PRELIMINARY RESULTS OF ATMOSPHERIC PARAMETERS VARYING
WITH LT AROUND VOLCANOES FROM PFS-MEx OBSERVATIONS
P. Wolkenberg, Istituto Nazionale di Astrofisica (INAF), Istituto di Astrofisica e Planetologia Spaziali (IAPS),
Rome, Italy (paulina.wolkenberg@inaf.it), M. Giuranna, D. Grassi, Istituto Nazionale di Astrofisica (INAF),
Istituto di Astrofisica e Planetologia Spaziali (IAPS), Rome, Italy, A. Spiga, Laboratoire de Météorologie
Dynamique, IPSL, Sorbonne Université, Paris, France, A. Cardesin-Moinelo, D. Merritt, J. Marin-Yaseli de
la Parra, European Space Astronomy Center, Madrid, Spain,

Introduction:
We present a new type of observations (scan
mode) to study atmospheric parameters varying with
LT over volcanoes in the Tharsis region. Scan orbits
are measured by the Planetary Fourier Spectrometer
(PFS) across the track of Mars Express spacecraft.
We focus on observations from the southern summer
season in MY 35. In order to improve fits between
modeled and observed spectra, a correction on surface pressures was introduced. We found a hot air
close to the top of Olympus while the cold air is observed at 40 – 50 km of altitude. As a result, potential temperatures are almost constant from 15 to 30
km of altitude. Thus, the very deep vertical mixing
layer occurs there. Atmospheric thermal fields can be
used to study the planetary boundary layer and local
circulation around volcanoes. The depth of the planetary boundary layer can be estimated from a behavior
of atmospheric temperatures. It turns out that the
depths of the planetary boundary layer are larger
over the Tharsis than over the other regions [1].
Here, we report the LT variations of dust and water
ice opacities along with atmospheric and surface
temperatures. In the future we will investigate the
behavior of the planetary boundary layer with LT
and thus the local circulation around volcanoes by
means of atmospheric temperatures obtained from
the PFS observations.
Methodology:
The observations are measured across the track of
Mars Express spacecraft orbits. Thanks to the observations, PFS aboard the Mars Express can measure
radiation from the atmosphere over regions at different longitudes but similar latitudes so different local
time zones. This way, we analyze LT variations of
vertical temperature profiles, total column dust, water ice opacities and surface temperatures. Atmospheric parameters such as vertical temperature profiles, total dust, water ice opacities and surface temperatures are retrieved from the long-wavelength
channel of PFS [2]. The retrieval is performed for
spectra from 300 to 1000 cm-1. Because of noisy
spectra near 250 cm-1 and 1000 cm-1 we constrain our
spectral range to 300 – 900 cm-1 to check the quality
of fit between modeled and observed. For this purpose, the mean absolute percentage error (MAPE) is

calculated in the latter spectral range. This spectral
range includes absorption bands by CO2, dust and
water ice. Eventually, dust and water ice opacities
are weighted by the PFS field of view (FOV). We
found that around volcanoes MAPEs were as large as
7% during the daytime and 30% during the night.
This means that the model does not match well to
observations. We notice an inappropriate fit mainly
in the wings of the CO2 absorption band due to overor underestimated pressures. Thus, a correction of
our retrieval code on surface pressures helped a lot in
obtaining better fits. Surface pressures are necessary
to determine a vertical pressure grid for a retrieval
from each spectrum. Orbits in scan mode are performed where the spacecraft is quite far away from
the pericenter at altitudes above around 2000 km.
Regarding this, the PFS field of view (FOV) is larger
than at the pericenter which is very important when
the spacecraft flies over volcanoes. Pressure variations are very large along the slope of volcanoes.
Thus, we calculated the average of surface pressures
from the whole PFS FOV and introduced into the
retrieval procedure. It turned out that the model fitted
better to observed spectra for orbits performed at
high spacecraft altitudes. MAPEs averagely reduced
to 2 – 4% during the daytime around volcanoes.
Results:
An example of preliminary results is presented in
Figure 1 after the correction on surface pressures for
orbit 21216. Figure 2 represents thermal fields with
dust and water ice opacities before the correction for
the same orbit.

Fig.1. Thermal fields after the correction on surface
pressures. MAPE is plotted as yellow ‘+’. Black and
red lines are water ice and dust opacities, respectively.

highest sounding point of Olympus close to the surface while the cold air is observed at 40-50 km of
altitude. The planetary boundary layer has around 10
km of depth. In future we will then study the planetary boundary layers around volcanoes for different
LTs derived from atmospheric temperatures by
means of potential temperatures and their derivatives.

Fig.2. Thermal fields before the correction. MAPE is
plotted as yellow ‘+’. Black and red lines are water
ice and dust opacities, respectively.
Figure 1 and 2 present two different thermal structures over volcanoes. The correct version is given in
Fig.1. Changes of thermal structures are observed
over Olympus with respect to Fig.2. The hot structure is observed over the highest sounding point of
Olympus. While the cold air is found at 40 – 50 km
of altitude.

Fig.3. Surface temperatures along the orbit 21216.

Fig.4. Potential temperatures along the orbit 21216.
Figure 3 and 4 present surface temperatures along the
track of the same orbit (21216) and potential temperatures. Surface temperatures increase with LT and
southward (Fig.3) as expected. Potential temperatures are almost constant from the top of the volcano
up to 30 km (Fig.4). Thus, we conclude that the atmosphere over Olympus is in the neutral stability.
Thereby, the vertical mixing layer occurs with a
depth of around 10 km.
Conclusions:
We presented the example of scan orbit measured
by PFS. For this orbit, we noted the hot air over the

Acknowledgements:
The PFS experiment has been built at the “Istituto
di Astrofisica e Planetologia Spaziali” (IAPS) of the
“Istituto Nazionale di Astrofisica” (INAF) and is
currently funded by the Italian Space Agency (ASI)
in the context of the Italian participation to the
ESA’s Mars Express Mission (Grant ASI/INAF
n.2018-2-HH.0)
Bibliography:
[1] Hinson D.P. et al., Icarus, 326, (2019), 105 –
122. [2] Grassi, D. et al., (2005). Planetary and
Space Science, 53 (10), 1017–1034.