Eddy evolution during large dust storms

Abstract

The evolution of eddy kinetic energy during the development of large regional dust storms on Mars is investigated using the Mars Analysis Correction Data Assimilation (MACDA) reanalysis product and the dust storm data derived from Mars Global Surveyor Mars Daily Global Maps. Transient eddies in MACDA are decomposed into different components according to their eddy periods: P ≤ 1 sol, 1 < P ≤ 8 sols, 8 < P ≤ 60 sols. This paper primarily focuses on the Mars year 24 pre-solstice "A" storm that starts with many episodes of frontal/flushing dust storms from the northern hemisphere and attains its maximum global mean opacity after dust expansion in the southern hemisphere. During the development of this storm, the dominant eddies in terms of eddy kinetic energy progress from the 1 < P ≤ 8 sol eddies in the northern mid/high latitudes to the P ≤ 1 sol eddies (dominated by thermal tides) in the southern mid latitudes, and the 8 < P ≤ 60 sol eddies show a prominent peak with the increased global-mean dust opacity. The peaks of the 1 < P ≤ 8 sol eddies are found to best correlate with the average area of textured frontal/flushing dust storms within 40 • N -60 • N. The region where the 1 < P ≤ 8 sol eddies increase the most corresponds to the main flushing channel. The eddy kinetic energy of the P ≤ 1 eddies, dominated by P = 1 and its harmonics, increases with the global mean dust opacity both before and after the winter solstice in Mars year 24. The 8 < P ≤ 60 sol eddies briefly spike during large, regional dust storms but remain weak if dust storm sequences do not lead to a major dust storm. Zonal wavenumber analysis of eddy kinetic energy shows that the peaks of the 1 < P ≤ 8 eddies often result from combinations of zonal wavenumbers 1 to 3, while the P ≤ 1 eddies and 8 < P ≤ 60 sol eddies are each dominated by zonal wavenumber 1.

Annular modes of variability in the atmospheres of Mars and Titan

“…The EKE-AM links to poleward eddy heat fluxes that vary vertically (Fig. 2e-h), which matches the behavior of Earth's baroclinic mode and demonstrates that the EKE-AM represents (baroclinic) instabilities that instigate the type of traveling waves that initiate large dust events 33 . The relationship between eddy heat fluxes and the EKE-AM holds across hemispheres and datasets excepting the southern hemisphere MACDA domain, wherein fluxes are weaker.…”

“…The annular feature achieves a maximum at 60-70º N/S and 10-150 Pa and is robust across both hemispheres and both datasets. Given the large degree of importance Earth's mode has in explaining extratropical wave activity, the comparatively larger percentage of variance explained by the EKE-AM points to its immense influence in determining wave activity, and therefore dust events 33 , on Mars.…”

“…The connections between the EKE-AM and dust storm-producing traveling waves on Mars are corroborated by comparing the storm tracks on Mars to the EKE-AM. The mass-integrated EKE 33 , which is a measure of the intensity of waves, regressed on the EKE-AM peaks at 45-75º N and 15-60º S (Fig. 3c, d).…”

“…3e-h). Indeed, each of these regions hosts areas of increased storm activity from transient waves 22,33,34,40 . Furthermore, the clear annular structure, with longitudinal localization in storm tracks, is remarkably reminiscent of Earth's EKE-AM, which also pinpoints the Pacific, Atlantic, and Southern Ocean storm tracks (Fig.…”

Mars Climate Sounder Observations of Gravity-wave Activity throughout Mars’s Lower Atmosphere

“…The minimal or small positive impact of 34P on northern extratropical GW activity is attributed to orographic GW sources, which are apparently less affected by the effects of high dust opacity, though it seems possible that the persistence of GW activity in the northern extratropics during 34P is the result of the robustness of the winter westerly jet, embedded baroclinic activity, and the polar vortex. The observational test for this would be to look for changes in GW activity from a regional dust storm or PEDE that significantly disturbed the polar vortex, such as 26C (a regional dust storm in MY 26) or 28P (Wang 2007;Guzewich et al 2016;Kass et al 2016;Battalio & Wang 2020), rather than 34P, which minimally impacted 50 Pa temperatures north of 60°N (Kass et al 2020). The Ω GW for the observation is provided in the legend.…”