Measurements of desert dust optical characteristics at Porte au Sahara during SAMUM     

By W. VON HOYNINGEN-HUENE  T. DINTER  A. A. KOKHANOVSKY  J. P. BURROWS  M. WENDISCH  E. BIERWIRTH  D. MÜLLER  M. DIOURI 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):206-215

Main optical characteristics of desert dust, such as phase function and single scattering albedo, have been derived from combinations of sun-/sky-radiometer and satellite measurements during the SAMUM experiment (10 May–10 June 2006) at the site Porte au Sahara (30.237°N, 5.607°W) in South Morocco. Scattering phase functions have been retrieved using combined data of spectral aerosol optical thickness (AOT) and spectral sky brightness in the almucantar, considering non-spherical light scattering. Intercomparisons of modelled top-of-atmosphere (TOA) reflectance with satellite observations of the Medium Resolution Imaging Spectrometer (MERIS) and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography () instrument have been used for the estimation of spectral single scattering albedo. For the radiative transfer calculations scattering phase functions and AOT from ground-based observations have been used. The spectral single scattering albedo ranges from 0.93 in the blue to 0.98 at 753 nm.  相似文献   

Desert dust aerosol air mass mapping in the western Sahara, using particle properties derived from space-based multi-angle imaging     

By RALPH KAHN  REAS PETZOLD  MANFRED WENDISCH  EIKE BIERWIRTH  TILMAN DINTER  MICHAEL ESSELBORN  MARCUS FIEBIG  BIRGIT HEESE  PETER KNIPPERTZ  DETLEF MÜLLER  ALEXANDER SCHLADITZ  WOLFGANG VON HOYNINGEN-HUENE 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):239-251

Coincident observations made over the Moroccan desert during the Sahara mineral dust experiment (SAMUM) 2006 field campaign are used both to validate aerosol amount and type retrieved from multi-angle imaging spectroradiometer (MISR) observations, and to place the suborbital aerosol measurements into the satellite's larger regional context. On three moderately dusty days during which coincident observations were made, MISR mid-visible aerosol optical thickness (AOT) agrees with field measurements point-by-point to within 0.05–0.1. This is about as well as can be expected given spatial sampling differences; the space-based observations capture AOT trends and variability over an extended region. The field data also validate MISR's ability to distinguish and to map aerosol air masses, from the combination of retrieved constraints on particle size, shape and single-scattering albedo. For the three study days, the satellite observations (1) highlight regional gradients in the mix of dust and background spherical particles, (2) identify a dust plume most likely part of a density flow and (3) show an aerosol air mass containing a higher proportion of small, spherical particles than the surroundings, that appears to be aerosol pollution transported from several thousand kilometres away.  相似文献   

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

By EIKE BIERWIRTH  MANFRED WENDISCH  RÉ EHRLICH  BIRGIT HEESE  MATTHIAS TESCHE  DIETRICH ALTHAUSEN  ALEXANDER SCHLADITZ  DETLEF MÜLLER  SEBASTIAN OTTO  THOMAS TRAUTMANN  TILMAN DINTER  WOLFGANG von HOYNINGEN-HUENE  RALPH KAHN ‡ 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):252-269

In May–June 2006, airborne and ground-based solar (0.3–2.2 μm) and thermal infrared (4–42 μm) 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.  相似文献   

Lateglacial and early Holocene vegetation and climate gradients in the Nordfjord–Ålesund area,western Norway     

HILARY H. BIRKS  MARIEKE VAN DINTER 《Boreas: An International Journal of Quaternary Research》2010,39(4):783-798

