Operations Updates
ARM Climate Research Facility Operations Update - September 30, 2007
This bimonthly report provides a brief summary of significant accomplishments and activities in the operations area of the ARM Climate Research Facility (ACRF).
Atqasuk Joins International Network of Meteorological Stations
On the skydeck at Atqasuk, the new met pack (above right) and GPS receiver (circled at left) acquire data for the SuomiNet.
At the North Slope of Alaska, the ACRF operates a research site in the remote town of Atqasuk, Alaska, to provide continental Arctic data to the climate research community. The Atqasuk site is proving useful to climate modelers since this inland site is more homogenous and uniform than coastal sites during summer months. Enhancements to the instrument suite in Atqasuk last year led to a recent addition that solidified Atqasuk's position on the international science map as a key site for atmospheric measurements. On July 15, 2007, Atqasuk instruments began providing meteorological data to SuomiNet, an international network of global positioning system (GPS) receivers. These receivers are configured and managed to generate near real-time estimates of precipitable water vapor in the atmosphere, total electron content in the ionosphere, and other meteorological and geographical information. The low-cost addition of the Atqasuk site to SuomiNet provides an additional meteorological datastream for use by the science community.
In 2006, scientific partners installed a GPS receiver at the ACRF Atqasuk site to provide a highly accurate geographic reference. The same type of GPS receiver is deployed at ACRF's Tropical Western Pacific sites at Manus, Nauru Island, and Darwin, Australia, on behalf of SuomiNet. The relatively minor addition of a "met pack"—for measuring barometric pressure, temperature, and relative humidity—to the GPS receiver qualified the Atqasuk site for inclusion in the SuomiNet community. The same model of met pack is also deployed at 15 extended facilities at the ACRF Southern Great Plains site that are part of the SuomiNet. Estimates of precipitable water vapor at 30-minute intervals are now included in the gec30suomigpsX1.c1 data files available from the ARM Archive.
Improved Instrument Calibration Capabilities Benefit All Sites, Users
To ensure that ACRF precipitation measurements are as accurate as possible, the SGP rain gauges (white cylinder above left) are inspected every two weeks, are statically calibrated in the field every six months, and will now be dynamically calibrated on an annual basis using the system shown above.
The ACRF fills a unique position in the scientific community by obtaining long-term continuous measurements of cloud and radiation properties critical to climate modeling. Central to this mission is the ability to maintain and quickly repair instruments, as well as providing integrated instrument calibration processes to ensure ACRF provides high quality data products. In the past 15 years of operations, the ACRF Southern Great Plains (SGP) site has developed many onsite repair and calibration capabilities that have led to increased efficiencies and cost savings that benefit not just the SGP site and its users, but the other ACRF sites as well. In the past year, enhancements to various components of the site's Radiometer Calibration Facility further increase its ability to provide timely and accurate data to the scientific user community.
A dynamic rain gauge calibration procedure was implemented in 2007. A basic rain gauge calibration is done by dripping a known amount of water into the gauge and reading the amount of water measured. However, this procedure does not take into account errors that might occur during a heavy rainfall event, a common occurrence during spring and summer in Oklahoma. A dynamic rain gauge calibration compares known "rainfall rates" generated by computer-controlled equipment to rates measured by the gauge being calibrated. Differences can then be accounted for in the rain gauge data processing.
The equipment necessary to calibrate multifilter rotating shadowband radiometers and other similar sensors was also recently acquired at the SGP. Because each instrument has seven detectors that require calibration and characterization at all solar viewing angles (sunrise to sunset), a very precise calibration setup is required, as well as a significant amount of time to complete the procedure. Calibration procedures have been formalized, staff training has been completed, and some calibration activities have already begun. This enhancement adds a significant and important calibration capability to the ACRF.
