Wintertime observations of Subtropical Mode Water formation within the Gulf Stream

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 36 (2009): L02607, doi:10.1029/2008GL035918.We study the structure of Subtropical Mode Water (STMW) within the eastward-flowing Gulf Stream as it forms during strong winter cooling. Shipboard observations using SeaSoar and ADCP reveal that while active mixing by gravitational instabilities is common, large vertical and lateral shears of the Gulf Stream play a central role in determination of the modes of active mixing. Evidence is presented that low static stability and large vertical shear can combine to cause slantwise convection/symmetric instabilities, while the large anticyclonic shears to the south of the Gulf Stream core can cause low absolute vorticity and precondition the Ertel potential vorticity to be small and more susceptible to instabilities. The area of active mixing driven by surface forcing in the presences of shear occupies a swath 50–90 km wide immediately south of the Gulf Stream core at the northern edge of the Sargasso Sea.Support came from the National Science Foundation grants OCE-0424865 (TJ and FB) and OCE-0549699 (LT)

The CLIMODE field campaign : observing the cycle of convection and restratification over the Gulf Stream

Author Posting. © American Meteorological Society, 2009. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 90 (2009): 1337-1350, doi:10.1175/2009BAMS2706.1.A major oceanographic field experiment is described, which is designed to observe, quantify, and understand the creation and dispersal of weakly stratified fluid known as “mode water” in the region of the Gulf Stream. Formed in the wintertime by convection driven by the most intense air–sea fluxes observed anywhere over the globe, the role of mode waters in the general circulation of the subtropical gyre and its biogeo-chemical cycles is also addressed. The experiment is known as the CLIVAR Mode Water Dynamic Experiment (CLIMODE). Here we review the scientific objectives of the experiment and present some preliminary results.Physical Oceanography program of NS

New perspectives on eighteen-degree water formation in the North Atlantic

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Journal of Oceanography 68 (2012): 45-52, doi:10.1007/s10872-011-0029-0.In this report, Eighteen Degree Water (EDW) formation will be discussed, with emphasis on advances in understanding emerging within the past decade. In particular, a recently completed field study of EDW (CLIMODE) is suggesting that EDW formation within a given winter can have at least two different dominant physics and distinct locations: one type formed in the northern Sargasso Sea, largely away from the strong flows of the Gulf Stream where 1D physics may apply, and a second type formed along the southern flank of the Gulf Stream, in a region where the background vorticity of the flow and cross-frontal mixing plays a key role in the convective formation process.National Science Foundation (OCE 0959387)2012-06-0