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

Abstract

The redistribution of a finite amount of Martian surface dust during global dust storms and in the intervening periods has been modelled in a dust lifting version of the UK Mars General Circulation Model. When using a constant, uniform threshold in the model's wind stress lifting parameterisation and assuming an unlimited supply of surface dust, multiannual simulations displayed some variability in dust lifting activity from year to year, arising from internal variability manifested through surface wind stress, but dust storms were limited in size and formed within a relatively short seasonal window. Lifting thresholds were then allowed to vary at each model gridpoint, dependent on the rates of emission or deposition of dust. This enhanced interannual variability in dust storm magnitude and timing, such that model storms could cover most of the observed ranges in size and initiation date within a single multiannual simulation. Peak storm magnitude in a given year was primarily determined by the availability of surface dust at a number of key sites in the southern hemisphere. The observed global dust storm (GDS) frequency of roughly one in every three years was approximately reproduced, but the model failed to generate these GDSs spontaneously in the southern hemisphere, where they have typically been observed to initiate. After several years of simulation, the surface dust density field showed good qualitative agreement with the observed pattern of Martian surface dust cover. The model produced a net northward cross-equatorial dust mass flux, which necessitated the addition of an artificial threshold decrease rate in order to allow the continued generation of dust storms over the course of a multiannual simulation. At standard model resolution, for the southward mass flux due to cross-equatorial flushing storms to offset the northward flux due to GDSs on a timescale of ∼ 3 3 years would require an increase in the former by a factor of 3-4. Results at higher model resolution and uncertainties in dust vertical profiles mean that this nevertheless appears to be a plausible explanation for the observed GDS frequency.

Orbit-spin coupling and the interannual variability of global-scale dust storm occurrence on Mars

“…The redistribution of dust in a MY 33 storm might prevent the occurrence of a global-scale storm in MY 34 [Mulholland et al, 2013;Newman and Richardson, 2015]. If no storm occurs in MY 33, then we would have greater confidence in forecasting a GDS for MY 34, based on the significantly larger waveform amplitude of MY 34.…”

“…Leovy et al, 1973;Haberle, 1986;Zurek et al, 1992;Ingersoll, 2002, 2004;Fenton et al, 2006;Rafkin, 2009], prior attempts to account for the interannual variability of GDS events through numerical modeling have not met with great success [cf. Pankine and Ingersoll, 2002;Basu et al, 2006;Rafkin, 2009;Mulholland et al, 2013;Newman and Richardson, 2015].…”

The physics of Martian weather and climate: a review

“…Simple, low-order models have even suggested (Pankine and Ingersoll 2004) that this slow variation in effective saltation threshold can act as a form of self-organized criticality, holding large areas close to the critical threshold for dust lifting on interannual timescales and leading spontaneously to the chaotic occurrence of major storms. Attempts to implement a parameterization of this kind of variable threshold into more complex atmospheric models are the subject of current research, though preliminary results (Wilson and Kahre 2009, Wilson 2011, Mulholland et al 2013 are promising in terms of affecting simulated interannual variability of major storms. But this is clearly an area where more research is needed, in global modelling and in both field measurements (ideally on Mars, but also on terrestrial analogues of the martian environment) and laboratory measurements.…”

Dust Devil Sediment Transport: From Lab to Field to Global Impact

“…Figure 17 shows the depth of dust removed by dust devils according to the first ("dust devil activity"-based) parameterization and its seasonal evolution for regions included in the dust devil survey by Fisher et al (2005). While both of the dust devil parameterizations described above have been implemented into and used in global dust cycle studies for Mars, the first scheme has been used more consistently because it is simpler and it provides a smoothly varying background dust loading during northern hemisphere spring and summer (Newman et al 2002b;Basu et al 2004;Kahre et al 2006;Mulholland et al 2013). Additionally, it has been shown to reproduce the observed seasonal behavior of dust devil activity in both the northern and southern hemispheres (Fisher et al 2005;Kahre et al 2006).…”

“…As noted in Section 4.2.2, many Mars models employ specific parameterizations for dust devils (e.g. Newman et al 2002a,b;Basu et al 2004;Kahre et al 2006;Mulholland et al 2013;Newman and Richardson 2015). In these models the dust devils parameterization contributes up to one half of the total annual dust budget (Newman et al 2005;Kahre et al 2006).…”