Cross Sections of Ice Nucleus Concentrations at Altitude over Long Paths

Abstract

Measurements of ice nucleus concentrations using Millipore filters at altitudes of about 4 and 11 km over lengthy paths are described. Bands of ice nuclei between latitudes 23S and 30S were frequently found at both altitudes, narrower and of higher concentration than those observed at the ground. Broad regions at 10?12 km markedly deficient in ice nuclei were found near the equator on each of two flights. There was no conspicuous difference in ice nucleus concentrations in the two hemispheres and no obvious change was found at the northern boundary of the pall of volcanic dust then present.