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Todd A. Cerni

Abstract

A 10 cm radar was employed in an effort to measure the radar cross section of cloud-to-ground lightning channels and its temporal variation. A data acquisition system was developed which is capable of recording the amplitude and range of lightning echoes in the presence of precipitation echoes, provided that the lightning echoes are initially greater in amplitude. Failure to detect any cloud-to-ground channels and measurement of the amplitude of the echo from intracloud channels formed the basis for the conclusion that the peak amplitude of echoes from cloud-to-ground lightning channels are less than or about equal to the peak amplitude of the associated precipitation echoes, at 10 cm. Suggestions are made with respect to optimum radars for future work.

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Todd A. Cerni

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Todd A. Cerni

Abstract

A detailed size calibration of the Forward Scattering Spectrometer Probe (FSSP) over the size ranges of interest to cloud physics (2–47 μm), is presented. The calibration includes laboratory tests with glass spheres, Mie scattering calculations and airborne cloud measurements. Each size bin of the FSSP was found to have errors of 0–5 μm in diameter. The magnitude and sign of the errors were dependent on airspeed for airspeeds greater than 55 m s−1. This sizing error can lead to errors of 70% or more in derived cloud liquid water content. In addition, a concentration algorithm was derived from laboratory tests with pseudo-random pulse generators which properly corrects for probe dead time. After application of both calibration algorithms the instrument is capable of yielding mean diameters that agree with predicted mean diameters to within a few tenths of a micron and liquid water contents which are in good agreement with an independent liquid water measurement. Even after corrections, the instrument still produces significant artifical broadening of a cloud drop spectrum.

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Todd A. Cerni

Abstract

The development and testing of a field durable, infrared differential absorption hygrometer is described. This noncontact hygrometer offers reliable operation in harsh environments while maintaining subsecond response speed. A modified exponential response function was derived from laboratory calibration data. Absolute humidity resolution is better than 1% for absolute humidities greater than 2.0 g m−3, and better than 6% for absolute humidities in the range of 0.1–2.0 g m−3. The lower limit of sensitivity is less than or equal to 10 ppmv. A field trial was conducted at White Sands Missile Range, New Mexico, utilizing a total of six humidity sensors and four temperature sensors. The infrared hygrometer was determined to be the most accurate humidity sensor in the field trial, with a dew/frost-point measurement error of less than 0.5°C over the dew/frost-point range of −15° to 10°C. A combination of numerical modeling, laboratory measurements, and field data was used to investigate possible humidity measurement errors caused by hydrometeors or aerosols present in the sample volume or deposited on the external optical surfaces. The marine boundary layer was found to be the only natural environment capable of producing such errors.

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Todd A. Cerni and Thomas R. Parish

Abstract

A graybody, longwave, radiative transfer model based on revised estimates of the absorption characteristics of CO2 and H2O is proposed. The model is computationally efficient and is designed for use within larger mesoscale primitive equation models. Tests have shown that the graybody model accurately simulates atmospheric heating rates as predicted by more detailed radiation models. When incorporated within a simple one-dimensional model, the radiation parameterization provides realistic simulations of the strong temperature inversion over the interior of Antarctica in winter.

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