Complexities of modeled waterice clouds near Olympus Mons, Mars

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Complexities of modeled water-ice clouds near
Olympus Mons, Mars
Tim Michaels Southwest Research
Institute Boulder, Colorado, USA
Mars Water Cycle Workshop Paris, France 21-23
April 2008
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Brief model introduction

• MRAMS (Rafkin et al., 2001, Icarus Michaels et
  al., 2006, GRL)?
• Non-hydrostatic, finite-difference mesoscale
  regional model for Mars
• Initial state and BCs from NASA Ames Mars GCM

Experiment setup

• Three nested grids, with the third having a
  grid-spacing of 40 km
• 60 vertical levels, to 70 km above the MOLA
  areoid
• 8 dust bins (0.05 to 5 µm)?
• 18 water-ice aerosol bins (0.07 to 102 µm)
• Heterogeneous nucleation only
• All aerosols subject to diffusion, advection,
  and sedimentation
• All aerosols treated as radiatively active

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Clouds over Tharsis (Ls100)?
Portion of composite color MOC wide-angle imagery
(M23-006301)?
MRAMS (mesoscale model) water-ice cloud total
column opacity (400-800 nm), white shading model
topography, gray contours
Adapted from Michaels et al., 2006 (GRL)?
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Vertical cross-section
Day
Night
Vertical velocity, shaded cloud water-ice mass
mixing ratio, black contours water vapor mass
mixing ratio, green contours
Upslope flow, clear over caldera, water vapor
largely trapped by cloud particle formation
Downslope flow, extensive cloud deck, vertical
water vapor conduit
Adapted from Michaels et al., 2006 (GRL)?
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Mountain-induced vertical pumps
air
water / dust
water m.r. plumes at Z43 km
Water substance mass mixing ratio, shaded
topography, contoured
Illustrating net mass pump effect of
circulations associated with Olympus (dotted) and
Ascraeus Mons (solid)
Plumes at 43 km have an order of magnitude more
water substance than the surrounding environment.
The large-scale general circulation then widely
distributes this material.
Adapted from Michaels et al., 2006 (GRL)?
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Size distributions
Water-ice cloud particles tend to exhibit bimodal
size distributions Such bimodality appears to
be largely due to rapid, dynamical mixing of
populations Strong size sorting occurs above and
below the plume Modeled cloud particle radii and
relatively broad size distributions are
consistent with the telescopic observations of
Elysium Mons clouds by Glenar et al. (2003,
Icarus)?
grid-point
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Conclusions

• Rapid and deep (greater than the local boundary
  layer depth) vertical atmospheric circulations
  likely play an important role on Mars and its
  water cycle
• Such phenomena may occur in association with the
  great volcanoes of Mars, large crater rims and
  canyons, even strong atmospheric convergence
  zones
• Potentially exhibit complex (even
  counterintuitive) interactions between
  smaller-scale dynamics and time-of-day effects
• Earth Thunderstorm/cumulus updrafts ascending
  Hadley cell branch
• Mars These rapid, deep circulations ascending
  Hadley cell branch (?)?
• Aerosol particle populations associated with such
  circulations can exhibit complex behavior in time
  and space
• Implications for remote sensing retrievals near
  these phenomena, particularly with respect to
  assumptions about aerosol size and vertical
  distributions
• Implications for the minimum complexity needed
  by microphysical parameterizations on Mars (in
  order to achieve a satisfactory accuracy)?