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Near-Real Time Estimates of UV Dose using EP/TOMS data |
These maps represent local noon estimates of the UV Index (UVI) and total daily integrated erythemal dose amounts generated at a 1x1 degree latitude/longitude resolution using near-real time total column ozone abundances measured by NASA's Total Ozone Mapping Spectrometer (TOMS) instruments carried on board the Earth Probe (EP) satellite platform.The UV Index and Daily Erythemal Dose: Definitions
The UVI scale calculated in these images is the index defined by the World Meteorological Organization (WMO). This value is calculated by finding the instantaneous erythemal UV exposure value at local noon (measured in watts per square centimeter) and scaling this value by a factor of 0.4; this procedure will typically result in values ranging from 0-15 in mid-latitudes. Tropical regions will experience indexes greater than 15, with extremely high values greater than 20 often occurring in high altitude regions. The daily integrated erythemal dose is found by estimating the instantaneous dose values at every half hour during the day, and summing these values over the course of the day using a simple trapezoidal numerical integration scheme. When summed over time, the instantaneous values calculated in watts per square centimeter are then given in kilojoules per square meter, the total amount of radiant energy received over a 1 square meter area during the daytime. As with the UV Index, daily erythemal dose levels will generally increase as latitude decreases, with highest levels found at elevation.Limitations
These estimates represent clear-sky values for these dose variables; cloud cover is not incorporated into the model due to the lack of a corresponding global gridded cloud cover data available in near-real time. As a result, these values represent the maximum potential UVI and daily integrated erythemal dose for the day; the presence of cloud cover, excessive airborne particulates and/or ground-level ozone would reduce these values. Note, however, that even under partly cloudy skies, the UVI can reach its maximum value if the sun appears between clouds and direct sunlight reaches the Earth's surface. For more information on the TOMS instruments and the radiative transfer model used to generate these maps, see the following documents:
These maps are generated using near-real time data transmitted from the EP/TOMS instrument, and thus have gone through minimal processing at NASA-GSFC prior to distribution. NASA provides these data with the understanding that the data are preliminary estimates, and are subject to further revision upon a more detailed analysis. As a result, the UV dose levels indicated in these maps should also be regarded as estimates that are subject to further revision based on updates to the TOMS data. For more information on model validation and status of the TOMS data, please visit the following:
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