Abrupt intensification of ENSO forced by deglacial ice-sheet retreat in CCSM3

The influence of ice-sheet retreat on the El Nio-Southern Oscillation (ENSO) variability is studied using a transient simulation in NCAR-CCSM3 forced only by variations in continental ice sheets during the last deglaciation. The most striking feature is an abrupt strengthening of ENSO (by similar to...

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Bibliographic Details
Published in:Climate Dynamics
Main Authors: Lu, Zhengyao, Liu, Zhengyu, Zhu, Jiang
Other Authors: Lu, ZY (reprint author), Peking Univ, Sch Phys, Lab Climate Ocean & Atmosphere Studies, Beijing 100871, Peoples R China., Peking Univ, Sch Phys, Lab Climate Ocean & Atmosphere Studies, Beijing 100871, Peoples R China., Univ Wisconsin, Dept Atmospher & Ocean Sci, Madison, WI 53706 USA., Univ Wisconsin, Nelson Ctr Climat Res, Madison, WI 53706 USA.
Format: Journal/Newspaper
Language:English
Published: CLIMATE DYNAMICS 2016
Subjects:
ENSO
Annual cycle
Frequency entrainment
Deglacial ice-sheet forcing
LAST GLACIAL MAXIMUM
EASTERN TROPICAL PACIFIC
OCEAN-ATMOSPHERE MODEL
EL-NINO VARIABILITY
PAST 21,000 YEARS
SOUTHERN-OSCILLATION
INTERGLACIAL CYCLE
COUPLED MODEL
CLIMATE
HOLOCENE
Pacific
Ice Sheet
North Atlantic
Sea ice
Online Access:https://hdl.handle.net/20.500.11897/438574
https://doi.org/10.1007/s00382-015-2681-3
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Summary:The influence of ice-sheet retreat on the El Nio-Southern Oscillation (ENSO) variability is studied using a transient simulation in NCAR-CCSM3 forced only by variations in continental ice sheets during the last deglaciation. The most striking feature is an abrupt strengthening of ENSO (by similar to 25 %) at 14 thousand years before present (ka BP) in response to a significant retreat (an equivalent similar to 5 m sea-level rise) of the Laurentide ice sheet (LIS). This abrupt intensification of ENSO is caused mainly by a sudden weakening of the equatorial annual cycle through the nonlinear mechanism of frequency entrainment, rather than an increase in the coupled ocean-atmosphere instability. The weakened annual cycle corresponds to a reduced north-south cross-equatorial annual mean SST contrast in the eastern Pacific. This reduced interhemispheric SST gradient-significant cooling north of the equator-is forced predominantly by an anomalous easterly from an abrupt polarward shift of the jet stream in the Northern Hemisphere, which extends to the northeastern tropical Pacific Ocean surface and is reinforced by the wind-evaporation-SST feedback then propagates equatorward; it could also be contributed by a fast sea-ice expansion and a consequent cooling in the North Pacific and North Atlantic that is induced by the retreat of the LIS. US NSF; DOE; China Scholarship Council; [NSFC41130105]; [MOST2012CB955200] SCI(E) ARTICLE luzhengyao88@gmail.com 5-6 1877-1891 46

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