INTERACTIVE SIMULATION OF DUST STORMS BY THE MarsWRF … · and air density. The relation of [7], which is based on low pressure wind tunnel measurements and theoretical considerations,

6. Renno, N. O., Burkett, M. L., and Larkin, M. P.: A simple thermodynamical theory for dust devils, J. Atmos. Sci., 55, 3244-3252, 1998.7. White, B. R.: Soil transport by wind on Mars, J. Geophys. Res., 84, 4643-4651, 1979.8. Petrosyan, A., et al., The Martian atmospheric boundary layer, Rev. Geophys., 49, RG3005, doi:10.1029/2010RG000351, 2011.9. https://en.wikipedia.org/wiki/Saltation_(geology)10. Wilson, R. J. and Richardson, M. I.: The martian atmosphere during the Viking mission, 1. Infrared measurements of atmospheric temperatures revisited, Icarus,

145, 555-579, 2000.11. Newman, C. E., Lee, C., Mischna, M. A., Richardson, M. I., Shirley, J. H.: An initial assessment of the impact of postulated orbit-spin coupling on Mars dust storm

variability in fully interactive dust simulations, Icarus, 317, 649-668, doi: 10.1016/j.icarus.2018.07.023, 2019.

Claus Gebhardt1, Abdelgadir Abuelgasim1, Ricardo Morais Fonseca2,3, Javier Martín-Torres1,2,4,6, Maria-Paz Zorzano5,2

1United Arab Emirates University, National Space Science and Technology Center, Al Ain, UAE, 2Luleå University of Technology, Group of Atmospheric Science, Luleå, Sweden, 3Masdar Institute of Science and Technology, Khalifa University, Abu Dhabi, UAE,

4Instituto Andaluz de Ciencias de la Tierra, Granada, Spain, 5Centro de Astrobiología (CSIC-INTA), Torrejon de Ardoz, Madrid, Spain6The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University, Japan

INTERACTIVE SIMULATION OF DUST STORMS BY THE MarsWRF GCM ON A 2°×2° GRID

IntroductionIn interactive dust mode, the MarsWRF General Circulation Model (GCM)

allows the user to explicitly simulate the Martian dust cycle. In this

configuration, dust is lifted from the surface by 2 mechanisms, dust devils

and near-surface wind stress. The lifted dust is injected into the Planetary

Boundary Layer, advected by the winds, and deposited back on the

surface. In the dust devil and near-surface wind stress parameterization

schemes, there are 3 tunable parameters that have to be adjusted by an

iterative approach. These parameters are resolution dependent, and have

been previously set up on a ~5°x5° grid [e.g. 1,2,11]. However, a finer

horizontal resolution is required for the model to better simulate fine-scale

wind features related to topography and associated dust lifting, and hence

give a more realistic representation of the observed dust cycle [3].

We present global model runs with interactive dust for a

considerably high horizontal resolution of 2°×2° in latitude and

longitude. The presented model runs aim at evaluating a potential

refinement of dust storm modelling from enhancing the model resolution to

a computationally level that is quite costly to date (for simplicity, an infinite

surface dust reservoir is considered). In addition, our model runs may

serve as a baserun for future modelling efforts achieving

mesoscale/microscale resolution within selected regions of interest by

applying the nesting technique (as has been done before withoutinteractive dust by [4]).

References

Basic Model SetupIn this study, the MarsWRF GCM was used. This model is the Martian

implementation of the Planetary Weather Research and Forecasting

Model [5]. The vertical grid has 45 levels with high resolution in the

Planetary Boundary Layer (PBL) region. The highest level is 120 km. The

presented model run spans 10 Martian Years (MYs). The first few years of

the run were discarded for reasons of the model spin-up.

The model was run globally with a horizontal resolution of 2°×2° in latitude

and longitude. The model topography is shown in Fig.1. It well represents

topographic gradients.

For non-dust parameters, the model setup was identical to the previous

study of [4]. These are

• Surface topography, albedo, and thermal inertia based on maps from

the Mars Global Surveyor (MGS),

• k-distribution radiative transfer model (KDM) with Non-Local

Thermodynamic Equilibrium (NLTE) adjustment to long-wave radiation

flux,

• a simplified CO2 microphysics scheme, and

• Medium Range Forecast (MRF) PBL scheme

Interactive DustIn the interactive dust mode, the exchange of dust between the surface and

atmosphere is controlled by 2 model schemes, one for dust devils and the

other for surface wind stress. These schemes require 3 input parameters:

1.) the dust devil lifting rate constant,

2.) the wind stress lifting threshold, and

3.) the wind stress lifting rate constant.

1.) is based on the assumption that dust devil activity is directly proportional

to the PBL thickness and the surface sensible heat flux [6]. For dust devils

imaged by the Mars Rover Spirit, see Fig.2.

2.) If the surface wind stress is in excess of this threshold, saltation and

horizontal dust flux start. The latter depends on the friction velocity, gravity,

and air density. The relation of [7], which is based on low pressure wind

tunnel measurements and theoretical considerations, is used. For an

illustration of wind stress saltation, see Fig.3.

3.) This is a constant of proportionality between the horizontal and vertical

dust flux by saltation.

Evaluation of Model PerformanceThe challenge is that the interactive dust parameters have to be determined

by a best-guess and trial-by-error approach. This makes such work a

computationally expensive and time-consuming process.

