QBO, Ondes, Effets stochastiques
La QBO dans le modèle LMDz QBO dans les modèles de CMIP5
Sources d'ondes de gravité Ondes équatoriales
La QBO dans LMDz
Results for the Equatorial winds:
QBO of irregular period around 26month, 20% too small amplitude
Westerly phase lacks of connection with the stratopause SAO
But such a relation is also absent in ERAI, why?
LMDz, 80 niveaux verticaux,
Ondes de gravité stochastiques liées à la convection (Lott and Guez 2013)
Soupe spectrale d OG (Hines 1997)
La QBO dans LMDz
Histogram of QBO periods
Relatively good spread of the periods taking into account that it is a forced
simulation with climatological SST (no ENSO)
Periods related to the annual cycle (multiples of 6 months) are not favoured:
probably related to the weak relations with the SAO
Without relation with convection, the sources Were more uniform and the QBO of 24month
(too strong link with SAO)
We change the dissipation on the vorticity only
Effect of dissipation Eq. wind at 20hPa
MERRA, High dissip, low dissip In its set-up for LMDz,
Hines decreases the QBO period By around 2-3 months
Guw=2.2 (instead of 2.4) increases the QBO period of 2 months (no effect on the histogram)
La QBO dans LMDz
Very sensitive to the model setup.
There are often experiences where the QBO stacks in easterly phases, and we do not knnow why ?
La QBO dans LMDz
No negative impacts on other climatological aspects of the model
January zonal mean zonal wind
CGWs improve the phase at the stratopause
CGWs reduce easterly biases in the subtropics summer mesosphere
(1) LMDz+CGWs
MERRA
(2) LMDz without CGWs
LMDz+CGWs
MERRA
LMDz without CGWs
Impact: (1) – (2)
100 10 1 0.1
100 10 1 0.1
100 10 1 0.1
100 10 1 0.1
1000
100 10 1 0.1
1000
100 10 1 0.1
1000 100
10 1 0.1
Eq 30N 60N 1000 30S
60S
90S 90N 90S 60S 30S Eq 30N 60N 90N
Eq 30N 60N 30S
60S
90S 90N
Eq 30N 60N 30S
60S
90S 90N
FEB
1979 APR JUN AUG OCT DEC
FEB 1979
APR JUN AUG OCT DEC
FEB
1979 APR JUN AUG OCT DEC
20 60 85
-10 -35 -50 -75
-90 5 45
20 60 85
-10 -35 -50 -75
-90 5 45 -90 -75 -50 -35 -10 5 20 45 60 85
20 60 85
-10 -35 -50 -75
-90 5 45
15 35 45 -5
-15 -25 -35
-45 5 25 55
-55
SAO:
La QBO dans CMIP5 et questions « brulantes »
Errors in spread of periods (24 month strictly
in MIROC).
Some stalling in MPI-MR
and most of all CMCC.
HadGEM2- CC seem sto
have a week contribution from explicit
equatorial waves.
4 modèles de CMIP5 simulent une QBO, ils ont tous une résolution fine dans la basse stratosphère et des paramétrisations des ondes de G non-orographiques, non liées aux
Sources.
La QBO dans CMIP5 et questions « brulantes »
SAO in models, the connection with the QBO varies a lot from one model to the other,
Note the problems in phase in HadGEM2, lack of Kelvin waves ? The too pronounced descents in MIROC and MPI-ESMs. Remember that the SAO seeds westerly phase of the QBO.
La QBO dans CMIP5 et questions «brulantes»
Pourquoi la QBO dans les modèles ne pénètre pas assez bas, impact sur la vapeur d'eau via la Température et les circulations
résiduelles associées à la QBO ?
Pourquoi les modèles sous estiment le mécanisme de Holton et Tan sur les liens QBO vortex aux moyennes latitudes ?
Correlation between the winter vortex (leading PC) at 20 hPa and the QBO at 50 hPa CMIP5 and CCMVal2 experiments Models
Red: No QBO, Blue: Prescribed QBO, Green: Spontaneous QBO.
Black is the NCEP Reanalysis.
