Lecture 4: Applications to the atmosphere, moist-convective RSW Introduction Methodology Constructing the model Limiting equations and relation to the known models General properties of the model Conservation laws Characteritics and fronts Example: scattering of a simple wave on a moisture front Introducing evaporation Moist vs dry baroclinic instability (Dry) linear stability of the baroclinic jet Comparison of the evolution of dry and moist instabilities Conclusions Literature Understanding large-scale atmospheric and oceanic flows with layered rotating shallow water models V. Zeitlin 1 Laboratory of Dynamical Meteorology, ENS, Paris, France Non-homogeneous Fluids and Flows, Prague, August 2012
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Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Understanding large-scale atmosphericand oceanic flows with layered rotating
shallow water models
V. Zeitlin
1Laboratory of Dynamical Meteorology, ENS, Paris, France
Non-homogeneous Fluids and Flows, Prague, August2012
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
PlanIntroductionMethodologyConstructing the modelLimiting equations and relation to the known modelsGeneral properties of the model
Conservation lawsCharacteritics and frontsExample: scattering of a simple wave on a moisturefrontIntroducing evaporation
Moist vs dry baroclinic instability(Dry) linear stability of the baroclinic jetComparison of the evolution of dry and moistinstabilities
ConclusionsLiterature
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
General problematics
Importance of moisture in the atmosphere: obvious.Influences large-scale dynamics via the latent heatrelease, due to condensation and precipitation.Atmospheric circulation modeling: equation of state of themoist air extremely complex. Discretization/averaging:problematic.Current parametrizations of precipitations and latent heatrelease:relaxation to the equilibrium (saturation) profile ofhumidity⇒ threshold effect⇒ essential nonlinearityConsequences: no linear limit; linear thinking: modaldecomposition, linear stability analysis, etc impossible⇒problems in quantifying predictability of moist - convectivedynamical systems.
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Aims and method I
Aim:Understanding the influence of condensation and latentheat release upon large-scale dynamical processes
Reminder:I Simplest model for large-scale motions: rotating
shallow water.I Link with primitive equations: vertical averagingI Baroclinic effects: 2 (or more) layers.
Problem with this approach for moist air: averaging ofessentially nonlinear equation of state.
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Aims and method II
Our approach
I Combine (standard) vertical averaging of primitiveequations between the isobaric surfaces with that ofLagrangian conservation of moist enthalpy
I Allow for convective fluxes (extra vertical velocity)across the isobars
I Link these fluxes to condensationI Use relaxation parametrization in terms of bulk
moisture in the layer for thecondensation/precipitation
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Aims and method III
Advantages:
I Simplicity, qualitative analysis of basic phenomenastraightforward
I Fully nonlinear in the hydrodynamic sectorI Well-adapted for studying discontinuities, in
particular precipitation frontsI Efficient numerical tools available (finite-volume
codes for shallow water)I Various limits giving known modelsI Inclusion of topography (gentle or steep)
straightforward
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Primitive equations in pseudo-heightcoordinates
ddt
v + fk × v = −∇φ
ddtθ = 0
∇ · v + ∂zw = 0
∂zφ = gθ
θ0
v = (u, v) and w - horizontal and vertical velocities,ddt = ∂t + v · ∇+ w∂z , f - Coriolis parameter, θ - potentialtemperature, φ - geopotential.
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Moisture and moist enthalpy
Condensation turned off: conservation of specifichumidity of the air parcel:
ddt
q = 0.
Condensation turned on: θ and q equations acquiresource and sink. Yet the moist enthalpy θ+ L
cpq, where L -
latent heat release, cp - specific heat, is conserved forany air parcel on isobaric surfaces:
ddt
(θ +
Lcp
q)
= 0,
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Vertical averaging with convective fluxes
3 material surfaces:
w0 =dz0
dt, w1 =
dz1
dt+ W1, w2 =
dz2
dt+ W2.
W
W2
1
θ
θ1
2
0
2z
z
z
1
Mean-field + constant mean θ →
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Averaged momentum and mass conservationequations:
{∂tv1 + (v1 · ∇)v1 + fk × v1 = −∇φ(z1) + g θ1
θ0∇z1,
∂tv2 + (v2 · ∇)v2 + fk × v2 = −∇φ(z2) + g θ2θ0∇z2 + v1−v2
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Linking convective fluxes to precipitation I
Bulk humidity: Qi =∫ zi
zi−1qdz. Precipitation sink:
∂tQi +∇ · (Qiv i) = −Pi .
In precipitating regions (Pi > 0), moisture is saturatedq(zi) = qs(zi) and the temperature of the air-massWidtdxdy convected due to the latent heat releaseθ(zi) + L
cpqs(zi), is the one of the upper layer: θi+1.
We assume "dry" stable background stratification:
θi+1 = θ(zi) +Lcp
q(zi) ≈ θi +Lcp
q(zi) > θi ,
with constant θ(zi) and q(zi).
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Integrating the moist enthalpy we get
Wi = βiPi
with a positive-definite coefficient
βi =L
cp(θi+1 − θi)≈ 1
q(zi)> 0.
Last step: relaxation formula with relaxation time τ .
Pi =Qi −Qs
iτ
H(Qi −Qsi )
where H(.) is the Heaviside (step) function.
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
s - propagation speed of the discontinuity.Remark: mass conservation→ moist enthalpyconservation in the lower layer.Due to limxs→a limb→xs
∫ ba P = 0, P does not enter RH
conditions for u, v ,h.
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Discontinuities in derivatives
RH conditions linearized about the rest state:{(s2 − C+)(s2 − C−)[∂xu1] = −(α− 1)gH2gβ[P],(s2 − Cm
+ )(s2 − Cm− )[∂xu1] = −s(α− 1)gH2gβ[∂xQ].
