Solskenstimmar

Solskenstimmar refers to the total amount of time during which direct sunlight reaches the Earth's surface, typically measured as hours of sunshine within a given period. It is a standard metric in meteorology and climatology, used alongside other variables such as cloud cover and precipitation. The measurements are usually reported as hours per day, per month, or per year and are relevant for applications in solar energy planning, agriculture, and climate studies.

Measurement methods have evolved over time. Traditionally, a Campbell-Stokes sunshine recorder was used, which records bright sunshine by burning a card at the location where the sun’s rays are intense enough. Modern weather stations often use automatic sensors, such as pyranometers, combined with algorithms to estimate sunshine duration from measured solar radiation. The official definition of sunshine duration typically relies on a threshold of surface irradiance (about 120 W/m2) to distinguish periods of bright sunshine from cloudy conditions.

Geographical and seasonal patterns influence solskenstimmar. Regions at lower latitudes or with dry climates tend to record higher annual sunshine hours, while higher latitudes exhibit strong seasonal variation, with long periods of darkness in winter and extended daylight in summer. Climate normals compile expected values for a location over a reference period, and long-term trends may indicate changes in atmospheric conditions or climate variability.

Applications include assessing solar energy potential, planning crop schedules in agriculture, and informing weather summaries. Limitations include dependence on instrument type and observer practices, as well as variations in how clouds, haze, or atmospheric scattering affect measured sunshine. Nonetheless, solskenstimmar remain a widely used measure of direct surface sunshine.