A modern analogue of western United States summer palaeoclimate at 6000 years before present

Abstract

A modern summer-climate analogue of western United States 6 ka palaeoclimate, based on broad-scale patterns from proxy data and general-circulation-model simulations, provides details concerning its sum mer synoptic climatology. August 1955 serves as a close analogue, featuring an amplified subtropical ridge aloft and anticyclonic flow near the surface over the central United States and stronger westerly flow along the Canadian/northwest United States border. The August 1955 summer-temperature pattern, similar to those from general-circulation-model simulations, exhibits positive anomalies throughout most of the continental interior. The August 1955 precipitation pattern corresponds very closely with patterns of effective moisture from proxy data, showing widespread aridity and some stronger monsoonal activity in the Southwest. The analogue suggests that the amplified subtropical ridge is a very important feature of 6 ka palaeoclimate, with the circulation pattern differing from that in the early Holocene, implying interactions between both Milankovitch and sub-Milankovitch forcing factors.

Keywords

Western United States modern analogue summer palaeoclimate subtropical ridge proxy data 500 mb heights synoptic climatology monsoon August 1955

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References

Barry, R.G. 1983. Late Pleistocene climatology. In Porter, S.C. , editor, Late Quaternary environments of the United States, Minneapolis, Minnesota: University of Minnesota Press , 390–403.

Bartlein, P.J. , Anderson, K.H. , Anderson, P.M. , Edwards, M.E. , Mock, C.J. , Thompson, R.S. , Webb, R.S. , Webb III, T. and Whitlock, C. 1998: Paleoclimate simulations for North America over the past 21,000 years: features of the simulated climate and comparisons with paleoenvironmental data . Quaternary Science Reviews 17, 549–585 .

Betancourt, J.L. 1990. Late Quaternary biogeography of the Colorado Plateau. In Betancourt, J.L. , Van Devender, T.R. and Martin, P.S. , editors, Packrat middens – the last 40,000 years of biotic change, Tucson, Arizona: University of Arizona Press , 259–292.

Bradley, R.S. , Barry, R.G. and Kiladis, G. 1982: Climatic fluctuations of the western United States during the period of instrumental records. Contribution No. 42. Amherst, Massachusetts: University of Massachusetts .

Bryson, R.A. 1966: Air masses, streamlines, and the boreal forest . Geographical Bulletin 8, 228–269 .

Carleton, A.M. 1987: Summer circulation climate of the American Southwest, 1945–1984 . Annals of the Association of American Geographers 77, 619–634 .

COHMAP Members 1988: Climatic changes of the last 18,000 years: observations and model simulations . Science 241, 1043–1052 .

Dean, W.E. , Ahlbrandt, T.S. , Anderson, R.Y. and Bradbury, J.P. 1996: Regional aridity in North America during the middle Holocene . The Holocene 6, 145–155 .

Diaz, H.F. and Andrews, J.T. 1982: Analysis of the spatial pattern of July temperature departures (1943–1972) over Canada and estimates of the 700 mb mid-summer circulation during middle and late Holocene . Journal of Climatology 2, 251–265 .

10.

Ely, L.L. 1997: Response of extreme floods in the southwestern United States to climatic variations in the late Holocene . Geomorphology 19, 175–201 .

11.

Fritz, S.C. , Juggins, S. , Battarbee, R.W. and Engstrom, D.R. 1991: Reconstruction of past changes in salinity and climate using a diatom-based transfer function . Nature 352, 706–708 .

12.

Hewitt, C.D. and Mitchell, J.F.B. 1996: GCM simulations of the climate of 6 kyr B.P., mean changes and interdecadal variability . Journal of Climate 9, 3505–3529 .

13.

Higgins, R.W. , Yao, Y. and Wang, X.L. 1997: Influence of the North American Monsoon system on the U.S. summer precipitation regime . Journal of Climate 10, 2600–2622 .

14.

Lawson, M.P. , Douglas, A.V. and Englehart, P.J. 1978. Analysis of seasonal persistence of climate in Nebraska. Occasional Papers No. 4. Lincoln, Nebraska: Department of Geography, University of Nebraska .

15.

Lorenz, S. , Grieger, B. , Helbig, P. and Herterich, K. 1996. Investigating the sensitivity of the Atmospheric General Circulation Model ECHAM 3 to paleoclimatic boundary conditions . Geologische Rundschau 85, 513–524 .

16.

Mock, C.J. 1996: Climatic controls and spatial variations of precipitation in the western United States . Journal of Climate 9, 1111–1125 .

17.

Mock, C.J. and Bartlein, P.J. 1995: Spatial variability of late-Quaternary paleoclimates in the western United States . Quaternary Research 44, 425–433 .

18.

Namias, J. 1983: Some causes of United States drought . Journal of Climate and Applied Meteorology 22, 30–39 .

19.

Namias, J. and Dunn, C.R. 1955: The weather and circulation of August 1955 . Monthly Weather Review 110, 824–838 .

20.

Overpeck, J.T. 1996: Warm climate surprises . Science 271, 1820–1821 .

21.

TenHarkel, J.H. 1980: A raininess index for the Arizona Monsoon. NOAA Tech. Memoirs. NWS WR-155, US Department of Commerce, NOAA/NWS.

22.

Ting, M. and Wang, H. 1997: Summertime U.S. precipitation variability and its relation to Pacific sea surface temperature . Journal of Climate 10, 1853–1873 .

23.

Thompson, R.S. , Whitlock, C. , Bartlein, P.J. , Harrison, S.P. and Spaulding, W.G. 1993: Vegetation, lake-levels and climate in the Western United States since 18,000 B.P. In Wright, H.E., Jr. , Kutzbach, J.E. , Webb, T. III , Ruddiman. W.F. , Street-Perrott, F.A. and Bartlein, P.J. , editors, Global climates since the last glacial maximum, Minneapolis, Minnesota: University of Minnesota Press , 468–513.

24.

Webb, T. III , Bartlein, P.J. , Harrison, S.P. and Anderson, K.H. 1993: Vegetation, lake levels, and climate in eastern North America for the past 18,000 years. In Wright, H.E., Jr. , Kutzbach, J.E. , Webb, T. III , Ruddiman. W.F. , Street-Perrott, F.A. and Bartlein, P.J. , editors, Global climates since the last glacial maximum, Minneapolis, Minnesota: University of Minnesota Press , 415–467.

25.

Whitlock, C. and Bartlein, P.J. 1993: Spatial variations of Holocene climatic change in the Northern Rocky Mountain Region . Quaternary Research 39, 231–238 .

26.

Worona, M.A. and Whitlock, C. 1995: Late-Quaternary vegetation and climate history near Little Lake, central Oregon Coast Range, Oregon . Geological Society of America Bulletin 107, 867–876 .