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Dust and weather in the Mediterranean

Researchers have improved our understanding of how dust outbreaks affect radiation, atmospheric dynamics and weather forecasting systems.
Dust and weather in the Mediterranean
Modern advances in atmospheric-dust modelling have allowed research into the effects of dust on radiation and atmospheric processes. To this aim, satellite platforms such as MODIS, EP-TOMS and OMI as well as ground monitoring networks, providing state-of-the-art measurements of high accuracy, can be utilized in conjunction with models in order to improve our knowledge regarding dust-atmosphere dynamics.

The EU-funded MDRAF (Effects of Mediterranean desert dust outbreaks on radiation, atmospheric dynamics and forecasting accuracy of a numerical mesoscale model) initiative worked on the description of Mediterranean desert dust outbreaks’ three dimensional structure, through a synergistic implementation of passive and active satellite retrievals, as well as on the investigation of their impacts on radiation and atmospheric dynamics, by means of dust-atmospheric modelling.

The desert dust outbreaks that affected the broader Mediterranean basin, over the period 2000 – 2013, have been identified through an objective and dynamic satellite algorithm while for their description in vertical, satellite lidar profiles have been utilized. The reliability of the satellite algorithm has been confirmed via the assessment of its outputs versus ground AERONET retrievals and surface PM10 concentrations.

From long-term averaged geographical distributions, the researchers found that the frequency of desert dust episodes decreases from south to north. Strong desert dust episodes take place more frequently in the western Mediterranean (10 episodes yr-1), while the extreme ones are more frequent over its central parts (3.3 episodes yr-1). Dissimilar spatial patterns, with respect to frequency, are revealed for the intensity, which is maximized in the central and eastern parts of the study region.

Among the Mediterranean sub-regions, the researchers found that dust layers' base height is decreased from 2 km to 0.5 km, moving from west to east, due to the local topography and thermal convection. On average, the top height of dust layers is recorded up to 6 km while dust particles are observed at very low concentrations mainly up to 8 km.

From the satellite algorithm outputs, 20 intense and widespread dust outbreaks have been selected based on objective criteria. For these cases, through short term (84 hours) numerical simulations of the NMMB/BSC-Dust model, the dust direct radiative effects (DREs) for a domain covering the Sahara and the most part of Europe are investigated. Under dust episodes conditions, mineral particles exert a strong perturbation of the Earth-Atmosphere system’s radiation budget. Due to dust-radiation interactions, mineral particles reduce the temperature at 2 meters by up to 4 K, the sensible heat fluxes by up to 150 Wm-2 and the latent heat fluxes by up to 100 Wm-2, at noon. During nighttime, reverse effects of lower magnitude are found. The vertical distribution of dust layers plays a key role of how mineral particles’ alter the temperature vertical profiles which in turn affect atmospheric dynamics.

When dust radiative effects are considered into the numerical simulations, the regional dust aerosol optical depth at 550 nm and the total emitted amount of dust are reduced by up to 7% and 20%, respectively, revealing thus negative feedbacks on both parameters. Finally, thanks to the consideration of dust-radiation interactions, the predictive skills of the NMMB/BSC-Dust model, in terms of reproducing the downward radiation at surface as well as temperature fields, are improved.

The data and findings generated by MDRAF will improve researchers' understanding of how dust affects local and regional weather systems. This will help researchers to improve weather and climate models.

Related information

Keywords

Weather, Mediterranean, dust outbreaks, radiation, satellites, atmospheric dynamics, MDRAF
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