Atmospheric angular momentum variations of earth mars and venus
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Atmospheric angular momentum variations of Earth, Mars and Venus. V. Dehant 1 , Ö. Karatekin 1 , O. de Viron 2 , S. Lambert 3 , and T. Van Hoolst 1 1 Royal Observatory of Belgium 2 IPGP &Universite Paris Diderot, France 3 Observatoire de Paris, France;. Introduction. External forcing.

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Atmospheric angular momentum variations of earth mars and venus

Atmospheric angular momentum variations of Earth, Mars and Venus.

V. Dehant1, Ö. Karatekin1, O. de Viron2, S. Lambert3, and T. Van Hoolst1

1Royal Observatory of Belgium

2IPGP &Universite Paris Diderot, France

3Observatoire de Paris, France;


Introduction

Introduction

External forcing

Orogenesis

Erosion

Post glacial rebound

Tectonics

Topographic

coupling

Electromagnetic

coupling

Mantle

convection

Geodynamo

tensions

frictions

Hydrology

Atmospheric dynamics


Effects of superficial fluids

Exchange of angular

momentum : the total

angular momentum of

the system Earth-fluids

is constant

Torques related to the

forces interacting on

the solid Earth :

the fluid is an

external excitation

Effects of superficial fluids

solid Earth

Ocean

Atmosphere

3 tanks of angular moment

interacting with 3 forces:

Pressure,

Gravitation,

Friction


Atmospheric angular momentum variations of earth mars and venus

Pressure

Friction

Gravitation

Interaction between the Earth and the atmosphere


Atmospheric angular momentum variations of earth mars and venus

Computation of the Atmospheric angular

momentum

Matter term : rigid rotation

of the atmosphere with

the solid Mars

Motion term

Matter term

Motion term

Motion term : relative

angular momentum of

the atmosphere

Matter term


Atmospheric angular momentum variations of earth mars and venus

  • The order of magnitude is similar when the dimension and dynamics are different!

  • Earth and Mars have seasons and insolation changes very similar

  • When looking at the symmetry, one would expect no angular momentum changes, but:

    • For the Earth, the ocean and their anti-symmetrical location induced angular momentum

    • For Mars, the eccentricity of the orbit plays a role, and as well, the properties of the soil

      • For Venus, diurnal timescale at 117 Earth days.

      • For Mars, additionally effects on global storms.

LOD

Earth: ~1 msec, seasonal variations of AAM. (Dickey 1995)

Mars: ~ 0.3 msec, seasonal variations of AAM.

Venus ?


Physical properties

Physical Properties


Atmospheric circulation

Atmospheric Circulation

Gierasch 2002

Svedhem 2007


Atmospheric angular momentum variations of earth mars and venus

Non-tidal length of day spectrum (from COMB02) for the Earth

ENSO Low Frequency band

ENSO Quasi-biennale Frequency band

Semi-annual

Amplitude

Annual

10

20

15

5

0

Period (year)


Atmospheric angular momentum variations of earth mars and venus

Non-tidal length of day spectrum (from COMB02) for the Earth

ENSO Low Frequency band

Annual

ENSO Quasi-biennale Frequency band

Semi-annual

Amplitude

Core Effect (Hide et al., 1999)

Wind atmospheric effect (NCEP)

10

20

15

5

0

Period (year)

Atmospheric pressure (NCEP)

Ocean (ECCO, Gross et al, 2003)


Aam variations earth

AAM Variations (Earth)


Aam variations mars

AAM Variations (Mars)

The surface pressure variations on Mars have the largest contribution while the winds have the smallest effect in contrast with the Earth where the winds are the dominant source for AAM.


Aam variations venus

AAM Variations (Venus)


Lod variations

LOD Variations

∆LODTotal= ∆LODPressure+∆LODWind

Mars

Venus


Comparison with observations

Comparison with Observations

Konopliv et al. (2006) determined amplitudes of DLOD using both lander and orbiter data. DLOD from the observations and MCD are in good agreement.


Effect of dust on mars

Effect of Dust on Mars

We calculated DLOD from the outputof the Mars Climate Database (MCD) version 4.2. (Forget et al. 2007) using the angular momentum approach.

