UV index and UV dose: data product description data version 2.x	UV radiation monitoring: UV index UV dose
Main data product description page

Introduction

The 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.

There are two UV data records, based on different ozone data:

• TEMIS operational ozone record
  started in July 2002 and uses satellite ozone data from
  * SCIAMACHY (2002/07/01 -- 2012/03/31)
  * GOME-2A (2012/04/01 -- 2019/03/20)
  * GOME-2B (2019/03/21 -- 2024/03/13)
  * GOME-2C (2024/03/14 -- present)

• Multi-Sensor Re-analysis (MSR-2) ozone record
  covers the period January 1960 -- December 2023

Clear-sky UV index and clear-sky UV dose data is provided for both ozone records and covers the whole world. Cloud-modified UV dose data is provided only for the operational ozone record and covers the part of the world observed by the geostationary Meteosat Second Generation (MSG) satellites.

 

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); see this page for some details.

  The weighting is related to so-called action spectra, i.e. the wavelength dependent response to UV radiation of biological 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 the following effects:
  • varying Sun-Earth distance
  • surface albedo
  • surface elevation
  • presence of aerosols

• The clear-sky erythemal UV index, the quantity communicated to the public to raise awareness, is computed at time t equal to local solar noon; see here for some details.
   
  The TEMIS UV index 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; see here for some details. A description of the modification of the UV by clouds is given here.
   
  The TEMIS UV dose data service provides data archives for three action spectra:
  • Eerythemal UV dose
  • Vitamin-D UV dose
  • DNA-damage UV dose

• The UV index and UV dose values are each accompanied by an error estimate; some information on this is given here.

 
===> Publications and references for the TEMIS UV data services and datasets.

 

Data files and plots

The 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.

In addition, the archive data is also gathered in yearly netCDF files, which is accompanied by climatologies, i.e. averages over a large number of years.

Structure and reading of the daily HDF-4 data files
and the yearly netCDF data files (v2.0 and above).

The website shows plots of the UV index and UV dose data in four domains: World, Europe, Netherlands and Dutch Caribbean.

 

Data version 2.2 improvements w.r.t. version 2.1

This version contains an improvement in the cloud modification factor for the cloud-modified UV dose, due to an update of the input MSG CPP cloud data -- see here for some notes. The previous data has not been reprocessed.

At the same time the regional map of the "Dutch Caribbean" is extented to "Dutch Caribbean & Suriname"; the maps of previous data have not been reprocessed.

For the operational processing TEMIS operational record v2.2 is effective as of 22 March 2021, while for the Multi-Sensor Re-analysis (MSR-2) record v2.2 is effective as of 1 January 2020.

 

Data version 2.1 improvements w.r.t. version 2.0

This version contains an improvement of surface albedo climatology used in the UV index and UV dose data. The impact of this on the UV index and UV dose values are small -- see the upgrade notes on the surface albedo correction page -- and therefore the previous data has not been reprocessed.

For the operational processing TEMIS operational record v2.1 is effective as of 16 December 2020, while for the Multi-Sensor Re-analysis (MSR-2) record v2.1 is effective as of 1 January 2020.

 

Data version 2.0 improvements w.r.t. older versions

A 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 once every 15 minutes, 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.

 

Version information
version	date	remarks
2.2	22 Mar. 2021	upgrade of the MSG CPP cloud data & extention of a regional map; no reprocessing of earlier data
2.1	15 Dec. 2020	minor upgrade of surface albedo correction; no reprocessing of earlier data
2.0	29 May 2017	major upgrade of the UV index & UV dose processing, with full data reprocessing
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

 

Data of versions prior to v2.0 is no longer made available

last modified: 14 March 2024
data product contact: Jos van Geffen & Michiel van Weele & Ronald van der A
Copyright © KNMI / TEMIS