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Atmospheric angular momentum variations of Earth, Mars and Venus .

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 .

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  1. 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;

  2. Introduction External forcing Orogenesis Erosion Post glacial rebound Tectonics Topographic coupling Electromagnetic coupling Mantle convection Geodynamo tensions frictions Hydrology Atmospheric dynamics

  3. 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

  4. Pressure Friction Gravitation Interaction between the Earth and the atmosphere

  5. 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

  6. 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 ?

  7. Physical Properties

  8. Atmospheric Circulation Gierasch 2002 Svedhem 2007

  9. 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)

  10. 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)

  11. AAM Variations (Earth)

  12. 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.

  13. AAM Variations (Venus)

  14. LOD Variations ∆LODTotal= ∆LODPressure+∆LODWind Mars Venus

  15. 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.

  16. 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

  17. Angular Momentum Density

  18. Time variation of Ps Venus Mars 0 day < t < 1 day 0 day < t < 117 days

  19. 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.

  20. Effect of dust storms on Mars’s rotation LOD PM

  21. Torque between Mars and its fluid layer Pressure torque

  22. Derivative of the topography

  23. Pressure torque

  24. Torque between Mars and its fluid layer Gravitational torque

  25. Gravitational torque

  26. Torque between Mars and its fluid layer Friction torque

  27. Torque approach Pressure torque Gravitational torque Friction torque

  28. Annual axial torque

  29. 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.

  30. 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

  31. 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

  32. 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

  33. Annual equatorial torque

  34. Non-tidal length of day spectrum for Mars Semi-annual Annual Amplitude 10 20 15 5 0 Period (Earth year)

  35. Non-tidal length of day spectrum for Venus diurnal Amplitude Core Effect ? 10 20 15 5 0 Period (Earth year) 117 days

  36. Surface Pressure

  37. Time-averaged Zonal Winds Mars Venus

  38. Time variation of Ps Venus Mars 0 day < t < 687 days 0 day < t < 117 days

  39. Axial AAM Pressure Latitude

  40. General circulation Global circulation

  41. Effect of the fluid layer(s) on LODAnnual cycle Wind term Matter IB Current term Mass ocean Wind term Atm. pressure Ice cap

  42. Effect on Polar MotionAnnual cycle

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