Atmospheric rotational effects on Mars based on the NASA Ames general circulation model: Angular momentum approach

Abstract

[1] The NASA Ames general circulation model has been used to compute time series for atmospheric products of inertia and relative angular momentum terms. Model outputs were used also to compute time series representing the inertia terms due to CO 2 condensation and sublimation on the surface of Mars. Some of these terms were used to generate time series representing the forcing functions for the equatorial components of the linearized Liouville equations of rotational motion. These equations were then solved numerically for a period of a Martian year (669 sols) to obtain a time series for the position of the rotation pole on the surface of Mars. The results of the investigation indicate that mass variation in the atmosphere is as important as the formation and sublimation of ice caps on the surface of the planet. Numerical integration of the equations of rotational motion yields pole displacements as large as 30.9 cm (ice caps solution), 39.5 cm (atmospheric effects), or 33 cm (both effects combined). Fourier analysis of the time series corresponding to the equatorial components of pole displacement for the ice caps solution as well as the atmospheric effects solution shows that the (1/3)-annual harmonic has the largest coefficient in three cases, with magnitudes in the 7-9 cm range. Fourier analysis of the equatorial components of polar motion for the combined solution yields main harmonics of 5.12 cm (x), (1/3)-annual and 7.50 cm (y), annual.

Rotation of the Terrestrial Planets

“…The main atmospheric forcing is at seasonal frequencies, resulting in largest wobble amplitudes of about 10 mas at 1, 1/2, and 1/3 year, the exact values depending on the atmospheric and internal structure models used (Chao and Rubincam, 1990;Defraigne et al, 2000;Sanchez et al, 2004;Van den Acker et al, 2002;Yoder and Standish, 1997). The annual and semiannual wobble amplitudes, respectively, 13.6 and 11.2 mas, observationally determined by Konopliv et al (2006) agree remarkably well with the theoretical values of 12.0 and 9.8 mas, respectively, of Van den Acker et al (2002).…”

“…The annual and semiannual wobble amplitudes, respectively, 13.6 and 11.2 mas, observationally determined by Konopliv et al (2006) agree remarkably well with the theoretical values of 12.0 and 9.8 mas, respectively, of Van den Acker et al (2002). The fact that the amplitude at 1/3 year is expected to be of the same order of magnitude as the amplitudes at 1 and 1/2 year is most likely due to the resonance with the Chandler wobble with a period of about 200 days (eqn [47], Dehant et al, 2003;Konopliv et al, 2006;Sanchez et al, 2004;Van Hoolst et al, 2000b;Yoder and Standish, 1997;Zharkov and Gudkova, 2005).…”

“…For the Earth, the Chandler wobble is the largest polar motion signal and is thought to be excited mainly by ocean bottom pressure fluctuations (Gross, 2000). Because Mars has no oceans and the Chandler wobble period for Mars (P CW % 200 days) is far from the annual and semiannual periods where most excitation power of the atmosphere is expected Sanchez et al, 2004), the CW is not expected to have a large amplitude. From the spectral amplitude in the pressure recordings of the Viking landers near the CW period, Yoder and Standish (1997) estimated a CW amplitude of about 10 mas and possibly as large as 50 mas with ice loading excitation included.…”

The Rotation of the Terrestrial Planets

“…The main atmospheric forcing is at seasonal frequencies, resulting in largest wobble amplitudes of about 10 mas at 1, 1/2, and 1/3 year, the exact values depending on the atmospheric and internal structure models used (Chao and Rubincam, 1990;Yoder and Standish, 1997;Defraigne et al, 2000;Van den Acker et al, 2002;Sanchez et al, 2004). The large amplitude at 1/3 year is most likely due to the resonance with the Chandler wobble with a period of about 200 days (eqn [46], Yoder and Standish, 1997;Van Hoolst et al, 2000b;Dehant et al, 2003;Zharkov and Gudkova, 2005;Konopliv et al, 2006).…”

“…The contribution of the atmospheric pressure is about twice that of the contribution of the ice caps. This effect is proportional to the Love number k 2 , for which Sanchez et al (2004) used the value determined by Yoder et al (2003), who showed that this value is a strong indication that the core is, at least partially, liquid. The NASA Ames GCM has been used by Sanchez et al (2004) to estimate polar motion series.…”