A mass-weighted isentropic coordinate for mapping chemical tracers and computing atmospheric inventories Journal Article uri icon



  • Abstract. We introduce a transformed isentropic coordinate Mθe,; defined as the dry air mass under a given equivalent potential temperature; surface (θe) within a hemisphere. Like θe, the; coordinate Mθe follows the synoptic distortions of the; atmosphere but, unlike θe, has a nearly fixed; relationship with latitude and altitude over the seasonal cycle. Calculation; of Mθe is straightforward from meteorological fields. Using; observations from the recent HIAPER Pole-to-Pole Observations (HIPPO) and Atmospheric Tomography Mission (ATom) airborne campaigns, we map the; CO2 seasonal cycle as a function of pressure and Mθe, where; Mθe is thereby effectively used as an alternative to; latitude. We show that the CO2 seasonal cycles are more constant; as a function of pressure using Mθe as the horizontal coordinate; compared to latitude. Furthermore, short-term variability in; CO2 relative to the mean seasonal cycle is also smaller when the data; are organized by Mθe and pressure than when organized by latitude; and pressure. We also present a method using Mθe to compute; mass-weighted averages of CO2 on a hemispheric scale. Using this method; with the same airborne data and applying corrections for limited coverage,; we resolve the average CO2 seasonal cycle in the Northern Hemisphere; (mass-weighted tropospheric climatological average for 2009–2018), yielding; an amplitude of 7.8 ± 0.14 ppm and a downward zero-crossing on Julian; day 173 ± 6.1 (i.e., late June). Mθe may be similarly; useful for mapping the distribution and computing inventories of any; long-lived chemical tracer.;

publication date

  • January 12, 2021

has restriction

  • gold

Date in CU Experts

  • June 15, 2021 7:09 AM

Full Author List

  • Jin Y; Keeling RF; Morgan EJ; Ray E; Parazoo NC; Stephens BB

author count

  • 6

Other Profiles

Electronic International Standard Serial Number (EISSN)

  • 1680-7324

Additional Document Info

start page

  • 217

end page

  • 238


  • 21


  • 1