Martian B Storm Evolution: Modeling Dust Activity over the Receding South Polar CO2 Ice Cap at Southern Hemisphere Summer Solstice

Abstract:

Observations of annually recurring, elevated (~25 km) atmospheric warming and associated dust concentrations over the south polar cap near Southern Hemisphere (SH) summer solstice are the defining features of the regional dust storm known as the B storm [1]. Our observational analysis of MCS and TES temperature and dust retrievals include all Mars Years (MY) lacking a global dust storm (GDS) between MY 26 and MY 33 (Figure 1). The data indicate the B storm is initiated around perihelion (L_s=252°) in the southern midlatitudes and reaches maximum height and intensity over the south pole near SH summer solstice at L_s~267°. At peak intensity, mid-level atmospheric temperatures are elevated by as much as 30 K and mid-level atmospheric dust mixing ratios are more than triple pre-B storm levels (1.5-2 ppm to 7-8 ppm). Cap edge lifting may contribute significantly to initial dust mobilization in the B storm since surface wind stress along the receding cap edge is likely strengthened by the combined effects of the sea breeze circulation and katabatic winds at this time of year [2, 3, 4].

We are investigating dust lifting and lofting near the south pole of Mars during SH summer using the NASA Ames Mars Global Climate Model (MGCM). The NASA Ames MGCM is a finite-volume numerical model with a cubed sphere grid ideal for modeling processes at high latitudes. Initial simulations at low resolution (4x4 degrees) capture some elevated dust and associated warming at the south pole around L_s=265°, but the model fails to capture the intensity of the B storm. We will examine and present the model-predicted surface stress and vertical velocities near the receding seasonal CO₂ cap edge and at the south pole during solstice. Finally, we will present higher resolution simulations to better capture small-scale dynamics and features at the pole.

[1] Kass D. M. et al. (2016) Geophysical Research Letters, 43, 6111–6118.

[2] Malin, M. C. et al. (1992). Journal of Geophysical Research, 97(E5),7699-7718.

[3] Toigo, A. D. et al. (2002). Journal of Geophysical Research, 107(E7), 4-13.

[4] Smith, I. B. et al. (2015). Geomorphology, 240, 54-69.

Figure 1. Zonal mean daytime 50 Pa temperatures during the dusty season for non-GDS years from TES (MY24, MY26) and MCS (MY29-MY33). The 200 K (red) contour indicates periods of regional-scale dust events as defined by Kass et al. 2016.