Tropical Pacific Forcing of North American Medieval Megadroughts: Testing the Concept with an Atmosphere Model Forced by Coral-Reconstructed SSTs

Publication Type  Journal Article
Year of Publication  2008
Authors  Seager, R.; Burgman, R.; Kushnir, Y.; Clement, A.; Cook, E.; Naik, N.; Miller, J.
Journal Title  Journal of Climate
Volume  21
Issue  23
Pages  6175-6190
Journal Date  Dec 1
ISBN Number  0894-8755
Accession Number  ISI:000261754100005
Key Words  sea-surface temperature; past 1000 years; united-states; last millennium; climate-change; dust-bowl; drought; variability; late-19th-century; teleconnections
Abstract  

The possible role that tropical Pacific SSTs played in driving the megadroughts over North America during the medieval period is addressed. Fossil coral records from the Palmyra Atoll are used to derive tropical Pacific SSTs for the period from A. D. 1320 to A. D. 1462 and show overall colder conditions as well as extended multidecadal La Nina-like states. The reconstructed SSTs are used to force a 16-member ensemble of atmosphere GCM simulations, each with different initial conditions, with the atmosphere coupled to a mixed layer ocean outside of the tropical Pacific. Model results are verified against North American tree ring reconstructions of the Palmer Drought Severity Index. A singular value decomposition analysis is performed using the soil moisture anomaly simulated by another 16-member ensemble of simulations forced by global observed SSTs for 1856-2004 and tree ring reconstructions of the Palmer Drought Severity Index for the same period. This relationship is used to transfer the modeled medieval soil moisture anomaly (relative to the modern simulation) into a model-estimated Palmer Drought Severity Index. The model-estimated Palmer Drought Severity Index reproduces many aspects of both the interannual and decadal variations of the tree ring reconstructions, in addition to an overall drier climate that is drier than the tree ring records suggest. The model-estimated Palmer Drought Severity Index simulates two previously identified "megadroughts," A. D. 1360-1400 and A. D. 1430-60, with a realistic spatial pattern and amplitude. In contrast, the model fails to produce a period of more normal conditions in the early fifteenth century that separated these two megadroughts. The dynamical link between tropical SSTs and the North American megadroughts is akin to that operating in modern droughts. The model results are used to argue that the tropical Pacific played an active role in driving the megadroughts. However, the match between simulated and reconstructed hydroclimate is such that it is likely that both the coral-reconstructed SST anomalies contain significant errors and that SST anomalies in other basins also played a role in driving hydroclimate variations over North America during the late medieval period.

Notes  

384OMTimes Cited:0Cited References Count:44

URL  <Go to ISI>://000261754100005
DOI  Doi 10.1175/2008jcli2170.1