Filled circles are 1960-2005, Squares the full historical period, and stars the piControl Vertical bars indicate 95% uncertainty band for uncorrelated time-series.
Christiansen B (2013, 2014)
La QBO dans CMIP5 et questions «brulantes»
Doit-on convaincre nos centres de recherches qu'il faut des modèles avec QBO pour CMIP6 (c'est quand meme un peu cher tout cela):
La QBO est un mode de variabilité dominant et assez prévisible, ce serait dommage de s'en passer.
La QBO et le cycle solaire interagissent dans leur modulation des conditions de propagation des ondes planétaires aux moyennes latitudes
La circulation résiduelle associée à la QBO affecte la circulation de Brewer Dobson, et la QBO affecte la Température à la tropopause dans les tropiques
et donc la vapeur d'eau
Les impacts de la QBO sur la MJO, ENSO ou les moussons sont moins robustes et restent à étudier
Les sources d'ondes de gravité
Subgrid scale precipitation over the gridbox considered as a stochastic series
P 'r=
∑
n=1∞ CnPn' where Pn'=ℜ[
Pnei kn⋅x−nt]
We take
∣
P n∣
=Pr The subgrid scale standard deviation of the precipitation equals the gridscale mean: White noise hypothesis!Distributing the related diabatic forcing over the vertical via a Gaussian function yields the EP-flux at the launch level (see also Beres et al.~(2004), Song and Chun (2005):
G
uw tuning parameter of the CGWs amplitudeThe kn's are chosen randomly between 0 and
k*
Fnl=r kn
∣kn∣
∣kn∣2e−mn2z2
N n3 Guw
R Lr H cWp
2Pr2 mn=N∣kn∣n
,n=n−kn⋅U
The ωn's are chosen randomly between 0 and knCmax
Tuning parameter max phase speed
z tuning parameter or scale of the heating depth
Les sources d'ondes de gravité
Lott and Guez, JGR 2013 CGWs
stress
CGWs drag
Same zonal mean stress
Real precip. Stress amplitude (CI=2mPa) Uniformized precip. Stress amplitude (CI=2mPa)
Eq 30N 60N 90N
30S 60S
90S0 60E 120E 180E 60W 120W 0 60E 120E 180E 60W 120W
Real precip. du/dt *e(-z/2H), CI= 0.1 m/s/d Uniformized precip. du/dt *e(-z/2H), CI= 0.1 m/s/d
Eq 30N 60N 30S
60S 60S 30S Eq 30N 60N
More drag near and above stratopause Slightly less drag in the QBO region
50 60
40 30 20 10
50 60
40 30 20 10
0.15 0.25 0.35 0.45
0.05 0.05 0.15 0.25 0.35 0.45
Benefit of having few large GWs rather than a large ensemble of small ones:
Les sources d'ondes de gravité
Replace Background GWs due to Hines by a stochastic scheme related to fronts
Gravity waves due to convection are not likely to be strong enough in the
midlatitudes and polar regions
Many models still needs parameterization of a gravity waves background
Thanks to Alvaro Camara
de la Illescas
Les sources d'ondes de gravité
Simulations to support these parameterizations:
O'Sullivan and Dunkerton (1995) Reeder and Griffiths (1997)
Les sources d'ondes de gravité
Plougonven Hertzog and Guez (2012)
When the frontogenesis function
Exceeds 0.045 (K2 (100km)-2 h-1), GWF=1.5 mPa!
Justification : the relation between frontal characteristics and wave amplitude have not been established to date (a 2010 paper)
Problems : Can this be viewed as an external thermodynamical forcing ? If yes, a good part of the response will be balanced, a smaller part made of GWs (Lott~2003)
−
(
acos1 ϕ∂ λ∂θ
) (1a ∂θ
∂ϕ
) (acos1 ϕ
∂v
∂ λ +1 a
∂u
∂ ϕ+utanϕ a
)
F=−
(
acos1 ϕ∂ θ
∂λ
)
2(
acos1 ϕ∂u
∂ λ− v tanϕ
a
)
−(
1a∂ θ
∂ ϕ
)
2(
1a∂v
∂ ϕ
)
Les sources d'ondes de gravité
Geostrophic adjustment
It is related to 2 rather different processes:
The «classical adjustment» where an initial unbalanced flow radiates GWs as it returns to a balanced situation. In this case, the initial imbalance is the ultimate source of the GWs: the problem is to know what causes this imbalance.
