Japanese-French model studies of planetary atmospheres on 13 May 2015 at Kobe

General circulation and high-latitude atmospheric
dynamics of a cloud-covered planet
M. Yamamoto (RIAM, Kyushu Univ)*
M. Takahashi (AORI, Univ Tokyo)

Contents
1. Dynamics of Venus’ polar vortex in the presence of strong
diurnal thermal tideusing Venus middle atmosphere GCM (see detail in Yamamoto &Takahashi 2012 Icarus; 2015, PSS)
2. Atmospheric superrotation of cloud-covered planets:
significance of planetary rotation and polar eddy heattransport
using a simple model setting of the ISSI VGCM intercomparison
project (Lebonnois et al. 2013).

1. Dynamics of Venus’ polar vortex in thepresence of strong diurnal thermal tide
PVO OBS
Pechmann & Ingersoll (1984)
PVO OBSElson(1983)

0306090

IR measurement(Taylor et al. 1979)

Objective
To elucidate dynamics of polar vortex
under the condition of strong polar tideModel results of VMAGCM (Yamamoto & Takahashi 2012)(T21L72, 5.5-day Kelvin wave forcing exper.)Temperature
70.5 km

Temperature spectrum
T’262,016 days

Observation

Slowly traveling diurnal tide
Transient fast waves

IR measurement(Taylor et al. 1979)

KVortexes in VMAGCM (gray shading is night hemisphere)
62016 days, T at 70.5 km+9 hr+18 hrPolar dipole grows with time, and changes to tripole.
+24 hr

The dipole rotates, andmergers into monopole.

+48 hr+72 hr

The monopole breaks up,and becomes dipole.
(Yamamoto & Takahashi 2012; 2015)

Relationship with DIV and VOR
62016 days (gray shading is warm areas of > 226 K at 70.5 km)

TWarm & convergencearea are in phase.

DIV induces temperature
anomaly in the vortex

Baroclinic wave(Young et al. 1984)

VOR’DIV

Both DIV & VOR’ havelarge amplitudes.
DIV & VOR’ are out ofphase by a 1/4 cycle

Vortical flow transport heat fromthe warm polar region to cold outside(Yamamoto & Takahashi 2015)

Summary (1)Under the condition of strong polar tide,
1. Superposition of diurnal tide and transient
waves could produce complex vortex patterns.

After the transient
wave rotates by ½ cycle(Yamamoto & Takahashi 2015)

Summary (2)2. Horizontal divergence is strong, and induces
temperature anomaly pattern.
3. Vortical flow transports heat from the hot polar
region to cold outside.
Transient baroclinic wave contributes to the vortex
pattern.

Future work
Maintenance mechanism of hot dipole is still unknown
under the condition of weak polar tide (VEX).
We need to further investigate them.

2. Atmospheric superrotation of cloudcovered planets: significance of planetaryrotation and polar eddy heat transport
using an idealized VGCM (baseline model setting of theISSI intercomparison project, Lebonnois et al. 2013).
CCSR (T21)

Zonal flow

Stream function

LMD

Large differences of superrotation strength and polar
indirect cells among GCMs

The polar circulation affects thehigh-latitude superrotation.

We needs high-resolution GCM
experiments to fully resolve
polar indirect circulation.

2. Atmospheric superrotation of cloudcovered planets: significance of planetaryrotation and polar eddy heat transport
using an idealized VGCM (baseline model setting of theISSI intercomparison project, Lebonnois et al. 2013).
 Easy to compare among different VGCMs
 Lee and Rechardson (2010), Lebonnois et al. (2013)

 Easy to conduct long-term and high-resolution simulation
We can examine the dynamical effect of polar indirect cell in superrotation
using a long-term and high-resolution GCM.

 Easy to apply cloud-covered planet with different rotation rate
For cloud-covered planet, the sensitivity of superrotation to the planetary rotation
rate is not fully understood.
We will examine superrotation structure of cloud-covered planet with arbitrary
planetary rotation rate ?

Objective
 To elucidate dynamical effect of polar indirect cell insuperrotation
 To elucidate superrotation structure of cloud-covered
planet with arbitrary planetary rotation rateWe investigate sensitivities of superrotation and polar circulation
to the planetary rotation rate of a cloud-covered planet.

