A warm path for Gulf Stream - troposphere interactions

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Title: A warm path for Gulf Stream - troposphere interactions
Authors: Sheldon, L
Czaja, A
Vanniere, B
Morcrette, C
Sohet, B
Casado, M
Smith, D
Item Type: Journal Article
Abstract: Warm advection by the Gulf Stream creates a characteristic ‘tongue’ of warm water leaving a strong imprint on the sea surface temperature (SST) distribution in the western North Atlantic. This study aims at quantifying the climatological impact of this feature on cyclones travelling across this region in winter using a combination of reanalysis data and numerical experiments. It is suggested that the Gulf Stream ‘warm tongue’ is conducive to enhanced upward motion in cyclones because (i) it helps maintain a high equivalent potential temperature of air parcels at low levels which favors deep ascent in the warm conveyor belt of cyclones and (ii) because the large SST gradients to the north of the warm tongue drive a thermally direct circulation reinforcing and, possibly, destabilizing, the transverse circulation embedded in cyclones. This hypothesis is confirmed by comparing simulations at 12 km resolution from the Met Office Unified Model forced with realistic SST distribution to simulations with an SST distribution from which the Gulf Stream warm tongue was artificially removed or made colder by . It is also supported by a dynamical diagnostic applied to the ERA interim data-set over the wintertime period (1979–2012). The mechanism of oceanic forcing highlighted in this study is associated with near thermal equilibration of low level air masses with SST in the warm sector of cyclones passing over the Gulf Stream warm tongue, which is in sharp contrast to what occurs in their cold sector. It is suggested that this ‘warm path’ for the climatic impact of the Gulf Stream on the North Atlantic storm-track is not currently represented in climate models because of their coarse horizontal resolution.
Issue Date: 24-Mar-2017
Date of Acceptance: 12-Jan-2017
ISSN: 1600-0870
Publisher: Taylor & Francis
Journal / Book Title: Tellus Series A-Dynamic Meteorology and Oceanography
Volume: 69
Issue: 1
Copyright Statement: © 2017 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Sponsor/Funder: Natural Environment Research Council (NERC)
Funder's Grant Number: NE/J023760/1
Keywords: Meteorology & Atmospheric Sciences
0401 Atmospheric Sciences
0405 Oceanography
Publication Status: Published
Article Number: 1299397
Appears in Collections:Space and Atmospheric Physics
Centre for Environmental Policy
Faculty of Natural Sciences

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