Tuesday, 15 January 2002: 9:00 AM
The development of concepts of the Tropopause and the exchange of the trace constituents between the stratosphere and Troposphere
With the advent of meteorologically instrumented manned and unmanned balloons during the late 1800s, scientists discovered that the atmosphere's temperature profile was often characterized by a near-zero-order discontinuity in temperature lapse rate in the altitude range ~7-16 km. This discontinuity was referred to as the tropopause and was treated as a quasi-material interface between the quiescent stratosphere above and the turbulent troposphere beneath. Advances in upper-air observing technology during the first half of the 1900s led to the discovery of fronts that extended from the surface well into the upper troposphere, as well as those forming in the vicinity of the tropopause. Synoptic meteorologists, such as Jacob Bjerknes, Erik Palmén, Chester Newton, Richard Reed, Fred Sanders, Ed Danielsen, and the author, debated the structural and dynamical relationship between fronts in the upper troposphere and the tropopause, and the degree of permeability of the tropopause to the rapid exchange of air between the stratosphere and the troposphere. The awareness of the rapid exchange of air and associated trace constituents across the tropopause came after the unexpected discovery of radioactive debris in the agricultural food chain of central and eastern North America. This discovery occurred shortly after the onset of atmospheric testing of nuclear weapons in the years following World War II. It was initially thought that most of the dangerous radioactive debris, such as strontium-90 and short-lived (~8 day) radioactive iodine, would fall out within the confines of the nuclear test sites at White Sands, New Mexico,Yucca Flats, Nevada, and Christmas Island, and that the debris injected into the stratosphere would remain there for month to years and decay to non-harmful levels before crossing the tropopause and settling into the troposphere. It was never anticipated that these highly-dangerous trace constituents would appear within the US milk supply as far away as the eastern shores of North America, arriving 3-5 days after weapons detonation over the southwestern US. The study of the rapid exchange of nuclear debris and other trace constituents across the tropopause was undertaken in the late1950s by a team of meteorologists, atmospheric chemists and project managers under the support of the Atomic Energy Commission (AOC) and Defense Atomic Support Agency (DASA). This team included Dick Reed and his protegee Ed Danielsen, Elmar Reiter, Dean Staley, Edward Martel, Rudi Engelman, Joshua Holland, Harry Moses, and Eugene Bierly. Reed and Danielsen applied the revolutionary conceptual perspective of the potential vorticity (PV) tropopause, based on the quasi-conservative characteristic of potential vorticity for adiabatic Lagrangian motions introduced earlier by Hans Ertel and applied to cyclone life cycles by Ernst Kleinschmidt. The Reed and Danielsen studies established the link between PV tropopause folding and the observed rapid (1-3 day) exchange of air and attendant radioactive and natural trace constituents (e.g., ozone) between the stratosphere and troposphere. Concurrent studies also identified the role of deep moist convection in the rapid exchange process. The efforts of these scientists contributed to the development of public policy and international treaties banning the atmospheric testing of nuclear weapons. This was a truly great scientific contribution to humanity.