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Project Description

The project is aimed to tackle one of the outstanding issues in atmospheric research, i.e., the cloudy sky radiative transfer and its consequences for the absorption of solar radiation. The present contribution is intended as a first initiative to included this exciting and still unresolved issue into the list of priority scientific goals (as outlined in the last paragraph of the concept's introduction.)

The proposer (IUP-Hei) contributes to the overall project (4Dwolken) with two activities i.e.,

1. The measurements of the probability density function of geometrical photon pathlength (PDF-GP), and
2. the investigation of spatial scaling of the cloudy sky RT.

To 1.) In recent years, the measurements of PDF-GP by high resolution oxygen A-band spectroscopy in zenith scattered skylight has emerged into a powerful tool to investigate 3-D effects of the cloudy sky RT (Pfeilsticker et al., 1998, Veitel et al., 1998, Pfeilsticker, 1999). The accurate knowledge of the cloudy sky PDF-GP is one of the major ingredients to calculate properly the cloudy sky shortwave (SW) absorption. The proposer has pioneer-ed the development of the high resolution oxygen A-band technique and still keeps a worldwide leading position. The previous measurements, however, still suffered from some technical drawbacks (i.e., long signal integration time, too view absorption lines within the spectral range) that are to be avoided with a new instrumental set-up (i.e., highly sensitive CCD for which the funding is not asked for within the present proposal). Also, by performing the PDF-GP measurements together with other cloud parameters in dedicated field campaigns, as suggested here, new and exciting insights into the cloudy sky RT are likely to be obtained (e.g., Pfeilsticker, 1999).

To 2.) Also, temporally highly resolved, and small band, radiometric measurements of the zenith scattered skylight have recently been shown to provide new information on the typical spatial scaling of cloudy sky RT (Savigny et al., 1999). A proper knowledge the typical cloudy sky RT spatial scaling is a major ingredient for an improved parameterization of clouds in GCM's and the remote sensing of cloud covers from space as well.

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Atmospheric Chemistry Division
Institute for Environmental Sciences
University of Heidelberg
Im Neuenheimer Feld 229
69120 Heidelberg, Germany

Sekretariat: Heidelinde Schwarz-Brasch, Tel.: +49 (0)6221 54-6350, Fax: +49 (0)6221 54-6405, e-mail: