FREQUENCY OF DUST STORMS IN THE WESTERN ARCADIA PLANITIA: COMPARISON WITH REANALYSIS DATA
K. Ogohara, Faculty of Science, Kyoto Sangyo University, Kyoto, Japan (ogohara@cc.kyoto-su.ac.jp)

Introduction:
The Arcadia Planitia (Fig. 1) is one of the most
outstanding dust storm zones in the northern midlatitudes on Mars. Wang, Zurek, & Richardson
(2005) and Guzewich et al. (2015) showed that the
northern mid-latitude dust storms tended to occur in
three regions, the Acidalia, the Arcadia, and Utopia.
Kulowski, Wang, & Toigo (2017) reported that most
of dust storms observed in the three regions were
categorized into “plume-like dust storm”, which is
apparently different from dust storms that tend to be
observed in the low-latitudes and the southern midlatitudes. Mars. Wang, Zurek, & Richardson (2005)
additionally revealed that the dust storm frequency
got lower near the northern winter solstice in the
regions and was associated with the eddy activity in
the northern mid-latitudes. The eddy activity they
mentioned means the baroclinic instability and the
associated frontal system. Although I agree with
their suggestion, a correlation between dust storm
initiations and the phase of the baroclinic eddies is a
key to understand the initiation mechanisms of the
dust storms if the baroclinic eddies contribute to initiations of the dust storms. That is whether dust
storms tend to break out in the trough, ridge, or
boundary between them. In this study, the phase of
the baroclinic waves suitable for dust storm initiations in the northern mid-latitudes are investigated.

Data and method:
I used reflectance data from red and blue bands
(575–675 nm and 400–450 nm, respectively) images
acquired by Mars Orbiter Camera onboard Mars
Global Surveyor (MGS/MOC), limiting our investigation to the region centered around 180◦E−40◦N
(the west of the Arcadia Planitia, WAP). We examined 800 × 600-pixel (40◦ × 30◦) subsets of the full
size MOC wide angle camera (MOC-WA) image
swathes. The subsets are centered at 180◦E− 40◦N
and were extracted from the MOC-WA images taken
outside the global dust storm period in Mars Year
(MY) 25. Fig. 2 shows four examples of MOC red
images including dust storms. Dust storms in the
western Arcadia Planitia were listed based on the
automated segmentation algorithm for Martian dust
storms developed by Ogohara & Gichu (2022). After
the automated detection of dust storms, false positives were removed by visually inspecting all the
detection results. The three-dimensional distributions
of the atmospheric temperature, zonal wind, meridional wind, geopotential height, surface pressure, and
the surface stress at the initiation date of the dust
storms are based on the background data (short-term
forecast from analysis) included in the Ensemble
Mars Atmosphere Reanalysis System (EMARS)
(Greybush et al., 2019). The variables on a few pressure levels were interpolated from the original vertical coordinate, the hybrid coordinate of σ-p.

Figure 1 Mars topography distributed through Mars Climate Database 5.0. A black rectangle indicates the target region, the western Arcadia Planitia.

Figure 4 The seasonal variability of dust storm
area in km2.

Figure 2 Examples of (left) MOC red images
including dust storms and (right) areas covered
by dust storms. White areas in the right column are dust storms determined subjectively
by the author.

Figure 3 The seasonal variability of dust storm
frequency in WAP observed by MGS/MOC in
MYs 24, 26, and 27. The Blue bars indicate the
total number of images, and the red bars indicate the number of images capturing dust
storms.
Dust storm frequency in WAP: Fig. 3 shows
the seasonal variation of dust storm frequency in
WAP and is consistent with Wang, Zurek, &

Richardson (2005). During the northern mid-winter
season, dust storm activity in WAP temporally decreases. In contrast, the seasons before and after that
season show high dust storm frequency. As Wang,
Zurek, & Richardson (2005), such seasonal variability of dust storm frequency in WAP is reminiscent of
the relationship with the activity of baroclinic waves
in the mid-latitudes, which also paused in the northern mid-winter (Lee, Richardson, Newman, &
Mischna, 2018; Lewis et al., 2016).
Fig. 4 shows the seasonal variability of dust
storm size in km2. Some regional dust storms, which
were defined as events larger than 1.6 x 106 km2 by
(Cantor, James, Caplinger, & Wolff, 2001) were
detected in this study. Area of the regional dust
storms was underestimated because they were
trimmed by the edges of the image subsets. The
mean sizes of dust storms are not largely different
between the seasons before and after the northern
winter solstice.
Relationship with the synoptic scale phenomena:
By extracting from EMARS the threedimensional distributions of several variables (e.g.,
temperature, wind) at the date and time closest to the
dust storm observation time and calculating their
time averages, a typical synoptic scale atmospheric
state at the initiations of the dust storms can be derived. Your abstract should not be more than 4 pages
long. Fig. 5 demonstrates the composite means of
zonal wind, meridional wind, the surface pressure,
and the surface stress anomalies from the zonal
means during the season from the northern late winter in MY24 to the next northern spring equinox.
Anomalies in zonal and meridional winds shown in
the figure are derived on the 3 hPa pressure level.
WAP is located at the center of each panel of the
figure. The low frequency components and the diurnal tides were attenuated in advance by the running
means at each grid point with the full widths of one
month and one sol, respectively.
It is easily found in Fig. 5 that, at the dust storm

spreads.

Figure 5 The composite means of (a) zonal
wind, (b) meridional wind, (c) the surface pressure, and (d) the surface stress anomalies at the
dates and times of the dust storm initiations.
initiations, WAP tends to be in the southerly wind
and low-pressure phase of the baroclinic waves. Area with negative anomaly in zonal wind is elongated
from the northeast to the southwest. The surface
stress tends to be high especially in the northern part
of WAP. In any case, it can be seen that dust storms
in the WAP tend to occur at the southern end of the
latitudinal range where the baroclinic eddies are active.
Discussions and conclusions: Fig. 5 seems to
imply the synoptic scale atmospheric conditions typical to the dates and time of the dust storm initiations.
However, considering that the typical period of the
baroclinic waves is a few sols on Mars, Fig. 5 may
contain non-negligible uncertainty. It is widely
known that MGS could observe WAP only once
every sol, ~14LT. All of dust storms investigated in
this study were recorded as if they all broke out
around 14LT. This means that there is an uncertainty
of one sol in the onset time of the dust storms, and if
the period of the baroclinic waves is two sols, this
corresponds to an uncertainty of half a wavelength.
Then, dust storms in WAP are not necessarily more
likely to occur in the low-pressure and southerly
wind phase. More frequent observations are needed
to better clarify the relationship between dust storm
onsets and the phase of the baroclinic waves. In addition, it is necessary to verify that reanalysis data is
reliable so that it can be used for such studies, for
example, by trying to use the analysis data instead of
the background data or by investigating ensemble

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