Sky type classification in Central England during winter

In the present work, we studied the exterior daylight conditions in Sheffield in Central England (53.38° N, 1.50° W) during winter. The study makes use of the 15 standard sky types defined by Kittler et al. These sky types are presented as diagrams of the ratio of the zenith luminance (Lz) to the diffuse horizontal illuminance (Dv) against solar altitude (γ). The illuminance parameters used are time series of half-hourly values of Dv, Lz, global (Ge) and diffuse (De) horizontal irradiance and γ for the period from November 1, 1993, to February 10, 1994.