Tropical and orographic clouds and their association with dust aerosols
B. K. Guha1, J. Panda2, C. Gebhardt1, Z. Wu3, A. S. Arya4. 1National Space Science and Technology Center,
UAE University, Al Ain, UAE (bijayguha@uaeu.ac.ae). 2Department of Earth and Atmospheric Sciences, National Institute of Technology Rourkela, Odisha, India. 3School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai, Guangdong, China. 4Space Applications Centre, Indian Space Research Organization, Jodhpur
Tekra, Ahmedabad, India.

Abstract:
Dust and water ice have an intricate relationship,
where dust particles may impact the water ice both
dynamically and microphysically [1, 3, 6]. The dynamical relationship between dust and water ice is
emphasized in several studies, which is not valid for
the dust-cloud microphysical interaction, and most of
the previous studies assumed homogenous nucleation
[2, 5]. The microphysical interaction between dust
and water ice enables water vapor saturation at comparatively lower altitudes with larger particle sizes,
primarily within -10–30°N latitudes during the aphelion period. Therefore, we have analyzed the evolution of the tropical cloud belt (TCB) within northern
spring and summer (solar longitude (LS) ~45–135°)
using the observations from Mars Climate Sounder
onboard Mars Reconnaissance Orbiter [4]. A northward evolution of the cloud belt is observed starting
from LS ~76°, which is the peak phase of the TCB.
This variation does not show any noticeable match
with the air temperature. However, a possible influence from the upper-tropospheric (~18–35 km altitude) dustiness is observed, which significantly correlates with the TCB’s northward evolution. The
mechanism observed is supported by the amplitude
of migrating semidiurnal tide (SMD) as a proxy of
dust forcing and the estimated upper tropospheric
dust-driven energy from the density-scaled opacity
(Figure 1). Both of these variables and the column
water ice opacity showed an apparent northward
movement of their maximum values within the three
phases of the TCB.
Furthermore, the orographic clouds being a part
of TCB shows a strong association with the highaltitude dustiness. However, this association is only
observed in the case of haze clouds during the second half of the year (LS ~225–315°), and it seems
more prominent for the Arsia Mons orographic
clouds compared to Olympus Mons. MarsWRF
model simulations suggested a dynamical influence
of dust-laden vertical transport during the perihelion
season, which is insignificant over Olympus Mons
and the nearby region.

References:
[1] Clancy, R. T., et al. (2003). Journal of Geophysical Research: Planets, 108(E9).

[2] Guha, B. K., et al. (2021). Advances in Space
Research, 67(4), 1392-1411.
[3] Heavens, N. G., et al. (2018). Nature Astronomy,
2(2), 126-132.
[4] Kleinböhl, A., et al. (2009). Journal of Geophysical Research: Planets, 114(E10).
[5] Navarro, T., et al. (2014). Journal of Geophysical
Research: Planets, 119(7), 1479-1495.
[6] Smith, M. D. (2004). Icarus, 167(1), 148-165.
Figure:

Figure 1. Latitudinal variation of the (a) zonal mean
upper tropospheric dust driven energy input (m2) at
10–40 km altitude, (b) column water ice opacity averaged for MY 29 – 33, and (c) amplitude of migrating semidiurnal tide (K).