The Ratio of Diffuse to Direct Solar Irradiance (Perpendicular to the Sun's Rays) with Clear Skies—A Conserved Quantity Throughout the Day

Abstract

The ratio of diffuse irradiance to direct normal is a conserved quantity throughout the day. Though its absolute value depends on the condition of the atmosphere, ground reflection and obstruction of horizon, once this value is established (by a single measurement) in rung regions. it persists over the entire day. Urban and heavy polluted areas may show considerable daily trends.