The Mobility of Tropospheric Ions Above the Exchange Layer

Abstract

Measurements of both polar conductivities, the densities and mobility distributions of small ions, electric field intensity, and other related atmospheric variables were made from an airplane from 30 m to 5.6 km. A Blackwood type mobility chamber and a Gerdien condenser were used simultaneously to determine the mobility distribution and the conductivity. The mobility instrumentation and the technique for obtaining the ion spectrum from the measurements are discussed. The results of five flights 100 miles cast of the Virginia coast and one over Lake Ontario are presented. The mobilities of ions in the free atmosphere lie between 0.3 and 5 cm sec?1 per v cm?1 at STP with a peak near the low mobility end and a broadening toward the high end. The average mobility reduced to STP is about 1.2 cm sect ?1 and the negative-to-positive ratio is nearly 1.1, both with no significant dependence upon altitude from 3.0 to 5.2 km. The mobility is smaller and the ratio closer to unity than values given for artificially produced ions in filtered air. The positive and negative ion densities are nearly equal, with the conductivity ratio about equal to the mobility ratio. Conductivities and ion densities computed from the mobility spectrum are compared with direct measurements.