thoughts on climate theory based on collaborations with
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Thoughts on Climate Theory Based on collaborations with Wenyu Zhou, Dargan Frierson , Sarah Kang, Erica Staehling , Gang Chen, Steve Garner, Ming Zhao Isaac Held, Reading, 2013. Complex number analogy: Examples of moving off the real axis. Dependence of climate on convection schemes - PowerPoint PPT PresentationTRANSCRIPT
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Thoughts on Climate Theory
Based on collaborations with
Wenyu Zhou, Dargan Frierson, Sarah Kang, Erica Staehling, Gang Chen, Steve Garner, Ming Zhao
Isaac Held, Reading, 2013
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1. Dependence of climate on convection schemes2. Non-rotating radiative-convective equilibrium3. Rotating radiative-convective equilibrium4. Hypohydorstatic rescaling5. Relative importance of upper and lower level baroclinicity in 3-layer QG model
Complex number analogy:Examples of moving off the real axis
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Idealized moist atmospheric modelZonally symmetric climate,
No seasons, no diurnal cycle, no clouds3 different idealized convection
schemes
Dargan Frierson
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Rather than (or in addition to) trying to find the bestconvection parameterization, define interesting classes
of schemes and try to map out how climate statistics varyacross this space of models
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Non-rotating radiative convective equilibriumHard to use as benchmark because of “aggregation”
Larger domain
Muller, Zhao
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Z
Q(Z)
Remove cloud-radiative interactions and wind speed dependence in surfaceflux, and keep domain small, to minimize worry about aggregation
Compare response ofradiative-convective equiliibriumto upper tropospheric heatingin cloud-resolving and hydrostaticmodels with convective parameterization(in progress,Muller and Zhou). Initial result isthat the two models behave very differently
Is this a useful test?
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Wenyou Zhou – 25km hydro
307K295Kf=20 (near surface winds)
Rotating radiative-convective equilibrium
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8
Aqua – slab ocean(Tim Merlis.Andrew Ballinger)
Comprehensive model
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5N 20NSST = 301K
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1,000 km => 10,000 km
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Radius ofMaximum winds
Although resolution ismarginal, model doesproduce systematic changesas parameters are varied
As f increases, externalscale of storm decreasesbut RMW decreases
As SST increases, externalscale increases but RMWdecreases
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Study climate as a function of g – work in progress
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El Nino
trend
Poleward shift unlikely to be primarily forced by tropical warming
Model generated zonal wind responses
We have no quantitiatve theory for eddy momentum fluxes
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3 layer QG
3 winds, two interfaces (temperatures) Simplest system allowing one to talk about upper vs lower level temperature gradients(ongoing work with Erica Staehling)
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Statistically steady 3 layer QG, forced by thermal relaxationto produce a localized baroclinically unstable jet;Linear friction in lower layer only
Parameters in analogous two-layer model:
• supercriticality• radiative relaxation • surface damping• width of radiative equilibrium jet • relative mass of two layers
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Can configure to try to make top layer look like stratosphere, but we focus here on very symmetric configuration:
equal depth layers,
identical density jumps, uniform radiative damping,
identical strength and width of baroclinic zones in rad. eq.
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Modest displacement => jet and eddy energies shift latitude but remain vertically aligned
Larger displacement => eventually splits into two jets, both winds and eddy energies vertically aligned
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Vertically averaged APE(upper layer radiative equilibrium jet)
Upper level radiative eq. shear
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Upper level baroclinicity appears to exert surprisingly strong control on latitude of stormtrack/surface westerlies in this model
Developing a closure theory for this system challengingbecause of non-local character of eddy momentum fluxes
Developing a “perturbation theory” (as in fluctuation-dissipation theory)for the response to a small change in upper level baroclinicity, given the statistics of a control simulation, might be easier.