The Diurnal and Seasonal Variation of Dust Aerosol as Observed by EMIRS
Khalid Badri, Mohammed Bin Rashid Space Centre, Dubai, UAE, M. D. Smith, NASA Goddard Space Flight
Center, Greenbelt, MD, United States, C. S. Edwards, Northern Arizona University, Department of Physics and
Astronomy, Flagstaff, AZ, United States, E. Altunaiji, Mohammed Bin Rashid Space Centre, Dubai, UAE, P. R.
Christensen, Arizona State University, School of Earth and Space Exploration, Tempe, AZ, United States, and the
EMIRS Team.

Introduction:
The Emirates Mars Mission (EMM) successfully
began the science phase on 23rd of May 2021 to
explore the dynamics of the Martian atmosphere on a
global scale (Amiri et al., 2022). The Emirates Mars
Infrared Spectrometer (EMIRS) instrument as seen in
figure 1, one of three instruments onboard EMM, is
an interferometric thermal infrared spectrometer
developed by Mohammed Bin Rashid Space Centre
(MBRSC) and Arizona State University (ASU)
(Edwards et al., 2021). The EMIRS instrument
collects spectral data from 6-100+ µm at 5 and 10
cm-1 spectral sampling, which is enabled by a
Chemical Vapor-Deposited (CVD) diamond beam
splitter and digital interferometer control electronics.

Figure 1: Emirates Mars Infrared Spectrometer
(EMIRS).
The EMIRS instrument is designed to
characterize the geographic, seasonal, and diurnal
variability of key characteristics of the red planet
such as atmospheric dust and water ice optical depth,
water vapor abundance, surface temperature, and
atmospheric temperature profiles on sub-seasonal
timescales. EMIRS observations provide full local
solar time coverage at multiple emission angles
providing data on these constituents over the entire
Martian disk. EMIRS observations will enhance our
understanding of the dust cycle on Mars and how

dust influences the current climate and atmospheric
dynamics on Mars.
Methodology:
EMIRS data is available at the EMM Science
Data Center website in which the global science
community can access and download the data set for
free
and
perform
their
own
analysis
(https://sdc.emiratesmarsmission.ae). In this paper the
variation of dust observed by EMIRS, including the
regional dust storm that occurred in January 2022
will be analyzed. Here, we present initial results of
the spatial, seasonal and diurnal variation of
retrievals of dust optical depth on a global scale.
These results also will aid in understanding the
relationship between the upper and lower
atmosphere, but also enhance the accuracy of models
about the Martian planet especially for time-variable
phenomena such as the atmospheric behavior due to
dust storms (Almatroushi et al., 2021).

Results for the Aphelion-Season Climatology
of Dust:.
Figure 2 below shows the seasonal and diurnal
variation of dust optical depth and includes retrievals
from the EMIRS observations taken between 24 May
2021 (Ls=49°) and 24 February 2022 (Ls=180°). The
gap between solar longitude of 100° to 120° is due to
solar conjunction, and times when the spacecraft had
to enter safe mode. The general dust distribution
during this period shows relatively clear conditions
with increasing dust as Mars is getting closer to the
Northern hemisphere autumn equinox when typically
the dust storm period begins at approximately
Ls=180°, however it is noticeable that there was a
regional dust storm earlier at Ls=153° as seen from
the sudden increase in dust optical depth in Figure 2
below.
Additionally, it is notable that the daytime local
time variation of dust during this season is relatively
small with no significant change diurnally unlike the
large changes observed seasonally. In addition, the
data presented here is only during the day time, in

which there is significant thermal contrast between
the dust and the atmosphere in order to accurately
retrieve results from the data, however there is work
being done on the night time retrievals.

optical depth at Ls=153°. The main concentration of
the storm was within the equatorial regions, with
some high optical depths in both the northern and
southern regions.

Figure 4: EMIRS Observation before Regional
Dust Storm.
Figure 2: Variation in Dust Optical Depth with
Solar Longitude and Local time
In Figure 2 it is noticeable that the dust optical
depth has decreased a bit after the regional dust storm
but still remains higher than it was before the dust
storm since the more recent data were taken closer to
the beginning of the dust storm season.

Figure 5: EMIRS Observation during Regional
Dust Storm.

Figure 3: Latitudinal Variation in Dust Optical
Depth with Solar Longitude
Figure 3 above, which gives the variation of dust
as a function of season and latitude, shows more
clearly the beginning and the end of the regional dust
storm that occurred in January 2022. The sudden
increase is clearly portrayed within the figure in dust

Figure 6: EMIRS Observation after Regional
Dust Storm.
As seen from the figures above, the high abundance
of the column integrated quantities of dust suggests a
regional dust storm that began between 90° and 180°
longitude. The dust storm was observed to begin in
the southern hemisphere and move northward
expanding to a regional size in approximately 11 to
12 days. After the active portion of the dust storm
ended, dust was transported to all longitudes
increasing the dust load over most of the planet. After
the dissipation of the dust storm as seen in figures 2
and 3, there remained a general increase in dust
optical depth throughout the regions which could
indicate that a lot of the dust that was lifted into the
atmosphere due to the active dust storm has not yet
completely settled out, and since the dust is still in
the atmosphere it relates to a higher optical depth. In
addition, the recent observations capture the
transition between the aphelion season with cooler
temperatures and less dust, and the perihelion season
with warmer temperatures and more dust lifted into
the atmosphere.

Future Work:
We will continue analyzing the seasonal, spatial,
and diurnal variations of dust using observations
from EMIRS, with particular attention to the
evolution of large dust storms. Addition work will be
done in order to have a better understanding of the
effect that dust storms have on other quantities
retrieved by EMIRS (such as atmospheric
temperatures, cloud opacity, and water vapor
abundance) as well as aiding in exploring one of the
main EMM science goals in further understanding the
connection between the upper and lower atmosphere.
References:
Amiri, H.E.S., Brain, D., Sharaf, O. et al. The
Emirates Mars Mission. Space Sci Rev 218, 4 (2022).
https://doi.org/10.1007/s11214-021-00868-x
Almatroushi, H., AlMazmi, H., AlMheiri, N.,
AlShamsi, M., AlTunaiji, E., Badri, K., ... & Young,
R. (2021). Emirates Mars Mission characterization of
Mars Atmosphere dynamics and processes. Space
Science Reviews, 217(8), 1-31.
Edwards, C.S., Christensen, P.R., Mehall, G.L. et
al. The Emirates Mars Mission (EMM) Emirates
Mars InfraRed Spectrometer (EMIRS)
Instrument. Space Sci Rev 217, 77 (2021).
https://doi.org/10.1007/s11214-021-00848-1