DUST STORM OF MY28 EFFECTS ON WATER VAPOR IN THE SOUTH
POLAR REGION
C. W.S. Leung, Jet Propulsion Laboratory/Caltech, Pasadena, USA (cecilia.leung@jpl.nasa.gov), A. Pankine,
Space Science Institute, Boulder, USA (apankine@SpaceScience.org), L.Tamppari, Jet Propulsion Laboratory/Caltech, Pasadena, USA, M. Giuranna, Istituto Nazionale di Astrofisica, Veneto, Italy, A. Trokhimovskiy,
Space Research Institute of the Russian Academy of Sciences (IKI RAS), Moscow, Russia
Introduction:
Understanding the current water cycling in and
out of the polar regions is key to unraveling the climatic history of Mars. Atmospheric circulation provides the main mechanism for the transport of
around one-third of the mass of water in and out of
the polar caps and in the annual exchange between
the northern hemisphere to the southern hemisphere
and back through the cross-equatorial Hadley circulation [1, 2]. Meanwhile up to ~ 1010-1011 kg of water is deposited every year at the surface near the
south pole due to the permanent cold trap for water
vapor maintained by the presence of a residual CO2
ice layer near the south pole [3,4]. Placing limits on
the modern-day transport of water into the poles, and
the water deposition rate in the south polar region
(SPR) will allow us to better comprehend its important role in the mass balance and the modern-day
stability of the polar ice cap.
A number of recent studies [5, 6, 7, 8, etc.] have
highlighted the strong coupling between the water
and dust cycles particularly during global dust
storms (GDS), as the radiative effects of dust can
dramatically alter atmospheric and surface temperatures, leading to significant modifications in the
global circulation, water vertical distribution, waterice cloud saturation conditions, as well as the rate of
water escape.
The goal of this project is to test the hypothesis
that Martian Global Dust Storms (GDS) can significantly affect the water cycle in the lower atmosphere. As part of the test we compare the evolution
of the water vapor in the Southern Region of Interest
(SRI) during the second half of MY28 and MY29.
For the purposes of this project, we define the SRI to
extend over 9040S. For this work, we make use
of datasets from the SPICAM IR and PFS/LW instruments aboard the Mars Express (ME) spacecraft,
which conducted near simultaneous observations of
the Martian atmosphere [9, 10].
Water cycle in the Southern Region of Interest:
Figure 1 illustrates the water cycle in the SRI
during the second half of a typical year without a
GDS. Figure 1 shows the evolution of SPICAM IR
water vapor abundances (scaled by surface pressure
to avoid topographic effects) in the latitudinal band
9080S as a function of Ls. SPICAM IR observations [9] were obtained at local times of
10:0015:00h for Ls=180250, and 01:0010:00h

& 15:0024:00h for Ls=250360. Vapor abundances generally increase during southern spring and
early summer (Ls=180280) reflecting southward
transport of vapor by atmospheric circulation and
sublimation of seasonal surface frost. A temporary
decrease in abundances at Ls=240255 coincides
with a regional dust storm [11]. Vapor abundances
reach their maximum values (~30 pr-μm) in this
band at Ls~280295 after the seasonal polar cap
completely disappears. Abundances start to decline
after Ls~295.

Figure 1. SPICAM IR zonally averaged scaled
water vapor abundances in latitudinal band
9080S for MY29 Ls=180360. Error bars
indicate scatter of data within the band.

Figure 2 shows a polar map of SPICAM IR
scaled water vapor abundances in MY29 Ls=280290, at the time when highest annual abundances
were observed at the South Pole. This map shows
that vapor abundances generally increase towards the
pole.
Similar behavior of the water vapor in the SRI is
observed in the PFS/LW data [10]. Local times of
PFS/LW observations are similar to SPICAM IR
times. Figure 3 shows the evolution of the zonally
averaged PFS/LW water vapor abundances retrieved
from data collected at approximately the same times
and locations as the SPICAM IR data. Small systematic differences between the two datasets can be
attributed to the differences between the two retrieval approaches and is generally within the uncertainty
of the retrieval (~20%).
Spatial distribution of PFS/LW water vapor in

the SRI during MY29 Ls=280-290 shown in Figure
4 is generally similar to the SPICAM IR distribution
(
Figure 2), except for more frequent appearances
of high vapor abundances near the South Pole.

Figure 4. Polar map of PFS/LW scaled water
vapor abundances in MY29 Ls=280290. Thin
contours are MOLA topography.
Figure 2. Polar map of SPICAM IR scaled water
vapor abundances in MY29 Ls=280290. Thin
contours are MOLA topography.

