Temporal And Spatial Variability Of Extratropical Climate Patterns

Author : Steven Simon
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (915 download)

DOWNLOAD NOW!

Download or read book Climate Model Simulations of Spatiotemporal Western North American Hydroclimate Variability During the Medieval Climate Anomaly and Little Ice Age written by Steven Simon and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Despite the immense impacts that large, modern North American droughts, such as those of the 1930s and 1950s, had on economic, social, environmental, and agricultural systems, they were ultimately shorter in duration than the multidecadal to centennial scale megadroughts that affected North America, in particular the western United States,during the Medieval Climate Anomaly (MCA, ~ 850-1300 AD)and the Little Ice Age (LIA, ~1450-1850 AD. Although various proxy records have been used to reconstruct the timing of these MCA and LIA megadroughts in the western United States, there still exists great uncertainty in the magnitude and spatial coherence of such droughts in various cross sections of western North America (i.e. the Pacific Northwest region),especially on decadal to centennial timescales. This uncertainty motivated the following study to establish a causal link between the climate forcing that induced these megadroughts and the spatiotemporal response of regional North American hydroclimates,such as those of the Pacific Northwest, American Southwest, and the Great Plains,to this forcing. This study seeks to establish a better understanding of the influence of tropical Pacific,tropical Indian, extratropical North Pacific, and North Atlantic sea surface temperatures (SSTs) on North American drought during the MCA (950-1250 AD) and LIA (1400-1700 AD). We force NCAR's Community Atmosphere Model version 5.1.1 (CAM 5), as part of a special configuration of the fully coupled Community Earth Systems Model version 1.0.5 (CESM 1.0.5), with prescribed proxy-reconstructed tropical Pacific, tropical Indian, extratropical North Pacific, and North Atlantic SST anomalies from the MCA and LIA, in order to investigate the influence that these SST anomalies had on the spatiotemporal patterns of drought in North America. To isolate the effects of individual and multiple ocean basin SSTs on the North American climate system, the conducted model experiments use a variety of SST permutations in the tropical Pacific, tropical Indian, extratropical North Pacific, and North Atlantic basins as climate forcing. In order to quantify the spatiotemporal response of the western North American hydroclimate system to these SST forcing permutations, precipitation data derived from the MCA and LIA model experiments are presented here as MCA anomalies relative to the LIA reference period. The spatiotemporal precipitation patterns from the model experiments indicate that in the Pacific Northwest, the MCA and LIA were anomalously wet and dry periods, respectively, a finding that is largely supported by the available lake sediment proxy records. This pattern contrasts with the dry MCA/wet LIA pattern diagnosed in model experiments for the U.S. Southwest and Great Plains regions and indicated by tree ring-based proxy data. Thus, the CAM 5 model experiments confirm the wet/dry meridional precipitation dipole pattern suggested by proxy data for the western U.S. during the MCA and LIA and highlight the role that the natural variability of tropical Pacific, tropical Indian, extratropical North Pacific, and North Atlantic SSTs played in driving this spatiotemporal climate pattern and its related teleconnections. Lastly, this study conducts a diagnosis of the physical mechanisms of causality which link the remote SST forcing specified by any given MCA and LIA model experiment and the regional atmospheric response in western North America. This diagnosis ultimately reveals that the simulated MCA-LIA tropospheric circulation anomalies (sea level pressure, mid-tropospheric vertical velocity, and upper-tropospheric geopotential height fields) associated with the MCA megadroughts dynamically support the prevalent western North American MCA-LIA precipitation anomaly patterns identified in the conducted model experiments, and exhibit spatial coherency, in the horizontal and vertical, resembling those of tropically-forced Rossby wave train-like structures which link remote SST forcing regions with local, regional response regions in the western North American troposphere.