Definition of AOA1 and AOA2 age tracers

[tmooring]

I am attempting to use the archived CESM2(WACCM6) output available at NSF NCAR GDEX Dataset d651045 for a study of stratospheric mixing and have a question about the tracers AOA1 and AOA2. Their names indicate that they are some sort of age of air, and the distributions of these tracers in the stratosphere suggests that they are both implemented as being conserved except at some boundary at which a time-dependent boundary condition is being imposed.

However, the rather odd tropospheric structures of these tracers as well as their actual numerical values mean that the exact nature of the boundary condition and the units of measure of the tracers are not at all obvious. I am a bit surprised that I have not managed to find anything in the literature or elsewhere online about the precise definitions of these tracers—can anyone here help?

Thanks in advance for any assistance you can provide, and please let me know if you have any questions.

Sincerely,

Todd Mooring
Research Associate
Linz Group
Department of Earth and Planetary Sciences
Harvard University

 

[yhanw]

Hello Todd, I run into this exact same confusion today with a different CESM2 dataset. Like you, I couldn't find it explicitly documented.

Just to add some info from my end if useful: In my case, AOA1 values are in a very narrow range (~2.3-2.4). I tried plotting AOA1 lat-lev field (using a 2.3~2.4 colorbar), and the expected physical structure does appear, so likely some sort of conversion is needed? The description says "Age-of_air tracer 1", but unit in netcdf metadata is "kg/kg".

Hope to echo this question, and I'd appreciate any insight from fellow forum users. Thanks!

Yuhan Wang
Postdoc
Earth System Science
Stanford University