Identification

Title

Sensitivities and mechanisms of the zonal mean atmospheric circulation response to tropical warming

Abstract

Although El Niño and global warming are both characterized by warming in the tropical upper troposphere, the latitudinal changes of the Hadley cell edge and midlatitude eddy-driven jet are opposite in sign. Using an idealized dry atmospheric model, the zonal mean circulation changes are investigated with respect to different patterns of tropical warming. Generally speaking, an equatorward shift in circulation takes place in the presence of enhanced tropical temperature gradient or narrow tropical warming, similar to the changes associated with El Niño events. In contrast, the zonal mean atmospheric circulations expand or shift poleward in response to upper-tropospheric warming or broad tropical warming, resembling the changes under future global warming. The mechanisms underlying these opposite changes in circulation are investigated by comparing the dry dynamical responses to a narrow tropical warming and a broad warming as analogs for El Niño and global warming. When running the idealized model in a zonally symmetric configuration in which the eddy feedback is disabled, both the narrow and broad warmings give rise to an equatorward shift of the subtropical jet. The eddy adjustment is further examined using large ensembles of transient response to a sudden switch-on of the forcing. For both narrow and broad tropical warmings, the jets move equatorward initially. In the subsequent adjustment, the initial equatorward shift is further enhanced and sustained by the low-level baroclinicity under the narrow tropical warming, whereas the initial equatorward shift transitions to a poleward shift associated with altered irreversible mixing of potential vorticity in the upper troposphere in the case of broad warming.

Resource type

document

Resource locator

Unique resource identifier

code

http://n2t.net/ark:/85065/d7qr4xzg

codeSpace

Dataset language

eng

Spatial reference system

code identifying the spatial reference system

Classification of spatial data and services

Topic category

geoscientificInformation

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title

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reference date

date type

publication

effective date

2016-01-01T00:00:00Z

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date type

publication

effective date

2013-08-01T00:00:00Z

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Copyright 2013 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be "fair use" under Section 107 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Law (17 USC, as revised by P.L. 94-553) does not require the Society's permission. Republication, systematic reproduction, posting in electronic form on servers, or other uses of this material, except as exempted by the above statements, requires written permission or license from the AMS. Additional details are provided in the AMS Copyright Policies, available from the AMS at 617-227-2425 or amspubs@ametsoc.org. Permission to place a copy of this work on this server has been provided by the AMS. The AMS does not guarantee that the copy provided here is an accurate copy of the published work.

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None

Responsible organisations

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contact position

OpenSky Support

organisation name

UCAR/NCAR - Library

full postal address

PO Box 3000

Boulder

80307-3000

email address

opensky@ucar.edu

web address

http://opensky.ucar.edu/

name: homepage

responsible party role

pointOfContact

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