Support for Global Climate Reorganization During the MCA 
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               World Data Center for Paleoclimatology, Boulder 
                                  and 
                     NOAA Paleoclimatology Program 
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NOTE: PLEASE CITE ORIGINAL REFERENCE WHEN USING THIS DATA!!!!! 


NAME OF DATA SET: 
Support for Global Climate Reorganization During the MCA 

LAST UPDATE: 11/2010 (Original receipt by NOAA/WDC Paleo)
CONTRIBUTORS: Graham, N.E., C.M. Ammann, D. Fleitmann, K.M. Cobb, 
and J. Luterbacher. 
IGBP PAGES/WDCA CONTRIBUTION SERIES NUMBER: 2010-122


WDC PALEO CONTRIBUTION SERIES CITATION: 
Graham, N.E., et al. 2010. 
Support for Global Climate Reorganization During the MCA. 
IGBP PAGES/World Data Center for Paleoclimatology 
Data Contribution Series # 2010-122. 
NOAA/NCDC Paleoclimatology Program, Boulder CO, USA. 


ORIGINAL REFERENCE: 
Graham, N.E., C.M. Ammann, D. Fleitmann, K.M. Cobb and J. Luterbacher. 2010. 
Support for global climate reorganization during the "Medieval Climate Anomaly". 
Climate Dynamics.  DOI: 10.1007/s00382-010-0914-z 
http://www.springerlink.com/content/g4w18p0400188572/ 


ABSTRACT: 
Widely distributed proxy records indicate that the Medieval Climate Anomaly 
(MCA; ~900-1350 AD) was characterized by coherent shifts in large-scale 
Northern Hemisphere atmospheric circulation patterns. Although cooler 
sea surface temperatures in the central and eastern equatorial Pacific 
can explain some aspects of medieval circulation changes, they are not 
sufficient to account for other notable features, including widespread 
aridity through the Eurasian sub-tropics, stronger winter westerlies 
across the North Atlantic and Western Europe, and shifts in monsoon 
rainfall patterns across Africa and South Asia. We present results from 
a full-physics coupled climate model showing that a slight warming of 
the tropical Indian and western Pacific Oceans relative to the other 
tropical ocean basins can induce a broad range of the medieval circulation 
and climate changes indicated by proxy data, including many of those not 
explained by a cooler tropical Pacific alone. Important aspects of the 
results resemble those from previous simulations examining the climatic 
response to the rapid Indian Ocean warming during the late twentieth 
century, and to results from climate warming simulations - especially 
in indicating an expansion of the Northern Hemisphere Hadley circulation. 
Notably, the pattern of tropical Indo-Pacific sea surface temperature (SST) 
change responsible for producing the proxy-model similarity in our results 
agrees well with MCA-LIA SST differences obtained in a recent proxy-based 
climate field reconstruction. Though much remains unclear, our results 
indicate that the MCA was characterized by an enhanced zonal Indo-Pacific 
SST gradient with resulting changes in Northern Hemisphere tropical and 
extra-tropical circulation patterns and hydroclimate regimes, linkages 
that may explain the coherent regional climate shifts indicated by proxy 
records from across the planet. The findings provide new perspectives 
on the nature and possible causes of the MCA - a remarkable, yet 
incompletely understood episode of Late Holocene climatic change. 


GEOGRAPHIC REGION: Global 
PERIOD OF RECORD: Medieval Climate Anomaly, ~900-1200 AD 


FUNDING SOURCES: 
N.E.G. was supported by funding from grants NA06OAR4310120 
and NA08OAR4310732 from the US National Oceanographic 
and Atmospheric Administration (NOAA) CCDD program. 
N.E.G. is also grateful to the PAGES program and the 
Oeschger Centre for Climate Research at the University of Bern 
for their support of a visit to the Oeschger Centre in 2008 
during which the research reported here was advanced. 
C.M.A. acknowledges support from the WCIAS Program at NCAR 
(Linda Mearns, Director) and NSF-CMG ATM 0724828 from the 
US National Science Foundation. 
D.F. was supported by the Swiss National Science Foundation 
under grants 2000-059174.99 and PP002-110554/1. 
K.M.C. acknowledges support from NOAA CCDD grant NA06OAR4310120. 



DESCRIPTION: 
Model output for the IOWP25 Medieval Climate Anomaly simulation 
from Graham et al. 2010, in netCDF format.  
Files and contents are as follows:

pcp_ratio_djfm.nc:  Ratio of December-March precipitation, IOWP25/CNTL 
                    (expressed as fraction of CNTL), as plotted in Fig. 6.  

slp_diff_djfm.nc:   Differences in December-March Sea Level Pressure (hPa)
                    IOWP25 - CNTL, as plotted in Fig. 6. 

tdiff_djfm.nc:      Differences in December-March temperature between 
                    the IOWP25 and CNTL simulations (C), as plotted in Fig. 7. 

pcp_ratio_jjas.nc:  IOWP25-CNTL ratio of summer (June-September) precipitation 
                    (expressed as fraction of CNTL), as plotted in Fig. 8 

slp_diff_jjas.nc:   IOWP25-CNTL differences in summer (June-September) 
                    Sea Level Pressure, as plotted in Fig. 8. 

tdiff_jjas.nc:      Differences in June-September temperature (IOWP25-CNTL) 
                    as plotted in Fig. 9 

graham-2010-fig5-corrected.gif: corrected version of figure 5,
updated 28 October 2010 (An incorrect version of Figure 5 was published 
in Graham et al. 2010).




DATA: 
NetCDF data files listed above and the corrected Figure 5 
GIF image file are archived at:
ftp://ftp.ncdc.noaa.gov/pub/data/paleo/gcmoutput/graham2010/