5 research outputs found
Kinematic structure and dynamics of the Denmark Strait Overflow from ship-based observations
Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 50(11), (2020): 3235â3251, https://doi.org/10.1175/JPO-D-20-0095.1.The dense outflow through Denmark Strait is the largest contributor to the lower limb of the Atlantic meridional overturning circulation, yet a description of the full velocity field across the strait remains incomplete. Here we analyze a set of 22 shipboard hydrographicâvelocity sections occupied along the LĂĄtrabjarg transect at the Denmark Strait sill, obtained over the time period 1993â2018. The sections provide the first complete view of the kinematic components at the sill: the shelfbreak East Greenland Current (EGC), the combined flow of the separated EGC, and the North Icelandic Jet (NIJ), and the northward-flowing North Icelandic Irminger Current (NIIC). The total mean transport of overflow water is 3.54 ± 0.29 Sv (1 Sv ⥠106 m3 sâ1), comparable to previous estimates. The dense overflow is partitioned in terms of water mass constituents and flow components. The mean transports of the two types of overflow waterâAtlantic-origin Overflow Water and Arctic-origin Overflow Waterâare comparable in Denmark Strait, while the merged NIJâseparated EGC transports 55% more water than the shelfbreak EGC. A significant degree of water mass exchange takes place between the branches as they converge in Denmark Strait. There are two dominant time-varying configurations of the flow that are characterized as a cyclonic state and a noncyclonic state. These appear to be wind-driven. A potential vorticity analysis indicates that the flow through Denmark Strait is subject to symmetric instability. This occurs at the top of the overflow layer, implying that the mixing/entrainment process that modifies the overflow water begins at the sill.Funding for the study was provided by National Science Foundation (NSF) Grants OCE-1259618, OCE-1756361, and OCE-1558742. The German research cruises were financially supported through various EU Projects (e.g. THOR, NACLIM) and national projects (most recently TRR 181 âEnergy Transfer in Atmosphere and Oceanâ funded by the German Research Foundation and RACE II âRegional Atlantic Circulation and Global Changeâ funded by the German Federal Ministry for Education and Research). GWKM acknowledges the support of the Natural Sciences and Engineering Research Council of Canada. LP was supported by NSF Grant OCE-1657870
Cirene : air-sea iInteractions in the Seychelles-Chagos thermocline ridge region
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:10.1175/2008BAMS2499.1.The VascoâCirene program ex-plores how strong airâsea inter-actions promoted by the shallow thermocline and high sea surface temperature in the SeychellesâChagos thermocline ridge results in marked variability at synoptic, intraseasonal, and interannual time scales. The Cirene oceano-graphic cruise collected oceanic, atmospheric, and airâsea flux observations in this region in Jan-uaryâFebruary 2007. The contem-poraneous Vasco field experiment complemented these measure-ments with balloon deployments from the Seychelles. Cirene also contributed to the development of the Indian Ocean observing system via deployment of a moor-ing and 12 Argo profilers.
Unusual conditions prevailed in the Indian Ocean during Janu-ary and February 2007, following the Indian Ocean dipole climate anomaly of late 2006. Cirene measurements show that the SeychellesâChagos thermocline ridge had higher-than-usual heat content with subsurface anomalies up to 7°C. The ocean surface was warmer and fresher than average, and unusual eastward currents prevailed down to 800 m. These anomalous conditions had a major impact on tuna fishing in early 2007. Our dataset also sampled the genesis and maturation of Tropical Cyclone Dora, including high surface temperatures and a strong diurnal cycle before the cyclone, followed by a 1.5°C cool-ing over 10 days. Balloonborne instruments sampled the surface and boundary layer dynamics of Dora. We observed small-scale structures like dry-air layers in the atmosphere and diurnal warm layers in the near-surface ocean. The Cirene data will quantify the impact of these finescale features on the upper-ocean heat budget and atmospheric deep convection.CNES funded the Vasco part of the experiment; INSU
funded the Cirene part. R/V SuroĂźt is an Ifremer ship. The
contributions from ODU, WHOI, and FOI (Sweden) are
supported by the National Science Foundation under Grant
Number 0525657. The participation of the University of
Miami group was funded though NASA (NNG04HZ33C).
