34 Global potential of dust devil occurrence

Monday, 9 June 2014
Palm Court (Queens Hotel)
Bradley Colin Jemmett-Smith, University of Leeds, Leeds, United Kingdom; and J. H. Marsham, P. Knippertz, and C. Gilkeson

Dry boundary-layer convection serves as an effective mechanism for dust uplift, typically through a combination of rotating dust devils and non-rotating larger and longer-lived convective plumes. These microscale dry-convective processes occur over length scales of several hundred metres or less. They are difficult to observe and model, and therefore their contribution to the global dust budget is highly uncertain. Using an analytical approach to extrapolate limited observations, we use a new method for quantifying the potential of dust devil occurrence.

Observations have shown that dust devil and convective plume occurrence is favored in hot arid regions under relatively weak background winds, large ground-to-air temperature gradients and deep dry convection. These observed constraints are tested against large eddy simulations of dust devils (2m horizontal grid spacing) and results presented here. By applying these constraints to operational analyses from the European Centre for Medium Range Weather Forecasts (ECMWF), we provide, to the best of the authors' knowledge, the first hourly estimates of dust devil occurrence including an analysis of sensitivity to chosen threshold uplift.

The results show the expected diurnal variation and allow an examination of the seasonal cycle and day-to-day variations in the boundary-layer conditions required for dust devil formation. They confirm that desert regions are expected to have by far the highest frequency of dry convective vortices, with winds capable of dust uplift.

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