Orbit‐Spin Coupling and the Triggering of the Martian Planet‐Encircling Dust Storm of 2018

Abstract

The Martian global dust storm (GDS) of 2018 began soon after the southern spring equinox, which is quite early in the dust storm season. The origins of early‐season GDS, including those of 1977, 2001, and now 2018, have been mysterious, as atmospheric dynamical investigations and numerical modeling experiments have been unable to explain or reproduce the timing of these events. We employ a newly expanded catalog of historic Martian GDS for our investigation, which includes 2018 and the telescopically observed equinoctial dust storms of 1877 and 1909. All of the GDS of this catalog took place either (1) when orbit‐spin coupling torques on the Martian atmosphere were near peak values or (2) near times when the orbit‐spin coupling torques were changing most rapidly. The second category, here termed “Mode 2,” includes all six of the equinoctial GDS of the historic record, including 2018. Recognition of the existence of two triggering modes for GDS occurrence leads to a significant improvement in temporal resolution for both hindcasting and forecasting. Orbit‐spin coupling now provides explanations for the late‐season inception dates of the 1924 and 1973 storms, as well as for the equinoctial events. We provide conditional forecasts, with sub‐seasonal time resolution, for GDS occurrence and non‐occurrence in Mars years 35 through 40. We introduce a detailed working hypothesis for the genesis of equinoctial GDS that may be validated through numerical modeling. The characteristic timescale for frictional damping of an intensified Martian Hadley circulation is estimated to be O(10) sols.

Surface Dust Redistribution on Mars From Interannual Differences in Temperature and Albedo

“…GCMs initialized with a finite supply of surface dust show source regions will be depleted quickly and inhibit dust storm activity (Kahre et al, 2005;Mulholland et al, 2013;Newman & Richardson, 2015). This is inconsistent with multidecadal observations (Shirley et al, 2020;. Kahre et al (2005) concluded that source regions are large reservoirs, providing dust for lifting on at least multidecadal timescales, and that the interannual variability in dust storms is not due to the availability of surface dust.…”

Possible Origin of Some Periodicities Detected in Solar‐Terrestrial Studies: Earth's Orbital Movements

“…Specifically, short‐term orbital forcings also need to be analyzed in the frame of the modeled feedbacks of the Earth system, such as fast‐slow responses of dynamical systems (see e.g., Seshadri, 2017). In addition, other unexpected mechanisms involving orbital changes and internal climate dynamics could be operating on the Earth, as in the case of planet Mars, where the orbital dynamics of this planet has been linked to large‐scale atmospheric circulation patterns; indeed, a weak spin‐orbit coupling between the orbital and rotational angular momenta of Mars has been argued to possibly explain its remarkable dust storms (Newman et al., 2019; Shirley et al., 2020). In our opinion, regardless of the amplitudes of the forcing involved, one of the most promising mechanisms called upon to explain the bases of these complex mechanisms behind the interactions among these orbital oscillations and the Earth system will be through the Kuramoto models of synchronization, assuming that their components are under non‐linear couplings.…”

Studies of the 2018/Mars Year 34 Planet‐Encircling Dust Storm

“…The strengthened Hadley circulation lofted dust to very high altitudes, ∼70 km, and led to almost anvil‐cloud‐like distributions of dust in the middle and upper atmosphere. Additionally, this seasonally atypically strong Hadley circulation produced dynamical heating of mid‐altitude air at high latitudes in both hemispheres due to adiabatic warming in the descending branches of the equinoctial circulation (Shirley et al., 2020b). Indeed, both observations (Kass et al., 2019) and modeling (e.g., Bertrand et al.…”