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Gerhard Langer

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Joe Wisniewski and Gerhard Langer

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Ice nuclei measurements were made aboard a cloud-base aircraft during the 1975 Florida Area Cumulus Experiment. Two techniques were used to obtain the ice nuclei concentrations; membranes were collected and analyzed using the NCAR membrane development chamber and continuous ice nuclei concentrations were obtained using the NCAR acoustical counter. Results showed that the membrane technique failed to effectively detect ice nuclei in this maritime tropical area. However, the concentrations recorded by the acoustical counter showed natural afternoon diurnal increases which may have ramifications on cloud development and seeding potential within the particular study area.

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Gerhard Langer and James Rodgers

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An experimental study was made of a membrane filter technique for the detection of ice nuclei in which air of controlled humidity flows across the cooled membrane as opposed to the usual static thermal diffusion procedure. This is necessary to overcome water vapor losses to various sinks on the sample substrate; the procedure also makes it possible to observe the nucleation process directly by microscope. However, for very small nuclei such as AgI, even this flow system is not able to activate the nuclei. This is overcome by letting a puff of supersaturated air pass over the deposited aerosol, which should be on a water-repellent substrate, to promote vapor flow to the ice and condensation nuclei, rather than onto the substrate. At temperatures warmer than −12°C, the puff procedure is not necessary since the water vapor pressure is sufficient to keep up with the vapor sinks. Following the above procedures, consistent results are obtained for AgI, kaolin, soil particles and pollution aerosols in both laboratory and field applications in the −5 to −20°C range.

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B. G. Mendonca and Gerhard Langer

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Farn P. Parungo and Gerhard Langer

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Rudolf F. Pueschel and Gerhard Langer

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Edward E. Hindman II, Dennis M. Garvey, Gerhard Langer, F. Kirk Odencrantz, and Gerald L. Gregory

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Small quantities of solid rocket motor propellant, of the type to launch the Space Shuttle, were burned at ambient pressure in the laboratory to provide aerosol samples for characterization. A portion of each sample was injected into an isothermal cloud chamber and the remainder into a 770 ℓ holding tank. Portable ice nucleus (IN) counters, filter devices for IN determinations and a cloud condensation nucleus (CCN) counter sampled from the tank.

The measurements show that particles resulting from the combustion of the propellant are active IN (3.3 × 108 to 1.5 × 1011 g−1 active at −20°C). The portable counters and filters detected significantly fewer IN than the isothermal cloud chamber. The propellant aerosol is a prolific source of CCN that swamped the instrument.

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Roger L. Steele, C. P. Edwards, Lewis O. Grant, and Gerhard Langer

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The NCAR acoustical ice nucleus counter was calibrated against a Bigg-Warner Weather Bureau type chamber modified as a mixing chamber. The mixing chamber was in turn calibrated against the CSU-NSF isothermal diffusion cloud chamber. This work was carried out using a 300-liter aluminized mylar bag into which known samples of silver iodide nuclei were introduced. Nuclei were transferred from the bag to the NCAR counter in a carrier gas, at a flow rate of 10 liters min−1. It was found that the NCAR counter measured from 16–52% of the count given by the mixing chamber. An NCAR unit was modified with a velvet liner to test the feasibility of eliminating the glycol system, and measurements were made as described above. The modified unit did not count reliably.

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Andreas Stohl, Kathrin Baumann, Gerhard Wotawa, Matthias Langer, Bruno Neininger, Martin Piringer, and Herbert Formayer

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This paper describes a simple method, based on routine meteorological data, to produce high-resolution wind analyses throughout the planetary boundary layer (PBL). It is a new way to interpolate wind measurements. According to this method, high-frequency information from surface wind measurements is extrapolated to greater heights by assuming that the vertical shear of the horizontal wind, that is, the differential vertical wind profile, is horizontally more homogeneous than the wind profile itself. Under this assumption, it is sufficient to combine high-resolution surface wind measurements with low-resolution vertical profiles of differential winds—for which high-resolution measurements usually do not exist—to yield high-resolution wind analyses throughout the PBL. The method can thus be viewed as a diagnostic downscaling of large-scale wind fields. Downscaling works best during daytime within a homogeneous air mass and in flat terrain. A validation against sodar wind measurements demonstrates that downscaling actually improves large-scale wind fields. A comparison of trajectories calculated from large-scale wind fields, from downscaled wind fields, and from wind fields produced by a conventional diagnostic wind field model, with daytime constant level balloon flights, again shows that the downscaled wind fields are most accurate.

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Richard D. Cadle, Gerhard Langer, J. B. Haberl, A. Hogan, James M. Rosen, William A. Sedlacek, and J. Wegrzyn

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Laboratory comparisons have been made of aerosol concentrations indicated by four different types of condensation nucleus counters. Three of these counters, the Langer, Rosen, and General Electric SANDS instruments have been used to measure Aitken nuclei concentrations in the upper troposphere and the stratosphere, and the fourth, a Pollak counter, had been carefully calibrated to serve as a standard. Except for the smallest particles employed, quite good agreement was experienced among the Rosen, SANDS and Pollak counters, and the tests served to calibrate the Langer instrument.

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