A spectral meteorological model on the ICL DAP (Q1110983)

The author analyses the implementation of a spectral meteorological model on the ICL distributed array processor (DAP). In the spectral method, the model variables are expanded as a truncated set of spherical harmonics defined by \(Y_{m,n}(\lambda,\mu)=e^{im\lambda}P_{m,n}(\mu)\), where m is the number of waves around a latitude circle, n is the total wave number, \(\lambda\) is the longitude, \(\mu =\sin \theta\) (\(\theta\) is the latitude) and \(P_{m,n}\) are normalised Legendre polynomials. The use of the property of the Legendre transforms: \(P_{m,n}(-\mu_ j)=(- 1)^{| m| +n}P_{m,n}(\mu_ j)\) is a computational advantage to store Legendre polynomials and their derivatives and the computing in parallel. The computing times for equivalent spectral and finite difference models on serial and vector computers are approximately the same.