FIRST ATTEMPT TO RETRIEVE A MARS ATMOSPHERIC WIND MAP FROM
EARTH, USING VLT/UVES DURING THE 2018 GLOBAL DUST STORM.
P. Machado [1,2], H. Valido [1, 2], G. Gilli [3,1], A. Cardesin-Moinelo [4,1], F. Brasil [1,2], J. E. Silva [1,2],
[1] Instituto de Astrofisica e Ciencias do Espaco, Lisbon, Portugal (machado@oal.ul.pt), [2] Faculdade de Ciencias
da Universidade de Lisboa, Lisbon, Portugal, [3] Instituto de Astrofisica de Andalucia (IAA-CSIC), Granada, Spain,
[4] European Space Astronomy Centre, Spain.

Abstract
This work presents ground-based wind velocity measurements of Mars during the 2018 global dust storm
using Doppler velocimetry techniques based on observations made with the Ultraviolet and Visual Echelle
Spectrograph (UVES) at the European Southern Observatory’s Very Large Telescope (VLT) facility in Chile.
This instrument’s high resolution ( R ∼100 000) allows
for the dust cloud velocity to be measured, by computing the Doppler shift induced in the Fraunhofer lines
(in the λ of 420-1100 nm) in the solar radiation that is
backscattered in the dust suspended in the Martian atmosphere, by the motion of that same dust, with an average
error of approximately 5 ms−1 . This allows us to sound
Mars’ middle atmosphere during a global dust storm and
obtain latitudinal wind profiles and a first approach of a
planetary wind map at the altitude level sounded, i.e. the
altitude level where the optical depth reaches the unity.

1972). Some of the consequences that increased dust
loading imposes on the thermal state of the atmosphere
are related with the warming of the atmosphere’s layers as a direct consequence of the increased dust optical
depth. Airborne dust absorbs and scatters visible radiation which acts to heat itself and its surroundings. Furthermore, the heating of the atmosphere creates pressure
gradients which in turn lead to winds. The dusty season
on Mars has a much more vigorous circulation - the mass
flux of the Hadley circulation can even double (Haberle
et al., 1993).

Introduction
The purpose of this research project is to successfully
apply and validate a new approach to investigate Mars’
middle atmosphere wind velocities from ground-based
observations. This is the first time that a Doppler velocimetry method based on observations made in the
visible and ultraviolet wavelength range has been employed to study the Martian atmosphere.
Global dust storms are complex stochastic events
that can drastically alter the atmospheric dynamics. During such events, dust can be lifted to heights above 50
km across all latitudes and longitudes, increasing the
optical depth form on the sand, and consequently, the
heating rates strengthen the Martian circulation. The
processes that allow for the development of global dust
storms are poorly understood. Furthermore, the cut-off
mechanisms that spur the end of these storms are also
without consensus and may even vary from storm to
storm. These storms usually develop in the southern
hemisphere during southern Summer and Spring (Ls ≈
180◦ - 360◦ ), however, the 2018 storm started developing in the northern hemisphere on Ls ≈ 185◦ (SánchezLavega et al., 2019).
The martian atmosphere is extremely sensitive to the
amount of dust in the atmosphere (Gierasch and Goody,

Figure 1: Topographic region on Mars covered by the
VLT/UVES survey along our run of observations during the
Martian Global Dust Storm on 2018.

Global dust storms are unique to Mars and are,
perhaps, the most spectacular atmospheric event taking place anywhere in the Solar System. These storms
induce thermodynamic responses throughout the whole
atmosphere however, their occurrence is unpredictable
and shows inter-annual variability, and despite the massive development our understanding of Mars has suffered over the last 50 years, these storms are still viewed
as stochastic events, and the issue of their year-to-year
variability remains largely unresolved.
One could see the evidence that Global dust storms
do strengthen the atmospheric circulation, however, due
to the low mass of the Martian atmosphere, the winds
carry little momentum. Their characterisation is nonetheless crucial, as they are critical to the Martian climate,
and it is important to study the atmospheric role of the
energy input due to the infrared radiation absorption by

