Stratospheric Dynamics and Chemistry
Nacreous clouds over McMurdo Staition, Antarctica.
Simulation of stratospheric tracer mixing using winds at 30 km elevation for the time period of January through February, 1992.
The AVE/WIIF (Aura Validation Experiment / Water Isotope Intercomparison Flights) aircraft instrument platform (an old 1960's era U2 spy plane) prepares to take off with stratospheric spectroscopy instruments designed to study the isotopic composition of water vapor.
Research in stratospheric dynamics and chemistry focusses on three areas of interest: the pathways of water vapor transport above the tropopause, the fluid-dynamic characterization of stratospheric winds, and the analysis of interactions between stratospheric trace constituents and radiation.
A developing research emphasis within the department is designed to determine the pathways by which water vapor reaches the stratosphere using high-altitude measurements of a new atmospheric tracer. The tracer is the isotopic composition of that water: the tiny amounts of naturally occurring HDO or H218O relative to ordinary H216O.
Ongoing work into the nature of stratospheric winds focusses on the extension of traditional GFD concepts into the special realm of the stratosphere. Numerical work on the quantification of asymmetric wave breaking, two-way transport, isentropic transport via equivalent latitude methods and eddy diffusivity diagnostics are being used to quantify important aspects of stratospheric chemistry, including low-column ozone concentrations over populated regions.
Studies of solar radiative transfer, ground-based radiation measurements, and interpretation of satellite-based data are additionally underway to characterize the role of stratospheric trace gasses and tropospheric effects in the control of ultraviolet solar radiation at the Earth's surface. Specific topics of interest include the roles of scattering by clouds and absorption by atmospheric trace gases in shielding the biosphere from damaging solar radiation. An issue under study centers on the possibility that molecules contained in cloud droplets over industrialized regions can lead to detectable absorption of ultraviolet radiation. Great concern exists in the Southern Hemisphere over a possible influence of the Antarctic ozone depletion on middle latitudes. In response to this, a network of ground-based ultraviolet radiation monitors has been established over the latitudinal extent of Argentina. Analysis of data obtained from Tierra del Fuego reveals periods of enhanced ultraviolet radiation levels in the weeks after the breakup of the polar "ozone hole" during some years. The largest percentage increases in biologically damaging irradiances appear in the late spring and summer months when the natural background radiation levels are already large. The extent to which such increases appear at lower latitudes, where most of the country's population resides, is still to be determined.
Faculty:
• John Frederick
• Liz Moyer
• Noboru Nakamura
• Raymond Pierrhumbert
Research Scientists:
