Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.s12a1186s&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #S12A-1186
Physics
5409 Atmospheres: Structure And Dynamics, 5430 Interiors (8147), 7255 Surface Waves And Free Oscillations
Scientific paper
It has been suggested that the excitation source of the Earth's background free oscillations (BFO) is the random force exerted on the surface due to atmospheric disturbance (e.g. Kobayashi and Nishida, 1998). The previous studies also suggested a possibility for detection of the BFO on Mars. In this study we estimate the excitation level of the Mars' BFO by applying an atmospheric excitation theory to the Mars' atmospheric pressure data obtained in the Mars Pathfinder mission. The atmospheric excitation theory used here is based on the seismic normal-mode theory and it can well predict the observed power spectrum of the Earth's BFO (Fukao et al. in press). The theory uses a power spectrum of the surface atmospheric pressure and a correlation length of atmospheric disturbance as the inputs. Since no direct observation of the correlation length is available to date, a correlation length should be assumed to calculate the theoretical power spectrum. A weakly frequency-dependent correlation length, about 1 km at 1 mHz, was assumed for Earth. Using a simple theory of atmospheric disturbance, Kobayashi and Nishida (1998) estimated the excitation level of the Mars' BFO. A more sophisticated theory predicts values of 102 Pa2s and 2 km for the pressure power at 1 mHz and the correlation length, respectively, for Mars. Using these values and eigenfunctions calculated from the Mars model of Sohl and Spohn (1997), we obtain the theoretical excitation level of about 0.5*E-18 m2/s3, which is an observable level with a high-sensitivity broadband seismometer installed at a very quiet site. Surface atmospheric pressure on Mars was measured with a maximum resolution of 0.25 μbar in the Mars Pathfinder mission (Schofield et al. 1997). We analyze records for 5 Martian days and calculate an averaged power spectrum. It exhibits the well-known f-2 dependence at frequencies between 0.5 and 4.0 mHz, but a value of 10 Pa2s at 1 mHz, which is an order of magnitude smaller than the theoretically predicted value. Using this spectrum and assuming a correlation length of 2 km, we obtain the excitation level of about 10-19 m2/s3, which seems too low to observe. We can obtain an observable excitation level when assuming a correlation length of 10 km, but such a long correlation length seems to be unlikely. If a value of 10 Pa2s at 1 mHz is typical for the atmospheric disturbance on Mars, it is very hard to observe the Mars' BFO.
Kobayashi Nami
Mitani C.
Nishida Kouzou
Suda Naoki
No associations
LandOfFree
Theoretical Calculation of Mars' Background Free Oscillations does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Theoretical Calculation of Mars' Background Free Oscillations, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Theoretical Calculation of Mars' Background Free Oscillations will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1892431