From Tropospheric Folding to Khamsin and Foehn Winds: How Atmospheric Dynamics Advanced a Record-Breaking Dust Episode in Crete
2018
A record-breaking dust episode took place in Crete on 22 March 2018. The event was characterized by surface concentrations exceeding 1 mg m−3 for a period of 4–7 h, reaching
record valueshigher than 6 mg m−3 at the background station of Finokalia. We present here a detailed analysis of the atmospheric dynamical processes during this period, to identify the main reasons for such extreme dust advection over Crete. At the synoptic scale, the weakening of the
polar vortexand the meridional transport of polar air masses at upper
troposphericlayers resulted in a strong jet streak over north Africa and Central Mediterranean and corresponding
troposphericfolding that brought cold stratospheric air in mid and upper
troposphere.
Cyclogenesisoccurred at the Gulf of Sirte in Libya, resulting in strong winds over the north-east parts of Libya, enhancing particle emissions. The dust plume traveled at low altitude (0.5–3 km) along the warm
conveyor beltpreceding the depression
cold front. This type of dusty southerly wind is commonly known as “Khamsin”. As the flow approached Crete,
Foehn windsat the lee side of the island favored the downward mixing of dust towards the surface, resulting in local maxima of PM10 in Heraklion and Finokalia. The analysis is based on the combination of high-resolution WRF-Chem simulations reaching up to 1 × 1 km grid space over Crete, ground-based and satellite remote sensing of the dust plumes (PollyXT LiDAR, MSG-SEVIRI, MODIS) and detailed surface aerosol in situ measurements at urban (Heraklion, Chania, Greece) and background (Finokalia) stations in Crete.
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