A mass-weighted isentropic coordinate for mapping chemical tracers and computing atmospheric inventories

Furthermore, short-term variability in CO2 relative to the mean seasonal cycle is also smaller when the data are organized by M-theta e and pressure than when organized by latitude and pressure. We also present a method using M-theta e 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 zerocrossing on Julian day 173 +/- 6.1 (i.e., late June).

M-theta e may be similarly useful for mapping the distribution and computing inventories of any long-lived chemical tracer.