Previous studies
 Earth-like GCMs

Many (Williams & Holloway1982,Mitchell & Vallis 2010, …)

 Cloud-covered GCMs

A few (Del Genio et al. 1993,
Yamamoto & Takahashi 2008 AA490, L11)however, low-resolution

Present study
Model settingBaseline run of ISSI
(Lebonnois et al. 2013)
T21  T106
 Exp V 2/ = 243 Edays
 Exp T 2/ = 16 Edays
 Exp E 2/ = 1 Edays

Held & Suarez (1994)

simplified by Newtonian cooling relaxing temperature
T to the Earth’s tropospheric temperature. This is wellused as an idealized Earth-like planet.

Baseline run of ISSI VGCM intercomparisonPressure (Pa)simplified by Newtonian cooling relaxing T to Venus’value. This is used as an idealized cloud-covered planet.
102104Venus International
Reference Atmosphere

Cloud
10+Idealized cloud heating
Cloud

6(Seiff et al. 1985)
250
500
Tref (K)(Lee 2006)
750

Zonal mean wind speed(Color shading is jet core)

Exp T

Exp V: Weak jets are extended tolower atmos. below the cloud layer.
Exp T: Strong jets are locatedin the cloud layer.

CloudExp E: Moderate jets are locatedabove the cloud layer.

The strength and location of the jetcore depend on the planetary rot. rate.

Exp VExp ECloudCloudMass stream func.
(Green contour is clockwise flow)(Blue contour is anticlockwise flow)

Exp T

Exp V: Equator-pole Hadley cells+ Polar indirect cells
 Jets extend to the lower atmos.
Exp T: Equator-pole Hadley cells
 Jets effectively develop in the cloud.
Exp E: Equator-pole multiple cells
 Jets do not develop in and below thecloud.

Exp VExp E

Horizontal eddy heat flux
(color shading is 0 cos  ' v' )(Contour is zonal-mean temperature)

Exp TPoleward heat flux is strongin Exp V.

The strong eddy heat flux induces
polar indirect circulation, andreduces meridional temperature
gradient.

Exp VExp E

Spectrum of horizontal eddy heat flux at 2.03  105 Pa
The most predominant modes in the flux spectrum in Exp. VT 'v'

128-day Rossby wave
(contour is eddy geopotential height)

Eddy temperature (K) The strong poleward eddy heat flux is produced by slowly traveling planetaryscale polar Rossby waves with meridional winds across the poles.

 The poleward (equatorward) eddy flows are in phase with respect to the eddy
temperature, and advect warm (cold) air masses.

Horizontal eddy heat flux & indirect circulation
Indirect meridional
circulation

divergence

convergence

Eddy heat flux

ColdWarm

Indirect circulation“Strong” eddy heat flux
modifies atmospheric heating via
the eddy heat flux convergence.

Indirect meridional circulation
is induced by strong eddy heat flux,and largely modifies angularmomentum.

Transformed Eulerian-Mean(TEM) equation system is used.

Transformed Eulerian-Mean (TEM) equation system(Andrews and McIntyre 1976)
Residual-mean Meridional Circulation (RMC)
v *  v  ( 0 v'' /  z ) z / 0w *  w  (cos  v'' /  z ) / a cos RMC is “direct circulation”,
in which eddy-driving
indirect circulations areremoved.

Eulerian zonal-mean
meridional circulation

Eliassen-Palm (E-P) flux
FEP   0 a cos  (u'v'  u z v'' /  z )E-P flux is “effective eddy
angular momentum flux”, inwhich eddy-driving indirect
circulations are added.

FEP   0 a cos {u'w'  [ f  (u cos  ) / a cos  ]v'' /  z }zEulerian zonal-mean
eddy momentum flux

Horizontal E-P fluxes(Color shading is E-P flux)(Contour is 0 a cos  u'v' )Exp T

Exp V: equatorward near the surface
Exp T: equatorward near the cloud base
Exp E: poleward in the cloud layer
 As planetary rotation rate is faster,
the level of the strongest E-P flux islocated at the higher level.

Exp VExp E

Spectrum of horizontal eddy momentum fluxes at 6.0  106 Pa
The most predominant modes in the flux spectrum in Exp. Vu 'v'

Stationary mixed Rossby-gravity wave
(contour is eddy geopotential height)

Eddy temperature (K)Stationary mixed Rossby-gravity wave contributes to horizontal momentum
transport.
The meridional flow across the equator tilts at mid- and high-latitudes. The windtilt produces equatorward momentum flux (Yamamoto &Takahashi, 2003).

