Abstract
The BSC-DREAM8b model and its predecessor are analysed in terms of aerosol optical depth (AOD) for 2004 over Northern Africa, the Mediterranean and the Middle East. We discuss the model performance and we test and analyse its behaviour with new components. The results are evaluated using hourly data from 44 AERONET stations and seasonally averaged satellite observations. The operational versions strongly underestimate the winter AOD over the Sahel and overestimate the AOD over the Middle East and the Mediterranean achieving a low average annual correlation (~0.35). The use of a more detailed size distribution and a corrected wash-out ratio, together with a new dry deposition scheme, improves the transport over the Mediterranean, although underestimations remain over the Sahel and overestimations over the Middle East. The inclusion of a ‘preferential source’ mask improves the localisation of the main North African sources and consequently the dust transport towards Europe and the Atlantic. The use of a more physically based dust emission scheme and a new soil texture database leads to significant improvements in the representation of emissions and the transport over the Sahel, achieving an average annual correlation of 0.53. In this case, the use of a preferential source mask does not introduce significant improvements.
Highlights
A large amount of mineral dust is mobilised over arid regions and injected into the atmosphere under specific weather conditions
In the model comparison we have ascribed observed dust aerosol optical depth (AOD) of 0 for α>1.5. Measurements outside these ranges are associated with mixed aerosols and not included in the quantitative model evaluation. At those sites where the Spectral Deconvolution Algorithm (SDA) products are available the AOD evaluation is complemented with AODcoarse which is fundamentally associated to maritime/oceanic aerosols and desert dust
The transport is driven by the latitudinal shift of the Intertropical Front which corresponds to the convergence zone between the dry northern winds, called the Harmattan, and the humid monsoon winds coming from the South
Summary
A large amount of mineral dust is mobilised over arid regions and injected into the atmosphere under specific weather conditions. The history of the model starts with its predecessor, a single particle size dust model (Nickovic and Dobricic, 1996) initially developed in the World Laboratory Centre, Erice, Italy in the period 1991–1993 This model was implemented in the Tunisian Meteorological Service, where the first ever-successful operational regional dust forecast was performed during March–May 1995. Investigations for the treatment of a particular aerosol type may be limited to seasons and regions, when or where that aerosol type dominates the aerosol composition In this contribution, we first evaluate the performance and discuss the limitations of DREAM and BSC-DREAM8b and we test and discuss updates in the emission and deposition schemes. B41: Bagnold (1941); D87: D'Almeida (1987); D87N01: D'Almeida (1987) modified with the correction factors used by Nickovic et al (2001); G01: Ginoux et al (2001); G86: Giorgi (1986); IW82: Iversen and White (1982); MB95: Marticorena and Bergametti (1995); N01: Nickovic et al (2001); S93: Shao et al (1993), P06: Pérez et al (2006a); White (1979); Z01: Zhang et al (2001)
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