Dresden 2011 – scientific programme

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UP: Fachverband Umweltphysik

UP 7: Aerosols

UP 7.9: Talk

Thursday, March 17, 2011, 12:00–12:15, HSZ 204

Discrete dipole approximation for scattering by cloud ice particles - fast parallel implementation on an ordinary PC graphics card — •Marcus Huntemann, Georg Heygster, and Christian Melsheimer — Institut für Umweltphysik, Universität Bremen, Otto-Hahn- Allee 1, 28359 Bremen

The global distribution and climatology of ice clouds are among the main uncertainties in climate modelling and prediction. In order to retrieve ice cloud properties from remote sensing measurements, the scattering properties of all cloud ice particle types must be known.

The Discrete Dipole Approximation (DDA) simulates scattering of radiation by arbitrarily shaped particles and is thus suitable for cloud ice crystals. The DDA models the particle as a collection of equal dipoles on a lattice, and is computationally much more expensive than approximations restricted to more regularly shaped particles.

On a single computer the calculation for an ice particle of a specific size, for a given scattering plane at one specific wavelength can take several days. We have ported core routines or the scattering suite “Amsterdam DDA” (ADDA) to the Open Computing Language (OpenCL), a framework for programming parallel devices like PC graphics cards (Graphics Processing Units, GPUs) or multicore CPUs. In a typical case we can achieve a speed-up on a GPU as compared to a CPU by a factor of 5 in double precision and a factor of 15 in single precision. Spreading the work load over multiple GPUs will allow calculating the scattering properties even of large cloud ice particles.