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Sergey Kravtsov Department of Mathematical Sciences, UWM November 15, 2006

Role of Nonlinear Processes and Multi-Scale Interactions in Mid-Latitude Decadal Climate Variability. (Workshop on Multidecadal to Centennial Global Climate Variability, Honolulu, Hawaii). Sergey Kravtsov Department of Mathematical Sciences, UWM November 15, 2006.

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Sergey Kravtsov Department of Mathematical Sciences, UWM November 15, 2006

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  1. Role of Nonlinear Processes and Multi-Scale Interactions in Mid-Latitude Decadal Climate Variability (Workshop on Multidecadal to Centennial Global Climate Variability, Honolulu, Hawaii) Sergey Kravtsov Department of Mathematical Sciences, UWM November 15, 2006 Collaborators: William Dewar, Pavel Berloff, Michael Ghil, James McWilliams, Andrew Robertson

  2. Multi-scale problem!!! North Atlantic Ocean — Atmosphere System: Large-scale (1000 km) high-frequency (monthly) atmospheric patterns vs. small-scale (100 km) low-frequency (interannual) oceanic patterns associated with Gulf Stream variability Atmosphere: some degree of scale separation between synoptic eddies (somewhat smaller and faster) and large-scale low-frequency patterns Ocean: some spatial-scale separation in along-current direction (“eddies” vs. “jet”)

  3. Nonlinear problem!!! • Persistent atmospheric patterns, which are most likely to be affected by coupling, are result of complex eddy–mean flow interaction • The region of potential coupling is also characterized by the most vigorous oceanic intrinsic variability • Linear response of atmosphere to relatively weak SST anomalies is small. Hence, “active coupling” = “nonlinear atmospheric sensitivity to SSTA.”

  4. Coupled QG Model • Eddy-resolving atmospheric and ocean components, both cha- racterized by vigorous intrinsic variability • (Thermo-) dynamic coupling via constant- depth oceanic mixed layer with entrainment

  5. Atmospheric circulation

  6. Zonal-jet bimodality in the model

  7. Atmospheric driving of ocean • Coupled effect: Occupation frequency of atmospheric low-latitude state exhibits (inter)-decadal broad-band periodicity

  8. Oceanic circulation

  9. I. O-jet’s adjustment to A-jet shift • A-jet shift (final state of O-jet as well) Initial state O-jet is maintained in its transient position for a few years due to eddy forcing via rectification

  10. II. A-jet regime dependence on O-jet • High Ocean Energy = High- Latitude (HL) O-Jet State • HL ocean state = A-jet’s Low-Latitude (LL) state • O-Jet stays in (transient) HL state for a few years due to O-eddies

  11. III. Oscillation period • Oscillation’s period is of about 20 yr in low- ocean-drag case and is of about 10 yr in high- ocean-drag case • Period scales as eddy- driven adjustment time

  12. Summary • Mid-latitude climate model involving turbulent oceanic and atmospheric components exhibits inter-decadal coupled oscillation • Bimodal character of atmospheric LFV is res- ponsible for atmospheric sensitivity to SSTAs • Ocean responds to changes in occupation frequency of atmospheric regimes with a delay due to ocean eddy effects

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