Spatio-temporal Vairation Of Earth Surface UV-B Irradiance And Sensitivity Analysis

In recent decades, ozone reduction owing to human activity caused increase ofthe earth surface ultraviolet irradiance, which has been confirmed by many researchresults. The status of global ultraviolet irradiance and long term variation trend attractextensive concern all around the world. As animals and plants are most sensitive toUV-B irradiance and UV-B irradiance is more harmful to human bodies and biology,the study focuses on the global UV-B irradiance distribution characteristics,spatio-temporal variation and sensitivity to its important impact factors.The ground-baesd ultraviolet irradiance data from world ozone and ultravioletradiation data center was used to do the calibration of the daily noon surface UV-Birradiance data which is from TOMS/Nimbus-7(1979.1.1--1993.4.30), TOMS/EarthProbe (1996.8.1--2005.12.31) and OMI/EOS-Aura (2005.1.1--2008.12.31). So thesatellite observation data is closer to the earth surface real irradiance and thespatio-temporal variation characteristics of earth surface UV-B irradiance in nearlythirty years could be analyzed more accurately by using satellite data after calibration.Currently, sensors involved ultraviolet irradiance wavelength at home and abroadmainly adopt nadir and limb detection modes. SCIATRAN is one of the matureradiative transfer simulation models, providing nadir and limb both observationmodes and a much more detailed parameters input system. So SCIATRAN is used inthis study to analyze the UV-B sensitivity to ultraviolet irradiance impact factors, andsimulate surface UV-B irradiance at different ground types. The study focuses on fiverecognized factors: observation geometry, total ozone, thickness of the cloud, aerosolthickness, and surface albedo.Global UV-B irradiance distribution shows zonal distribution feature obviously,gradually decreasing with the increase of latitude. And ultraviolet irradiance of oceanis higher than that of the land at the same latitude. Furthermore, global monthlyaverage of UV-B irradiance presents sine curve variation characteristics. March(vernal equinox) and September (autumnal equinox) are the peaks, while June(summer solstice) and December (winter solstice) are the valleys due to the seasonaldifferences in southern and northern hemispheres. At the same time, southern hemisphere receives more UV-B irradiance than northern hemisphere in a year. Inaddition, global ultraviolet irradiance increased about3%nearly thirty years andozone depletion is relatively serious at the South Pole, extending to the mid-latituderegions. EOF analysis shows that variation trend of global UV-B irradiance isbasically uniform. There is key region with large value at the ocean, which indicatesthat ultraviolet irradiance over ocean changes more distinct. On the whole, UV-Birradiance has certain cyclic variation from1979to2008. Morlet wavelet analysisillustrates that global UV-B irradiance has change cycle when scale factors are0.8,1.8and5.1, whose time periods are6,13and127months. So the significant cycleperiods of global UV-B irradiance are about half a year, one year and eleven years(solar cycle).Firstly, UV-B irradiance decreases with the increase of solar zenith angle in bothobservation modes, but sensitivity is relatively weaker in limb. Secondly, azimuth isnot a main factor in nadir, while UV-B irradiance increases slightly with the azimuthincrease in limb. Thirdly, UV-B irradiance is directly proportional to observationangle and tangent height before302nm, and opposite occurs after302nm. Then,irradiance reduces not much when ozone is less than normal, but increases a lot whenozone exceeds the normal. In addition, Cloud optical thickness has similar effect ontwo observation modes, which weaken UV-B irradiance well when it is thinner, thenweaken level reduces gradually. What is more, Aerosol optical thickness only hasinfluence in nadir after305nm, and the sensitivity feature is similar with cloudoptical thickness. At last, irradiance increase obviously with the rise of albedo in nadirmode, while effect is very weak in limb. The surface UV-B irradiance simulationusing SCIATRAN is close to the actual ground-baesd observed data with thedifference about±10%.