CUVRA: Characteristics of the UV radiation field in the alps

• Research unit: EU RFP
• Project number: 97.0041

Key words (English)

Solar UV irradiance; albedo; snow reflectivity; radiative transfer models

Alternative project number (English)

EU project number: ENV4-CT97-0575

Research programs (English)

EU-programme: 4. Frame Research Programme - 3.1 Environment

Short description (English)

See abstract

Further information (English)

Full name of research-institution/enterprise:
Weltstrahlungszentrum
Physikalisch-Meteorologisches Observatorium Davos

Partners and International Organizations (English)

UINN.IMP ; UBW.IMP ; FHG.IFU ; USTLIL.LOA ; UJFG.IRSA
Coordinator:Universität Innsbruck (A)

Abstract (English)

The Alps are one of the areas in Europe with the highest UV-B levels at all. This is a consequence of several special characteristics of the UV radiation field in the Alps: the Alpine atmosphere is mostly free from industrial pollution and aerosols; in the thinner atmosphere due to higher elevation the extinction of radiation and especially of UVB radiation is less; snow surfaces have a high reflection and enhance significantly scat-tered radiation; lower lying layers of the atmosphere also contribute to the albedo at mountain sites, as they scatter back part of the incident irradiance. All the effects mentioned above will influence the spectrum in quite different ways and results from other studies cannot necessarily be applied to the Alpine region. Although these im-pacts are smaller than ozone and cloud impact, they are not at all negligible, and they interfere with the in-fluence of the ozone trend on an UV radiation trend. Alpine regions are in this context areas that need special attention. However, the knowledge of the UV radiation field there is important for many fields of ex-ploitation, such as tourism, Alpine agriculture and forestry.
This project addresses these special questions for Alpine areas, where albedo investigations play a key role in the understanding of radiative transfer over Alpine terrain. Investigations will start with the evaluation of data of spectral global and direct UV-irradiance, which are already available at nine stations, covering a wide range of elevations and different geographic and climatic regions of the Alps. Based on the results of these first studies, the measurement sta-tions will be equipped with ancillary measurements aimed especially at the characterisation of albedo. Broad-band meters will be used in addition to the spectroradiometers and additionally, newly developed UV-Pre-ci-sion-Filter-Radiometers will assure highest quality requirements, as they are calibrated by ra-diometric methods to an accuracy of better than 0.5%.
Methods will be developed to incorporate reflections from complex and mixed surfaces in an area of about 30 km around an observing station in radiative transfer calculations. This leads to an ‚effective albedo', which will be linked to parameters from a set of ancillary measurements which will be provided by a coordinated campaign at a site in a snow-covered Alpine valley.
In this study, the Alps are representative for mountainous areas in Europe, and therefore the results are representative for much larger areas than the Alps as such. The better understanding of the UV-B levels under real atmospheric conditions in mountainous areas is a prerequisite for an asses-sment of the impact of possible changes of the UV flux in relation to stratospheric ozone variations.

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 97.0041