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Reduction of radiation biases by incorporating the missing cloud variability by means of downscaling techniques: a study using the 3-D MoCaRT model

Gimeno Garcia, Sebastian and Trautmann, Thomas and Venema, Victor (2012) Reduction of radiation biases by incorporating the missing cloud variability by means of downscaling techniques: a study using the 3-D MoCaRT model. Atmospheric Measurement Techniques, 5 (9), pp. 2261-2276. Copernicus Publications. DOI: 10.5194/amt-5-2261-2012 ISSN 1867-1381

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Official URL: http://www.atmos-meas-tech.net/5/2261/2012/amt-5-2261-2012.html


Handling complexity to the smallest detail in atmospheric radiative transfer models is unfeasible in practice. On the one hand, the properties of the interacting medium, i.e., the atmosphere and the surface, are only available at a limited spatial resolution. On the other hand, the computational cost of accurate radiation models accounting for three-dimensional heterogeneous media are prohibitive for some applications, especially for climate modelling and operational remote-sensing algorithms. Hence, it is still common practice to use simplified models for atmospheric radiation applications. Three-dimensional radiation models can deal with complex scenarios providing an accurate solution to the radiative transfer. In contrast, one-dimensional models are computationally more efficient, but introduce biases to the radiation results. With the help of stochastic models that consider the multi-fractal nature of clouds, it is possible to scale cloud properties given at a coarse spatial resolution down to a higher resolution. Performing the radiative transfer within the cloud fields at higher spatial resolution noticeably helps to improve the radiation results. We present a new Monte Carlo model, MoCaRT, that computes the radiative transfer in three-dimensional inhomogeneous atmospheres. The MoCaRT model is validated by comparison with the consensus results of the Intercomparison of Three-Dimensional Radiation Codes (I3RC) project. In the framework of this paper, we aim at characterising cloud heterogeneity effects on radiances and broadband fluxes, namely: the errors due to unresolved variability (the so-called plane parallel homogeneous, PPH, bias) and the errors due to the neglect of transversal photon displacements (independent pixel approximation, IPA, bias). First, we study the effect of the missing cloud variability on reflectivities. We will show that the generation of subscale variability by means of stochastic methods greatly reduce or nearly eliminate the reflectivity biases. Secondly, three-dimensional broadband fluxes in the presence of realistic inhomogeneous cloud fields sampled at high spatial resolutions are calculated and compared to their one-dimensional counterparts at coarser resolutions. We found that one-dimensional calculations at coarsely resolved cloudy atmospheres systematically overestimate broadband reflected and absorbed fluxes and underestimate transmitted ones.

Item URL in elib:https://elib.dlr.de/98368/
Document Type:Article
Title:Reduction of radiation biases by incorporating the missing cloud variability by means of downscaling techniques: a study using the 3-D MoCaRT model
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Gimeno Garcia, Sebastiansebastian.gimenogarcia (at) dlr.deUNSPECIFIED
Trautmann, Thomasthomas.trautmann (at) dlr.deUNSPECIFIED
Journal or Publication Title:Atmospheric Measurement Techniques
Refereed publication:Yes
Open Access:Yes
Gold Open Access:Yes
In ISI Web of Science:Yes
DOI :10.5194/amt-5-2261-2012
Page Range:pp. 2261-2276
Wagner, Thomasthomas.wagner@mpic.de
Laj, Paololaj@lgge.obs.ujf-grenoble.fr
Joiner, Joannajoanna.joiner@nasa.gov
Richter, Andreasandreas.richter@iup.physik.uni-bremen.de
Harder, Hartwighartwig.harder@mpic.de
Publisher:Copernicus Publications
Keywords:Radiative transfer, Monte Carlo, Atmosphere, Clouds
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Earth Observation
DLR - Research area:Raumfahrt
DLR - Program:R EO - Erdbeobachtung
DLR - Research theme (Project):R - Vorhaben Spektrometrische Verfahren und Konzepte der Fernerkundung (old)
Location: Oberpfaffenhofen
Institutes and Institutions:Remote Sensing Technology Institute > Atmospheric Processors
Deposited By: Schreier, Dr.rer.nat. Franz
Deposited On:02 Oct 2015 10:56
Last Modified:02 May 2019 14:13

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