Retrieval of aerosol optical thickness for desert conditions using MERIS observations during the SAMUM campaign

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This journal is published under the terms of the Creative Commons Attribution-Noncommercial 3.0 Unported LicenseIn May-June 2006, airborne and ground-based solar (0.3-2.2 mu m) and thermal infrared (4-42 mu m) radiation measurements have been performed in Morocco within the Saharan Mineral Dust Experiment (SAMUM). Upwelling and downwelling solar irradiances have been measured using the Spectral Modular Airborne Radiation Measurement System (SMART)-Albedometer. With these data, the areal spectral surface albedo for typical surface types in southeastern Morocco was derived from airborne measurements for the first time. The results are compared to the surface albedo retrieved from collocated satellite measurements, and partly considerable deviations are observed. Using measured surface and atmospheric properties, the spectral and broad-band dust radiative forcing at top-of-atmosphere (TOA) and at the surface has been estimated. The impact of the surface albedo on the solar radiative forcing of Saharan dust is quantified. In the SAMUM case of 19 May 2006, TOA solar radiative forcing varies by 12 W m(-2) per 0.1 surface-albedo change. For the thermal infrared component, values of up to +22 W m(-2) were derived. The net (solar plus thermal infrared) TOA radiative forcing varies between -19 and +24 W m(-2) for a broad-band solar surface albedo of 0.0 and 0.32, respectively. Over the bright surface of southeastern Morocco, the Saharan dust always has a net warming effect

Section: Spectral Surface Albedosupporting

confidence: 74%

Spectral surface albedo over Morocco and its impact on radiative forcing of Saharan dust

Bierwirth

Wendisch²,

Ehrlich

et al. 2009

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“…For instrument intercomparison, the airborne HSRL measurements over this ground station were coordinated as well. Moreover, the Falcon flight missions were coordinated with satellite overpasses of the Multi‐angle Imaging SpectroRadiometer (MISR) and the Medium Resolution Imaging Spectrometer (MERIS; Dinter et al, 2008) for validation purposes. A comparison of the AOT measurements obtained by MISR and HSRL can be found in Kahn et al (2008).…”

Section: Experimental Methodsmentioning

confidence: 99%

Spatial distribution and optical properties of Saharan dust observed by airborne high spectral resolution lidar during SAMUM 2006

Esselborn

Wirth

Fix

et al. 2009

Airborne measurements of pure Saharan dust extinction and backscatter coefficients, the corresponding lidar ratio and the aerosol optical thickness (AOT) have been performed during the Saharan Mineral Dust Experiment 2006, with a high spectral resolution lidar. Dust layers were found to range from ground up to 4-6 km above sea level (asl). Maximum AOT values at 532 nm, encountered within these layers during the DLR Falcon research flights were 0.50-0.55. A significant horizontal variability of the AOT south of the High Atlas mountain range was observed even in cases of a well-mixed dust layer. High vertical variations of the dust lidar ratio of 38-50 sr were observed in cases of stratified dust layers. The variability of the lidar ratio was attributed to dust advection from different source regions. The aerosol depolarization ratio was about 30% at 532 nm during all measurements and showed only marginal vertical variations. ?? 2008 The Author Journal compilation ?? 2008 Blackwell Munksgaard

“…Müller, 2008, personal communication). At TNF the AOT was measured at eight different wavelengths using a Cimel Sun Photometer CE 318 (Cimel Electronique; Paris, France) with slightly modified channels (Dinter et al, 2008). In this paper we will only consider AOTs at 500 nm wavelength.…”

Section: Datamentioning

confidence: 99%

Dust mobilization and transport in the northern Sahara during SAMUM 2006 – a meteorological overview

Knippertz¹,

Ansmann²,

Althausen³

et al. 2009

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102

138

The SAMUM field campaign in southern Morocco in May/June 2006 provides valuable data to study the emission, and the horizontal and vertical transports of mineral dust in the Northern Sahara. Radiosonde and lidar observations show differential advection of air masses with different characteristics during stable nighttime conditions and up to 5‐km deep vertical mixing in the strongly convective boundary layer during the day. Lagrangian and synoptic analyses of selected dust periods point to a topographic channel from western Tunisia to central Algeria as a dust source region. Significant emission events are related to cold surges from the Mediterranean in association with eastward passing upper‐level waves and lee cyclogeneses south of the Atlas Mountains. Other relevant events are local emissions under a distinct cut‐off low over northwestern Africa and gust fronts associated with dry thunderstorms over the Malian and Algerian Sahara. The latter are badly represented in analyses from the European Centre for Medium–Range Weather Forecasts and in a regional dust model, most likely due to problems with moist convective dynamics and a lack of observations in this region. This aspect needs further study. The meteorological source identification is consistent with estimates of optical and mineralogical properties of dust samples.