Operations Updates
ARM Climate Research Facility Operations Update - October 31, 2004
This bimonthly report provides a brief summary of significant accomplishments and activities in the operations area of the ARM Climate Research Facility (ACRF).
Intensive Arctic Field Campaign Concludes
The Citation aircraft—equipped with a standard set of microphysical measurement systems and an ice nucleation counter—completed 13 flights during M-PACE, collecting in situ measurement data.
The Mixed-Phase Arctic Cloud Experiment (M-PACE), the largest and most ambitious field campaign conducted thus far at the ACRF North Slope of Alaska locale, concluded on October 23, after almost a month of concentrated measurement activity. The experiment involved four weeks of intensive ground, remote sensing, aircraft and radiosonde measurement activities focused on obtaining microphysical data on clouds consisting of both water droplets and ice crystals (i.e., mixed phase). Throughout much of the study period, radiosonde data was acquired at six-hour intervals from Barrow, Atqasuk, Oliktok Point and Toolik Lake. These four locations delimited the roughly rectangular study area.
To obtain in situ measurements, the University of North Dakota Citation aircraft probed low-level clouds (between 1,500 and 3,000 ft.) over the entire study area, but particularly over Barrow (ACRF's primary measurement site at NSA) and Oliktok. The Citation was based at Deadhorse/Prudhoe Bay, where experimental headquarters was also located. Another aircraft, the Proteus high altitude remote sensing aircraft, probed clouds in the area from about 25,000 to 43,000 ft. Proteus flights originated from Fairbanks, and most were timed to coincide with satellite overpasses. Pacific Northwest National Laboratory's Atmospheric Remote Sensing Laboratory—a mobile measurement facility with many of the same instrument capabilities as the ACRF fixed sites—was located at Oliktok Point, near the United States Air Force Long Range Radar Station. A tethered balloon measurement system was also deployed from this location. The Department of Energy's Multispectral Thermal Imager satellite system surveyed Barrow and Oliktok at high resolution in 15 spectral bands as often as possible throughout the experiment.
Many months will be spent analyzing the data. However, early results show that observed low ice nucleation particle counts can, in part, explain the prevalence of super-cooled liquid clouds in the Arctic, even to temperatures as low as -25 °C. The microphysical characteristics of these mixed-phase clouds, where thoroughly documented under a variety of environmental conditions, provide the measurements needed to study the basic physics of these hitherto poorly understood clouds.
ACRF Lends Support to Military Flare Tests
Prior to the flare tests, SGP personnel informed local landowners and fire departments about the nature of the tests, particularly the large amount of smoke anticipated from the flares.
On October 19 and 20, 2004 a series of aircraft flares were ignited at the ACRF Southern Great Plains (SGP) site on behalf of the U.S. Missile Defense Agency. While the flares burned, measurements were collected from infrared sensors on board the High-Altitude Laser Observatory (HALO) aircraft developed and operated by L3-Aeromet. During the tests, personnel from Johns Hopkins University and L3-Aeromet operated ground-based instruments from the elevated deck of the SGP Guest Instrument Trailer, which received high marks for the excellent facilities it offers visiting scientists. Data collected during these tests will be used in the development and testing of techniques to reduce "optical clutter" from surveillance images.
Representatives of Hanscom Air Force Base (AFB) organized the tests, which were approved by the Oklahoma Department of Environmental Quality and coordinated with the Bureau of Alcohol, Tobacco, and Firearms. Hanscom AFB personnel prepared the test site by spreading a layer of sand over a 10-m by 10-m area in the pasture just north of the SGP Central Facility, so that the prevailing southerly winds would carry the smoke from the flares away from the site personnel and instrumentation. SGP personnel secured the area with fencing and provided safety oversight for the tests, while representatives of Armtec Esterline Corporation, the flare manufacturer, set up and ignited the flares. A post-test inspection was carried out at the ignition site to ensure all materials associated with the flares were collected.
New Pump Shelter Kicks Off Upgrades to Aerosol Observing System
Representing the first of several planned improvements to the Aerosol Observing System (AOS) at the SGP site, ACRF operations staff completed installing a new pump shelter for the system in late September, followed by relocation of the pumps and connection of the electrical hookups in October. Though the enclosure was designed primarily to move the nine vacuum pumps out of the existing AOS trailer—thereby reducing the potential for damage to the AOS instruments from heat generated by the pumps—noise reduction in the AOS trailer was another desired outcome. Anticipated instrument additions were also considered in designing the new enclosure.
The new pump shelter sits on a concrete pad near the south end of the AOS. Four adjustable, open-wire shelves run the width of the shelter, and can accommodate sixteen large pumps and associated ventilation equipment.
The completed cabinet assembly was received from the vendor in late September and attached by operations staff to a concrete foundation next to the AOS. About a month later, the pumps were moved into the shelter and aerosol sample lines were extended from the existing pump locations and routed to the new shelter through a tubing chase (conduit). The pumps, exhaust lines, and associated electrical outlets were all color-coded to aid in identifying related pieces of equipment.
The AOS represents the primary platform for in-situ aerosol measurements at surface level. Instruments contained in the AOS include two nephelometers, and one each of the following: light absorption photometer, condensation nuclei counter, optical particle counter, and ozone monitor. Combined, these instruments measure the optical properties of ambient aerosol particles to help scientists better understand how the particles interact with solar radiation and influence the earth's radiation balance and climate system.
In addition to reducing the heat and noise levels in the AOS trailer, relocation of the vacuum pumps frees up room for the addition of a Tandem Differential Mobility Analyzer. This instrument, which measures the size distribution, refractive index and moisture absorption potential of aerosols, will be built by Texas A&M University and is scheduled for deployment in the AOS in 2005. Additional AOS upgrades to occur in 2005 include expanded measurements for the particle soot absorption photometer instruments, which currently provide measurements of absorption at 565 nm. These instruments will be upgraded to add measurements at 450 nm and 700 nm to complement nephelometer measurements of total scatter and hemispheric backscatter at 450 nm, 550 nm, and 700 nm.