The GDS started around Ls~260 and the dust
optical depth did not return to pre-storm levels in this
band until Ls~310. At the peak of the storm
(Ls~270290) average dust opacities in this band
were close to 2. In contrast, the southward transport
of dust into the SRI was limited, as illustrated in
Figure 6, which shows dust opacity in the latitudinal
band 9080S. Here dust opacities increase to a
value slightly higher than 1 at the peak of the storm
(Ls~270), and quickly return to pre-storm levels (by
Ls=280290).

Figure 3. PFS/LW zonally averaged scaled water
vapor abundances in latitudinal band 9080S
for MY29 Ls=180360.
Global Dust Storm of MY28:
A rare Martian GDS occurred in MY28 [12].
Figure 5 illustrates the evolution of the dust optical
depth during the MY28 GDS in the latitudinal band
6050S. The dust optical depth is from SPICAM
IR dataset, and represents THEMIS dust observations [13] scaled to the wavelength of 1.4 μm [9] and
by surface pressure, to remove the effects of topography.

Figure 5. SPICAM IR zonally averaged scaled
dust optical depth at 1.4 μm in latitudinal band
6050S for MY28 Ls=180360.

Figure 6. SPICAM IR zonally averaged scaled
dust optical depth at 1.4 μm in latitudinal band
9080S for MY28 Ls=180360.
Figure 7 shows evolution of the SPICAM IR water vapor abundances in the latitudinal band
9080S before, during and after the GDS of
MY28. During most of the spring the abundances
increase quantitatively similar to the way they increased in MY29. The onset of the GDS at Ls~260
is marked by the sharp decrease in water vapor
abundances that continues until Ls~290. After that
time abundances remain approximately constant
until Ls~320 and begin decline afterwards. Abundances remain lower than in MY29 even after dust
opacities return to pre-storm levels after
Ls~280290. Scaled dust distribution in SRI during that time is shown in Figure 8. Areas south of
latitude ~75S are clear of dust. Water vapor abundances over these areas (Figure 9) are noticeably
lower than during the same time in MY29 (
Figure 2).

Figure 8. Polar map of SPICAM IR scaled dust
optical depth at 1.4 μm in MY29 Ls=290300.

Figure 9. Polar map of SPICAM IR scaled water
vapor abundances in MY28 Ls=290300.

Figure 7. SPICAM IR zonally averaged scaled
water vapor abundances in latitudinal band
9080S for MY28 Ls=180360.

PFS/LW abundances behave qualitatively similar
to SPICAM IR in MY28 (Figure 10). PFS/LW abundances increase during summer, similar to the way
they do in MY29. During this time PFS/LW abundances are higher than the SPICAM IR abundances
at the same time, but there are fewer PFS/LW observations and the scatter of the retrieved vapor abundances in the band is relatively large. The onset of

the GDS at Ls~260 is marked by a decline in abundances that generally continues until the end of the
summer (Ls~360). The difference between vapor
abundances between MY28 and MY29 is much
smaller in PFS/LW retrievals than in SPICAM IR
retrievals. The comparison between different
PFS/LW years is difficult because there are significantly fewer PFS/LW retrievals in MY28. Figure 11
shows a polar map of the PFS/LW water vapor
abundances in the SRI in MY28 Ls=290300.
Abundances near the South Pole, where dust opacities are low, are similar to the PFS/LW abundances
in MY29 at this time and are higher than the
SPICAM IR abundances at the same time in MY28.

Figure 10. PFS/LW zonally averaged scaled water
vapor abundances in latitudinal band 9080S
for MY28 Ls=180360.

Figure 11. Polar map of PFS/LW scaled water
vapor abundances in MY28 Ls=290300.

Conclusion: Water vapor abundances retrieved
by SPICAM IR and PFS/LW in MY28 and MY29
show qualitatively similar behavior in the SRI in
MY28 and MY29. Both datasets reflect a strong
response of the water vapor cycle to the GDS of
MY28. SPICAM IR abundances decline sharply at
the onset of the GDS and remain lower than in the
year without a GDS (e.g. MY29) even when the dust
opacity decreases to pre-storm levels. This behavior
may reflect the disruption of the southward transport
of water vapor by atmospheric circulation by the
GDS. PFS/LW abundances in MY28 also decline at
the onset of the storm, but low number of retrievals
and the large scatter in the values of retrieved abundances make comparison to MY29 difficult.

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