|The balloon-borne replicator collects and preserves ice crystals and cloud droplets using the Formvar replication technique. Details of the instrument design and measurement capabilities are described in Miloshevich and Heymsfield (1997, J. Atmos. Oc. Tech., 14, 753).|
The brief description given below references these photographs of the instrument.
Top Panel: The replicator consists of a lightweight plastic frame with a continuous loop of transparent 8 mm film base (NOT photographic). The film base is precoated with a thin layer of Formvar (a plastic), which is softened in-flight by dispensing solvent onto the film just prior to the sample opening in the box that houses the replicator. A small motor moves the film across the sample opening, where the airflow from the ascending balloon package impacts cloud particles in the softened Formvar. The particles are preserved as plastic replicas after the solvent evaporates and the Formvar hardens.
Middle Panel: The replicator is launched with a Vaisala radiosonde, and the two instruments are interfaced in such a way that the microphysical data can be correlated with the radiosonde data. This allows construction of altitude profiles for studying the variability in the vertical of cloud microphysical properties, and also allows correlation with complimentary measurements such as ground-based radar reflectivity. The radiosonde also reports lat/lon position coordinates that aid in locating the replicator after it has descended on a parachute to the ground. Radio direction-finding equipment, of the type used by wildlife biologists to track collared animals, is used to track the locator beacon on the front of the replicator box. Locating and retrieving replicators from the field is often quite an adventurous experience!
Bottom Panel: The flow of air and cloud particles through the sample opening and onto the coated film has been rigorously studied with a numerical model and windtunnel measurements (see above-referenced paper). The sample volume of the instrument and its "collection efficiency" as a function of crystal size have been determined, thus this is a quantitative instrument and crystal size distributions and number concentrations can be calculated. The replicator data are imaged through a microscope, and individual crystals are identified and characterized (i.e., size, cross-sectional area, and perimeter) with image processing software. The data are ideally-suited for case-study analyses because the measurements show the variability of cloud microphysical properties in a vertical cloud column, and the crystal shapes (which are important in determining the crystal scattering and radiative properties) are imaged at high resolution (2-5 microns).
Go to Index of Replicator Data (the main page).