Archive of Spotlight Feature Articles

Interannual Variability of UV Irradiance, Ozone and Aerosol Chemistry in the Arctic

by Melanie Wetzel

An array of monitoring instruments on the roof of the Poker Flat facility

New long-term continuous monitoring site at Poker Flat Research Range, Alaska, for obtaining UV, visible and near-infrared radiation measurements, established through collaboration between NOAA and USDA.

The NOAA-supported project "Interannual Variability of UV Irradiance, Ozone and Aerosol Chemistry in the Arctic" is a collaborative effort of scientists from DRI/CIASTA (Randy Borys and Melanie Wetzel), University of Alaska/CIFAR (Cathy Cahill and Glenn Shaw) and Colorado State University/USDA (Jim Slusser), to improve the monitoring and analysis of the UV irradiance climatology in Alaska. A long-term UV and visible solar radiation monitoring site has been established at the Poker Flat Research Range, Alaska. Continuous measurements (every three minutes) are made of the total, diffuse, and direct irradiance at 13 wavelengths through the UV region (from 300 nm) through the near-infrared (940 nm). Column ozone, and spectral aerosol and cloud optical depths are derived from these data. The data from March 15, 2001 onwards can be downloaded from the Web as part of the USDA UVB Monitoring and Research Program's 30 site climatological network: http://uvb.nrel.colostate.edu/UVB/uvb_climate_network.html

An orange tethered balloon is being launched at the Poker Flat facility

Tetherballoon system used at the Poker Flat Research Range to demonstrate the similarity of aerosol size distribution measurements taken at the ridge-top Climate Monitoring Laboratory with those in the free air above the valley.

The wide spectral range of measurements provides valuable new information on aerosol optical depths in UV wavelengths. Simultaneous sampling and size-specific optical and chemical analysis of aerosol samples in time series offers new opportunities for characterizing aerosol effects on visibility, UV transmission, multiple-scattering between the surface and atmosphere, and cloud microphysical/radiative processes. Chemical, optical and physical aerosol measurements during Spring indicate separate episodes of long range transport to the region of "arctic haze" pollution as well as dust from the Gobi and Taklamakan Deserts in Asia. Aerosol size distributions and visible scattering coefficients of the ambient aerosol were measured continuously at the University of Alaska's Climate Monitoring Laboratory at Poker Flat during Spring 2001. A tethered balloon system was also operated to obtain vertical profiles in the lower 2 km of the atmosphere. These measurements for aerosol size distribution and thermodynamic conditions indicate the representativeness of surface based aerosol measurements at the ridge-level Climate Monitoring Laboratory site. Digital satellite data from the NOAA Advanced Very High Resolution Radiometer (AVHRR) instrument have been collected over the Fairbanks region from the TeraScan groundstation system at the University of Alaska Geophysical Institute and are being applied to mesoscale mapping of downward UV irradiance at the surface, using a combined approach of radiative transfer modeling and multispectral image pixel classification.

The Cooperative Institute for Atmospheric Sciences and Terrestrial Applications (CIASTA), the Cooperative Institute for Research in the Atmosphere (CIRA), and the Cooperative Institute for Arctic Research (CIFAR), are three of NOAA's Joint Research Institutes. These partnerships bring together the resources of research-oriented universities or institutions, NOAA Research, and other branches of NOAA in order to develop and maintain a center of excellence in research relevant to understanding climate, the atmosphere, Arctic regions and long term UV and visible solar radiation.

[11/5/01]

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