Geoscience Reference
In-Depth Information
Table 3.2
Surface wind measurements
Planet, location
Wind speed
Dataset, height
Reference
Venus, Venera-9
0.4 ± 0.1 m/s
Cup anemometer 1.3 m
49 min, 0.4 Hz
Avduevskii et al. (1976)
Venus, Venera-10
0.9 ± 0.15 m/s
Cup anemometer 1.3 m
1.5 min, 0.4 Hz
Avduevskii et al. (1976)
Mars, Viking-1
Up to 20 m/s, usually \10 m/s
Hot Wire anemometer, 1.6 m
45 sols, hourly
Hess et al. (1977)
Mars, Viking-2
Up to 20 m/s, usually \10 m/s
Hot Wire anemometer, 1.6 m
1070 sols, hourly
Hess et al. (1977)
Hot Wire anemometer
a
, 1.1 m
Mars, Pathfinder
\5-10 m/s
*1 m/s at night
Schofield et al. (1997)
Mars, Pathfinder
7-10 m/s, usually less
Images of windsocks at 0.33, 0.62 and 0.92 m
Sullivan et al. (2000)
Mars, Phoenix
2-10 m/s
Images of tell-tale at 1.6 m
7600 measurements over 150 sols
Holstein-Rathlou et al. (2010)
Titan, Huygens
0.6 m/s
0.3 m/s
\0.25 m/s
Doppler tracking at 300-1000 m
Parachute shadow V*10 m
Cool-down of probe \1m
Folkner et al. (2007)
Karkoschka et al. (2008)
Lorenz (2006)
a
The Mars Pathfinder anemometer suffered from inadequate superheating such that the windspeed calibration was inapplicable during strongly
convective conditions when temperatures fluctuated severely
Fig. 3.8
Plots of the number of days on which the strongest
wind gust exceeds a given threshold at a weather station near Great
Sand Dunes National Monument. Note that the x-axis covers a
narrower range in the linear plot at left. Extending it to the same
extent as the right (logarithmic) plot would not show anything
useful and on a linear plot the frequency would be indistinguishable
from zero. At the right, a logarithmic plot exposes the very rare
strongest gusts
horseshoe vortices, can be similarly tied to impact craters on
Mars. Artificial topography can be introduced (see
Chap. 23
)
such as dune fences can be introduced to prevent deposition.
Topography also plays an important role in shaping
winds due to heating, through so-called slope winds. Gen-
erally, solar-heated slopes will see uphill flow, and cooler
slopes will see downhill flow. These patterns, influenced by
the orientation of the slope relative to the sun, may be a
major influence on Venus (although we have very little data
on Venus winds), simply because the other factors are so
small. On Earth and Mars, another prominent example is the
katabatic flow that develops off the polar caps, where cold,
dense air runs downhill; the Olympia Undae dunefield
around the Martian north polar cap is undoubtedly affected
by this pattern.
On top of these steady-state patterns, there is seasonal
and diurnal forcing. Diurnal variation on Venus and Titan,
with their dense, optically-thick atmospheres, is modest
compared to Mars, whose thin atmosphere warms up and
cools rapidly. Seasonal variation is almost nonexistent on
Venus, because it has almost zero obliquity.
Finally, rotating fluids have a dynamical mind of their
own. Characteristic internal dynamical modes or waves can
be excited by the forcings above, and these modes are a
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