inDust webinar: advances towards dust seasonal predictions

Abstract

In recent years, user demand for forecasts that fill the gap between medium-range weather (up to 15 days) and long-range or seasonal (3–6 months) forecasts has increased. Skillful subseasonal to seasonal prediction can support decision-making and help optimizing resource management decisions. Prediction at the S2S scale, however, is particularly challenging because it is both an initial value problem, much like the standard Numerical Weather Prediction (NWP) medium-range, and a boundary value problem like seasonal prediction. Over the years, researchers have been trying to find source of predictability at this scale, looking at natural-occurring patterns or processes both in the troposphere and the stratosphere that have a periodicity of weeks up to a few months. The Madden-Julian oscillation has been identified as one of the most important of such patterns. However, much debate is still ongoing as far as what the triggers of the MJO and what the important feedbacks connected to it are. Recent work has shown that the atmospheric constituents such as aerosols and other tracers (i.e., ozone) can be important modulators of the radiative processes at the S2S scale. For example, the direct effect of aerosols may influence predictability via the MJO modulation of the aerosol fields. In clear sky, the cumulative aerosol forcing can modify the radiative balance of the atmospheric column and introduce temperature perturbations which depend on the dominant aerosol types and their optical properties. Wind-emitted aerosols such as desert dust appear to be the main contributors. However, sensitivity studies performed with the ECMWF’s coupled Ensemble Prediction System have shown that biomass burning aerosols may also play an important part, in particular for areas where extensive seasonal biomass burning takes place such as central Africa and Indonesia. Aerosols of volcanic origin have also been shown to affect stratospheric processes and to also have a large impact on the S2S prediction. In this talk a review of current efforts to understand the impact of aerosols on the S2S prediction will be presented and discussed with particular focus on dust. The possibility of dust prediction per se at the S2S scale will also be discussed.