Spectrum of horizontal eddy momentum fluxes at 5.5  105 Pa
The most predominant modes in the flux spectrum in Exp. Tu 'v'

14.2-day Kelvin-Rossby wave
(contour is eddy geopotential height)

Eddy temperature (K)High-latitude Rossby and low-latitude Kelvin wave structure across the criticallatitude is similar to a Kelvin-Rossby mode (Iga and Matsuda, 2005) which wassimulated in Venus GCMs (e.g., Yamamoto and Takahashi, 2004).

Spectrum of horizontal eddy momentum fluxes at 3.8  104 Pa
The most predominant modes in the flux spectrum in Exp. E
u 'v'

2.78-day Rossby wave
(contour is eddy geopotential height)

Eddy temperature (K)The strongest momentum flux is caused by a Rossby wave with a phase velocity
slower than the zonal-mean wind velocity at midlatitudes
The eddy temperature component is small, and in phase with the eddy
geopotential height at the central latitude of the wave.

Vertical E-P fluxes(Color shading is E-P flux)(Contour is 0 a cos  u'w' )Exp T

Exp V: Downward E-P flux is caused bystrong poleward eddy heat flux.
Exp T: Downward E-P flux is caused by
downward momentum flux.
Exp E: Downward E-P flux is caused byweak eddy heat flux and strong Coriolisparameter.

Exp VExp E

Vertical ang. mom. fluxes by RMC

Exp T

The global-mean angular momentum
flux is upward.
 RMC pumps up angular mom.
Exp V and T: The Hadley cells areextended to the poles.
 RMC efficiently pumps up ang. mom.
Exp E: The Hadley cell is confined withintropical region.

Exp VExp E

Summary (Exp V, 2/ = 243 Edays)

PEQEP

 Strong poleward heat flux due topolar wave produces the strong
downward E-P flux and its related
polar indirect circulation, which
weaken the superrotation in thecloud layer.

RMC

EPRMC

RMC

 Strong equatorward angularmomentum flux is produced bystationary mixed-RG wave near thesurface.

P Strong poleward heat flux also
reduces the meridional temperature
gradient and vertical shear of highlatitude jets in accordance with thethermal-wind relation.

 Weak high-latitude jets are extended to ‘the lower atmosphere’ in thepresence of polar indirect circulation.

Summary (Exp T, 2/ = 16 Edays)
 Strong horizontal angular momentum
flux is produced by fast traveling KelvinRossby waves, and is located near thecloud base.

PEPEQ

EPRMC

JRMC

RMC

J

 Polar indirect circulation is absent,
while horizontal heat flux is weak.
Only the equator-pole Hadley cell ispredominant.

P Meridional temperature gradientis strong below the strong jets inaccordance with the thermal-windrelation.

 Strong mid-latitude jets and meridional temperature gradient are
maintained “in the cloud layer” in the absence of polar indirect circulation.

Summary (Exp E, 2/ = 1 Eday)

JJ

 Although poleward heat flux isweak, large Coriolis parameter
contributes to strong downward E-P
flux within the cloud layer.

EQRMC

EPRMC

RMCEPP Strong poleward angular momentum
flux is produced by fast traveling
midlatitude Rossby waves in the cloudlayer.

P Strong RMC is confined within low
latitudes in and below the cloudlayer. The multiple meridional
circulation reduces upward angularmomentum transport.

 Weak midlatitude jets are formed ‘above the cloud layer’ by weak globalscale Hadley circulation of the low-density upper atmosphere, whereas
superrotation is not formed in and below the cloud layer in the presence ofequator-pole multiple circulation.

Conclusion
 Three different types of middle-atmospheric jetstructures depend on the planetary-rotation rate ofcloud-covered planets.
 Poleward eddy heat transport induces polar indirect
circulation and weakens cloud-level superrotation via
vertical E-P flux and thermal wind relation in Exp. V.
 Poleward eddy heat transport is driven by planetaryscale eddy meridional winds across the poles, whichis unique to the slow superrotation seen in Exp. V.
The presence or absence of strong poleward eddy heat flux is
one of the important factors determining the slow or fast
superrotation state in the cloud layer through the E–P flux andthe thermal-wind relation.

Future works
 Sensitivity experiments for model resolution (T21,42, 63, and 106) were done, based on the ISSI
protocol (baseline, Exp. V). We are analyzing
sensitivity of wave activity.
We can compare with dynamical cores of different
GCMs. If the resolution is increased, the differencesamong GCMs are expected to become smaller.
 The simplified modeling is changed to realistic
Venusian cloud-covered condition towards
understanding of the atmospheric dynamics.