Cloud Radars on the Screen at Southern Great Plains Site

 
Published: 15 May 2008

With the flip of a switch, a mysterious cirrus dilemma turned from serious to solved recently, as the millimeter wavelength cloud radar (MMCR) passed inspection at the ARM Southern Great Plains (SGP) site in February. In addition, concerns about data from the ARM Mobile Facility (AMF)’s W-band ARM Cloud Radar (WACR) were alleviated through an intercomparison with the SGP WACR in March. Both radar issues turned out to be minor, but solving them was critical to ensuring the quality of data obtained by the radars in past field campaigns and into the future.

Antennas for the various cloud radars include, from left to right, the SGP WACR, the SGP MMCR, and the AMF WACR.

With their high sensitivity for detecting cloud boundaries, the MMCR and WACR are critical components of the ARM instrument suite. However, for some time the MMCR at the SGP site was unable to detect cirrus clouds as well as it should. Unable to determine the source of the problem, ARM operations staff hoped a planned processor upgrade might do the trick. However, just prior to the upgrade, the ARM radar mentor and the developer of the MMCR from the National Oceanic and Atmospheric Administration visited the site and attempted to track down the source for the loss of sensitivity. They uncovered a benign-looking diagnostic switch hidden from view that had apparently been bumped, putting the radar into a polarization diagnostic mode that impacted the MMCR’s cirrus mode performance. Flipping the switch corrected the problem, the processor upgrade was subsequently completed, and the radar is operating properly once again. Users of MMCR data will be notified of any data quality issues related to this event per the routine reporting process used by the Data Archive.

With the WACR traveling around the world for its AMF deployments, the team was growing concerned about potential damage to the antenna during shipping. Any subsequent calibration offsets could affect data obtained from previous campaigns, as well as the 2008 deployment in China. To provide data quality assurance, the AMF WACR was shipped from Germany at the conclusion of that deployment to the SGP site and compared against the SGP WACR for 3 weeks. After sufficient comparisons, the operations team and WACR manufacturer determined that the AMF WACR agreed with the calibrated SGP WACR within 1 dB; as good as can be done. With confidence in the calibrations, no data corrections were required for the prior AMF deployments in Niger and Germany, and future data collections should be worry-free.