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Solar radiative effects of a Saharan dust plume observed during SAMUM assuming spheroidal model particles

Otto, Sebastian und Bierwirth, Eike und Weinzierl, Bernadett und Kandler, Konrad und Esselborn, Michael und Tesche, Matthias und Schladitz, Alexander und Wendisch, Manfred und Trautmann, Thomas (2009) Solar radiative effects of a Saharan dust plume observed during SAMUM assuming spheroidal model particles. Tellus B - Chemical and Physical Meteorology, 61B, Seiten 270-296. DOI: 10.1111/j.1600-0889.2008.00389.x.

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Offizielle URL: http://www3.interscience.wiley.com/journal/118533053/home

Kurzfassung

The solar optical properties of Saharan mineral dust observed during the Saharan Mineral Dust Experiment (SAMUM) were explored based on measured size-number distributions and chemical composition. The size-resolved complex refractive index of the dust was derived with real parts of 1.51�1.55 and imaginary parts of 0.0008�0.006 at 550 nm wavelength. At this spectral range a single scattering albedo ��<sub>o</sub> and an asymmetry parameter g of about 0.8 were derived. These values were largely determined by the presence of coarse particles. Backscatter coefficients and lidar ratios calculated with Mie theory (spherical particles) were not found to be in agreement with independently measured lidar data. Obviously the measured Saharan mineral dust particles were of non-spherical shape. With the help of these lidar and sun photometer measurements the particle shape as well as the spherical equivalence were estimated. It turned out that volume equivalent oblate spheroids with an effective axis ratio of 1:1.6 matched these data best. This aspect ratio was also confirmed by independent single particle analyses using a scanning electron microscope. In order to perform the non-spherical computations, a database of single particle optical properties was assembled for oblate and prolate spheroidal particles. These data were also the basis for simulating the non-sphericity effects on the dust optical properties: ��<sub>o</sub> is influenced by up to a magnitude of only 1% and g is diminished by up to 4% assuming volume equivalent oblate spheroids with an axis ratio of 1:1.6 instead of spheres. Changes in the extinction optical depth are within 3.5%. Non-spherical particles affect the downwelling radiative transfer close to the bottom of the atmosphere, however, they significantly enhance the backscattering towards the top of the atmosphere: Compared to Mie theory the particle non-sphericity leads to forced cooling of the Earth-atmosphere system in the solar spectral range for both dust over ocean and desert.

Dokumentart:Zeitschriftenbeitrag
Titel:Solar radiative effects of a Saharan dust plume observed during SAMUM assuming spheroidal model particles
Autoren:
AutorenInstitution oder E-Mail-Adresse der Autoren
Otto, SebastianNICHT SPEZIFIZIERT
Bierwirth, EikeJohannes Gutenberg Univ., Mainz
Weinzierl, BernadettNICHT SPEZIFIZIERT
Kandler, KonradDarmstadt Univ. of Technology, Darmstadt
Esselborn, MichaelNICHT SPEZIFIZIERT
Tesche, MatthiasLeibniz Institute for Tropospheric Research, Leipzig
Schladitz, AlexanderLeibniz Institute for Tropospheric Research, Leipzig
Wendisch, ManfredJohannes Gutenberg Univ., Mainz
Trautmann, ThomasNICHT SPEZIFIZIERT
Datum:2009
Erschienen in:Tellus B - Chemical and Physical Meteorology
Referierte Publikation:Ja
In Open Access:Ja
In SCOPUS:Ja
In ISI Web of Science:Ja
Band:61B
DOI :10.1111/j.1600-0889.2008.00389.x
Seitenbereich:Seiten 270-296
Status:veröffentlicht
Stichwörter:Saharan mineral dust, optical properties, spheroidal aerosol particles, scattering database, radiative transfer simulations, spectral radiative flux densities
HGF - Forschungsbereich:Verkehr und Weltraum (alt)
HGF - Programm:Weltraum (alt)
HGF - Programmthema:W EO - Erdbeobachtung
DLR - Schwerpunkt:Weltraum
DLR - Forschungsgebiet:W EO - Erdbeobachtung
DLR - Teilgebiet (Projekt, Vorhaben):W - Vorhaben Entwicklung von Atmosphärenprozessoren (alt)
Standort: Oberpfaffenhofen
Institute & Einrichtungen:Institut für Physik der Atmosphäre > Atmosphärische Spurenstoffe
Institut für Methodik der Fernerkundung > Atmosphärenprozessoren
Hinterlegt von: Prof.Dr. Thomas Trautmann
Hinterlegt am:21 Jan 2009
Letzte Änderung:12 Dez 2013 20:32

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