The Lettau–Schwerdtfeger Balloon Experiment: Measurement of Turbulence via Austausch Theory

In the early 1930s, Heinz Lettau and Werner Schwerdtfeger made direct measurements of air motion in the lowest 4 km of the troposphere by using the manned free balloon as an instrumented platform. The experiment was motivated by Wilhelm Schmidt’s and Ludwig Prandtl’s work onAustausch(exchange) theory in the second and third decades of the twentieth century. As a prelude to investigating the Lettau–Schwerdtfeger experiment, historical developments that had bearing on the field program are reviewed. Following this review, the experiment is analyzed by 1) documenting the scientific goals, 2) discussing the strategy for data collection, 3) examining one flight in detail (the flight of 25 February 1934), and 4) summarizing results from the experiment. The paper ends with a retrospective view ofAustauschtheory.