UV index and UV dose: data product description
|Main data product description page|
IntroductionThe TEMIS UV index and UV dose data are computed from the assimilated global ozone field at local solar noon, i.e. at the moment the Sun is highest in the sky. which in case of the UV dose is combined with the daily variation of the position of the Sun above the horizon.
The clear-sky UV index and UV dose data cover the whole world. The cloud-modified UV dose data is given the part of the world covered by the geostationary Meteosat Second Generation (MSG) satellites.
NOTE: This product description is not yet complete.
Details of the computation of the UV index and UV dose
- A first guess of the UV irradiance weighted with a specific action spectrum at time t using the global assimilated ozone field at local solar noon is determined from a parametrisation developed by Allaart et al. (2004).
The weighting is related to so-called action spectra, i.e. the wavelength dependent response to UV radiation of health effects. The action spectra used for the TEMIS UV data products are detailed here, and some info on the ozone field is given here.
- This first guess is corrected for these effects:
- The clear-sky erythemal UV index, the quantity communicated to the public to raise awareness, is computed at time t equal local soler noon.
The TEMIS UV data service provides:
- forecast for today and the 8 coming days
- data archive from July 2002 onwards, using the operational TEMIS global ozone field
- The daily UV dose is computed by integration of the time dependent UV index and is provided as cloud-free and cloud-modified daily UV dose. A description of the modification of the UV by clouds is given here.
The TEMIS UV data service provides data archives for three action spectra:
- The UV index and UV dose values are each accompanied by an error estimate; some information on this is given here.
Data files and plotsThe UV index and UV dose data are given at a latitude-longitude grid of 0.25 by 0.25 degrees covering the whole world in HDF-4 files. UV index files contain the clear-sky local noon UV index data, whereas UV dose files contain both the clear-sky and cloud-modified UV dose data. All files also contain the local solar noon ozone data at the UV grid.
The structure of these files is described on a separate page.
The website shows plots of the UV index and UV dose data in four domains: World, Europe, Netherlands and Dutch Caribbean.
Data version 2.0 improvements w.r.t. older versionsA first evaluation of the data has shown that the differences in the cloud-free UV index and UV dose data lie on the whole within the error on the v2.0 data, except for a few specific events.
The major improvements lie in the treatment of the attenuation of the UV radiation by clouds and the estimate of the error on the UV index and UV dose.
Overview of the main improvements of version 2.0 with respect to version 1.4:
- The spatial resolution has been increased from 0.5 x 0.5 degrees to 0.25 x 0.25 degrees.
- The most recently available, if possible official, action spectra have been included; cf. this page.
- The error estimate has been improved: previously only the error on the ozone column was accounted for, while as of v2.0 the errors in the parametrisation, the cloud modification factor, the surface elevation and the surface altitude are accounted for too.
- The cloud modification factor is determined from the surface downwelling solar (SDS) radiation measured by the Meteosat Second Generation (MSG) satellites Meteosat 8, 9 and 10. cf. this page.
- Previously the MSG data we used covered only most of Europe; as of v2.0 we use the data from the full MSG field-of-view.
- Cloud information is now included at a quarterly based, instead of once every half hour.
- The UV dose is now the integrated amount of UV radiation between what we call ScatterRise and ScatterSet: from the moment the first scattered sunlight comes across the horizon (solar zenith angle about 102 degrees) to the moment the last sunlight disappears across the horizon. (Previously, the integration was between sunrise and sunset.)
- The climatology of the surface albedo correction has been updated; cf. this page.
- The digital evelation map used for the surface elevation correction has been upgraded from GTOPO30 to GMTED2010; cf. this page
The differences between the older versions (v1.0-1.4) are minimal.
Version information version date remarks 2.0 29 May 2017 major upgrade of the UV index & UV dose processing 1.4 9 Jan. 2012 UV dose processing chain ported to new system 1.3 24 May 2009 UV dose processing updated to new MSG cloud cover area 1.2 April 2008 reprocessed GOME-1 data using GDP-4 ozone (was GDP-3) 1.2 June 2006 switch to Meteosat Second Generation cloud data 1.1 Feb. 2004 updated cloud modification 1.0 April 2003 first operational version
26 June 2017
data product contact: Jos van Geffen & Michiel van Weele & Roanld van der A
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