Final Results of Doppler Velocimetry Winds on Mars’ Atmosphere
the dust grains while in atmospheric suspension.
These storms can lift enough dust into suspension
to dramatically increase the opacity of the atmosphere
for several months, as was the case of the major global
dust storm observed in 2018. A consequence example
is the recent ’demise’ of NASA’s Opportunity Rover which was solar powered and did not survived the 2018
global dust storm. These storms are also believed to be
electrically charged, which can pose a serious threat to
any operational electronic devices. Furthermore, recent
findings suggest that such storms may have played an
important role in Mars’ loss of water (Vandaele et al.,
2019, Fedorova et a., 2020).
Since surface winds are generally too weak to lift
dust particles, sand particles saltation is the chief contributor to the suspension of dust. By being greater in
size these particles are easier to lift, however when lifted
they tend to saltate and upon their return to the surface,
they impart additional momentum onto the dust, allowing for its lifting (Mackwell et al., 2013), enhancing a
reinforced positive feed-back mechanism that increases
substantially the amount of dust particles in atmospheric
suspension. Direct suspension may also play a role, particularly in locations where sand is not abundant (Kahre
et al., 2017).
Global dust storms and Martian dust cycle are among
the more complex and least-understood events related to
Mars’ climate. These events cover large fractions of
the planet with optically thick dust (τvisible >3) they can
even envelop the entire planet. Global storms are rare
and stochastic in nature - occurring in one out of three
years (R. Zurek and J. Martin, 1993) - as their interannual variability is poorly understood (R. M. Haberle,
1986). There have been eight confirmed global dust
storms observed (1956, 1971-1972, 1973, 1977, 2001,
2007, 2009 and 2018; Kahre et al., 2017; R. Haberle
(2015); Sànchez-Lavega et al.,2019). All of these events
initiated during the aphelion season (southern spring and
summer) when the insolation is near peak values and the
circulation is most vigorous.

Observations and Method
Unlike Venus, Mars’ atmosphere is very transparent in
the visible and ultraviolet ranges and the radiation in
those wavelength ranges that is back-scattered in the
atmosphere is negligible which precludes the application
of our method. However, during global dust storms, the
opacity of the atmosphere increases and allows for the
scattering of enough light in the suspended dust in the
middle atmosphere for the application of our method to
be feasible.
The Doppler velocities were retrieved using the Doppler
velocimetry technique, developed and fine-tuned at Widemann et al. 2008, Machado et al. 2012, 2014, 2017,
2021 and Gonçalves et al. 2020, for the case of Venus.

Figure 2: Scheme with the slit positions of the observations in
relation to Mars, as seen from VLT at the time of the observations.

This technique was also adapted for dynamic studies
upon Saturn (Silva et al., in preparation).
The adaptation of our Doppler velocimetry method
for the case of Mars atmospheric studies, took into account the geometry of our observations. Spherical geometry was used to locate the observations within the
planet, as seen from Earth at the time of each observation, and compute the de-projection factors for each
point of the slit and for each exposure, in order to deproject the radial Doppler velocities from the observer’s
(Earth) line-of-sight.
The rotation velocity’s contribution to the overall
Doppler shift was removed by computing and subtracting the rotation velocity at each point on Mars sounded
by the spectroscopic slit, that was done for all the positions surveyed on Mars. Furthermore, the contributions
made to the total shift by the Young effect were evaluated and deemed negligible under the specific geometry
of our observations.
The wind velocities retrieved from the motion of
the dust particles in atmospheric suspension, during the
2018 Global Dust Storm on Mars, were computed and
we will present the output of this work.

