Representative Alpine Climatology for Erythemal UV (RACE-UV)

• Forschungsstelle: COST
• Projektnummer: C04.0242
• Projekttitel Englisch: Representative Alpine Climatology for Erythemal UV (RACE-UV)

Schlüsselwörter (Englisch)

Ultraviolet radiation; Atmospheric transmission and scattering of radiation; Radiative processes; Atmospheric Global Change; Effective albedo; Ozone

Forschungsprogramme (Englisch)

COST-Action 726 - Long term changes and climatology of UV radiation over Europe

Kurzbeschreibung (Englisch)

This project is a contribution to the COST 726 action, whose general aim is building a European UV climatology by developing capabilities for estimating ground UV doses in Europe using ancillary data and models. The particular aim of the project is to adapt and test this methodology for Switzerland by 1) analyzing and selecting UV observations time series adequate for establishing UV estimation relationships representative of varying conditions met in Switzerland and 2) testing the dependency of the established UV estimation relationships on the location environment and conditions. The latter point will allow assessing how the relationships can be generalized to apply to other locations with similar but not identical environment and conditions.

Weitere Hinweise und Angaben (Englisch)

Full name of research-institution/enterprise: Bundesamt für Meteorologie und Klimatologie MeteoSchweiz Atmospheric Data Department

Partner und Internationale Organisationen (Englisch)

AT, BE, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GR, HU, IT, NL, NO, PL, PT, RO, SE, SK, UK

Abstract (Englisch)

RACE-UV is a contribution to COST 726, with the aim of building a Representative Alpine Climatology for Erythemal UV in Switzerland. This involves being able to estimate the past evolution of erythemal UV at various locations representative of the different environmental conditions found in Switzerland. Observed time-series of ultraviolet radiation (UV) are spatially sparse and temporally too short for addressing climatological questions. Therefore, this project is based on reconstruction techniques that are investigated for their appropriateness in the framework of COST 726. ln parallel, this project was linked to other COST 726 activities in Switzerland that were focused on improving the accuracy of erythemal UV measurements. As a consequence, it was also possible to improve the accuracy of past UV measurements in Switzerland by applying post-processing corrections. The application of radiative transfer models (RTMs) for estimating UV for time periods and locations where no observations are available leads to good results for clear-sky situations, while the treatment of cloudy situations is far more difficult. We developed a UV reconstruction method based on modeled clear-sky radiation and cloud modification factors derived from observed total shortwave irradiance (SW). Relationships between the cloud effects on UV and SW radiation were investigated for their dependencies on different environmental effects and climate conditions using measurements from four stations in Switzerland (Payerne, Davos, Jungfraujoch, and Locarno-Monti). Our method captured the short-term variability caused by changing cloud coverage and demonstrated good agreement with observed UV during an approximately one year validation period, which confirms that it performs well in different climate regions in Switzerland without further adaptations. Root mean square differences (RMS) between 4.5 and 7.2 mW/m2 (9.7-12.1%) were found for 10 minutes data, and for estimated daily doses the RMS were smaller than 8.5%. The derived relationship was used for reconstructing UV radiation at the four stations for the time period between 1981 and 2007, establishing a climatology of UV radiation at locations representative of different climate regions in Switzerland. This allowed analyzing the evolution of the reconstructed UV time-series. Positive decadal trends for the median daily UV values between 5.6-11.5% were found for the months of the first half year (January-June), with largest relative changes for March, while in May and June, the absolute increase in UV-index increased over the last 27 years was between 0.54 and 0.85 units. The temporal evolution of observed SW radiation and total ozone was identified as being statistically non-significant for most stations and months. Thus, the significant increase of UV radiation found at most stations in January-June results from the combination of mainly non-significant increases of SW radiation and reductions of ozone. On the other hand, a statistically significant decrease in regional snow cover counteracts the effects from SW and ozone changes.

Datenbankreferenzen (Englisch)

Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. [phone] Swiss Project-Number: C04.0242