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3:00 pm in Harshbarger Building #11, Room 110 (room confirmed)
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While much attention has been given to understanding how anthropogenic radiative forcing influences the mean state of the climate system, far less scrutiny has been paid to how it may modulate naturally occurring modes of variability. In this study, we investigate forced changes to unforced modes of wintertime atmospheric circulation variability and associated impacts on precipitation over the North Pacific and North America based on the 40-member CESM1 Large Ensemble during 1920-2100. Each simulation is subject to the same radiative forcing protocol but starts from a slightly different initial condition, leading to different sequences of internal variability. Evolving forced changes in the amplitude and spatial character of the leading internal modes of 500 hPa geopotential height variability are determined by applying Empirical Orthogonal Function analysis across the ensemble dimension at each time step. The results show that the leading modes of internal variability intensify and expand their region of influence in response to anthropogenic forcing, with concomitant impacts on precipitation. Linkages between the Pacific and Atlantic, and between the tropics and extratropics, are also enhanced in the future. These projected changes are driven partly by teleconnections from amplified ENSO activity and partly by dynamical processes intrinsic to the extra-tropical atmosphere. The marked influence of anthropogenic forcing on the characteristics of internal extratropical atmospheric circulation variability presents fundamental societal challenges to future water resource planning, flood control, and drought mitigation.
Dr. Clara Deser is a Senior Scientist at the National Center for Atmospheric Research where she leads the Climate Analysis Section. She has spent her career studying global climate variability and change in observations and models, with an emphasis on interactions among the atmosphere, oceans and sea ice. Recent projects include the role of internal variability in regional climate trends, the effects of projected Arctic sea ice loss on global climate, asymmetries between El Nino and La Nina events, and modes of decadal-multidecadal climate variability in the Atlantic and Pacific. She pioneered the use of Earth System Model Large Ensemble Simulations to elucidate the combined influences of natural and human-induced contributions to climate variability. Deser has co-authored over 200 peer-reviewed publications, and is a member of the National Academy of Sciences, a Fellow of the American Geophysical Union and a Fellow of the American Meteorological Society. She received her Ph.D in Atmospheric Sciences from the University of Washington in 1989, and her B.S. from the Massachusetts Institute of Technology in 1982. She joined NCAR in 1997.