Results and Discussion
The scope of this work is to study the behaviour of
Mars’ middle atmosphere during a global dust storm
using ground-based observations made with VLT-UVES
and Doppler velocimetry techniques, for the first time,
to complement observations of orbiter instruments. The
success and validation of the application of this method

REFERENCES

Figure 3: Raw Doppler shift retrieved at each position sensed
along the spectroscopic slit (VLT/UVES).

to the atmosphere of Mars may provide a new, unique
way to investigate the Martian atmosphere during dust
storms.
The intent is to contribute to a better understanding
of the circulation during planet-encircling dust events.
We measured the wind velocity and its spatial variability, through high-resolution spectroscopy and Doppler
velocimetry. The observations were made with the highresolution spectrograph UVES at ESO’s Very Large
Telescope (VLT) in the visible wavelength range.

each pixel sounding the planet through the spectroscopic
slit were obtained simultaneously) wind measurements
using visible Fraunhofer lines scattered at Mars’ dust
hazes, which allows spatial wind variability studies and
will make possible to obtain a latitudinal profile of the
wind along with the cited global dust storm and a wind
map of the dust storm as a function of the latitude and
local time over the planet as seen from Earth.
After the success of this exploratory project, we intend to deeper explore Mars’ atmosphere dynamics using this tool. The main developments are two-fold: we
will sound Mars from the ground for several successive
days and we will prepare a coordinated observation campaign in order to observe in the visible and in the infrared
domain at the same time, that will allow us to study different altitudes in a synchronous way. Finally, it would
be relevant to have access of space-based coordinated
observations which will allow us to better estimate the
atmospheric altitudes sensed.
Acknowledgements
We acknowledge support from the Portuguese Fundação
Para a Ciência e a Tecnologia (ref. PD/BD/ 128019/2016,
ref. 2021.05455.BD. and ref. PTDC/FIS-AST/29942/
2017) through national funds and by FEDER through
COMPETE 2020 (ref. POCI-01-0145 FEDER-007672).
We acknowledge support from ESA Faculty Science
Exchange MWWM - Mars Wind and Wave Mapping
project and EXPRO RFP/3-17570/22/ES/CM.
References
[1] Esposito, L. et al., Venus III, Bougher, Hunten and
Philips Eds., Sp. Sci. Ser., Arizona U. Press, pp. 415,
1997.
[2] Fedorova et al., 2020. DOI: 10.1126/ science.aay 9522 https://science.sciencemag.org /content/367/6475/297.

Figure 4: Example of retrieved wind velocities of dust particles in atmospheric suspension. The VLT/UVES spectroscopic slit was aligned with Mars’ equator at the centre of the
planetary disc, as seen from Earth.

Conclusions and Prospects
The main goal of this research line is, therefore, to provide direct instantaneous (the velocities retrieved for

[3] Gierasch, P.J., and Goody, R.M. (1972, Jan).The effect of dust on the temperature of the Martian atmosphere. Journal of Atmospheric Sciences, 29, 400402.
doi:10.1175/15200469(1972)029<0400: TEODOT>
2.0.CO2
[4] Gilli G. et al. 2017, Icarus, Vol. 281, pp. 55-72.
[5] Haberle, R.M., et al. (1993, Feb). Mars atmospheric
dynamics as simulated by the NASA Ames General Circulation Model. 1.The zonal mean circulation.
Journal of Geophysics Research, 98(E2), 30933123.
doi: 10.1029/92JE02946
[6] Haberle, R.M. (1986). Inter annual variability of
global dust storms on mars. Science, 234(4775), 459461. doi:10.1126/science.234.4775.459

