TAS-I/ESA Progress Meeting – 11 th July 2012 Design of a new global dust storm scenario for GCM simulations L. Montabone, E. Millour, F. Forget

Background Recent improvements of the global climate model related to dust:  New SW radiative transfer code for dust (Toon vs Fouquart)  New dust optical properties (Wolff vs Ockert-Bell)  Interactive dust scheme (i.e. 3D transport of dust mass mixing ratios and number of particles). A new global dust storm scenario for the GCM should be designed in accordance to the above improvements

Background Goals of a global dust scenario for GCM simulations:  It should be an extreme, yet realistic, scenario for a planet-encircling dust storm  It should bracket the extreme temperatures retrieved during real planet-encircling storms (MY 25 and MY 28 in particular)  It should take into account model uncertainties on dust properties such as single-scattering albedo, and on spatial distribution and value of total opacity. We use a spatially and temporally fixed high total opacity combined with uncertainty optimization. We carry out validation with retrieved observations.

Dust Storm Scenario The new dust storm scenario: An extreme case of fixed high opacity (τ=5) combined with “darker dust” properties (i.e: lower single scattering albedo ω with respect to nominal) to cope with uncertainties on dust radiative properties. We explored interactive and non-interactive dust, and ω=90%-95% of nominal case Further investigations needed to design the optimal case.

Observations Mars Global Surveyor / Thermal Emission Spectrometer MY 25 global dust storm (retrievals in Meridiani Planum) L s = [190, 220] Lon = [-24, +12] Lat = [-20, +16]

1D simulations Simulations with the 1D (physics-only) version of the GCM Conrath dust distribution in the vertical Effects of top-of-the-dust parameter for several opacities L s = 200°, Lat = 0°, Lon = 0°, No diurnal tide

1D simulations Toon (left) vs Fouquart (right) SW radiative scheme

1D simulations Wolff (left) vs Ockert-Bell (right) SW dust optical properties

1D simulations SW Wolff dust optical properties and Fouquart radiative tranfer Single scattering albedo nominal (left), reduced to 95% in the blue region of the SW band (centre), and reduced to 95% in the whole SW band (right)

1D simulations SW Wolff dust optical properties and Fouquart radiative tranfer Single scattering albedo nominal (left), reduced to 90% in the blue region of the SW band (centre), and reduced to 90% in the whole SW band (right)

1D simulations From the results of the 1D simulations, good candidates for an optimal dust storm scenario are:  Total opacities τ = 5-8  Ockert-Bell SW dust optical properties or  Slightly darker SW single scattering albedo (ω), i.e. reduced to 95% of its nominal value (Wolff)

3D simulations Simulations with the full 3D GCM, interactive dust, fixed total opacity  We extract from the simulations the thermal profiles corresponding to each single MGS/TES profile in Meridiani (L s = [190, 220], Lon = [-24, +12], Lat = [-20, +16])  We average these profiles for both the model simulations and for TES, and compare averages as well as min and max values for the envelope.  We calculate the differences between model temperature and TES temperature at each TES pressure level, and carry out statistics.

3D simulations Interactive (left) vs Non-interactive (right) dust (τ=5)

3D simulations Total opacity τ=5 (left) vs τ=8 (right)

3D simulations Wolff (left) vs Ockert-Bell (right) dust optical properties (τ=5)

3D simulations SW Wolff dust optical properties (τ=5) Single scattering albedo nominal (left), reduced to 95% in the blue region of the SW band (centre), and reduced to 95% in the whole SW band (right) ω = 100% ω = 95% blue ω = 95% all SW

3D simulations SW Wolff dust optical properties (τ=5) Single scattering albedo nominal (left), reduced to 90% in the blue region of the SW band (centre), and reduced to 90% in the whole SW band (right) ω = 90% blue ω = 90% all SW ω = 100%

3D simulations SW Wolff dust optical properties Single scattering albedo nominal and τ=5 (left), ω reduced to 95% in the whole SW band and τ=5 (centre), ω reduced to 95% in the whole SW band and τ=8 (right) τ = 5 τ = 5, ω = 95% τ = 8, ω = 95%

3D simulations SW Wolff dust optical properties (Toon radiative transfer) τ=5 Lon = [-24, +12] Lat = [-20, +16] Ls = [190, 220] Pseudo-altitudes ~ 11, 22, 32, 40 km

3D simulations SW Ockert-Bell dust optical properties (Toon radiative transfer) τ=5 Lon = [-24, +12] Lat = [-20, +16] Ls = [190, 220] Pseudo-altitudes ~ 11, 22, 32, 40 km

3D simulations SW Wolff dust optical properties (Toon radiative transfer) τ=5 ω = 95% at SW Lon = [-24, +12] Lat = [-20, +16] Ls = [190, 220] Pseudo-altitudes ~ 11, 22, 32, 40 km

3D simulations Lon = [-24, +12] Lat = [-20, +16] Ls = [190, 220] SW Wolff dust optical properties τ=5

3D simulations Lon = [-24, +12] Lat = [-20, +16] Ls = [190, 220] SW Ockert-Bell dust optical properties τ=5

3D simulations Lon = [-24, +12] Lat = [-20, +16] Ls = [190, 220] SW Wolff dust optical properties τ=5 ω = 95% at SW

3D simulations: Zonal means Interactive vs Non-interactive dust (τ=5) Interactive Non- Interact. Non- Interact. minus Interactive

3D simulations: Zonal means Wolff vs Ockert-Bell dust (τ=5) Wolff Ockert-Bell Ockert-Bell minus Wolff

3D simulations: Zonal means Wolff nominal vs Wolff with ω=95% at SW (τ=5) ω =100% ω = 95% ω = 95% minus ω =100%

Design and validation of the new GDS scenario GDS MCDv4 (left) vs new GDS Ockert-Bell dust (right), τ=5 Validation with binned TES obs Daytime Night time Lon = [-180, +180] Lat = [-50, +50] Ls = [190, 230] P = 106 Pa (~18 km)

Design and validation of the new GDS scenario GDS MCDv4 (left) vs new GDS Wolff ω=95% at SW (right), τ=5 Validation with binned TES obs Daytime Night time Lon = [-180, +180] Lat = [-50, +50] Ls = [190, 230] P = 106 Pa (~18 km)

Design and validation of the new GDS scenario Comparison of different dust scenarios from the MCD at Meridiani

Conclusions: the new GDS scenario for GCM  We use a spatially and temporally fixed high total opacity combined with uncertainty optimization.  A total dust opacity τ = 5 is satisfactory for the new Toon SW radiative transfer (there are saturation effects above this value)  The use of Ockert-Bell dust optical properties is equivalent to using Wolff optical properties with a few percent uncertainty on the single scattering albedo at SW  The detailed comparison and validation with retrieved TES observations (profile-to-profile) show that an optimized GDS scenario can be obtained with τ = 5 and ω=95% of the nominal Wolff value at all solar wavelengths.