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Radiative Forcing from Cirrus and Contrail Cirrus

Ulrich Schumann(1), Kaspar Graf(1), Ulrich Hamann(1), Hermann Mannstein(1) and Bernhard Mayer(1)

(1) DLR, Muenchner Str. 20, 82234 Oberpfaffenhofen, Germany


This paper presents a new computationally efficient parameterization to compute the radiative flux changes induced by thin cirrus (including contrail cirrus) at top of the atmosphere. The background of this study will be explained: We analyzed aviation contributions to cirrus changes based on SEVIRI data from METEOSAT 8 and 9 (Meteosat second generation, MSG). By means of the MeCiDa algorithm developed at this institute (Krebs et al. ACP, 2007) we determine the cirrus cover over the North Atlantic for the time period February 2004-January 2008. From the SEVIRI IR and VIS channel data, the outgoing longwave radiation (OLR) and the reflected solar radiation (RSR) are determined for the same region and period. The aviation contribution to contrail cirrus is modeled using a new multiple aircraft plume model. In this model the radiative forcing is computed from the OLR and RSR values without contrails, based on ECMWF results. The parameterization computes the changes in OLR and RSR induced by thin cirrus (including contrail cirrus). The parameterization is calibrated using an extensive set of forward calculations performed with libRadtran. The paper will show details of the model calibration. The results suggest significant contrail cirrus contributions to the measured cirrus cover, as well as OLR and RSR values. The cirrus radiative flux parameterization may be used for other applications as well.


Workshop presentation