The interaction of oceanic jets with the midlatitude storm tracks

Two mechanisms through which oceanic jets and the atmospheric storm tracks interact in midlatitudes are considered. Firstly, the response of a two-layer ocean model to large- scale stochastic forcing, a simplified model of forcing by the North Atlantic Oscillation, is investigated. Long Rossby waves...

Full description

Bibliographic Details
Main Author: O'Reilly, Christopher Horkesley
Other Authors: Czaja, Arnaud
Published: Imperial College London 2014
Subjects:
530
Online Access:http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.634116
id ndltd-bl.uk-oai-ethos.bl.uk-634116
record_format oai_dc
spelling ndltd-bl.uk-oai-ethos.bl.uk-6341162016-08-04T03:44:52ZThe interaction of oceanic jets with the midlatitude storm tracksO'Reilly, Christopher HorkesleyCzaja, Arnaud2014Two mechanisms through which oceanic jets and the atmospheric storm tracks interact in midlatitudes are considered. Firstly, the response of a two-layer ocean model to large- scale stochastic forcing, a simplified model of forcing by the North Atlantic Oscillation, is investigated. Long Rossby waves are excited at the eastern boundary of the square model basin and the waves are baroclinically unstable. A novel aspect is that the instability leads to the generation of zonal jets throughout the domain. Unlike other theories of jet generation, the jets are actually wave-like in nature, and result directly from the instability. The “jets” appear when averaging the zonal velocity field over fixed periods of time. The longer the averaging period, the weaker the jets as the latter are actually time-varying. The jets occur for a wide range of stochastic forcing strength and the presence or not of a time mean circulation. The mechanism described here thereby provides an explanation for the recent observations of alternating zonal jets. The response of the Pacific storm track to the variability of the Kuroshio Extension jet is then studied. An index of the Kuroshio Extension front strength is produced using sea surface temperature and sea surface height observations. The index reflects the strengthening and weakening of the SST gradient associated with the bimodal states of the Kuroshio, and composites of the atmospheric state are presented during its positive and negative phases. The anomalous response of the transient eddy heat transport resembles a zonal dipole structure. With a weaker (stronger) SST front, the eddy heat transport is increased in the eastern (western) Pacific region, consistent with reduced (enhanced) low- level baroclinicity. The response of the large-scale atmospheric circulation is a barotropic blocking-type pattern in the east Pacific, which is interpreted in terms of the barotropic “eddy-straining” mechanism and eddy-mean flow interaction.530Imperial College Londonhttp://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.634116http://hdl.handle.net/10044/1/19231Electronic Thesis or Dissertation
collection NDLTD
sources NDLTD
topic 530
spellingShingle 530
O'Reilly, Christopher Horkesley
The interaction of oceanic jets with the midlatitude storm tracks
description Two mechanisms through which oceanic jets and the atmospheric storm tracks interact in midlatitudes are considered. Firstly, the response of a two-layer ocean model to large- scale stochastic forcing, a simplified model of forcing by the North Atlantic Oscillation, is investigated. Long Rossby waves are excited at the eastern boundary of the square model basin and the waves are baroclinically unstable. A novel aspect is that the instability leads to the generation of zonal jets throughout the domain. Unlike other theories of jet generation, the jets are actually wave-like in nature, and result directly from the instability. The “jets” appear when averaging the zonal velocity field over fixed periods of time. The longer the averaging period, the weaker the jets as the latter are actually time-varying. The jets occur for a wide range of stochastic forcing strength and the presence or not of a time mean circulation. The mechanism described here thereby provides an explanation for the recent observations of alternating zonal jets. The response of the Pacific storm track to the variability of the Kuroshio Extension jet is then studied. An index of the Kuroshio Extension front strength is produced using sea surface temperature and sea surface height observations. The index reflects the strengthening and weakening of the SST gradient associated with the bimodal states of the Kuroshio, and composites of the atmospheric state are presented during its positive and negative phases. The anomalous response of the transient eddy heat transport resembles a zonal dipole structure. With a weaker (stronger) SST front, the eddy heat transport is increased in the eastern (western) Pacific region, consistent with reduced (enhanced) low- level baroclinicity. The response of the large-scale atmospheric circulation is a barotropic blocking-type pattern in the east Pacific, which is interpreted in terms of the barotropic “eddy-straining” mechanism and eddy-mean flow interaction.
author2 Czaja, Arnaud
author_facet Czaja, Arnaud
O'Reilly, Christopher Horkesley
author O'Reilly, Christopher Horkesley
author_sort O'Reilly, Christopher Horkesley
title The interaction of oceanic jets with the midlatitude storm tracks
title_short The interaction of oceanic jets with the midlatitude storm tracks
title_full The interaction of oceanic jets with the midlatitude storm tracks
title_fullStr The interaction of oceanic jets with the midlatitude storm tracks
title_full_unstemmed The interaction of oceanic jets with the midlatitude storm tracks
title_sort interaction of oceanic jets with the midlatitude storm tracks
publisher Imperial College London
publishDate 2014
url http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.634116
work_keys_str_mv AT oreillychristopherhorkesley theinteractionofoceanicjetswiththemidlatitudestormtracks
AT oreillychristopherhorkesley interactionofoceanicjetswiththemidlatitudestormtracks
_version_ 1718370938423083008