Japanese Collaborators Take A Long Look at Lightning

 
Published: 15 March 2005

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 ARM 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 ARM Climate Research Facility 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 ARM Climate Research Facility’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.