Operations Updates
ARM Climate Research Facility Operations Update - March 15, 2005
This bimonthly report provides a brief summary of significant accomplishments and activities in the operations area of the ARM Climate Research Facility (ACRF).
Japanese Collaborators Take A Long Look at Lightning
Mounted on tripods, numerous interferometer antennas are secured to the roof of the Darwin site observers building, while the computer and electronics are located inside.
While the ACRF sites contain extensive instrumentation for measuring the outflow of convective cloud (storm) systems, they include very little capability for characterizing the convection that produces that outflow. Electrical energy produced by lightning is a useful indicator of convective potential. In December 2004, the Tropical Western Pacific site in Darwin, Australia, began hosting the Darwin Lightning Detection Field Campaign to evaluate the performance of an instrument system for monitoring lightening activity. At the conclusion of the campaign in February 2006, the instrument will be considered for continuous operation at the Darwin site. If approved, the additional instrument will enable the fusion of lightning data with radar data, and broaden the base of potential ACRF users, both scientifically and geographically.
Developed by the Lightning Research Group of Osaka University in Japan, the Very High Frequency Broadband Digital Interferometer uses extremely high (one microsecond) time resolution to capture the spatial distribution of lightning events. The instrument system includes an array of passive antennas, data processing electronics, and a computer to collect the data. Broadband signals received by the antennas are amplified and then digitized at a sampling rate of 200 MHz with 10-bit resolution. Up to two thousand electromagnetic pulses per second can be recorded for one lightning flash. A global positioning receiver is also included to accurately record when a lightning strike occurs.
Lightning measurements in the Darwin area—where electrical storms are common—will be an important complement to ACRF's existing radar capabilities. The instrument will also be valuable for aircraft safety during mission planning for the Tropical Warm Pool-International Cloud Experiment that begins in January 2006, by providing information about electrical activity in the Darwin area that could influence flight patterns.
Bad Gas Examined During Field Campaign at North Slope of Alaska
About the size of a toaster, the MAX-DOAS instrument system at Atqasuk is well-insulated to protect it from the Arctic cold. As the unit rotates on its side axis, measurements are obtained through the optical inlet.
Springtime in the Arctic produces reactive halogen gases, such as bromine monoxide, that form from evaporating sea salt. These gases destroy ground-level ozone and convert gaseous mercury into toxic snow-bound mercury ions that can end up in the ecosystem. To better understand this atmospheric chemistry and the subsequent impacts to environmental and human health, researchers funded by the National Science Foundation (NSF) are measuring the concentration of halogen gases during a three-month field campaign hosted at ACRF's Atqasuk site at the North Slope of Alaska (NSA). The focus of the field campaign, referred to as Studies of the Northern Alaskan Coastal System, is a remote-sensing technique that uses multiple axis differential optical absorption spectroscopy (MAX-DOAS). The MAX-DOAS instrument scans the sky from the zenith to the horizon, taking measurements of halogen oxide. Vertical profiles of this gas show its presence in both the stratosphere and in the planetary boundary layer (typically the lowest kilometer of the earth's atmosphere). It is bromine monoxide in the boundary layer that is of interest to researchers in this field campaign.
The instrument was installed at Atqasuk on February 16, 2005. At the conclusion of the field campaign in May, data from the instrument will be correlated with meteorological information from the ARM Data Archive to investigate how air mass origin affects halogen oxides. The measurements will also be compared with those taken by a similar instrument located at NSF facilities in Barrow, Alaska, approximately 70 miles north of Atqasuk. Comparison of the measurements between the two sites will provide information on how the halogen oxides are formed and their concentration gradients at NSA. Through improved understanding of these halogen oxides, scientists can better predict how changes in pollutant emissions and global climate affect the deposition of toxins and their atmospheric oxidation.
