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Multi-scale dust modeling to describe near surface PM10 concentrations

by Enric Terradellas last modified Sep 22, 2018 12:00 PM
Multi-scale dust modeling to describe near surface PM10 concentrations

Left: The Khamsin dust outbreak on 22 March 2018. Right: The Foehn wind bringing dust downwards towards the north coast of Crete (click to enlarge)

We are pleased to announce the release of the article 'From Tropospheric Folding to Khamsin and Foehn Winds: How Atmospheric Dynamics Advanced a Record-Breaking Dust Episode in Crete' by Solomos et al.

Introduction

On 22 March, Crete was affected by a particularly severe North African dust event. The presence of dust was initially detected in the western parts of the island (Chania), where the phenomenon peaked at noon, with maximum recorded PM10 of 500 μg m-3. The dust concentration increased rapidly so that at 1500 UTC in the afternoon it reached a record value of 4730 μg m-3 in Heraklion and at 1720 UTC a new record value for Greece was recorded at 6340 μg m-3 in Finokalia. Analysis of this episode indicates the need for high resolution dust modeling especially over complex terrain areas and whenever near surface dust forecast is required. The main driver for strong dust events in Mediterranean is atmospheric dynamics at various scales: (i) At synoptic scale, the weakening of the polar vortex allows descending of cold stratospheric air of high potential vorticity towards lower latitudes at Mediterranean and north Africa. (ii) At mesoscale, the tropospheric folding favors cyclogenesis and intensifies the low-pressure systems along the surface baroclinic zones. The formation of mid-latitude cyclones at this area results in mobilization of dust particles from the Sahara and the scale and movement of these Mediterranean depressions determines also the dust pathways towards Europe (e.g. Khamsin winds). (iii) At local scale, the vertical stability of the dusty air mass is disturbed when the plumes reach the orographic barriers of Mediterranean islands (e.g., Crete, Cyprus, Sicily) or the inland continental mountain ranges. Depending on the relevant heights between the mountain ridge and the elevated plumes, topography may act either as a stopping barrier that leads to increased dust concentrations at the windward ridge or as a primary reason for the generation of downslope Foehn winds and downward mixing of dust over the leeward side, which was the case for the current event.

From a modeling point of view, resolving of such complex atmospheric patterns is a very challenging task since a high-resolution nested grid may often be required at both the origin areas of dust and at the arrival areas, several hundred kilometers away. Even at the fine grid scale of 1 × 1 km, certain limitations are evident regarding the model performance, mostly related to sub-grid unresolved topographic features and to the associated dynamics induced by terrain variability at the low-level tropospheric flow. Following the consideration that stratospheric intrusions are the primary force for dust-storm generation, any possible future changes in polar vortex properties due to climate change may be relevant to changes in the frequency and strength of dust events in the Mediterranean.

Reference

Solomos, S.; Kalivitis, N.; Mihalopoulos, N.; Amiridis, V.; Kouvarakis, G.; Gkikas, A.; Binietoglou, I.; Tsekeri, A.; Kazadzis, S.; Kottas, M.; Pradhan, Y.; Proestakis, E.; Nastos, P.T.; Marenco, F. From Tropospheric Folding to Khamsin and Foehn Winds: How Atmospheric Dynamics Advanced a Record-Breaking Dust Episode in Crete. Atmosphere 20189, 240.

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