High resolution general circulation
model experiments of the Martianatmosphere
Yoshiyuki O. Takahashi1,2,and coinvestigators[1] Center for Planetary Science[2] Kobe University

Purpose of this study• We perform medium and high resolution (∆x∼11-90km) experiments of Martian atmosphere by using ageneral circulation model (GCM)
1. to survey the small and medium disturbances in theMartian atmosphere,
2. to examine the effects of small and medium scaledisturbances on dust lifting.

•In the followings,–––

model description,
disturbances observed in the model,
dust lifting events observed in the model,

are presented.

Introduction: Example of 10 km resolution
experiment of the Earth’s atmosphereAn example of a global 3-hourly precipitation field (Ohfuchi et al., 2004)

Model description• Dynamics (AFES; Ohfuchiet al., 2004)– primitive equation system• Physics (Takahashi et al.,2003, 2006)– radiation (CO2, dust),– turbulent mixing (Mellorand Yamada, 1982)– thermal conduction in thesoil,– mass exchange between
atmosphere and polar cap,
– dust liftingparameterization with athreshold following
Newman et al. (2002),• dust devil parameterization
is not included.

Experimental setup• Resolutions– T639L96, T319L96, T159L96, T79L96• horizontal grid size ∆x∼11, 22, 44, 89 km• 96 vertical levels up to ∼90 km• Dust condition– “passive dust experiment”– Dust optical depth is fixed to be 0.2.

• Seasonal condition and integration period– 40 Mars days at northern fall season from an initial conditionof a snapshot of low resolution experiment• Sensitivity test experiment with uniform surface properties– In these experiments, surface orography is flat, and surface
albedo and thermal inertia are assumed to be constant.

• Experiments are performed on the Earth Simulator.

Zonal mean temperature and zonal windin the T639L96 experimentVorticity distribution at 4 hPa
T639L96 (grid size∼11 km)•

A lot of disturbances ranging from planetary scale to ∼10 km are represented.
––A lot of small scale vortices, which would be caused by convective motions in the model,
Local orography related circulations.

Orography-related disturbances around
Alba Patera, Elysium, and north of Hellas
Alba Patera at 18 LST• Orography-related
disturbances with horizontal
scales of orography.
– Clear diurnal variation isobserved.
– Interaction between the meanwind and mountain anddiurnally varying slope windaround the mountain would
cause these disturbances.

Elysium at 18 LST

north of Hellas at 0 LST

Vortices around Alba Patera
Composite plot of vorticity• Analysis indicates that this would be caused by– interaction between the mean wind and mountain (AlbaPatera),– diurnally varying slope wind around the mountain.

Comparison of vorticity distribution at 4 hPa
T639L96 (grid size∼11 km), T159L96 (∼44 km)
T639L96

T159L96• Low latitude small scale vortices– Horizontal size decreases with increasing resolution.
• Horizontal size does not seem to converge even in highest
resolution (∼11 km).

– Vortices appears earlier local solar time with increasing
resolution.

Vorticity distribution at 4 hPa
T639L96, No surface property variations• Modulation of small scale vortices by large scale disturbance.
• Organization of motion is not observed.

Dust lifting in the model• Intense dust lifting
events occur aroundfronts.
• Dust lifting associatedwith somecharacteristic
orography is alsoobserved.
• Small scale vortices
seem to contribute on
dust lifting too.

Dust lifting in the model with uniform
surface properties• Even without
orographic variation,
dust is lifted in theregion where small
scale vortices aregenerated.
• Intense dust liftingaround fronts seemto occur at thetiming when thesmall scale vortices
are generated.

Resolution dependence of global mean
dust flux• In both cases with andwithout surface property
variations, global mean
dust mass flux
increases withincreasing resolution.
• Dust mass flux in thecase with surface
property variation islarger than that in thecase without surface
property variations.
– Importance of orographyrelated circulation ondust lifting.

Resolution dependence of dust flux inlatitude bands• Dust flux is nearlysaturated in middle
and high latitude,
while it continues toincrease even withhighest resolution.

Latitude band used for analysis
Green : 60°S - 30°N
Blue : 90°S - 60°S
: 30°N - 90°N

Summary• High resolution GCM experiments of the Martian atmosphereare performed with the horizontal resolutions of T639L96,
T319L96, T159L96, and T79L96 (∆x∼11, 22, 44, 89 km).
• The results show following disturbances:– baroclinic waves with clear frontal structures,– orography-related disturbances,• medium scale lee vortices,• a lot of streaks with horizontal resolutions of tens of kilometers,– small scale vortices in low latitude.
• Modulation of these vortices are also observed.

• The horizontal size of small scale vortices has not converged
even with T639 horizontal resolutions. The relationship between
small vortices in the model and dust devils on real Mars isunclear.
• It is shown that small scale disturbances represented in themodel contribute to dust lifting significantly.
• In future, I would like to examine wave activity in the highresolution simulations.