UV-B irradiance reaching the Earth's surface depends strongly on the ozone amount of the atmosphere
and links day to day variations of stratospheric ozone, ozone depletion, and the Antarctic ozone to
the biosphere. The effects on human beings are described by the erythemal (sunburn) effective UV and
given by the internationally harmonised UV Index. Besides the altitude of the sun above the horizon
and the ozone amount, clouds (most important factor), the altitude above mean sea level, aerosol
optical depth and aerosol type, as well as the UV surface albedo (important only snow and ice)
affecting UV radiation at the ground. The UV Index has been introduced collaboratively by the World
Meteorological Organisation (WMO), the World Health Organisation (WHO), the United Nations
Environmental Programme (UNEP) and the International Commission on Non-Ionising Radiation
Protection (ICNIRP) to inform the public by means of an elementary physical quantity The UV Index
serves as an important vehicle to raise public awareness on risks of excessive UV exposure and
to alert people to adopt protective measures when exposed to UV radiation. The PROMOTE forecasts
provided by DWD are based on the PROMOTE ozone forecasts and an hourly resolution. They are
presented according to the recommendations of WHO (2002). The daily maximum of the UV Index cloudy
accounts for all effective atmospheric conditions; the forecasts for clear sky allow to estimate
the potential maximum of sunburn effective UV irradiance in the case of longer lasting cloud gaps.
Forecasts for more than 1150 sites world-wide are given in a WHO-conform presentation with 48 maps.
They are accompanied by short sun protection messages displayed by click on the UV Index of a site.
The site specific forecasts are target to serve the general public and to supplement national
campaigns on radiation protection offering UV Index information for abroad. The erythemal effective
daily UV dose represents the accumulation of the hourly values for one day and enables to assess
the UV effects in the course of the day. The global maps have a spatial resolution of 60 km, the
high resolution European maps of 7 km. The forecast maps supplement the PROMOTE UV monitoring.
They allow persons in charge of science and politics duly to assess risks and to take
Figures 1a to c give an example of the PROMOTE forecast products how the 2004 Antarctic ozone has
influenced the biosphere.
Fig. 1a: PROMOTE forecast of total column ozone, valid 28 Oct. 2004. Antarctic ozone hole 2004 three
to four weeks past its broadest extension and lowest ozone levels.
Fig. 1b: PROMOTE forecast of UV Index clear sky, valid 28 Oct. 2004. The erythemal effective UV
irradiance (UV Index) under assumed conditions of a cloudless sky demonstrates the potential effect
of the ozone hole onto the biosphere. A sun elevation distinctly higher than three weeks ago
accounts for an enhanced UV irradiance. In the area of the ozone hole the UV irradiance increases
due to the reduced ozone column proportional according to a power law, and results in UV Index
values never observed in same latitudes of the Northern Hemisphere. Additionally the effects are
amplified by the altitude of the Antarctic plateau as well as the albedo of snow and of sea ice
having its broadest expansion in the seasonal cycle.
Fig. 1c: PROMOTE forecast of daily maximum of UV Index cloudy, valid 28 Oct. 2004. The potentially
amplified UV irradiance is markedly masked by cloud effects, if it is accounted for all effective
atmospheric conditions in particular for clouds. Thus, accounting for clouds, altitude, albedo of
snow and ice, and aerosols is an important aspect in evaluation of the ozone hole effects onto
Figures 2a and b provide examples for the products "daily erythemal effective UV dose clear sky and
cloudy". The accumulation of the hourly calculations to a daily dose allows to assess the UV effects
during the entire daily cycle.
Fig. 2a: PROMOTE forecast of the daily erythemal effective UV dose under assumed clear sky
conditions, valid 06 July 2005. The daily clear sky dose is calculated from the hourly erythemal
effective UV and represents the potential maximum of the erythemal effects. In the summer of the
Northern Hemisphere the maximum of the UV irradiance is located in the subtropics north of the
equator. Impressing feature is the enhanced UV dose over the Himalaya mountains and the Tibetan
highland. Mineral dust, showing strong absorption in the short wave UV, reduces the daily dose over
the great deserts. PROMOTE forecasts exclusively account for aerosol optical properties applying a
monthly climatology since current and forecasted values with a global coverage are not yet
Fig. 2b: PROMOTE forecast of the daily erythemal effective UV dose cloudy, valid 06 July 2005.
Clouds attain UV depending on their optical depth and essentially shape the global distribution of
the UV dose. Monsoon rain over the Indian subcontinent decreases the daily dose to about 50 % of
the potential clear sky values. Low clouds and fog over the up-welling cold waters off the western
coasts of Southern Africa and of South America lower the daily dose too.
Figures 3a and b present the products "high resolution European maps of UV index and dose". The
PROMOTE high resolution UV monitoring products are supplemented by forecasts enabling duly to assess
risks and to take countermeasures.
Fig. 3a: PROMOTE high resolution European forecast of daily maximum of UV Index cloudy, valid
23 June 2005. Due to reduced total column ozone the forecasted UV Index for Southwest Germany exceeds
8.5. This regional unusual high value excites a UV warning for the German Upper Rhine valley.
Fig. 3b: PROMOTE high resolution European forecast of the daily erythemal effective UV dose cloudy,
valid 23 June 2005. The expected almost unclouded sky over Southwest Germany for the entire day
increases the daily UV dose to about 6 kJ m-2
, and backs to issue the UV warning.
Site specific forecasts facilitates the information about UV levels of specific locations and are
linked with short WHO-conform sun protection messages according to the exposure category of the UV
Index value. They are targeted at the general public and are intended to supplement national
radiation protection campaigns offering UV Index information for abroad.
Fig. 4: PROMOTE site specific forecasts “daily maximum of UV Index cloudy” for Australia and
New Zealand, valid 10 Oct 2005. The forecasts for more than 1150 sites are given in a WHO-conform
(2002) presentation with 48 maps covering the whole globe. The region can be selected via a global
and several continental maps. A short health protection message according to the exposure category
is displayed by click on the forecasted UV Index.
The UV Index forecasts are calculated in a strong module strutcture facilitating improvements
if new algorithms or forecasts input is available. Figure 5a presents an example of the single steps
of forecasting. Figure 5b contains the same example but animated.
Fig. 5a: PROMOTE: Module structure to calculate the UV Index for all effective atmospheric
conditions, valid 06 July 2005, 15 UTC.
a) PROMOTE forecast of total column ozone;
b) large-scale UV Index valid for mean sea level, clear sky and set values of aerosol
optical depth at 550 nm (0.20), aerosol type (continental average), and UV surface albedo (3 %);
c) adjusting to seasonal and regional variable aerosol properties (monthly climatology);
d) adjusting to altitude a.m.s.l. (DWD GME topography);
e) adjusting to the albedo of snow and (sea) ice;
f) cloud modification.
Fig. 5b: Similar to 5a but animated.
Fig. 6: PROMOTE hourly forecasts of UV Index cloudy,
valid 06 July 2005, periods +00h to +78h, animated, 1.5 MB.