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Coordinated Abrupt Weakening of the Eurasian and North African Monsoons in the 1960s and Links to Extratropical North Atlantic Cooling

Journal Article · · Journal of Climate
 [1];  [2]
  1. Univ. of California, Berkeley, CA (United States); University of California, Berkeley
  2. Univ. of California, Berkeley, CA (United States)
+ Show Author Affiliations
Previous modeling and paleoclimate studies have suggested that cooling originating from the extratropical North Atlantic can abruptly weaken the Eurasian and North African monsoons. The climatic signature includes a widespread cooling over the Eurasian and North African continents and an associated increase to surface pressure. It is explored whether such coordinated changes are similarly exhibited in the observed twentieth-century climate, in particular with the well-documented shift of Sahel rainfall during the 1960s. Surface temperature, sea level pressure, and precipitation changes are analyzed using combined principal component analysis (CPCA). The leading mode exhibits a monotonic shift in the 1960s, and the transition is associated with a relative cooling and pressure increase over the interior Eurasia and North Africa, and rainfall reduction over the Sahel, South Asia, and East Asia. The local circulation changes suggest that the rainfall shift results from the regional response of the summer monsoons to these continental- wide changes. A similar CPCA analysis of atmospheric general circulation model (AGCM) simulations forced by twentieth-century-observed forcings shows similar results, suggesting that origins of the climate shift reside in the sea surface temperature changes, specifically over the extratropical North Atlantic. Finally, an AGCM forced with extratropical North Atlantic cooling appears to simulate these climate impacts, at least qualitatively. The result herein shows that the observed climate signature of the 1960s abrupt shift in Eurasian and North African climate is consistent with the influence of the abrupt highlatitudeNorthAtlantic cooling that occurred in the late 1960s.Adefinitive causal relationship remains to be shown, and mechanisms elucidated.
Research Organization:
Univ. of California, Berkeley, CA (United States)
Sponsoring Organization:
USDOE SC Office of Biological and Environmental Research (SC-23)
DOE Contract Number:
FG02-08ER64588
OSTI ID:
1053832
Report Number(s):
DOE/08ER64588--1
Journal Information:
Journal of Climate, Journal Name: Journal of Climate Journal Issue: 10 Vol. 25; ISSN 0894-8755
Publisher:
American Meteorological Society
Country of Publication:
United States
Language:
English

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Related Subjects

Climate change
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Monsoons