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Nebraska Sand Hills, Western North America
Reference
Sridhar, V., Loope, D.B., Swinehart, J.B., Mason, J.A., Oglesby, R.J. and Rowe, C.M. 2006. Large wind shift on the Great Plains during the Medieval Warm Period. Science 313: 345-347.

Description
The authors studied the orientation, morphology and internal structure of dunes in the easternmost portion of the Nebraska Sand Hills (in about the center of the state), where shallow core and outcrop samples indicate the dunes were formed some 800 to 1000 years ago. Using a computer program, they then calculated what type of wind field had to have been operative during the MWP of AD 1000-1200 in order to produce the dunes, which are oriented quite differently from those that would form under today's wind regime (where air currents from the south in the spring and summer bring moist air from the Gulf of Mexico to the U.S. Great Plains) if the dune sand were free to move and not protected by prairie grasses. Their work revealed that the spring and summer winds of the MWP would have had to have come primarily from the southwest, bringing much drier and hotter-than-current air from the deserts of Mexico, along with greatly reduced opportunities for rain. In addition, they note that the drier and warmer conditions may have been even further "enhanced and prolonged by reduced soil moisture and related surface-heating effects," which, we might add, are not operative in our day to the degree they were 800 to 1000 years ago, as was demonstrated by still other of Sridhar et al.'s computer analyses. The overall effect of these phenomena was suggested by them to have impacted much of western North America and the U.S. Great Plains.