HR: 16:00h
AN: A14B-01 INVITED     [Abstracts]
TI: Mid-Latitude Ocean-Atmosphere Coupling on Decadal Time Scales
AU: * McWilliams, J C
EM: jcm@atmos.ucla.edu
AF: University of California, Los Angeles, Dept. of Atmospheric & Oceanic Sciences, Los Angeles, CA 90095-1565
AU: Kratsov, S
EM: sergey@atmos.ucla.edu
AF: University of California, Los Angeles, Dept. of Atmospheric & Oceanic Sciences, Los Angeles, CA 90095-1565
AU: Berloff, P
EM: pberloff@whoi.edu
AF: Woods Hole Oceanographic Institution, and U. Cambridge, Physical Oceanography Department, Woods Hole, MA 02543
AU: Dewar, W
EM: dewar@ocean.fsu.edu
AF: Florida State University, Oceanography Department, Tallahassee,, FL 32306
AU: Ghil, M
EM: ghil@atmos.ucla.edu
AF: University of California, Los Angeles, Dept. of Atmospheric & Oceanic Sciences, Los Angeles, CA 90095-1565
AU: Ghil, M
EM: ghil@atmos.ucla.edu
AF: Ecole Normale Sup‚rieure - Paris, Ecole normale sup‚rieure 45, rue d?Ulm F - 75230, Paris, Cedex 05 France, Metropolitan
AB: The mid-latitude natural variability of the climate on decadal scales --- manifested in North-Atlantic, Pacific-Decadal, and Antarctic-Annular "modes" --- has the default mechanistic paradigm of being atmospherically controlled with passive thermal adjustment by the ocean. A related conventional wisdom is that the mid-latitude atmosphere is insensitive to oceanic temperature variations. In this talk several reasons to question this paradigm will be discussed. In particular, evidence will be presented from idealized, highly turbulent, quasigeostrophic computational simulations that there is an important oceanic circulation control on the coupled decadal variability. Its origin is in the intrinsic, low-frequency, large-scale variability of the inertial recirculation gyres of the wind-driven circulation. This in turn creates oceanic temperature anomalies to which the atmosphere responds in a nonlinear way to make irregularly spaced transitions between two different zonal flow states, viz., high-latitude and low-latitude jet locations. The atmospheric transitions alter the wind forcing patterns, with a decadal adjustment response time for the inertial recirculation gyres. The transitions lead to a statistically significant, broad-band signal in the period range of 5-20 years evident in both oceanic and atmospheric variables. Accompanying atmosphere-only and ocean-only simulations both have weaker decadal variability compared to the coupled one. Implications for observational analysis and standard climate models are assessed.
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3344 Paleoclimatology
DE: 4522 El Ni¤o
DE: 3220 Nonlinear dynamics
DE: 1620 Climate dynamics (3309)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting