Atmospheric Radiation Measurement Program Facilities Newsletter, August 2003 PDF Download

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Languages : en
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This Monthly newsletter discusses the following topic: New Atmospheric Profiling Instrument Added to SGP CART Suite--A new atmospheric profiling instrument at the SGP CART site is giving researchers an additional useful data stream. The new instrument is a microwave radiometer profiler (MWRP) developed by Radiometrics Corporation.

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This Monthly newsletter discusses the following three topics: (1) Representative Lucas and Senator Myers Support SGP Site; (2) Broadband Outdoor Radiometer Calibration (BORCAL) Takes Place at SGP; and (3) ARM Program Research Featured in ''Science'' Magazine.

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Cloudiness Inter-comparison IOP--Clouds are an important part of Earth's energy system. We take clouds for granted, but their role in weather and climate is considerable. Without clouds, life on Earth would be impossible. By helping to regulate surface temperatures, clouds establish livable conditions on the planet. Clouds produced by water vapor condensation play a complicated role in our climate system. Clouds decrease the amount of sunlight received by Earth's surface. Decreased sunlight reduces evaporation driven by sunlight and thus reduces cloud formation. With fewer clouds, Earth receives more sunlight, which eventually increases evaporation and cloud production. On the other hand, clouds also trap longwave (infrared) radiation emitted by Earth, as does water vapor. This heating effect increases evaporation. In summary, cloud formation is a complex, self-regulating, cyclic process. The SGP CART site is conducting a Cloudiness Inter-comparison IOP (intensive operational period) from mid-February through mid-April. The central facility near Lamont, Oklahoma, currently is home to several cloud-measuring instruments. The process of measuring cloudiness has always been somewhat subjective. Cloud measurements were once made by solely human observation, but new technology enables instruments to view the sky and make the more objective cloud measurements needed by both operational and research meteorologists. The SGP site currently operates eight different instruments that make cloud-related measurements. Data are collected on cloud cover, cloud top and base location, cloud water vapor and liquid water, sunshine duration and amount, and cloud number and area. During the Cloudiness Inter-comparison IOP, three additional cloud-measuring instruments are being brought to the CART site to be tested and assessed against the current instruments. Researchers are interested in testing whether the additional instruments can collect better data during nighttime hours, when visible light is not available for measurements. One of the three additional instruments is a commercially produced analyzer called the Nephelo. The Nephelo uses a series of infrared detectors to yield estimates of fractional sky cover. A second instrument to be tested is an infrared cloud imager. This instrument was previously deployed for testing at ARM's North Slope CART site in Barrow, Alaska. The third system to be tested will be a narrow-field-of-view infrared thermometer, operated in scanning mode rather than in the fixed vertical orientation. Scanning with the instrument and analyzing high-frequency samples of its data will increase the sky area covered. Collection of cloud data is not straightforward, because determination of actual cloud cover is subject to the definition of what is and is not a cloud. An instrument's determinations and calculations depend on its ability to detect a cloud either via collection of backscatter from a directed signal or by computer analysis of digital photographs. Verification of the data is restricted by the difficulty of the establishing a ''ground truth'' value. Thus, the emphasis in this IOP has to be on comparing measurements from the different instruments. Earth's climate is directly affected by the presence and absence of clouds. However, the accuracy of computer depictions and prognostications of future climate is limited by inadequacies in the parameterization of clouds in global climate models. A high-priority ARM Program goal is to increase our understanding of the interactions between clouds and solar radiation in the atmosphere, so that this complicated duo can be incorporated accurately into computer climate models.

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This issue of the ARM facilities newsletter discusses the Spring 2000 cloud intensive observation period, March 1--21, 2000. The month of March brings researchers to the SGP CART site to participate in the Spring 2000 Cloud IOP. The purpose is to gather data about the three-dimensional structure and distribution of clouds over the CART site. This effort will help to produce a more accurate representation of the clouds and their influence on weather and climate for use in computer modeling.

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ARM in Australia--The Atmospheric Radiation Measurement (ARM) Program of the U.S. Department of Energy (DOE) has launched its newest Atmospheric Radiation and Cloud Station (ARCS) in Darwin, Australia. This is the fifth research site established since ARM Program inception in 1989. The new Darwin site and two other ARCS sites--on Manus Island and the island of Nauru--are in the Tropical Western Pacific region. The North American sites in the U.S. Southern Great Plains and on the North Slope of Alaska represent two different climate regions. A goal of the ARM Program is to improve understanding of (1) the ways clouds and atmospheric moisture interact with solar radiation and (2) the effects of these interactions on both a local and global climate. Years of collected data are being used to improve computer climate models so that their predictions are more accurate. The new Darwin site is at the Darwin International Airport, adjacent to the Darwin Airport Meteorological Office. The site features state-of-the-art instrumentation used to measure solar radiation and surface radiation balance; cloud parameters; and standard meteorological variables such as temperature, wind speed and direction, atmospheric moisture, precipitation rates, and barometric pressure. A data management system (DMS) consisting of two computer workstations collects, stores, processes, and backs up data from each of the ARCS instruments. Data are transmitted via the Internet to the United States for further processing and archiving with data from the other ARM sites. All ARM data are freely available via the Internet to the public and the worldwide scientific community (http://www.arm.gov/). Operational since April 2002, the Darwin site was officially dedicated on July 30, 2002, by dignitaries from both the United States and Australia. The site is a collaborative effort between DOE and the Australian Bureau of Meteorology's Special Services Unit--the equivalent of the U.S. National Weather Service--which will handle daily operation. U.S. Secretary of Energy Spencer Abraham remarked, ''Our collaboration with Australia in the establishment of this site represents an exciting expansion of the ARM Program and our ongoing quest to understand and predict the earth's climate.'' The five ARM Program research locations were chosen because of their varying and abundant cloud formations. More cloud types mean a more complete investigation. To the ARM collection, the Darwin site adds data sets detailing interactions between a unique type of cloud and solar radiation. This addition represents another step toward the ARM goal of more accurate predictions from computer climate models.

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In the realm of global climate modeling, numerous variables affect the state of the atmosphere and climate. One important area is soil moisture and temperature. The ARM Program uses several types of instruments to gather soil moisture information. An example is the soil water and temperature system (SWATS). A SWATS is located at each of 21 extended facility sites within the CART site boundary. Each system is configured to measure soil moisture and temperature at eight distinct subsurface levels. A special set of probes used in the SWATS measures soil temperature, soil-water potential, and volumetric water content. Sensors are placed at eight different depths below the soil surface, starting at approximately 5 cm (2 in.) below the surface and ending as deep as 175 cm (69 in.). Each site has two identical sets of probes buried 1 m (3.3 ft) apart, to yield duplicate measurements as a quality control measure. At some sites, impenetrable soil or rock layers prevented installation of probes at the deeper levels. The sensors are connected to an electronic data logger that collects and stores the data. Communication equipment transfers data from the site. All of the electronic equipment is housed in a weatherproof enclosure mounted on a concrete slab.

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Aerosol Observing System Upgraded--The Aerosol Observing System (AOS) at the SGP central facility recently received maintenance and was upgraded to improve its performance. The AOS measures the properties of the aerosol particles around it. Several AOS components were removed, repaired, and calibrated to operate within specifications. The system continuously gathers information about the way minute aerosol particles interact with solar radiation. A better understanding of these interactions will help climate change researchers integrate aerosol effects more accurately into global climate computer models. Polar Bears Make Work Dangerous at ARM North Slope of Alaska Site--The late development of seasonal sea ice has increased polar bear sitings at ARM's Barrow site. The bears were recently seen next to the ARM instrument towers at Barrow, making the normal work day a bit more tricky for the technicians who are at the site year-round. Polar bears are not afraid of people and will attack and kill. The bears usually spend most of their time on off-shore ice floes hunting seals. This season, a large storm pushed the floes out to sea while the bears were ashore at Barrow, leaving them to forage for food on land until the sea ice reforms with the onset of colder weather. The hungry bears have made working at the Barrow CART site a dangerous proposition. ARM workers carry shotguns with them at all times for protection. On a recent journey to the site, ARM instrument mentor Michael Ritsche encountered the animals. ''You become much more aware of your surroundings, '' said Ritsche after returning safely to Argonne. Barrow residents protect themselves by shooting warning shells to scare the bears away from developed areas. Hearing the firing in the early mornings and late evenings at Barrow reminded Ritsche that he was in a more dangerous world.

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The primary objective of this USDA program is to provide information to the agricultural community about the geographic and temporal climatology of UV-B radiation. Scientists also use the data to determine changes in stratospheric ozone levels, cloud cover, and aerosols as they pertain to UV-B radiation and to improve the understanding of factors that control transmission of UV-B radiation. Advances have been made in areas of agriculture, human health effects, ecosystem studies, and atmospheric science. ARM Program personnel are excited about being a part of such a worthwhile effort.

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With the end of summer drawing near, the fall songbird migration season will soon begin. Scientists with the ARM Program will be able to observe the onset of the migration season as interference in the radar wind profiler (RWP) data. An RWP measures vertical profiles of wind and temperature directly above the radar from approximately 300 feet to 3 miles above the ground. The RWP accomplishes this by sending a pulse of electromagnetic energy skyward. Under normal conditions, the energy is scattered by targets in the atmosphere. Targets generally consist of atmospheric irregularities such as variations in temperature, humidity, and pressure over relatively short distances. During the spring and fall bird migration seasons, RWP beam signals are susceptible to overflying birds. The radar beams do not harm the birds, but the birds' presence hampers data collection by providing false targets to reflect the RWP beam, introducing errors into the data. Because of the wavelength of the molar beam, the number of individuals, and the small size of songbirds' bodies (compared to the larger geese or hawks), songbirds are quite likely to be sampled by the radar. Migrating birds usually fly with the prevailing wind, making their travel easier. As a result, winds from the south are ''enhanced'' or overestimated in the spring as the migrating birds travel northward, and winds from the north are overestimated in the fall as birds make their way south. This fact is easily confirmed by comparison of RWP wind data to wind data gathered by weather balloons, which are not affected by birds.