4 results on '"Neil Malan"'
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2. Multidecadal Wind Variability Drives Temperature Shifts on the Agulhas Bank
- Author
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Arne Biastoch, Neil Malan, Juliet Hermes, Chris J. C. Reason, and Jonathan V. Durgadoo
- Subjects
0106 biological sciences ,010504 meteorology & atmospheric sciences ,010604 marine biology & hydrobiology ,Oceanography ,01 natural sciences ,Wind variability ,Geophysics ,13. Climate action ,Space and Planetary Science ,Geochemistry and Petrology ,Climatology ,Earth and Planetary Sciences (miscellaneous) ,Environmental science ,Regime shift ,14. Life underwater ,0105 earth and related environmental sciences - Abstract
Key Points: • A regional ocean model is used to examine multidecadal shelf temperature changes on the Agulhas Bank • There are distinct shelf temperature regime changes in 1966 and 1996 • These regime shifts are caused by changes in coastal upwelling linked to large-scale wind variability The Agulhas Bank is an important area for the spawning of small pelagic fish and other species. Here, within a NEMO ocean model, we investigate changes in temperature over the Bank on multidecadal time scales. In agreement with previous observational studies, a shift to colder temperatures is found in 1997. The model also simulates an earlier shift from colder to warmer temperatures in 1966. These shifts are coastally confined and shown, using a climatologically forced model run as a control, to be driven by a north‐south migration in the large‐scale wind belts, rather than by changes in downward heat fluxes or changes in the Agulhas Current itself. The zonal wind changes on the Agulhas Bank show a significant relationship with the Southern Annular Mode, showing some promise for future predictability of cold and warm regimes on the Agulhas Bank. Thus, while the Agulhas Current has been shown in previous work to have a large impact on intra‐annual and interannual temperature variability, this work shows that multidecadal variability in temperature on the shelf is likely to be wind forced.
- Published
- 2019
3. Agulhas Current Meanders Facilitate Shelf-Slope Exchange on the Eastern Agulhas Bank
- Author
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Arne Biastoch, Chris J. C. Reason, Jonathan V. Durgadoo, Neil Malan, Björn C. Backeberg, Juliet Hermes, and Annette Samuelsen
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Leading edge ,010504 meteorology & atmospheric sciences ,010505 oceanography ,Flow (psychology) ,Front (oceanography) ,Oceanography ,01 natural sciences ,Current (stream) ,Sea surface temperature ,Geophysics ,13. Climate action ,Space and Planetary Science ,Geochemistry and Petrology ,Downwelling ,Earth and Planetary Sciences (miscellaneous) ,Meander ,Upwelling ,14. Life underwater ,Geology ,0105 earth and related environmental sciences - Abstract
Large solitary meanders are arguably the dominant mode of variability in the Agulhas Current. Observational studies have shown that these large meanders are associated with strong upwelling velocities and affect the shelf circulation for over 100 days per year. Here 10-year time series from two ocean general circulation models are used to create a composite picture of the Agulhas Current and its interactions with the shelf circulation in meandering and nonmeandering modes. Both models show good agreement with the size, propagation speed, and frequency of observed meanders. These composite meanders are then used to examine the response of shelf waters to the onset of large meanders, with the use of model output enabling the dynamics at depth to be explored. Results show a composite mean warming of up to 3°C of depth-averaged temperature along the shelf edge associated with an intrusion of the current jet onto the shelf driven by an intensification of the flow along the leading edge of large meanders. However, this intensification of flow results in cooling of bottom waters, driving cold events at the shelf break of
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- 2018
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4. SIDDIES Corridor : a major east-west pathway of long-lived surface and subsurface eddies crossing the subtropical South Indian Ocean
- Author
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Juliet Hermes, W. P. M. de Ruijter, Pierrick Penven, Ahmad Fehmi Dilmahamod, Borja Aguiar-González, C. J. C. Reason, Neil Malan, Laboratoire d'Océanographie Physique et Spatiale (LOPS), and Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)
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Dynamic height ,Water mass ,South Indian Ocean ,long-lived eddies ,010504 meteorology & atmospheric sciences ,freshwater fluxes ,Oceanography ,01 natural sciences ,Geochemistry and Petrology ,Potential density ,Earth and Planetary Sciences (miscellaneous) ,14. Life underwater ,[SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography ,Argo ,0105 earth and related environmental sciences ,surface and subsurface eddies ,010505 oceanography ,eddy demography ,Salinity ,heat/freshwater fluxes ,Geophysics ,Eddy ,[SDU]Sciences of the Universe [physics] ,13. Climate action ,Space and Planetary Science ,Anticyclone ,Thermohaline circulation ,eddy corridor ,heat ,Geology - Abstract
International audience; South Indian Ocean eddies (SIDDIES), originating from a high evaporation region in the eastern Indian Ocean, are investigated by tracking individual eddies from satellite data and co-located Argo floats. A subsurface-eddy identification method, based on its steric dynamic height anomaly, is devised to assign Argo profiles to surface eddies (surfSIDDIES) or subsurface eddies (subSIDDIES). These westward-propagating, long-lived features (>3 months) prevail over a preferential latitudinal band, forming a permanent structure linking the eastern to the western Indian Ocean, that we call the 'SIDDIES Corridor'. Key features have been revealed in the mean thermohaline vertical structure of these eddies. Anticyclonic SIDDIES are characterized by positive subsurface salinity anomalies, with subSIDDIES not exhibiting negative surface anomalies, as opposed to surfSIDDIES. Cyclonic subSIDDIES also occur, but their related salinity anomalies are weaker. SubSIDDIES exhibit two cores of different temperature polarities in their surface and subsurface levels. Cyclonic subSIDDIES have their cores at around 150-200 m depth along the 25.4-25.8 kg m-3 potential density layer with anticyclonic subSIDDIES having their cores at 250-300 m along the 26-26.4 kg m-3 density layer. The SIDDIES corridor acts as a zonal pathway for both eddy-types to advect water masses and biogeochemical properties across the basin. This study provides a new insight on heat/salt fluxes, showing that 58% (32%) of the total heat eddy-flux is ascribed to cyclonic (anticyclonic) subSIDDIES, respectively, in the eastern South Indian Ocean. Anticyclonic subSIDDIES have also been found to be the sole high-saline water eddy-conveyor toward the western Indian Ocean.
- Published
- 2018
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