North African dust transport toward the western Mediterranean basin: atmospheric controls on dust source activation and transport pathways during June–July 2013

Kerstin Schepanski,Max Ulrich,Marc Mallet,Bernd Heinold

doi:10.5194/acp-16-14147-2016

Kerstin Schepanski, Max Ulrich + Show 2 more

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https://doi.org/10.5194/acp-16-14147-2016

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Abstract

Abstract. Dust transported from north African source region toward the Mediterranean basin and Europe is a ubiquitous phenomenon in the Mediterranean region. Winds formed by large-scale pressure gradients foster dust entrainment into the atmosphere over north African dust source regions and advection of dust downwind. The constellation of centers of high and low pressure determines wind speed and direction, and thus the chance for dust emission over northern Africa and transport toward the Mediterranean. We present characteristics of the atmospheric dust life cycle determining dust transport toward the Mediterranean basin with focus on the ChArMEx (Chemistry-Aerosol Mediterranean Experiment) special observation period in June and July 2013 using the atmosphere–dust model COSMO-MUSCAT (COSMO: COnsortium for Small-scale MOdeling; MUSCAT: MUltiScale Chemistry Aerosol Transport Model). Modes of atmospheric circulation are identified from empirical orthogonal function (EOF) analysis of the geopotential height at 850 hPa and compared to EOFs calculated from 1979–2015 ERA-Interim reanalysis. Two different phases are identified from the first EOF, which in total explain 45 % of the variance. They are characterized by the propagation of the subtropical ridge into the Mediterranean basin, the position of the Saharan heat low and the predominant Iberian heat low, and discussed illustrating a dipole pattern for enhanced (reduced) dust emission fluxes, stronger (weaker) meridional dust transport, and consequent increased (decreased) atmospheric dust concentrations and deposition fluxes. In the event of a predominant high-pressure zone over the western and central Mediterranean (positive phase), a hot spot in dust emission flux is evident over the Grand Erg Occidental, and a reduced level of atmospheric dust loading occurs over the western Mediterranean basin. The meridional transport in northward direction is reduced due to prevailing northerly winds. In case of a predominant heat low trough linking the Iberian and the Saharan heat low (negative phase), meridional dust transport toward the western Mediterranean is increased due to prevailing southerly winds resulting in an enhanced atmospheric dust loading over the western Mediterranean. Altogether, results from this study illustrate the relevance of knowing dust source location and characteristics in concert with atmospheric circulation. The study elaborates on the question of the variability of summertime dust transport toward the Mediterranean and Europe with regard to atmospheric circulation conditions controlling dust emission and transport routes of Saharan dust, exemplarily for the 2-month period of June–July 2013. Ultimately, outcomes from this study contribute to the understanding of the variance in dust transport into a populated region.

Highlights

Primary aerosols such as mineral dust can be considered to be intrinsically present in the Earth climate system (Carslaw et al, 2010)
To compose characteristics representing the opposed phases identified from the empirical orthogonal function (EOF) analysis (Fig. 4), days are assigned to a negative or a positive phase according to the first principal component (PC), which is characterized by a predominant high-pressure zone over the western and central Mediterranean for the positive phase, and a predominant heat low trough extending from the western Grand Erg Occidental toward the Bay of Biscay for the negative phase, respectively
This study aimed for an assessment of atmospheric circulation patterns that determine dust source activation and dust transport toward the western Mediterranean basin with regard to the ChArMEx/ADRIMED special observation period in June and July 2013

Summary

Introduction

Primary aerosols such as mineral dust can be considered to be intrinsically present in the Earth climate system (Carslaw et al, 2010). Mineral dust aerosol pays the largest contribution to the atmospheric aerosol burden and is of importance for the climate (Shao et al, 2011). Mineral dust impacts the Earth radiation budget, altering. K. Schepanski et al.: Saharan dust over the Mediterranean basin atmospheric dynamics and temperature distribution, and further provides micronutrients that contribute to the bioproductivity of land (Okin et al, 2008), marine (Jickells et al, 2005), and lacustrine ecosystems (Psenner, 1999). Mineral dust deposited on snow and ice surfaces changes the snow albedo and alters the melting characteristics of snowpack and glaciers (Painter et al, 2007)

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