For a configuration where it rains at the right side of thediscontinuity, P− = 0 and P+ = −Qs∂xu1+ > 0 , thereexist five types of precipitation fronts:
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Precipitation fronts
1. the dry external fronts,√
C+ < s <√
Cm+ ,
2. the dry internal subsonic fronts,√
Cm− < s <
√C−,
3. the moist internal subsonic fronts, −√
Cm− < s < 0,
4. the moist internal supersonic fronts,−√
C+ < s < −√
C−,5. the moist external fronts, s < −
√Cm
+ .
This result confirms previous studies within a linearbaroclinic model (Frierson et al, 2004).
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Wave scattering on a moisture front: setting
Localized internal simple wave centred at xP = 2 andmoving eastward:
u1(x ,0) =
{σ(x − xP)2 + U0 if −
√U0σ ≤ x − xP ≤
√U0σ ,
0 otherwise,U0 = 0.01, σ = −1(1)
Stationary moisture front at xM = 5, saturated air at theeast, unsaturated at the west:
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Linear stability diagram
0 0.5 1 1.5 2 2.50
0.2
0.4
k
c p
0 0.5 1 1.5 2 2.50
0.1
0.2
k
σ
Phase velocity (top) and growth rate (bottom)
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
The most unstable mode
0.5 1 1.5 2 2.5
−0.8
−0.6
−0.4
−0.2
0
0.2
0.4
0.6
0.8
ψ2
x/Rd
y/Rd
0.5 1 1.5 2 2.5
−0.8
−0.6
−0.4
−0.2
0
0.2
0.4
0.6
0.8
ψ1
x/Rd
y/Rd
Most unstable mode of the upper-layer Bickley jet.Upper(top) and lower (bottom) layer- geostrophic
streamfunctions and velocity (arrows) fields.
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Early stages: evolution of moisture
5Ti
(a)
0.5 1 1.5 2 2.5−1.5
−1
−0.5
0
0.5
1
1.5
−3
−2
−1
0
1
2
3x 10
−4
20Ti
(b)
0.5 1 1.5 2 2.5−1.5
−1
−0.5
0
0.5
1
1.5
−8
−6
−4
−2
0
2
4
6
8
x 10−4
200Ti
(c)
0.5 1 1.5 2 2.5−1.5
−1
−0.5
0
0.5
1
1.5
−0.11
−0.1
−0.09
−0.08
−0.07
−0.06
−0.05
−0.04
−0.03
−0.02
−0.01
300Ti
(d)
0.5 1 1.5 2 2.5−1.5
−1
−0.5
0
0.5
1
1.5
−0.7
−0.6
−0.5
−0.4
−0.3
−0.2
−0.1
0
Evolution of the moisture anomaly Q −Q0 withsuperimposed lower-layer velocity. Black contour:condensation zones.
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Early stages: growth rates
0 100 200 300 400 500−0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
t/Ti
σ/Ro
DryMoist
Red: moist, blue: dry simulations. ⇒Transient increase in the growth rate due to condensation.
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Cyclone-anticyclone asymmetry
0 500 1000 1500 2000
−0.5
0
0.5
t/Ti
UPPER LAYER
<ζ23 >/
<ζ22 >3/2
0 500 1000 1500 20000
2
4
6
t/Ti
LOWER LAYER
<ζ13 >/
<ζ12 >3/2
Skewness of relative vorticity. Red: moist, blue: drysimulations.
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
How condensation enhances cyclones:1-layer modelFor Ro → 0 and Bu ∼ O(1), close to saturationψ ∼ q << 1:
(∂t + v (0) · ∇)[∇2ψ − ψ
]= βP, (3)
(∂t + v (0) · ∇)[q −Qs∇2ψ
]= −P, (4)
v (0) = (−∂yψ, ∂xψ) - geostrophic velocity, ψ = η + η, andq is moisture anomaly with respect to Qs.⇒ PV of the fluid columns which pass through theprecipitating regions increases. For τ → 0 q ≈ 0, and:
Qs(∂t + v (0) · ∇)[∇2ψ
]≈ Pτ→0 > 0, (5)
⇒ increase of geostrophic vorticity in the precipitationregions.
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Dry vs moist simulations: evolution of relativevorticity
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Moist baroclinic instability in Nature
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Conclusions 1
The modelI Physically and mathematically consistentI Simple, physics transparentI Efficient high-resolution numerical schemes availableI Benchmarks: good
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
Conclusions 2
Moist vs dry baroclinic instability
I local enhancement of the growth rate of themoist-convective instability at the precipitation onset,
I significant increase in intensity of ageostrophicmotions during the evolution of the moist instability,
I substantial cyclone - anticyclone asymmetry, whichdevelops due to the moist convection effects.
I substantial differences in the structure of zonal jetsresulting at the late stage of saturation.
Lecture 4:Applications to the
atmosphere,moist-convective
RSW
Introduction
Methodology
Constructing themodel
Limiting equationsand relation to theknown models
General propertiesof the modelConservation laws
Characteritics and fronts
Example: scattering of asimple wave on a moisturefront
Introducing evaporation
Moist vs drybaroclinicinstability(Dry) linear stability of thebaroclinic jet
Comparison of the evolutionof dry and moist instabilities
Conclusions
Literature
References
Presentation based on:I Lambaerts J.; Lapeyre G.; Zeitlin V. and Bouchut F.
"Simplified two-layer models of precipitatingatmosphere and their properties" Phys. Fluids 23,046603, 2011.
I Lambaerts J.; Lapeyre G. and Zeitlin V. "Moist versusDry Baroclinic Instability in a Simplified Two-LayerAtmospheric Model with Condensation and LatentHeat Release" J. Atmos. Sci. 69, 1405-1426, 2012.