(3) Measuring Radiation Physics of the Atmosphere II Atmo II 57

Measuring Radiation Christoph Bichler Atmo II 58

Measuring Radiation Atmo II 59

Measuring Radiation At state-of-the-art meteorological stations, equipped with a sun- tracker, solar radiation (irradiance) measure- ments comprise: Direct solar radiation (S), with a pyrheliometer Global solar radiation (G) with a pyranometer, Diffuse solar radiation (H) with a shaded pyranometer. G = S cosθ + H UF S G H Atmo II 60

Measuring Radiation at UoG The University of Graz (UoG) performs “modern” radiation measurements – as part of the ARAD network (“Austrian radiation”) and “traditional ones” (TAWES = “Teilautomatische Wetterstation”) (credit: M. Mohr) Atmo II 61

Measuring Radiation at KSO IGAM/IP solar radiation measurements are also performed at KSO (Kanzelhöhe Observatory for Solar and Environmental Research) (UF) Atmo II 62

Measuring Radiation at KSO KSO is (usually) one of the places with maximum sunshine duration in Austria (above the notorious fog in the Klagenfurt basin (UF) Atmo II 63

Measuring Solar Radiation Measurement devices for solar radiation employ thermocouples, which use the thermoelectric effect: Thermocouples contain two dissimilar metal conductors in contact, which produce a voltage when heated (Picture credit: M. Mohr). Atmo II 64

Measuring Solar Radiation Pyranometers are used to measure global and diffuse solar radiation (from the halfspace). The thermopile is composed of several thermocouples, connected in series. The output is a voltage proportional to the temperature difference between the black surface of the sensor element and the housing as reference. Two quartz domes and a ventilation system (shall) minimize external influences (M. Mohr, after Kipp & Zonen) Atmo II 65

Measuring Radiation Pyrgeometers are used to measure long wave radiation, using a silicon window with a “solar blind” filter, which only transmits the radiation with wavelengths from 4.5 µm up to 42 µm. Pyrheliometers (below) measure direct solar radiation (M. Mohr, after Kipp & Zonen) Atmo II 66

Measuring Radiation (“traditional”) Most weather stations don’t have sun-trackers, they (may) have two (identical) Star pyranometers, one (left) measuring global solar radiation, the other one (shaded by a shadow ring) measuring (most of the) diffuse solar radiation. The direct solar radiation can only be derived. Star pyranometers measure the temperature difference between black and white sensors (credit: M. Mohr) Atmo II 67

Global Solar Radiation in Graz, Aug Atmo II 68 Global Solar Radiation on different summer days (August) (M. Mohr)

Global Solar Radiation - Eclipse Atmo II 69 Global Solar Radiation on sunny days with and without partial solar eclipse, and on a cloudy day in comparison (IGAM).

Global Solar Radiation in Styria, Jan Atmo II 70 Styrian Climate Atlas, ZAMG: t/cms/ziel/ /DE/

Global Solar Radiation in Styria, July Atmo II 71 Styrian Climate Atlas, ZAMG

Recording Sunshine (“traditional”) In the past, recording of sunshine duration was – literally – done with a “crystal sphere” (Campbell-Stokes autograph) (UF, M. Mohr) Atmo II 72

Recording Sunshine Duration The “Haenni Solar” device records differences between global and diffuse solar radiation (using rotating strip shades). Sunshine is – by WMO definition (World Meteorological Organization) – when the direct solar radiation, perpendicular to the sun, exceeds 120 W/m 2 (M. Mohr) Atmo II 73

Mean Sunshine Hours in Styria, Jan Atmo II 74 Styrian Climate Atlas, ZAMG

Sunshine in January? Atmo II 75 Sometimes, sunshine is a rare event during winter months.. (IGAM)

Sunshine in January! Atmo II 76 Above the low-level clouds this can be entirely different.. (UF)

Sunshine in November Atmo II 77 Under the low-level clouds you might not believe it.. (UF, IGAM)

Mean Sunshine Hours in Styria, July Atmo II 78 Styrian Climate Atlas, ZAMG

Increased Sunshine Atmo II 79 A part of the strong warming in Austria during the past ~35 years is due to increased sunshine (less clouds) in the same period (HISTALP)