Vertical distribution of dust in the Martian atmosphere during northern spring and summer: High-altitude tropical dust maximum at northern summer solstice

Abstract

[1] The vertical distribution of dust in Mars' atmosphere is a critical unknown in the simulation of its general circulation and a source of insight into the lifting and transport of dust. Zonal average vertical profiles of dust opacity retrieved by Mars Climate Sounder show that the vertical dust distribution is mostly consistent with Mars general circulation model (GCM) simulations in southern spring and summer but not in northern spring and summer. Unlike the GCM simulations, the mass mixing ratio of dust has a maximum at 15-25 km over the tropics during much of northern spring and summer: the high-altitude tropical dust maximum (HATDM). The HATDM has significant and characteristic longitudinal variability, which it maintains for time scales on the order of or greater than those on which advection, sedimentation, and vertical eddy diffusion would act to eliminate both the longitudinal and vertical inhomogeneity of the distribution. While outflow from dust storms is able to produce enriched layers of dust at altitudes much greater than 25 km, tropical dust storm activity during the period in which the HATDM occurs is likely too rare to support the HATDM. Instead, the lifting of dust by mesoscale circulations over topography, pseudomoist convection due to the solar heating of dust, and scavenging of dust by water ice are all possible drivers of the HATDM.

The impact of surface dust source exhaustion on the martian dust cycle, dust storms and interannual variability, as simulated by the MarsWRF General Circulation Model

“…Rafkin et al, 2002;Michaels et al, 2006;Goldenson et al, 2008;Davy et al, 2009;Heavens et al, 2011;Rafkin, 2012). Observations of the vertical dust distribution (Heavens et al, 2011;Guzewich et al, 2013b) indicate elevated dust maxima, suggesting a much larger amount of non-local dust mixing than predicted by MRF PBL. However, since parameterizations of deep dust injection are still under development, we continue to employ the more restricted non-local mixing allowed by the MRF PBL scheme.…”

“…Lian et al, 2012), and advecting only a single particle size, meaning that the evolution of size distribution and its radiative impact are not captured (Murphy et al, 1995;Wolff and Clancy, 2003;K08). Scavenging by ice is not included, nor is a detailed representation of vertical transport and mixing of dust in the PBL by strong organized updrafts, suggested by the presence of high-altitude dust maxima even outside of storms (Heavens et al, 2011). Significant errors may exist due to the lack of water ice microphysics.…”

Simulating the interannual variability of major dust storms on Mars using variable lifting thresholds

“…It is apparent that the net dust flux across the equator depends very much on the vertical distribution of dust mass in the tropics, and in this regard dust transport was most likely biased towards the northern hemisphere, since the model did not reproduce the dust mass mixing ratio profiles seen around aphelion by Mars Climate Sounder (Heavens et al, 2011). These profiles featured elevated dust maxima at 20-30 km above the surface, but model profiles showed dust to be fairly well-mixed up to ∼ 15 km, with mixing ratios decreasing with increasing height above this level.…”

Mars Express radio‐occultation data: A novel analysis approach

“…In the lower part, the error is larger, in particular below 50 km altitude. A possible explanation to this disagreement may lie in the presence of dust up to this range of altitudes, typical for the considered solar longitude [ Heavens et al , ], which might affect the refractive index in the lowest atmosphere.…”