V., Pitcher, M. T., Baranova, O. K., and Smolyar, I. V.: World Ocean Database 2005, NOAA Atlas NESDIS 60, US Government Printing Office, Washington, DC, s Levitus, edition, 190~pp., 2006. Cronin, M F. and McPhaden, M J.: Barrier layer formation during westerly wind bursts, J. Geophys. Res., 107(C12), 8020, doi:10.1029/2001JC001171, 2002. de~Boyer~Montégut, C.,~Mignot, J.,~Lazar, A., and~Cravatte, S.: Control of salinity on the mixed layer depth in the world ocean. Part I: general description, J. Geophys. Res., 112, C06011, doi:10.1029/2006JC003953, 2007. de~Boyer~Montégut, C.,~Madec, G., Fisher, A S.,~Lazar, A., and~Iudicone, D.: Mixed layer depth over the global ocean: an examination of profile data and a profile-based climatology, J. Geophys. Res., 109, C12003, doi:10.1029/2004JC002378, 2004. de Boyer Montégut, C., Durand, F., Bourdallé-Badie, R., and Blanke, B.: Barrier layers in the Arabian Sea during the summer monsoon, in preparation, 2009. Godfrey, J S. and Lindstrom, E J.: The heat budget of the equatorial western Pacific surface mixed layer, J. Geophys. Res., 94, 8007–8017, 1989. Levitus, S.: Climatological Atlas of the world ocean. \newblock Technical report, NOAA Prof. Pap. 13, 163~pp., 1982. Mignot, J.,~de~Boyer~Montégut, C.,~Lazar, A., and~Cravatte, S.: Control of salinity on the mixed layer depth in the world ocean. Part II: tropical and subtropical areas, J. Geophys. Res., 112, C10010, doi:10.1029/2006JC003954, 2007. Sprintall, J. and~Tomczak, M.: Evidence of the barrier layer in the surface layer of the Tropics, J. Geophys. Res., 97, 7305–7316, 1992. Sprintall, J. and McPhaden, M J.: Surface layer variations observed in multiyear time series measurements from the western equatorial Pacific, J. Geophys. Res., 99, 973–979, 1994. Thadathil, P., Muraleedharan, P. M., Somayajulu, Y K., Gopalakrishna, V V., and Reddy, G V.: Seasonal variability of the observed barrier layer in the Arabian Sea, J. Phys. Oceanogr., 38(3), 624–638, 2008. Tomczak, M.: Salinity variability in the surface layer of the tropical western Pacific Ocean, J. Geophys. Res., 100(C10), 20499–20515, 1995. WOCE Data~Product Committee: WOCE Global Data, version 3.0, Technical Report 180/02, WOCE Int. Project Off., Southampton, UK, 2002 You, Y.: Salinity variability and its role in the barrier-layer formation during TOGA-COARE, J. Phys. Oceanogr., 25(11), 2778–2807, 1995.