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Poleward Transport of African Dust to the Iberian Peninsula Organized by Multi-scale Terrain-Induced Circulations: Observations and High-Resolution WRF-Chem Simulation Analyses
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  • Saroj Dhital,
  • Michael L. Kaplan,
  • Jose Antonio Garcia Orza,
  • Stephanie Fiedler
Saroj Dhital
Desert Research Institute

Corresponding Author:[email protected]

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Michael L. Kaplan
Embry Riddle Aeronautical University - Prescott
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Jose Antonio Garcia Orza
Universidad Miguel Hernández de Elche, Elche, Spain
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Stephanie Fiedler
Institute of Geophysics and Meteorology, University of Cologne, Köln, Germany Abstract
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This study presents the meso-β/γ scale dynamical features involved in an extreme African dust outbreak, which occurred during 20-21 February 2016 over the Iberian Peninsula (IP), the southwest corner of Europe. During this episode, nearly 90% of the air quality stations in Spain exceeded the European Union’s PM10 daily limit. We used observations and performed nested-grid 2km simulations with the Weather Research and Forecasting model using coupled Chemistry (WRF-Chem) to understand the development of this dust outbreak. The surface observations and the false-color RGB dust product from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) revealed that the dust storm was initiated on the southeastern flank of the Saharan Atlas Mountains at two distinct phases of dust emissions. The first dust plume crossed the Saharan Atlas during midday on the 20th, the second one followed in the afternoon of the 21st. The first dust plume was advected towards the Western IP, while the second one towards the Eastern IP. The WRF-Chem simulation results indicated that the phase I dust emission was associated with strong barrier jet (BJ) formation on the southeastern foothills of the Saharan Atlas Mountains. The BJ strengthened just after sunrise on the 20th and emitted a massive amount of dust resulting in the first strong dust storm. In phase II, a long-lived westward propagating mesoscale gravity wave (MGW) was triggered near the northeastern edge of the Tinrhert Plateau in eastern Algeria. When this westward propagating long-lived MGW crossed the Tademaït Plateau, multiple hydraulic jumps were formed on its lee side. The strong winds accompanying these multiple hydraulic jumps emitted and mixed dust aerosols upwards which enabled the second strong dust plume to reach the IP. The lifted dust extended over 2-3 km in altitude in the growing daytime planetary boundary layer (PBL) and was advected poleward by the southerly/southeasterly wind at 700hPa. Our results underline the importance of resolving meso-scale processes to understand dust storm dynamics in detail, which are difficult to represent in coarse-resolution (aerosol-) climate models.