Towards the better forecasting of destructive dust storms

A thermal low in Syria combined with convective activity over Iraq and more erodible dust in Syria resulted in a dust storm that affected the entire Middle East and Cyprus in September 2015. The storm brought over record-breaking dust loads to Cyprus with aerosol optical depth exceeding 5.0 at 550 nm

Researchers, supported by a series of EU-funded projects, have just published a paper in the journal ''Atmospheric Chemistry and Physics'' in which they analyse the cause of the storm and identify the current methodology behind forecasting.

They state the dust was mobilised by cyclonic flow and haboob formation. Haboobs, local and mesoscale atmospheric density currents that move vast amounts of dust, create a propagating dust wall that can extend up to 2-3 km in the troposphere. The resulting storms cause poor visibility that generates disruption to transport and other activities, and have an adverse impact on human health.

The team, which was supported by the EU’s BEYOND, ACTRIS-2, ECARS and MARCOPOLO projects, explains that the entrainment of dust particles in the free troposphere takes place at the turbulent region of the density current head. This triggers secondary convective cells along their pathways that may evolve to synoptic-scale dust events. The dust residuals remain aloft after the cold pool declines.

The downdrafts are denser than the ambient air so they spread out as they hit the surface of the earth, causing gusty and turbulent boundaries. As they travel over bare soil and desert, sediment can be lifted. The war in Northern Iraq and Syria has caused land to be used differently with farming no longer as constant, leading to more erodible soil. When all factors combine, they can create a propagating dust wall.

Most ways of studying and forecasting such intense dust storms rely on passive and active remote sensing, such as that carried out by the European Aerosol Research Lidar Network and on high-resolution modelling simulations. As convective episodes and their associated wind gusts are hard to model, forecasting dust storms of this nature remains hard to do. Indeed, almost all operational models failed to forecast the 2015 event.

So how can these episodes be forecast?

According to the researchers, the key to forecasting these events in atmospheric models is the use of cloud-resolving grid space. ‘However,’ they say, ‘such high-resolution grid space can only be applied over limited areas due to restrictions in computational power.’ They maintain there is a place for remote sensing, such as that arising from the engagement of the geostationary satellite observations.

The paper also welcomes the expansion of the Lidar network in areas close to the source of the dust storms, which could complement modeling by providing, ‘ground truth observations’ for the vertical profile of dust plumes.

For more information, please see:
BEYOND project web site
ACTRIS-2 project web site
ECARS project web site
MARCOPOLO CORDIS project page