Low-frequency variability in the mid-latitude baroclinic atmosphere induced by an oceanic thermal front
This study examines the flow induced by an east–west-oriented oceanic thermal front in a highly idealized baroclinic model. Previous work showed that thermal fronts could produce energetic midlatitude jets in an equivalent-barotropic atmosphere and that barotropic instabilities of this jet had domin...
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ftciteseerx:oai:CiteSeerX.psu:10.1.1.146.86 2023-05-15T17:36:27+02:00 Low-frequency variability in the mid-latitude baroclinic atmosphere induced by an oceanic thermal front Yizhak Feliks Michael Ghil Eric Simonnet The Pennsylvania State University CiteSeerX Archives 2007 application/pdf http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.146.86 http://www.atmos.ucla.edu/tcd/PREPRINTS/FGS_2007.pdf en eng http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.146.86 http://www.atmos.ucla.edu/tcd/PREPRINTS/FGS_2007.pdf Metadata may be used without restrictions as long as the oai identifier remains attached to it. http://www.atmos.ucla.edu/tcd/PREPRINTS/FGS_2007.pdf text 2007 ftciteseerx 2016-01-07T15:09:42Z This study examines the flow induced by an east–west-oriented oceanic thermal front in a highly idealized baroclinic model. Previous work showed that thermal fronts could produce energetic midlatitude jets in an equivalent-barotropic atmosphere and that barotropic instabilities of this jet had dominant periods of 25–30 and 65–75 days. The present study extends this work to a two-mode baroclinic free atmosphere. The baroclinic jet produced in this case is subject to both barotropic and baroclinic instabilities. A barotropic symmetric instability propagates westward with periods of roughly 30 days and is similar to those found in the equivalent-barotropic model. A baroclinic instability results in standing-dipole anomalies and oscillates with a period of 6–8 months. A mixed barotropic–baroclinic instability results in anomalies that propagate northward, perpendicular to the jet, with a period of 2–3 months. The later anomalies are reminiscent of the 70-day oscillation found over the North Atlantic in observed fields. The atmospheric flow has two distinct states: the flow in the high-energy state exhibits two large gyres and a strong eastward jet; its antisymmetric component is dominant. The low-energy flow is characterized by small gyres and a weak jet. The model’s dynamics depends on the layer-depth ratio. When the model is nearly equivalent-barotropic, symmetric oscillatory modes dominate. As the two layers become nearly equal, antisymmetric oscillatory modes become significant and the mean energy of the flow increases. When the oceanic thermal front’s strength T * is weak (T * � 1.5°C), the flow is steady. For intermediate values of the strength (1.5°C � T * � 3°C), several oscillatory instabilities set in. As the frontal strength increases further (T * � 3°C), the flow becomes more turbulent. These results all depend on the atmospheric model’s horizontal resolution being sufficiently high. 1. Text North Atlantic Unknown |
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English |
description |
This study examines the flow induced by an east–west-oriented oceanic thermal front in a highly idealized baroclinic model. Previous work showed that thermal fronts could produce energetic midlatitude jets in an equivalent-barotropic atmosphere and that barotropic instabilities of this jet had dominant periods of 25–30 and 65–75 days. The present study extends this work to a two-mode baroclinic free atmosphere. The baroclinic jet produced in this case is subject to both barotropic and baroclinic instabilities. A barotropic symmetric instability propagates westward with periods of roughly 30 days and is similar to those found in the equivalent-barotropic model. A baroclinic instability results in standing-dipole anomalies and oscillates with a period of 6–8 months. A mixed barotropic–baroclinic instability results in anomalies that propagate northward, perpendicular to the jet, with a period of 2–3 months. The later anomalies are reminiscent of the 70-day oscillation found over the North Atlantic in observed fields. The atmospheric flow has two distinct states: the flow in the high-energy state exhibits two large gyres and a strong eastward jet; its antisymmetric component is dominant. The low-energy flow is characterized by small gyres and a weak jet. The model’s dynamics depends on the layer-depth ratio. When the model is nearly equivalent-barotropic, symmetric oscillatory modes dominate. As the two layers become nearly equal, antisymmetric oscillatory modes become significant and the mean energy of the flow increases. When the oceanic thermal front’s strength T * is weak (T * � 1.5°C), the flow is steady. For intermediate values of the strength (1.5°C � T * � 3°C), several oscillatory instabilities set in. As the frontal strength increases further (T * � 3°C), the flow becomes more turbulent. These results all depend on the atmospheric model’s horizontal resolution being sufficiently high. 1. |
author2 |
The Pennsylvania State University CiteSeerX Archives |
format |
Text |
author |
Yizhak Feliks Michael Ghil Eric Simonnet |
spellingShingle |
Yizhak Feliks Michael Ghil Eric Simonnet Low-frequency variability in the mid-latitude baroclinic atmosphere induced by an oceanic thermal front |
author_facet |
Yizhak Feliks Michael Ghil Eric Simonnet |
author_sort |
Yizhak Feliks |
title |
Low-frequency variability in the mid-latitude baroclinic atmosphere induced by an oceanic thermal front |
title_short |
Low-frequency variability in the mid-latitude baroclinic atmosphere induced by an oceanic thermal front |
title_full |
Low-frequency variability in the mid-latitude baroclinic atmosphere induced by an oceanic thermal front |
title_fullStr |
Low-frequency variability in the mid-latitude baroclinic atmosphere induced by an oceanic thermal front |
title_full_unstemmed |
Low-frequency variability in the mid-latitude baroclinic atmosphere induced by an oceanic thermal front |
title_sort |
low-frequency variability in the mid-latitude baroclinic atmosphere induced by an oceanic thermal front |
publishDate |
2007 |
url |
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.146.86 http://www.atmos.ucla.edu/tcd/PREPRINTS/FGS_2007.pdf |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_source |
http://www.atmos.ucla.edu/tcd/PREPRINTS/FGS_2007.pdf |
op_relation |
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.146.86 http://www.atmos.ucla.edu/tcd/PREPRINTS/FGS_2007.pdf |
op_rights |
Metadata may be used without restrictions as long as the oai identifier remains attached to it. |
_version_ |
1766135932137766912 |