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Obituary of Heinz Wolfram Kasemir

7 June 2007

Heinz Wolfram Kasemir, who made significant contributions in the field of Atmospheric Electricity, died on May 1, 2007 in Loveland, Colorado, USA.

He was born on August 30, 1913 in Tilsit, Germany, where he also grew up. He studied physics at the University of Königsberg. During WWII, he was involved in theoretical work and some experimentation on proximity fuses. After the war he did graduate work at the University of Aachen, under Prof. Israel. He received his Doctorate in Physics from this university in 1948. In 1954 Heinz emigrated with his family to the United States.

His interest in atmospheric electricity had surged after field observations at a high altitude site on the Jungfraujoch Mountain in Switzerland, where he made electric field and current measurements. Throughout his life, he was equally active and proficient in both experimentation and theory. He developed measurement techniques for conduction current density, by matching the input time constant of his electrometer amplifier with the relaxation time constant of the atmosphere, thus eliminating the high-amplitude variations of the displacement currents. He designed a sensor for measuring all three components of the ambient electric field, which eventually evolved into the cylindrical field mill, which he used on aircraft for measurements close to thunderstorms.

On the theoretical side, he recognized early the influence of air conductivity on the flow of air-earth currents. This led to the development of his theory for the transition from electrostatic potential distribution in the atmosphere to the electrodynamics potential field for slowly-changing processes. He applied his electrodynamics theory to explain the development of screening charges on clouds, the flux of thunderstorm charges into high altitudes due to the exponential increase of conductivity with height, the relationship of charges on an upward leader to the cloud electric field, and the "recovery time": the change of electric fields of return strokes from the initial electrostatic pattern to the electrodynamic pattern, producing a time constant of about 15 seconds, even with relaxation times inside the clouds of about 1000 seconds. He was one of the few remaining scientists completely comfortable with solving three dimensional partial differential equations, a tool! that has now been replaced by numerical solvers.

In lightning physics, he was aware early on of the shortcomings of Schonland's model of unipolar charges on leader channels, and the so-called discharge of the leader charges to ground, as lacking physical foundation. He used his vast database of leader and return stroke recordings to verify his ideas of the physics of the leader and return stroke process. Kasemir's idea, proposed in 1950, that lightning develops as a bidirectional leader with a net zero charge did not receive recognition in the lightning research community until the 1980s. This idea, crucial for the understanding of lightning physics, was finally confirmed during in-situ measurements of lightning strikes to aircraft in thunderstorms during the 1980s.

Heinz was always interested in physical models in atmospheric electricity (rather than empirical descriptions from measurements). His aim was always to deduce from remote and indirect measurements the physical state of the process. He applied this approach to the global circuit, by producing values of efficiencies with which cloud charges flow into the global circuit. He used electric field sensors in a net on the ground, and field mills on an aircraft near thunderstorms, to deduce the magnitude and distribution of thunderstorm charges. In lightning physics, he related measured electric fields near lightning flashes to the charge distribution on the leader and return stroke channels.

Everyone who worked with Heinz Kasemir during field measurements remembers his demand for good quality data and his repeated request to Calibrate, calibrate Heinz was always willing to share his experience and ideas with anyone willing to listen. He was sure that all the processes in atmospheric electricity would be explained sooner or later by proper experimental measurements and the laws of physics. His advice was appreciated by many, yet he never quarreled with colleagues who had ideas opposite to his own.

We will all miss Heinz Kasemir's insight and experience.

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