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Atmospheric angular momentum variations of Earth, Mars and Venus . PowerPoint Presentation

Atmospheric angular momentum variations of Earth, Mars and Venus .

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### 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 Venus

External forcing

Orogenesis

Erosion

Post glacial rebound

Tectonics

Topographic

coupling

Electromagnetic

coupling

Mantle

convection

Geodynamo

tensions

frictions

Hydrology

Atmospheric dynamics

Exchange of angular Venus

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 fluidssolid Earth

Ocean

Atmosphere

3 tanks of angular moment

interacting with 3 forces:

Pressure,

Gravitation,

Friction

Computation of the Atmospheric angular Venus

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

- 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.

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

Mars: ~ 0.3 msec, seasonal variations of AAM.

Venus ?

Physical dynamics are different! Properties

Non-tidal length of day spectrum (from COMB02 dynamics are different!) for the Earth

ENSO Low Frequency band

ENSO Quasi-biennale Frequency band

Semi-annual

Amplitude

Annual

10

20

15

5

0

Period (year)

Non-tidal length of day spectrum (from COMB02 dynamics are different!) 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 dynamics are different! (Earth)

AAM Variations (Mars) dynamics are different!

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 dynamics are different! (Venus)

Comparison dynamics are different! 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 dynamics are different!

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 dynamics are different!

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.

Torque between Mars and its fluid layer by solar

Pressure torque

Derivative of the topography by solar

Pressure torque by solar

Torque between Mars and its fluid layer by solar

Gravitational torque

Gravitational torque by solar

Torque between Mars and its fluid layer by solar

Friction torque

Annual axial torque by solar

Conclusions by solar

- 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 by solar

- 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

Non-tidal polar motion spectrum (from COMB02) by solar

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

Non-tidal polar motion spectrum (from COMB02) by solar

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 by solar

Non-tidal length of day by solar spectrum for Mars

Semi-annual

Annual

Amplitude

10

20

15

5

0

Period (Earth year)

Non-tidal length of day by solar spectrum for Venus

diurnal

Amplitude

Core Effect ?

10

20

15

5

0

Period (Earth year)

117 days

Surface by solar Pressure

General circulation by solar

Global circulationEffect of the fluid by solar layer(s) on LODAnnual cycle

Wind term

Matter IB

Current term

Mass ocean

Wind term

Atm. pressure

Ice cap

Effect on Polar Motion by solar Annual cycle

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