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A technique has been developed for deriving estimates of condensed water mixing ratio in cumulus clouds from measurements of potential temperature in the air in the compressor of a jet engine. Condensate that enters the engine at low temperatures (near −10°C) is evaporated in the compressor, causing a cooling of the air that is proportional to the amount of condensate evaporated. An important element of the technique is a correction for the time response of the temperature measurement system mounted in the compressed air. This new technique is simpler and more robust than an earlier technique based on measurement of the vapor concentration in the compressed air by an optical extinction (at Lyman-alpha wavelength) method. The values of condensed water mixing ratio derived from the new system are shown to be similar to those from the optical extinction system, previously reported in the literature.

While conducting a randomized seeding experiment, a storm was selected whose microphysical characteristics were so far from what was expected, given the existing thermodynamic environment, that some explanation was needed to account for the apparent errant behavior of this storm. More than a decade of sampling at −10°C using the project Lear jet has led to a simple classification technique, based on cloud-base temperature and buoyancy, which predicts the absence or presence, and to some extent the degree of coalescence (coalescence-freezing) precipitation growth in local convective storms. The unusual nature of this storm was recognized against this extensive microphysical database. The probable cause is attributed to emissions from a Kraft paper mill 10 km south of the storm's position. The mill had recently undergone an expansion program that had quadrupled its output of paper products. Using the radar characteristics of this unusual storm as a guide, a search of one season of radar data reveal...

Determination of the habits (ice or water) and therefore the densities of particles whose images are acquired by 2D probes is often an ambiguous process. A Learjet's radar measurements of equivalent reflectivity factors from a range gate 1800 m ahead of the aircraft are compared to reflectivities calculated from images acquired by a 2D-C probe over a range of assumed particle densities from 0.2 to 1 g cm−3. Although the comparisons suffer from many uncertainties, such as the vast disparity between the volumes sampled by the 2D-C probe and the aircraft radar, the method does discriminate well between water drops or recently frozen riming water drops and low density graupel particles.

Many of the severe and persistent hailstorms in Alberta propagate by means of new cloud development on the southern or western flank. A concept is proposed whereby these cumulus towers are seeded with freezing nuclei early in their development. In order to accomplish this a droppable pyrotechnic flare system was developed and tested. A T-33 jet aircraft was used as the seeding platform. It was equipped with a Ku-band weather radar, a flare rack and firing control panel, a 14 channel recorder and a 3-cm transponder. Seven inch pyrotechnic flares were manufactured to the following specifications: delay burn 50 sec, silver iodide burn time 30 sec, and flare output 24 gm of silver iodide producing a total of 2.4 × 1014 freezing nuclei active at −10C. A unique feature was the incorporation of 10-cm radar chaff which was released at the flare burn-out and used as a position marker. Flare performance was evaluated using radar, visual and photographic tracking. Total fall distance as a function of releas...