REFERENCES

[7] Haberle, R. (2015). Solar system/sun, atmospheres, evolution of atmospheres planetary atmospheres:
Mars. In G.R. North, J. Pyle,
and F. Zhang(Eds.), Encyclopedia of atmospheric sciences. Oxford:
Academic Press.
doi.org/10.1016/B9780123822253.003121
[8] Kahre, M., Murphy, J., and Haberle, R. (2006, 06).
Modeling the Martian dust cycle and surface dust
reservoirs with the nasa ames general circulation
model. Journal of Geophysical Research, 111. doi:
10.1029/2005JE002588
[9] Kahre, M.A., Murphy, J.R., et al., The atmosphere
and climate of mars (p. 295Ñ337). Cambridge University Press. doi 10.1017/9781139060172.010
[10] Leovy, C.B., Zurek, R.W., and Pollack, J.B.
(1973, Jan). Mechanisms for Mars dust storms.
Journal of Atmospheric Sciences, 30, 749762.
doi:10.1175/15200469(1973)
[11] Maattanen, A., et al. (2010,Oct). Mapping the
mesospheric CO2 clouds on Mars: MEx/OMEGA
and MEx/HRSC observations and challenges for
atmospheric models. Icarus, 209(2), 452-469.doi:
10.1016/j.icarus.2010.05.017
[12] Machado, P.(2014). Dynamics of Venus’ Atmosphere: Characterization of its Global Circulation
with Doppler velocimetry.
[13] Machado, P., Luz, D., Widemann, T., Lellouch, E., Witasse, O.(2012,Sep). Mapping zonal
winds at Venus’ cloud tops from ground-based
Doppler velocimetry. Icarus, 221(1), 248-261.doi:
10.1016/j.icarus.2012.07.012
[14] Machado, P., Widemann, T., Luz, D., Peralta, J. (2014,Nov). Wind circulation regimes at
Venus’ cloud tops: Ground-based Doppler velocimetry using CFHT/ESPaDOnS and comparison with
simultaneous cloud tracking measurements using
VEx/VIRTIS in February 2011. Icarus, 243, 249-263.
doi:10.1016/j.icarus.2014.08.030
[15] Machado, P., et al. (2017,Mar). Venus
cloud-tracked and doppler velocimetry winds
from
CFHT/ESPaDOnS
and
Venus
Express/VIRTIS in April2014. Icarus, 285, 826.doi:10.1016/j.icarus.2016.12.017
[16] Machado, P., et al., Two Altitude Levels Venus’
Atmospheric Dynamics from Cloud-Tracking (Akatsuki and Venus Express), Doppler Techniques

(Ground-Based Observations) and Comparison with
Modelling, 2021.
[17] Mackwell, S.J., Simon Miller, A.A., Harder, J.W.,
and Bullock, M.A. (2013). Comparative Climatology of Terrestrial Planets. doi:10.2458/azurua press
9780816530595
[18] Montabone, L., et al. (2015, May). Eight-year climatology of dust optical depth on Mars. Icarus, 251,
65-95.doi:10.1016/j.icarus.2014.12.034
[19] Moreno, R., et al. (2009, Jun). Wind measurements
in Mars’ middle atmosphere: IRAM Plateau de Bure
interferometric CO observations. Icarus, 201(2), 549563.doi:10.1016/j.icarus.2009.01.027
[20] Pollack, J.B., et al. (1979,Jun). Properties and effects of dust particles suspended in the Martian atmosphere. Journal of Geophysics Research, 84, 29292945.doi:10.1029/JB084iB06p02929
[21] Pollack, J.B., et al. (1990,Feb). Simulations of the
general circulation of the Martian atmosphere.1. Polar processes. Journal of Geophysics Research, 95,
1447-1473. doi: 10.1029/JB095iB02p01447
[22] Sanchez-Lavega ,A., et al. (2019).The onset and
growth of the 2018 Martian global dust storm.
Geophysical Research Letters, 46(11), 6101- 6108.
doi:10.1029/2019GL083207
[23] Vandaele, A.C., et al. (2019, Apr). Martian dust
storm impact on atmospheric H2O and D/H observed
by ExoMars Trace Gas Orbiter. Nature, 568 (7753),
521-525. doi:10.1038/s41586-019-1097-3.
[24] Widemann, T., Lellouch, E., Donati, J.-F.
(2008,Aug). Venus Doppler winds at cloud
tops observed with ESPaDOnS at CFHT.
Planetary Space Science,
56(10),
13201334.doi:10.1016/j.pss.2008.07.005
[25] Zurek, R., J., Martin, L. (1993, 03). Inter annual variability of planet-encircling dust storms
on Mars. Journal of Geophysical Research, 98.
doi:10.1029/92JE02936
[26] Zurek, R.W.(2017). Understanding Mars and its
atmosphere. In R.M. Haberle, R.T. Clancy, F. Forget,
M. D. Smith, R.W. Zurek (Eds.), The atmosphere and
climate of Mars (p. 3—19). Cambridge University
Press. doi 10.1017/9781139060172.002