PMEL participation was supported through NOAAâs Office
of Climate Observation
Partikelrörelser i vatten vid ett vindkraftverk : Akustisk störning pÄ fisk
Ett nytt mĂ€tinstrument har utvecklats och anvĂ€nts för att mĂ€ta ljudvĂ„gens partikelacceleration i vatten vid det nordligaste vindkraftverket vid Utgrundens vindkraftpark i Kalmarsund. Vindkraftsverkens fundament Ă€r av typen driven monopile. MĂ€tresultaten har satts samman med audiogram och responsstudier för torsk, abborre, rödspotta och lax. Syftet har varit att fĂ„ reda pĂ„ hur fiskar uppfattar den uppmĂ€tta partikelaccelerationen.Studien visar att torsk, abborre, rödspotta och lax uppfattar partikelaccelerationen inom en radie pĂ„ 10 meter frĂ„n vindkraftverket. UppmĂ€tta nivĂ„er kommer sannolikt inte att utlösa ett reflexmĂ€ssigt beteende. Utanför 10 meter uppfattar de studerade fiskarterna inte partikelaccelerationen frĂ„n vindkraftsverken. Genom jĂ€mförelse mellan mĂ€tningar pĂ„ olika fiskarter med uppmĂ€tta ljudnivĂ„er (partikelacceleration) kan man dra slutsatsen att vindkraftverken vid Utgrunden inte ger upphov till negativa effekter pĂ„ individuella fiskar. Trots det faktum att det saknas audiogram och responsstudier pĂ„ mĂ„nga fiskarter kan det förvĂ€ntas att denna slutsats gĂ€ller för de flesta fiskarter i Ăstersjön. Det bör pĂ„pekas att endast partikelaccelerationens effekter har studerats. Ljudtryckets effekter behandlas inte i rapporten
Partikelrörelser i vatten vid ett vindkraftverk : Akustisk störning pÄ fisk
Ett nytt mĂ€tinstrument har utvecklats och anvĂ€nts för att mĂ€ta ljudvĂ„gens partikelacceleration i vatten vid det nordligaste vindkraftverket vid Utgrundens vindkraftpark i Kalmarsund. Vindkraftsverkens fundament Ă€r av typen driven monopile. MĂ€tresultaten har satts samman med audiogram och responsstudier för torsk, abborre, rödspotta och lax. Syftet har varit att fĂ„ reda pĂ„ hur fiskar uppfattar den uppmĂ€tta partikelaccelerationen.Studien visar att torsk, abborre, rödspotta och lax uppfattar partikelaccelerationen inom en radie pĂ„ 10 meter frĂ„n vindkraftverket. UppmĂ€tta nivĂ„er kommer sannolikt inte att utlösa ett reflexmĂ€ssigt beteende. Utanför 10 meter uppfattar de studerade fiskarterna inte partikelaccelerationen frĂ„n vindkraftsverken. Genom jĂ€mförelse mellan mĂ€tningar pĂ„ olika fiskarter med uppmĂ€tta ljudnivĂ„er (partikelacceleration) kan man dra slutsatsen att vindkraftverken vid Utgrunden inte ger upphov till negativa effekter pĂ„ individuella fiskar. Trots det faktum att det saknas audiogram och responsstudier pĂ„ mĂ„nga fiskarter kan det förvĂ€ntas att denna slutsats gĂ€ller för de flesta fiskarter i Ăstersjön. Det bör pĂ„pekas att endast partikelaccelerationens effekter har studerats. Ljudtryckets effekter behandlas inte i rapporten