Seasonal Variations of Snow Depth on Mars D. E. Smith, M. T. Zuber, G. A. Neumann

Supplementary Material

Supplemental Figure 1. Altimetric profile of Mars taken on MGS orbit 10220 1999 MAR 27 00:12 UTC over the south polar cap, 87°S, at L_s = 115.5°. The profile shows reflections from terrain (black plus signs) and atmosphere (colored ellipses). Atmospheric returns, which represent condensation of CO₂ snow over the martian south polar cap, are colored black, red, green, and blue, to represent triggers by MOLA matched filter channels 1-4 (12, 41). Ellipse size is scaled to the strength of the returned signal. Atmospheric returns were detected at altitudes as high as 18 km during polar night. Vertical exaggeration 100:1.

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Supplemental Figure 2. Examples of annuli of topography (red) and median surfaces (blue) at latitudes 85°N, 82°N, 75°N and 60°N. Note the significant differences in the topography of different annuli that nonetheless result in similar patterns of seasonal elevation change.

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Supplemental Figure 3. Residuals representing the difference between topography and the median surface for the annuli in Web Fig. 2. Large residuals are a consequence of local topography and were smoothed.

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Supplemental Figure 4. compared to that predicted by a General Circulation Model simulation (26). At high latitudes the observed elevation change and GCM are in reasonable agreement, with the maximum at most latitudes occurring slightly earlier than predicted by the GCM. At lower latitudes the phase of the seasonal signal is not as well constrained, but there is evidence for transient CO₂ accumulation at these latitudes during the summer.

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Supplemental Figure 5. Condensed mass as a function of latitude in northern and southern hemispheres. The black arrow corresponds to the edge of the north polar residual ice cap. Note the greater accumulated mass on the north polar cap compared to that at corresponding southern latitudes. The dashed lines represent an extrapolation to correct for deposited mass that we may not have measured equatorward of latitude 60° (19).

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Supplemental Table 1. MOLA single-shot topography errors.
Error source	Error (cm)*
MGS orbital altitude	~90
Altimeter range error	37.5
Range walk#	Up to 100
Altimeter threshold change&	20-30
Uneven sampling of topography	Up to 30 cm
*Errors analyses are presented in G. A. Neumann, D. D. Rowlands, F. G. Lemoine, D. E. Smith, M. T. Zuber, J. Geophys. Res. 106, 23753 (2001) and D. E. Smith et al., J. Geophys. Res. 106, 2,689 (2001). #Accumulated effect of laser pulse width saturation, dusty atmosphere, surface albedo changes. &A one-time change due to detection threshold adjustment on July 1, 1999 (Ls = 163°).

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  Animation showing the seasonal deposition of CO₂ as measured by MOLA altimetry. The amplitude of the elevation change signal is greatly exaggerated for illustrative purposes.