The Martian atmosphere is highly variable. The MCD includes 4 different dust scenarios. The largest variations inDLOD occurs during 270<Ls<360


Angular momentum density

Angular Momentum Density


Time variation of ps

Time variation of Ps

Venus

Mars

0 day < t < 1 day

0 day < t < 117 days


Atmospheric angular momentum variations of earth mars and venus

Atmospheric circulations on Mars and Venus are both driven by solar insolation (Different mechanisms, time-scales, ...).LOD changes are mainly due to diurnal variations of the winds on Venus and seasonal variations of Ps on Mars ∆HAtm/HAtm is 2 order of magnitude(O) smaller on Venus, but since HAtm/Hsolid is 5O larger wrt Mars, ∆LOD/LOD on Venus is 2O more important.Venus GCM is under development. Nevertheless, similar ∆LOD are obtained with different versions of the GCM and GCM data of Lee et al. (2007)Future ∆LOD observations can help to better understand the wind variations near the surface (0>H>50) km. Precise measurements of wind variations can help to constrain the interior.


Effect of dust storms on mars s rotation

Effect of dust storms on Mars’s rotation

LOD

PM


Torque between mars and its fluid layer

Torque between Mars and its fluid layer

Pressure torque


Derivative of the topography

Derivative of the topography


Atmospheric angular momentum variations of earth mars and venus

Pressure torque


Torque between mars and its fluid layer1

Torque between Mars and its fluid layer

Gravitational torque


Atmospheric angular momentum variations of earth mars and venus

Gravitational torque


Torque between mars and its fluid layer2

Torque between Mars and its fluid layer

Friction torque


Torque approach

Torque approach

Pressure torque

Gravitational torque

Friction torque


Annual axial torque

Annual axial torque


Conclusions

Conclusions

  • Ellipsoidal torque very important for the equatorial budget of the ocean.

    • Compensation of the atmospheric ellipsoidal torque by the Earth reaction torque.

    • Contributing ocean mainly dictated by geometrical reason.

  • Indian ocean is a very important contributor to the total torque on the ocean for the X component.

  • Pacific ocean is a very important contributor to the total torque on the ocean for the Y component.

  • Atlantic ocean only important for the Y component of the torque.


Comments on the previous slide

Comments on the previous slide

  • Largest effect: atmospheric ellipsoidal torque, compensated by the Earth response to it. Only the much smaller part associated with the ocean mass remains.

  • Surface friction torque and the pressure torque on bathymetry are much larger than the bottom and side friction torque.

  • Fair match between dOAM/dt and total torque


Atmospheric angular momentum variations of earth mars and venus

Non-tidal polar motion spectrum (from COMB02)

Chandler Wobble

Annual

Amplitude

6 y

3.5 y

2 y

2 y

1 y

-5

0

15

-10

-15

5

20

10

-20

Retrograde polar motion

Prograde polar motion


Atmospheric angular momentum variations of earth mars and venus

Non-tidal polar motion spectrum (from COMB02)

Amplitude

Wind atmospheric effect (NCEP)

Atmospheric pressure (NCEP)

-5

0

15

-10

-15

5

20

10

-20

Ocean (ECCO, Gross

et al, 2003)

Retrograde polar motion

Prograde polar motion


Annual equatorial torque

Annual equatorial torque


Atmospheric angular momentum variations of earth mars and venus

Non-tidal length of day spectrum for Mars

Semi-annual

Annual

Amplitude

10

20

15

5

0

Period (Earth year)


Atmospheric angular momentum variations of earth mars and venus

Non-tidal length of day spectrum for Venus

diurnal

Amplitude

Core Effect ?

10

20

15

5

0

Period (Earth year)

117 days


Surface pressure

Surface Pressure


Time averaged zonal winds

Time-averaged Zonal Winds

Mars

Venus


Time variation of ps1

Time variation of Ps

Venus

Mars

0 day < t < 687 days

0 day < t < 117 days


Atmospheric angular momentum variations of earth mars and venus

Axial AAM

Pressure

Latitude


Global circulation

General circulation

Global circulation


Effect of the fluid layer s on lod annual cycle

Effect of the fluid layer(s) on LODAnnual cycle

Wind term

Matter IB

Current term

Mass ocean

Wind term

Atm. pressure

Ice cap


Effect on polar motion annual cycle

Effect on Polar MotionAnnual cycle


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