Mean circulation trends Natural modes
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Mutual interactions between secular trends and modes of variability in a changing climate
Grant Branstator, NCARFrank Selten, KNMI
Mean circulation trends Natural modes
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Dutch Challenge Project
Frank Selten KNMI
Henk Dijkstra Univ. Utrecht & CSU
CCSM1.4/T31/x3
Bette Otto-Bliesner
Caspar Ammann
1940-2080 scenario
1940-2000: prescribed GHG, sulphate aerosols, solar radiation, volcanic aerosols
2001-2080: business as usual GHG
62 member ensemble differing only in initial state
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5 m 5x10^5 m^2s^-1
0.5 ms^-1
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“Circumglobal Waveguide Pattern”
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PDFs of Forced Lorenz’ 3-Parameter Model
Palmer (1999)
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relative entropy
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Linear solutions
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Summary
•Trend in climate change experiment has structure of an intrinsic mode of variability – CWP
•The trend results from a linear shift in the planetary wave PDF combined with a rotation that corresponds to a change
in the structure of the leading intrinsic pattern
•The intrinsic pattern changes are largely a linear reaction to the changing mean circulation
Mean circulation trends Natural modes