NASA SOHO Mission,Yohkoh
science team
Ecological impacts of
UV-B radiation
Spatial and temporal patterns
The distribution of ozone, and associated levels of UV-B, can help to predict which, and to what degree, organisms and ecosystems are impacted by increases in UV-B. Methods of ozone and UV-B measurement are also important to put distribution patterns into context.
Methods for measurement of ozone
Stratospheric ozone concentrations were first measured in 1919 and 1920 from the ground when Fabry and Buisson designed a special spectrograph. The instrument was effective in taking measurements of stratospheric ozone, but the procedure requires direct sunlight and a long time for processing. Spectrophotometers have similarly been used to measure ozone from the ground. The ozone hole above Antarctica was first noticed in the 1970's using a spectrophotometer at Halley Bay Research Station.Stratospheric ozone is also measured by satellite-born instruments. The Total Ozone Mapping Spectrometer (TOMS) takes daily, global measurement of ozone from satellite measurements of back scattered light, mainly in the UV range. Daily and monthly averages of ozone and animations depicting changes of ozone over the past 15 years can be found here.
Methods for measurement of UV-B
Ground measurements of UV-B are taken using radiometers and pyranometers, but sensors are only capable of localized measurements. Some ground-measurements within the U.S. can be found here.More often, global UV levels are computed using the forecasted ozone data, a radiative transfer model, forecasted cloud amounts and the elevation of the forecast cities. The NOAA/EPA UV Index, for instance, is computed in this way. Find the daily UV index for your location (in the U.S.) here.
Spatial and temporal patterns of ozone and UV-B
Long-term measurements of ozone have identified stratospheric ozone losses over most of the Earth, with the exception of in the equatorial region. The largest losses have been observed over Antarctica (50%) and the Arctic (15%) in spring. A 5% loss has been observed year-round at mid latitudes in the Southern hemisphere and 6% and 3% losses have been observed at mid latitudes in the Northern hemisphere in the winter/spring and summer/fall, respectively. These losses illustrate both the spatial and temporal heterogeneity of ozone depletion.
Stratospheric ozone measurements from Halley Bay, Antarctica
UV-B radiation increases generally correlate with stratospheric ozone losses but exact levels of UV-B reaching Earth's surface are even more spatially and temporally variable than stratospheric ozone concentrations since they are also partially dependent on cloud cover, tropospheric pollution, and changes in UV throughout a day and with seasons. For example, Grant and Slusser (2003) found a 0.7 linear correlation in UV-B measurements from USDA UVB Monitoring Network locations 100 km apart and consistently very low levels of correlation between locations greater than 600 km apart. They attributed this low correlation in UV-B between locations to movements of cloud cover. Models, which incorporate cloud cover, also have problems accurately determining UV-B levels for specific locations due to high spatial and temporal variability in the factors used to determine UV-B. Direct measurements and modeled values of UV-B all indicate that UV-B levels reaching a location increase where stratospheric ozone destruction has occurred.
