Experimental observations and modelling of the downward longwave radiation in the Mediterranean region

Evaluating long-wave radiation is a critical task for controlling surface energy budgets in various application fields. The long-wave radiation can be estimated using surface observations alone, such as direct measurements by pyrgeometers in weather stations, or through empirical models based on air temperature and humidity, which are usually measured in most weather stations. Adaptability is the main limitation of the literature's empirical models; indeed, these models yield mediocre accuracy when applied in locations other than the original development site, where they were assessed. To overcome these limitations, this study presents the results of experimental observations to evaluate the accuracy of literature models when used within the Mediterranean Area. The cloudy cover, which is one of the main difficult data to retrieve for calculating the long wave radiation, has been determined using data derived from satellite data or metar stations. The comparisons between observations and literature models have evidenced that only a few literature models allow to achieve accurate results both under clear and cloudy sky conditions. This research presents observations on long-wave radiation in Catania, an area where no previous surveys were available. The identification of the most truthful literature models represents useful information for a more accurate evaluation of the long-wave radiation in the Mediterranean Region.