Birks, H. H. & van Dinter, M. 2010: Lateglacial and early Holocene vegetation and climate gradients in the Nordfjord–Ålesund area, western Norway. Boreas, Vol. 39, pp. 783–798. 10.1111/j.1502‐3885.2010.00161.x. ISSN 0300‐9483. Modern climate in western Norway shows a strong west–east gradient in oceanicity–continentality (coast to inner fjord) and altitudinal temperature gradients that control the regional and altitudinal zonation of vegetation. To discover if similar gradients existed during the Lateglacial and early Holocene, plant‐macrofossil analyses were made from five lacustrine sediment sequences in the Nordfjord–Ålesund region selected to sample the present climatic gradients. The macrofossil assemblages could be interpreted as analogues of the present vegetation, thus allowing reconstruction of past vegetation and climates. When the five sites were compared, climatic gradients could be detected. During the Lateglacial interstadial, mid‐alpine assemblages with Salix herbacea and S. polaris occurred at the lowland coast and upland inland sites, whereas the inland lowland site had low‐alpine dwarf‐shrub heath dominated by Betula nana, demonstrating a strong west–east gradient in temperature and precipitation and an altitudinal gradient inland. During the Younger Dryas stadial, assemblages at the lowland coast and upland inland sites resembled high‐alpine vegetation, whereas the inland lowland site was warmer with mid‐alpine vegetation, demonstrating west–east and altitudinal temperature gradients. Gradients became less pronounced in the Holocene. The early abundance of Betula nana in the inner fjord sites but its rarity at the coast is striking and reflects the oceanicity gradient. All sites became forested with Betula pubescens a few centuries into the Holocene. This forest was probably close to tree line at 370 m a.s.l. at the coast. Inland, there was no detectable altitudinal gradient, with the tree line well above 400 m a.s.l. reflecting the present pattern of tree‐line elevation.  相似文献   

Vertically resolved dust optical properties during SAMUM: Tinfou compared to Ouarzazate     

By BIRGIT HEESE  DIETRICH ALTHAUSEN  TILMAN DINTER  MICHAEL ESSELBORN  THOMAS MÜLLER  MATTHIAS TESCHE  MATTHIAS WIEGNER 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):195-205

Vertical profiles of dust key optical properties are presented from measurements during the Saharan Mineral Dust Experiment (SAMUM) by Raman and depolarization lidar at two ground-based sites and by airborne high spectral resolution lidar. One of the sites, Tinfou, is located close to the border of the Sahara in Southern Morocco and was the main in situ site during SAMUM. The other site was Ouarzazate airport, the main lidar site. From the lidar measurements the spatial distribution of the dust between Tinfou and Ouarzazate was derived for 1 d. The retrieved profiles of backscatter and extinction coefficients and particle depolarization ratios show comparable dust optical properties, a similar vertical structure of the dust layer, and a height of about 4 km asl at both sites. The airborne cross-section of the extinction coefficient at the two sites confirms the low variability in dust properties. Although the general picture of the dust layer was similar, the lidar measurements reveal a higher dust load closer to the dust source. Nevertheless, the observed intensive optical properties were the same. These results indicate that the lidar measurements at two sites close to the dust source are both representative for the SAMUM dust conditions.  相似文献   

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

By PETER KNIPPERTZ  ALBERT ANSMANN  DIETRICH ALTHAUSEN  DETLEF MÜLLER  MATTHIAS TESCHE  EIKE BIERWIRTH  TILMAN DINTER  THOMAS MÜLLER  WOLFGANG VON HOYNINGEN-HUENE  KERSTIN SCHEPANSKI  MANFRED WENDISCH  BERND HEINOLD  KONRAD KANDLER  REAS PETZOLD  LOTHAR SCHÜTZ  INA TEGEN 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):12-31

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.  相似文献   

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

By TILMAN DINTER  WOLFGANG VON HOYNINGEN-HUENE  JOHN P. BURROWS  ALEXANDER KOKHANOVSKY  EIKE BIERWIRTH  MANFRED WENDISCH  DETLEF MÜLLER  RALPH KAHN  MOHAMMED DIOURI 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):229-238

Approximately 30% of the land surface is arid, having desert or semi-desert conditions. Aerosol originating from these regions plays a significant role in climate and atmospheric chemistry of the atmosphere. Retrieving aerosol properties from space-borne platforms above desert conditions, where the surface reflectance is usually very bright, is a challenging task. The proportion of the surface to top of atmosphere (TOA) reflectance can reach values over 90%, especially for wavelength above 500 nm. For these reasons detailed knowledge of aerosol and surface optical properties from these regions is required to separate atmosphere from intrinsically bright surfaces.
An approach to retrieve aerosol properties over arid and semi-arid regions based on the Bremen Aerosol Retrieval (BAER) has been developed and validated within the Dust Aerosol Retrievals from Space-Born Instruments (DREAMS) Project, which is part of the Saharan Mineral Dust Experiment ( SAMUM, 2006 ). Combining measurements of the backscattered radiation from the Medium Resolution Imaging Spectrometer (MERIS) instrument aboard Environmental Satellite (ENVISAT) and ground-based measurements in Morocco in radiation closure experiments yields the aerosol optical properties of mineral dust at selected locations.  相似文献