The «spontaneous adjustment» where a well-balanced flow radiates Gws in the course of its evolution. Here the adjustment itself is the GWs source.
There always exists pronounced PV anomalies inside fronts
Les sources d'ondes de gravité
General setup: A 3D (x,y,z) PV anomaly advected in a rotating (f =cte), stratified (BV freq N=cte) shear flow (vertical shear =cte).
For the 2D results: Lott, Plougonven and Vanneste, JAS 2010.
Les sources d'ondes de gravité
General setup: A 3D (x,y,z) PV anomaly advected in a rotating (f =cte), stratified (BV freq N=cte) shear flow (vertical shear =cte).
For the 2D results: Lott, Plougonven and Vanneste, JAS 2010.
Les sources d'ondes de gravité
General setup: A 3D (x,y,z) PV anomaly advected in a rotating (f =cte), stratified (BV freq N=cte) shear flow (vertical shear =cte).
For the 2D results: Lott, Plougonven and Vanneste, JAS 2010.
Les sources d'ondes de gravité
General setup: A 3D (x,y,z) PV anomaly advected in a rotating (f =cte), stratified (BV freq N=cte) shear flow (vertical shear =cte).
For the 2D results: Lott, Plougonven and Vanneste, JAS 2010.
Les sources d'ondes de gravité
General setup: A 3D (x,y,z) PV anomaly advected in a rotating (f =cte), stratified (BV freq N=cte) shear flow (vertical shear =cte).
For the 2D results: Lott, Plougonven and Vanneste, JAS 2010.
Les sources d'ondes de gravité
General setup: A 3D (x,y,z) PV anomaly advected in a rotating (f =cte), stratified (BV freq N=cte) shear flow (vertical shear =cte).
For the 2D results: Lott, Plougonven and Vanneste, JAS 2010.
Les sources d'ondes de gravité
General setup: A 3D (x,y,z) PV anomaly advected in a rotating (f =cte), stratified (BV freq N=cte) shear flow (vertical shear =cte).
For the 2D results: Lott, Plougonven and Vanneste, JAS 2010.
Les sources d'ondes de gravité
General setup: A 3D (x,y,z) PV anomaly advected in a rotating (f =cte), stratified (BV freq N=cte) shear flow (vertical shear =cte).
For the 2D results: Lott, Plougonven and Vanneste, JAS 2010.
Les sources d'ondes de gravité
General setup: A 3D (x,y,z) PV anomaly advected in a rotating (f =cte), stratified (BV freq N=cte) shear flow (vertical shear =cte).
For the 2D results: Lott, Plougonven and Vanneste, JAS 2010.
Les sources d'ondes de gravité
General setup: A 3D (x,y,z) PV anomaly advected in a rotating (f =cte), stratified (BV freq N=cte) shear flow (vertical shear =cte).
Les sources d'ondes de gravité
For the 3D results: Lott, Plougonven and Vanneste, JAS 2013 Very simple formula, quantitive and not arbitrary
After stochastic implementation all the GWs will be related to sources GWs forcings will change when climate change
Will vary with Low Frequency Variability in the troposphere :
Does stochastic effects and intermittency associated to sources yield low frequency Variabilities in the GWs fluxes ?
Does it increase the simulations spread ? Via the SSWs for instance.
Les ondes équatoriales
ERAI 21, 11 cases
LMDz+CGWs 10 cases
LMDz without CGWs 10 cases 20S
20N
Eq
20S 20N
Eq
20S 20N
Eq
80E 0
80W 40W 40E
80E 0
80W 40W 40E
80E 0
80W 40W 40E
What are the relations between the stratospheric waves and the convectively coupled waves in the troposphere?
With organized convection in general (ENSO, MJO, monsoons).
Why do Kelvin waves break so rapidly when entering in the stratosphere ?
