BEGIN:VCALENDAR
VERSION:2.0
PRODID:https://murmitoyen.com/events/vanille/udem/
X-WR-TIMEZONE:America/Montreal
BEGIN:VEVENT
UID:69e1672d4443a
DTSTAMP:20260416T184813
DTSTART:20130405T113000
SEQUENCE:0
TRANSP:OPAQUE
DTEND:20130405T123000
URL:https://murmitoyen.com/events/vanille/udem/detail/173470
LOCATION:Université de Montréal - Pavillon Roger-Gaudry\, 2900\, chemin d
 e la Tour\, Montréal\, QC\, Canada\, H3T 1J6
SUMMARY:Emergent atmospheric laws: why the climate is not what you expect
DESCRIPTION:Shaun Lovejoy\, Department of Physics\, McGill UniversityRésum
 é/abstract:Physics is an interlocking hierarchy of theories and models. F
 undamental theories such as quantum or statistical mechanics are often too
  difficult to apply directly\; so that conventional weather and climate mo
 deling use the higher level laws of thermodynamics and fluid mechanics. Ho
 wever in the atmosphere\, nonlinear terms are typically about a trillion t
 imes larger than linear ones\; we anticipate the emergence of still higher
  level turbulence laws. The classical turbulence laws were restricted to h
 omogeneous and isotropic systems\; to apply them to the atmosphere they mu
 st be generalized to account for strong anisotropy (especially stratificat
 ion) and variability (intermittency). Over the last 30 years\, using scali
 ng symmetry principles and multifractal cascades\, this has been done. Whi
 le hitherto they were believed applicable only up to ≈ 100 m\, (generali
 zed) turbulence laws now cover spatial scales up planetary in extent and i
 n time well beyond weather scales to include the climate.In the time domai
 n the emergent laws for fluctuations ΔT (for example in temperature T) ha
 ve means <ΔT > ≈ ΔtH i.e. they are scaling (power laws). In the weathe
 r regime we generally find exponents H>0 so that fluctuations increase wit
 h scale: the temperature and other atmospheric variables seem to “wander
 ” like a drunkard’s walk. This continues up to ≈ 10 days which is th
 e lifetime of planetary scale structures (this scale is directly set by th
 e turbulent energy flux due to solar forcing). At larger Δt\, the spatial
  degrees of freedom are “quenched”\, there is a “dimensional transit
 ion” to a new “macroweather” regime in which on the contrary\, H<0\,
  so that successive fluctuations tend cancel each other out\, diminishing 
 with scale. Finally\, at scales >≈30 years\, new low frequency climate p
 rocesses begin to dominate\, leading to H>0: the signal again “wanders
 ” in an “unstable” manner.Scientific definitions of the climate are 
 close to the dictum: “The climate is what you expect\, the weather is wh
 at you get”. Indeed - since H<0 - averaging weather over periods increas
 ing to ≈ 30 yrs yields apparently converging values. However this “exp
 ected” behavior is macroweather\, not the climate. On the contrary\, the
  climate is the new lower frequency regime at scales > 30 yrs and it has s
 tatistical properties very similar to the weather. At these scales\, “ma
 croweather is what you expect\, the climate is what you get”.We discuss 
 the implications of the new emergent laws for weather\, macroweather and c
 limate including: new (stochastic) forecasting techniques\, distinguishing
  anthropogenic and natural variability and the evaluation of Global Climat
 e Models.Cette conférence s'adresse à tous\, y compris les professeurs\,
  les chercheurs et les étudiants des trois cycles.Le café est servi à p
 artir de 11h20.Cette conférence est présentée par le Département de ph
 ysique de l'Université de Montréal.
END:VEVENT
BEGIN:VTIMEZONE
TZID:America/Montreal
X-LIC-LOCATION:America/Montreal
END:VTIMEZONE
END:VCALENDAR