use of mesoscale and microscale results to improve the mars climate database near-surface...

Use of Mesoscale and Microscale Results

to Improve the Mars Climate Database

Near-Surface Variability Model

E. Millour, F. Forget, A. Spiga

April 6, 2011

LMD/TAS-I Progress Meeting

Purpose and scope of this study• In MCDv4.3.EXM.1 was added a near-surface variability

scheme (added to the “large scale” perturbation case), meant to account for the (GCM) sub-grid scale spatial variability due to unresolved sub-grid topographic features.

• In this work we critically review that scheme and its applicability to the Meridiani ExoMars landing site.

• To evaluate the GCM unresolved spatial variability (GCM mesh of the order of 100km), we use concurrent mesoscale (mesh of the order of 10km) and microscale (mesh of the order of 10m) simulations.

GCM

[-1950m:-1400m]

Mesoscale

[-2150m:-1400m]

What is meant by “spatial variability”Profiles from the Mesoscale area corresponding to the GCM “Meridiani” mesh (longitude [11.3:5.5]°W , latitude [3.8:0]°S)

The variability’s intensity and vertical extension change with time of day (and is most intense near the surface).

Diurnal evolution of the variability

• Two distinct dynamical regimes, day-time and night-time, with “pauses” in the variability when switching from one to the other.

Diurnal evolution of the temperature deviation

Daytime regime

Daytime regime

Nighttime regime

Nighttime regime

Tau=2 case (overall similar behaviours/trends for other tau)

Diurnal evolution of the variability

Variations in amplitude for different values of dust opacity

Diurnal Maxima of temperature RMSin the Meridiani area

• For all cases, the mesoscale variability is greater near the surface and the vertical extension of the (topographic-related) variability is of the order of 4-6 km.

Spatial variability not in the mesoscaleDiurnal evolution of temperature RMS, for tau=0.5 LES simulation

• With the same analysis as for the mesoscale or GCM domain, the spatial variability in the LES simulations can be evaluated.

• That variability is found to peek near the top of the developing boundary layer and near the surface.

• Overall, the LES variability is less than 2K.

Variability already present in the MCD• Some (limited) spatial variability is already present in the unperturbed MCD outputs (due to interpolation between values known at GCM grid points).

Mesoscale (unperturbed high-res.) MCD

Variability already present in the MCD

Mesoscale MCD

• As expected, there is more spatial variability in the mesoscale simulations than in the MCD (without perturbations, in high resolution mode).

Variability already present in the MCD

• The near-surface added variability scheme in MCD v4.3.EXM.1:

• A random Gaussian perturbation of 1% RMS of unperturbed value is added to surface pressure.

• A random Gaussian perturbation of temperature is added, with a vertically varying RMS:

RMS(z) = Tpert_level .( 1.0 – tanh[6.(z-zmid)/zdelta] ) / 2

zmid = 6000 m,

zdelta = 4000 m,

Tpert_level = 3 K

Synthesis on variability, for MeridianiMesoscale LES (at most 2K RMS)

MCD (unperturbed) MCD near-surface variability scheme

What is already in the MCD is already quite conservative (for Meridiani)

• To test if what is found about variability in Meridiani (and likewise “flat” regions), we look at another case, a cratered region with more salient topographic features.

Variability in other regions of Mars

Mesoscale

(-3000m:-400m)

GCM

(-1050m:-450m)

Variability in other regions of MarsMesoscale MCD

Variability in other regions of MarsMesoscale MCD

• Clearly, for this cratered case, the current additional near-surface variability scheme in the MCD does not suffice.

Conclusions

• From this study, we find that:– For the Meridiani ExoMars landing site region (and

other likewise essentially flat areas), the near-surface variability scheme already implemented in the MCD (since v4.3.EXM.1) is quite conservative (from an engineering point of view).

– This is not true when there are more unresolved (at GCM level) salient topographic features. Adapting the current scheme to make it applicable to all locations on Mars would require more quantitative studies.