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SUMMARY:A statistical mechanical apporach for the computation of the clima
 tic response to general forcing - Lucarini\, V (Reading)
DTSTART:20100908T100000Z
DTEND:20100908T110000Z
UID:TALK26064@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:The climate belongs to the class of non-equilibrium forced and
  dissipative systems\, for which most results of quasi-equilibrium statist
 ical mechanics\, including the fluctuation-dissipation theorem\, do not ap
 ply. We show for the first time how the Ruelle linear response theory\, de
 veloped for studying rigorously the impact of perturbations on general obs
 ervables of non-equilibrium statistical mechanical systems\, can be applie
 d to analyze the climatic response. We choose as test bed the Lorenz 96 mo
 del\, which has a well-recognized prototypical value. We recapitulate the 
 main aspects of the response theory and propose some new results. We then 
 analyze the frequency dependence of the response of both local and global 
 observables to perturbations with localized as well as global spatial patt
 erns. We derive analytically the asymptotic behaviour\, validity of Kramer
 s-Kronig relations\, and sum rules for the susceptibilities\, and related 
 them to parameters describing the unperturbed properties of the system. We
  verify the theoretical predictions from the outputs of the simulations wi
 th great precision. The theory is used to explain differences in the respo
 nse of local and global observables\, in defining the intensive properties
  of the system and in generalizing the concept of climate sensitivity to a
 ll time scales. We also show how to reconstruct the linear Green function\
 , which maps perturbations of general time patterns into changes in the ex
 pectation value of the considered observable. Finally\, we propose a gener
 al methodology to study Climate Change problems by resorting to few\, well
  selected simulations and discuss the specific case of surface temperature
  response to changes of the $CO_2$ concentration. This approach may provid
 e a radically new perspective to study rigorously the problem of climate s
 ensitivity and climate change.
LOCATION:Seminar Room 1\, Newton Institute
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