A device for measuring the point discharge emitted froma 2m length of copper wire, using a radiosonde as carrier platform, has been developed in order to measure the distribution of charged regions inside thunderclouds with respect to temperature and altitude. No modifications to the radiosonde or in the standard receiving equipment are required.

In four penetrations of electrified clouds over central New Mexico, corona currents were induced in the conducting wire. The measurements were characterized by reversals in the polarity of the current which can be interpreted as a result of the balloon's rising past the level at which charge of one sign is concentrated.