Strengthening and Westward Shift of the Tropical Pacific Walker Circulation during the Mid-Holocene: PMIP Simulation Results

Strengthening and Westward Shift of the Tropical Pacific Walker Circulation during the... AbstractBased on the zonal mass streamfunction, the mid-Holocene annual and seasonal changes in the tropical Pacific Walker circulation (PWC) are examined using numerical simulations from the Paleoclimate Modelling Intercomparison Project Phases 2 and 3. Compared to the preindustrial period, the annual mean of the PWC intensity strengthened (with an average increase of 0.26 × 1014 kg2 m−2 s−1 or 5%), and both the western edge and center of the PWC cell shifted westward (by an average of 4° and 3°, respectively) in the majority of the 29 models used for analysis during the mid-Holocene. Those changes were closely related to an overall increase in the equatorial Indo-Pacific east–west sea level pressure difference and low-level trade winds over the equatorial Pacific. Annual mean PWC changes come mainly from boreal warm seasons. In response to the mid-Holocene orbital forcing, Asian and North African monsoon rainfall was strengthened due to large-scale surface warming in the Northern Hemisphere in boreal warm seasons, which led to an intensified large-scale thermally direct east–west circulation, resulting in the enhancement and westward shift of the tropical PWC. The opposite occurred during the mid-Holocene boreal cold seasons. Taken together, the change in the monsoon rainfall over the key tropical regions of Asia and North Africa and associated large-scale east–west circulation, rather than the equatorial Pacific SST change pattern, played a key role in affecting the mid-Holocene PWC strength. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Climate American Meteorological Society

Strengthening and Westward Shift of the Tropical Pacific Walker Circulation during the Mid-Holocene: PMIP Simulation Results

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0442
D.O.I.
10.1175/JCLI-D-16-0744.1
Publisher site
See Article on Publisher Site

Abstract

AbstractBased on the zonal mass streamfunction, the mid-Holocene annual and seasonal changes in the tropical Pacific Walker circulation (PWC) are examined using numerical simulations from the Paleoclimate Modelling Intercomparison Project Phases 2 and 3. Compared to the preindustrial period, the annual mean of the PWC intensity strengthened (with an average increase of 0.26 × 1014 kg2 m−2 s−1 or 5%), and both the western edge and center of the PWC cell shifted westward (by an average of 4° and 3°, respectively) in the majority of the 29 models used for analysis during the mid-Holocene. Those changes were closely related to an overall increase in the equatorial Indo-Pacific east–west sea level pressure difference and low-level trade winds over the equatorial Pacific. Annual mean PWC changes come mainly from boreal warm seasons. In response to the mid-Holocene orbital forcing, Asian and North African monsoon rainfall was strengthened due to large-scale surface warming in the Northern Hemisphere in boreal warm seasons, which led to an intensified large-scale thermally direct east–west circulation, resulting in the enhancement and westward shift of the tropical PWC. The opposite occurred during the mid-Holocene boreal cold seasons. Taken together, the change in the monsoon rainfall over the key tropical regions of Asia and North Africa and associated large-scale east–west circulation, rather than the equatorial Pacific SST change pattern, played a key role in affecting the mid-Holocene PWC strength.

Journal

Journal of ClimateAmerican Meteorological Society

Published: Mar 14, 2018

References

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