With dust storms driving variations of up to several tens of degrees Kelvin,

the mid-level atmospheric temperature is an appropriate indicator of the

model performance. To this end, comparisons are made against the

T15 temperature from MGS/TES and Viking/IRTM [10]. The model

T15 temperature is calculated as weighted average of its vertical

temperature profile, using IRTM weighting functions. It is further averaged

spatially over latitudes from 40°N to 40°S.

In Fig. 4, model T15 temperature is shown for a period of 10 MYs,

numbered as MY1 to MY11. Note that the 1st half of MY1 and the 2nd half of

MY11 were discarded. Based on the dust storm classification scheme of

[11], there are global dust storm events (GDEs) in MY 5 and MY10. The

condition in MY2, MY7, and MY9 is at the boundary between a possible

GDE and non-major dust storm activity. The latter is definitely the case in

MY1, MY3, MY4, MY6, and MY8.

Fig. 1: The model topography for the 2°×2° latitude longitude grid used.

Topographic gradients are well represented.

Fig. 2: Dust devils imaged by Mars Rover Spirit,

source: [8] Fig.3: Saltation, source: [9]

Fig. 4: T15 temperature from the model for 10 MYs (solid lines) compared

against MGS/TES and Viking/IRTM (black dashed line).

1. Newman, C. E. and Richardson, M. I.: The impact of surface dust source exhaustion on the martian dust cycle, dust storms and interannual variability, as simulated by the MarsWRF General Circulation Model, Icarus, 257, 47-87, doi: 10.1016/j.icarus.2015.03.030, 2015.

2. Shirley, J. H., Newman, C. E., Mischna, M. A., Richardson, M. I.: Replication of the historic record of martian global dust storm occurrence in an atmospheric general circulation model, Icarus, 317, 197-208, doi: 10.1016/j.icarus.2018.07.024, 2019.

3. Toigo, A. D., Lee, C., Newman, C. E., and Richardson, M. I.: The impact of resolution on the dynamics of the martian global atmosphere: Varying resolution studies with the MarsWRF GCM, Icarus, 221, 276-288, doi: 10.1016/j.icarus.2012.07.020, 2012.

4. Fonseca RM, Zorzano-Mier M-P, Martin-Torres J.: Planetary boundary layer and circulation dynamics at Gale crater, Mars. Icarus 302:537–559, doi: 10.1016/j.icarus.2017.11.036, 2018.5. Richardson, M. I., Toigo, A. D., Newman, C. E.: PlanetWRF: A general purpose, local to global numerical model for planetary atmospheric climate dynamics, J.

Geophys. Res., E09001, doi:10.1029/2006JE0025, 2007.

6. Renno, N. O., Burkett, M. L., and Larkin, M. P.: A simple thermodynamical theory for dust devils, J. Atmos. Sci., 55, 3244-3252, 1998.7. White, B. R.: Soil transport by wind on Mars, J. Geophys. Res., 84, 4643-4651, 1979.8. Petrosyan, A., et al., The Martian atmospheric boundary layer, Rev. Geophys., 49, RG3005, doi:10.1029/2010RG000351, 2011.9. https://en.wikipedia.org/wiki/Saltation_(geology)10. Wilson, R. J. and Richardson, M. I.: The martian atmosphere during the Viking mission, 1. Infrared measurements of atmospheric temperatures revisited, Icarus,

145, 555-579, 2000.11. Newman, C. E., Lee, C., Mischna, M. A., Richardson, M. I., Shirley, J. H.: An initial assessment of the impact of postulated orbit-spin coupling on Mars dust storm

variability in fully interactive dust simulations, Icarus, 317, 649-668, doi: 10.1016/j.icarus.2018.07.023, 2019.

LS

Results and Discussion

Fig.5: Top panel: Surface dust lifting by wind stress averaged over the 10 MY

period of the presented model run (in units of kgm-2 per 10 sols).

Middle panel: Percentage change of surface dust during the 10 MY period of

the presented model run (initially assuming a uniform surface dust cover of

100 kgm-2). For clarity, regions with zero dust change are blank.

Bottom panel: For the time of the presented model run, the total amount of

surface dust lifted by wind stress was calculated and area-weighted for each

model grid cell (it is part of the nature of infinite dust simulations that only few

grid cells account for the entire wind stress lifting). The red point alone is ca.

16% of the entire amount of lifted dust. The red/yellow points stand for ca. 50%,

the red/yellow/green points for ca. 99%, and the blue points for the rest.

All in all, the dust lifting patterns well represent western boundary currents and

low-level jets. Moreover, there are dust deposition regions with global extent.

One of the most pronounced dust deposition region is inside the Hellas Basin.

Conclusions1.) The existence and interaction of different major dust lifting regions at low

latitudes is responsible for (possible) GDEs of quite different strength.

2.) Dust lifting regions at the southern slopes of the Hellas and Argyre Basin

allow for significant dust storm activity early in the Martian Year (an example is

the curve for MY10 in Fig.4; dust storm activity is indicated by some

temperature rise of ca. 5K around solar longitudes of 190).

3.) Combined with other innovative approaches in dust storm modelling,

increased model resolution is a promising perspective for refining the

interannual variability of GDEs, both in strength and time.

4.) A more detailed study will follow in Gebhardt et al., in preparation.