PP21F-08:
Why were Past North Atlantic Warming Conditions Associated with Drier Climate in the Western United States?
Tuesday, 16 December 2014: 9:45 AM
Corinne I Wong, University of California Davis, Earth and Planetary Sciences, Davis, CA, United States, Gerald L Potter, NASA Goddard Space Flight Center, Greenbelt, MD, United States, Isabel P Montanez, Univ of California, Davis, Earth and Planetary Sciences, Davis, CA, United States, Bette L Otto-Bliesner, National Center for Atmospheric Research, Boulder, CO, United States, Pat Behling, University of Wisconsin-Madison, Center for Climate Research, Madison, WI, United States and Jessica Leigh Oster, Vanderbilt University, Earth and Environmental Sciences, Nashville, TN, United States
Abstract:
Investigating climate dynamics governing rainfall over the western US during past warmings and coolings of the last glacial and deglaciation is pertinent to understanding how precipitation patterns might change with future global warming, especially as the processes driving the global hydrological reorganization affecting this drought-prone region during these rapid temperature changes remain unresolved. We present model climates of the Bølling warm event (14,500 years ago) and Younger Dryas cool event (12,200 years ago) that i) uniquely enable the assessment of dueling hypothesis about the atmospheric teleconnections responsible for abrupt temperature shifts in the North Atlantic region to variations in moisture conditions across the western US, and ii) show that existing hypotheses about these teleconnections are unsupported. Modeling results show no evidence for a north-south shift of the Pacific winter storm track, and we argue that a tropical moisture source with evolving trajectory cannot explain alternation between wet/dry conditions, which have been reconstructed from the proxy record. Alternatively, model results support a new hypothesis that variations in the intensity of the winter storm track, corresponding to its expansion/contraction, can account for regional moisture differences between warm and cool intervals of the last deglaciation. Furthermore, we demonstrate that the mechanism forcing the teleconnection between the North Atlantic and western US is the same across different boundary conditions. In our simulation, during the last deglaciation, and in simulations of future warming, perturbation of the Rossby wave structure reconfigures the atmospheric state. This reconfiguration affects the Aleutian Low and high-pressure ridge over and off of the northern North American coastline driving variability in the storm track. Similarity between the processes governing the climate response during these distinct time intervals illustrates the robust nature of the teleconnection, a novel result that provides context for understanding the climate processes governing the response of moisture variability to future climate change.
