Sunshine. It rejuvenates our gardens, illuminates our homes, and lightens our moods. In short, it makes this third planet more than a lifeless rock. But, despite our obvious dependence on our nearest star, there is a more sinister aspect to the sun.

Wrinkles, skin cancer, cataracts, thickening of the cornea, even suppression of our immune systems have all been linked to the sun, or more specifically, to the invisible ultraviolet (UV) radiation that emanates from it. In addition to threatening our health and vanity, UV radiation may threaten our food supply by impacting plant growth and productivity. To make it all even scarier, there is growing evidence that we're being exposed to more damaging UV rays than ever before, because of the depletion of the Earth's protective ozone layer. But don't worry. Our people are working on it.

Dr. Melanie Wetzel of DRI's Atmospheric Sciences Center is part of a nationwide team of researchers trying to learn more about UV radiation, specifically how it changes under different environmental conditions and from region to region. As part of the United States Department of Agriculture's (USDA) UV-B Radiation Monitoring Program, she's helping to provide the data and analysis needed to assess the potential impacts of increasing UV radiation on agriculture, forest productivity, and the people who spend time through work or recreation in rural and forest environments.

Under the program, the USDA has established a network of monitoring stations throughout the United States. The newest part of that network is DRI's Storm Peak Laboratory, located in the Park Mountain Range of northwest Colorado. The laboratory's location, at the lofty elevation of 10,525 feet, makes it an important and unique addition to the network. "The Storm Peak location provides new observational data from an alpine forest ecological zone," explains Wetzel. "It's important that the sites in the network represent a variety of ecosystems since UV radiation is influenced by many different factors, including elevation, humidity, snow and cloud cover, and the concentrations of atmospheric particulates and gases."

Of most concern, for health reasons, is the part of the ultraviolet spectrum known as UV-B. The project uses sensors to measure solar radiation at several different wavelengths to track the intensity and character of UV radiation reaching us under a variety of meteorological conditions.

The growing archive of measurements will provide valuable data for testing computer-based model calculations of UV flux in clear and cloudy conditions, verifying satellite-derived mapping of downward UV radiation and atmospheric ozone amount, and improving daily forecasts of UV exposure in mountainous terrain.

Brian Brong, a graduate student in the University of Nevada, Reno's Atmospheric Sciences graduate degree program, participated in a graduate course on meteorological field measurements held at the Storm Peak Laboratory during January 1999. The course was taught by DRI Atmospheric Sciences faculty, Dr. Randy Borys and Dr. Melanie Wetzel. Students designed and conducted individual research projects on topics such as UV flux variability, terrain-induced wind circulation patterns, calibration of cloud physics instrumentation, and detection of trace amounts of air contaminants.

As it turns out, the region represented by measurements at Storm Peak is great country, not just for hiking and skiing, but also for UV exposure. "Those who live in the West often get higher doses of ultraviolet radiation due to the clear skies, low humidity, and higher altitude," says Wetzel. Other important factors are cloudiness and snow cover. In Wetzel's words, "The reflectance of sunlight (known as albedo) by clouds and snow is greater in the UV wavelength than in the visible wavelength." It's easy to see that snow reflects visible light back at us-we enjoy those bright, sunny days while out on skis, snowshoes, or snowboard. What we can't see, however, is that even more of the invisible UV rays are being reflected back at us, making our perfect day on the slopes the perfect opportunity for skin and eye damage.

The sophisticated equipment used at Storm Peak lets researchers look in detail at how such environmental variables affect UV radiation. With measurements taken every 20 seconds, researchers can see how passing clouds, or the amount of atmospheric ozone or airborne particles, affect the flux of ultraviolet radiation. In combination with other instrumentation at the lab for measurement of cloud microphysical characteristics, the UV and solar radiation data will also be used to characterize how effectively clouds transmit and scatter the radiation. At its high- elevation site, the Storm Peak Laboratory is frequently immersed in cloud and provides an ideal opportunity for simultaneously sampling the cloud particle conditions as well as the flux of atmospheric radiation.

Three of the 16 teachers working with atmospheric instrumentation and measurements while attending field training workshops at Storm Peak Laboratory during summer 1998. Shown from left to right are Alan Lewis (Bonanza High School, Las Vegas), Pat Wulster (FranklinMiddle School, New Jersey), and Barbara Graham (Community College of Southern Nevada). Participants installed four different instrument towers, including this system with UV and solar radiometers in addition to other sensors.

Besides shedding more light on the factors that control the amount of UV radiation reaching Earth, DRI's new radiation monitoring instrumentation also has great potential for collaborative research on how that radiation affects living things. "We are collecting the atmospheric radiation measurements to establish a long-term database," says Wetzel, "and now the challenge is to examine how the observations relate to biological and human impacts-to connect it to the ecological risks. It is important to collaborate with biological scientists to pursue research to improve our understanding of these risks."

Toward that end, Wetzel will be making similar UV and solar radiation measurements while working in the Reno/Tahoe area this summer with Dr. Ray Kepner from DRI's Biological Sciences Center. Together, they will investigate biological impacts such as the variation in UV exposure within the forest vegetation canopy and the responses of algae and zooplankton in Lake Tahoe to UV flux.

A long-term goal of research collaborations at DRI is to make comparison studies of UV climatology and ecological impacts at multiple western sites such as the Reno/Tahoe area of the Sierra Nevada Mountains and the Storm Peak Laboratory site in the Rocky Mountains. This year's summer research project is also tied to a unique instructional program funded by the National Science Foundation. The Nevada Science Teacher Enhancement Program will team high school teachers and students with DRI scientists to introduce the high school participants to measurement and research methods related to studies of UV flux climatology at various sites in the Reno/Tahoe area.

"These studies are important for research on ecosystem risk from ozone depletion," explains Wetzel, "and also for understanding ecosystem response to the combined effects of UV increases and other climate variations." The popularity of these programs points to a growing awareness of, and concern for, the harmful effects of ultraviolet radiation. Thanks to the work of Wetzel and Kepner, and other scientists interested in this interdisciplinary field of research, we're learning the best ways to live with the sun's darker side.

Jackie Allen

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