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Intercomparison of shortwave radiative transfer schemes in global aerosol modeling: Intercomparison of shortwave radiative transfer schemes in globalaerosol modeling: results from the AeroCom Radiative Transfer ExperimentRandles, Cynthia A., Kinne, Stefan, Myhre, Gunnar, Schulz, Michael, Stier, Philip, Fischer, Jürgen, Doppler, Lionel, Highwood, Eleanor, Ryder, Claire, Harris, Bethan, Huttunen, Jani, Ma, Y., Pinker, Rachel T., Mayer, Bernhard, Neubauer, David, Hitzenberger, Regina, Oreopoulos, Lazaros, Lee, Dongmin, Pitari, Giovanni, Di Genova, Glauco, Quaas, Johannes, Rose, Fred G., Kato, Seiji, Rumbold, Steve T., Vardavas, Ilias, Hatzianastassiou, Nikos, Matsoukas, Christos, Yu, Hongbin, Zhang, F., Zhang, Hua, Lu, P. January 2013 (has links)
In this study we examine the performance of 31 global model radiative transfer schemes in cloudfree conditions with prescribed gaseous absorbers and no aerosols (Rayleigh atmosphere), with prescribed scatteringonly aerosols, and with more absorbing aerosols. Results are compared to benchmark results from high-resolution, multiangular line-by-line radiation models. For purely scattering
aerosols, model bias relative to the line-by-line models in the top-of-the atmosphere aerosol radiative forcing ranges from roughly −10 to 20 %, with over- and underestimates of radiative cooling at lower and higher solar zenith angle, respectively. Inter-model diversity (relative standard deviation) increases from ~ 10 to 15% as solar zenith angle decreases. Inter-model diversity in atmospheric and surface forcing decreases with increased aerosol absorption, indicating that the treatment of multiple-scattering is more variable
than aerosol absorption in the models considered. Aerosol
radiative forcing results from multi-stream models are generally
in better agreement with the line-by-line results than the
simpler two-stream schemes. Considering radiative fluxes,
model performance is generally the same or slightly better
than results from previous radiation scheme intercomparisons.
However, the inter-model diversity in aerosol radiative
forcing remains large, primarily as a result of the treatment of
multiple-scattering. Results indicate that global models that
estimate aerosol radiative forcing with two-stream radiation
schemes may be subject to persistent biases introduced by
these schemes, particularly for regional aerosol forcing.
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Derivation of aerosol optical properties using ground-based radiation measurementsDonth, Tobias, Jäkel, Evelyn, Mey, Britta, Wendisch, Manfred 03 November 2017 (has links)
The knowledge of the optical and microphysical properties of aerosol particles in the atmosphere is relevant in various scientific fields from public health issues to climate modeling. A retrieval method is presented that estimates the single scattering albedo and asymmetry parameter of aerosol particles in regions of high pollution using spectral ground-based radiance and irradiance measurements, radiative transfer simulations, and a priori knowledge of the aerosol optical depth (AOD) derived from sun photometer observations. The used measurement data originated from the Pearl River Delta in China. The results are compared with sun photometer data and show a high agreement for AODs larger than 0.5. For low AODs and for cloudy conditions the method did not work due to the strong sensitivity of the initial parameters. / Kenntnisse über optische und mikrophysikalische Eigenschaften von Aerosolpartikeln in der Atmosphäre werden in vielen verschiedenen wissenschaftlichen Gebieten benötigt. Diese reichen vom Gesundheitswesen bis hin zur Klimamodellierung. Deswegen wird im Folgenden eine Ableitungsmethode vorgestellt, die die Einfachstreualbedo und Asymmtrieparameter von Aerosolpartikeln bestimmt. Diese Methode wurde dabei für Messungen im Pearl River Delta, China, in denen oft hohe Luftverschmutzungen auftreten, angewandt. Es werden dazu bodengebundene Messungen der spektralen abwärtsgerichteten Strahlungsflussdichte und Strahldichte, gekoppelt mit Strahlungsübertragungsrechnungen durchgeführt. Um die aerosoloptischen Parameter ableiten zu können, wird als zusätzliche Randbedingung die aerosol-optische Dicke (AOD) benötigt. Sonnenphotometermessungen liefern dabei zum einen die AOD und zum anderen die aerosoloptische Eigenschaften, die mit den Ergebnissen der Ableitungsmethode verglichen werden. Dabei wurden für große AOD-Werte (über 0.5) gute Übereinstimmungen zwischen beiden Methoden festgestellt werden. Für AOD-Werte kleiner als 0.5 und bei bewölkten Bedingungen zeigt die Methode große Unsicherheiten, weil die Parameter zu empfindlich auf diese Begebenheiten reagieren.
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