Presentations and Publications
Stanier, C., Schoenfelder, J., Yarker (Brown), M. Evaluation of the Vaisala CL31 ceilometer as a tool for boundary layer characterization within carbon cycle studies. Report to the NOAA Global Monitoring Division and Vaisala. April 2009.
During the period June 18 to July 18, 2008, a Vaisala CL31 ceilometer was operated at the
Southern Great Plains (SGP) ARM site in Oklahoma. Then the same instrument was shipped to
Iowa and operated at the WBI (West Branch Iowa) tall tower CO2 characterization site. The
operation period at WBI was from July 25, 2008 to Aug 26, 2008. The backscatter product from
the CL31 was compared qualitatively to three operational measurements at SGP – the previous
generation Vaisala CT25K ceilometer, the Micropulse LIDAR, and the four per day
rawinsondes. Boundary layer heights were determined manually from inflection points in
potential temperature and relative humidity in the rawinsonde data. These were compared to
software-determined mixed layer heights from the CL31 using two approaches: Vaisala’s MLH
software package version 3.0 (a MATLAB executable with extensive graphical user interphase)
Both algorithms performed well for matching rawinsonde-derived PBL features between 0.5 and 2 km. Ceilometer-derived boundary layer heights were within 15% of the sonde-derived heights in about 60% of the examined cases. For matching sonde features less than 0.5 km (these were not typically mixed layer heights, but rather the height of stable atmospheric boundary layers) only the Vaisala algorithm was used. In this height range, the Vaisala algorithm tended to cluster the height around a smaller range (120-220 m) than determined by the sondes (40-350 m). Therefore, relative error in the boundary layer height is high. Although there was high correlation between rawinsonde-derived PBL features and ceilometer-based features, the multilayer structure of the atmosphere (corresponding to 2-4 different layers in any given launch) will make interpretation of CL31 data alone difficult.
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