Using Satellite FTS-IR Measurements of tracers to quantify the strength of the mean overturning circulation of the stratosphere

Speaker: Marianna K. Linz, fourth year PhD student in the MIT-Woods Hole Oceanographic Institute Joint Program in Physical Oceanography.

The Brewer-Dobson circulation is the overturning circulation of the stratosphere and was originally inferred from observations of ozone and water vapor. It is critical for the stratospheric ozone distribution and for troposphere-stratosphere coupling. The consensus from climate models is that the Brewer-Dobson circulation will intensify under global warming scenarios. Although the general structure of the circulation can be qualitatively assessed from ozone and water vapor, the quantitative strength of the circulation has been much more difficult to measure. Certain trace gases, SF6 and CO2, can be used to estimate the “age” of air, or how long on average air has been in the stratosphere since upwelling through the tropical tropopause. I will present a new time-dependent theory for quantitatively assessing the magnitude of the stratospheric circulation using this theoretical age. I will show results from an idealized atmospheric model with a seasonal cycle, which reveal the required spatial and temporal sampling necessary to observe the circulation. Then I will use measurements from the ACE and MIPAS FTS-IR limb sounders in this theoretical framework to determine the magnitude and variability of the circulation of the stratosphere. Between 2007 and 2011, while there was little change in the strength of the circulation in the lowermost stratosphere, the upper stratosphere exhibited changes in SF6 concentrations consistent with a 20% weakening of the strength of the overturning circulation.

Marianna Linz is a fourth year PhD student in the MIT-Woods Hole Oceanographic Institute Joint Program in Physical Oceanography, where she studies the stratospheric circulation with her advisor Alan Plumb. She completed her bachelors in Chemistry and Physics and Earth and Planetary Sciences at Harvard University in 2011. She is currently a National Defense Science and Engineering Graduate Fellow. She is interested in climate dynamics, and has previously worked on ocean eddies, large-scale ocean heat transport, and the representation of El Nino in climate models.

Meeting Location: MIT Lincoln laboratory – Forbes Road Cafeteria – 3 Forbes Road Lexington, MA 02421.

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