Characterizing Blocking Episodes with Local Finite ...
Transcript of Characterizing Blocking Episodes with Local Finite ...
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Characterizing Blocking Episodes with Local Finite-amplitude Wave Activity:
Climatology and Life-cycleClare S. Y. Huang ([email protected])
Noboru Nakamura
The University of Chicago
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Outline
1. Review on the finite-amplitude local wave activity formalism
2. Climatology of wave activities, comparison with existing blocking statistics and physical significance
3. Wave activity flux evolution in the Life cycle of a blocking episode over Pacific
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The Finite-Amplitude Local Wave Activity (LWA): Definition
FAWA: Nakamura and Zhu (2010); LWA: Huang and Nakamura (2016)
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The Finite-Amplitude Local Wave Activity (LWA): Definition
Contour with PV = Q(y)
y(Q) = equivalent latitude of PV=Q
FAWA: Nakamura and Zhu (2010); LWA: Huang and Nakamura (2016)
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The Finite-Amplitude Local Wave Activity (LWA): Definition
Huang and Nakamura (2016)
Contour with PV = Q(y)
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QGPV LWA
Huang and Nakamura (2016)
LWA can pick up blocking patterns from QGPV field.
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Finite-amplitude Local Wave Activity Flux
Huang and Nakamura (2016)
Conservation of PV
Wave Activity Budget equation(Exact on x-y plane)
Zonal flux of PV Meridional flux of PV
We have an evolution equation for the conservative dynamics of LWA.
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Local Non-acceleration Relation
Huang and Nakamura (2016)Vertically integrated zonal wind
Vertically integrated (interior) LWA
Surface wave activity (analogous to v’T’ at surface boundary)
Increase in barotropic wave activity <A>+B implies deceleration in barotropic zonal wind <u>.
Relatively small terms
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Climatology of wave activity in N. Winter (1979-2014) from ERA-Interim
Interior wave activity <A>
Interior + Surface wave activity <A>+B
Surface wave activity B
Waviness of (QG)PV field at the upper level
Deceleration of zonal wind by finite-amplitude eddies
Siberia: cold air intrusionGulf stream: warm current poleward
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Adapted from Barnes et al (2014)Reanalysis data from MERRA
Adapted from Barnes et al (2014)Reanalysis data from MERRA
Climatology of wave activity in N. Winter (1979-2014) from ERA-Interim
Dunn-Sigouin et al. [2013]
Masato et al. [2013]
Interior wave activity <A>
Interior + Surface wave activity <A>+B
Surface wave activity B
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Proposed Strategy to study Blocking
Blocking ⇒ Large <A> (and <A>+B)(Note that ⇒ is a one-way arrow)
• Use wave activity as a measure of the blocking stage. (I won’t push hard now to say it is a blocking index.)
• Study the life cycle with:• (1) Conservation of (<u>+A+B);• (2) Wave activity flux formalism
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Case Study: a block over N Pacific
Black contour: regions with positive Blocking index based on Z500 outlined in Masato et al (2014, GRL)
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Comparison between LWA (color), zonal wind (contour) and Z500
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Covariation of <A>+B and <u> (Anomalies from seasonal mean)
<A>+B ↑
<u> ↓
Note: Δ(<A> + B) ≈ 2 (Δ<u>) due to thermal damping.Thermal Damping less negative surface wave activity B
See Wang and Nakamura (2015, GRL) for analysis on BAM.
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Wave activity tendency ≈ Wave Activity Flux convergence
Wave Activity tendency
Wave Activity Flux Convergence
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EP flux v.s. Zonal Advective Flux
EP flux convergence
Advective Flux convergence
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Before onset: anticyclonic wave breaking (warm air intrusion)
EP flux conv < 0
Adv Flux conv > 0
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Onset: poleward transport of warm air
EP flux conv > 0
Adv Flux conv ≈ 0
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Decay: anticyclonic wave breaking (cold air moving poleward)
EP flux conv ≈ 0
Adv Flux conv < 0
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Summary of Ideas
• Blocking ⇒ Large <A> (and <A>+B)
• Conservative budget equation of <A>:• Zonal advective flux and E-P flux
• Can be used to back out non-conservative effect aloft
• Approximate local non-acceleration relation (i.e. constant <u>+<A>+B)• More relevant to the deceleration of zonal wind <u>
• Quantify non-conservative effect at the surface such as thermal damping
Clare’s email: [email protected]: home.uchicago.edu/~csyhuang/
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Summary of the talk
• Evolution of (interior) local wave activity is given by the wave activity fluxes (Zonal advective flux and generalized E-P flux).
• The barotropic component of wave activity (interior+surface) negatively covariate with zonal wind.
• Climatology of local wave activity resembles some existing blocking statistics, and may hint on the physical processes highlighted by each index.
• A case study of North Pacific blocking episode shows the difference in roles of zonal advection and momentum flux convergence in onset and decay of a block.
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Unused Back-up Slides
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Case Study – LWA looks like…
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Local Non-acceleration Relation
• Barotropic budget equation:
• Interior LWA: d(<A>)/dt = (…)
• Barotropic LWA: d(<A>+B)/dt = d(…)/dx
(Tells about the physical meaning)
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Strategy
Blocking ⇒ Large <A> (and <A>+B)(Mind that ⇒ is a one-way arrow)
• Persistent (>5 days), large <A> (and <A>+B) events [to be modified]
• Study the life cycle with:• (1) Conservation of (<u>+A+B);
• (2) Wave activity flux formalism [new]
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Research Questions
1. What can the finite-amplitude local wave activity (LWA, Huang & Nakamura 2016) tell us about blocking?
2. Climatology of interior LWA and barotropic LWA (and their correspondence to 2 blocking indices climatology)
3. Life cycle: _________
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Climatology of <A> and <A>+B
• Show <A>, <A>+B and B
• N Hemisphere Winter (S Hem Summer)
• Comparison with M2D and D2D
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Climatology of <A> and <A>+B
• Show <A>, <A>+B and B
• N Hemisphere Summer (S Hem Winter)
• Comparison with M2D and D2D
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Siberia and Gulf stream
• Large B (What does that imply?)
• Implication on understanding difference between M2D and D2D? large-scale overturning implies more on zonal wind?