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| Titel |
Increasing vertical mixing to reduce Southern Ocean deep convection in NEMO3.4 |
| VerfasserIn |
C. Heuzé, J. K. Ridley, D. Calvert, D. P. Stevens, K. J. Heywood |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 8, no. 10 ; Nr. 8, no. 10 (2015-10-06), S.3119-3130 |
| Datensatznummer |
250116597
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| Publikation (Nr.) |
 copernicus.org/gmd-8-3119-2015.pdf |
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| Zusammenfassung |
| Most CMIP5 (Coupled Model Intercomparison Project Phase 5) models unrealistically form Antarctic Bottom Water by open ocean
deep convection in the Weddell and Ross seas. To identify the mechanisms
triggering Southern Ocean deep convection in models, we perform sensitivity
experiments on the ocean model NEMO3.4 forced by prescribed atmospheric
fluxes. We vary the vertical velocity scale of the Langmuir turbulence, the
fraction of turbulent kinetic energy transferred below the mixed layer, and
the background diffusivity and run short simulations from 1980. All
experiments exhibit deep convection in the Riiser-Larsen Sea in 1987; the
origin is a positive sea ice anomaly in 1985, causing a shallow anomaly in
mixed layer depth, hence anomalously warm surface waters and subsequent
polynya opening. Modifying the vertical mixing impacts both the
climatological state and the associated surface anomalies. The experiments
with enhanced mixing exhibit colder surface waters and reduced deep
convection. The experiments with decreased mixing give warmer surface waters,
open larger polynyas causing more saline surface waters and have deep
convection across the Weddell Sea until the simulations end. Extended
experiments reveal an increase in the Drake Passage transport of 4 Sv
each year deep convection occurs, leading to an unrealistically large
transport at the end of the simulation. North Atlantic deep convection is not
significantly affected by the changes in mixing parameters. As new climate
model overflow parameterisations are developed to form Antarctic Bottom Water
more realistically, we argue that models would benefit from stopping Southern
Ocean deep convection, for example by increasing their vertical mixing. |
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