Coalescence Enhancement in large Multicell Storms Caused by the Emissions from a Kraft Paper Mill

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...