Simplified modelling of the nocturnal clear sky atmospheric radiation for environmental applications

The energy loss from plants leaves and other interface surfaces to the sky is a relevant component of the surface radiation budget (SRB). This heat transfer mechanism plays a major role in many climate dependent ecological processes, especially during calm and clear sky night periods, when these loses can produce interface temperatures lower than ambient temperature increasing, for example, the risk of the dew condensation or the frost formation over the soil and the plants. This work deals with the modelling of the so called equivalent sky temperature, Tsky, a simplified index for the representation of the thermal loses for that situations. The used models are based on the relation between meteorological surface data and incoming longwave observations carried out during a three-year period in Almerı́a (south eastern Spain), a coastal location characterised by a high frequency of clear sky situations and a semiarid landscape. An upgrade of some of the analysed methods is also proposed in order to increase the exactitude of the Tsky calculation in our case. In spite of its site dependent nature, the obtained results can be immediately related to physical parameters, being possible its generalisation in those cases where requested input criteria will be available.