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https://doi.org/10.5194/acp-2020-841
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-841
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  19 Aug 2020

19 Aug 2020

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This preprint is currently under review for the journal ACP.

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

Yuming Jin1, Ralph F. Keeling1, Eric J. Morgan1, Eric Ray2, Nicholas C. Parazoo3, and Britton B. Stephens4 Yuming Jin et al.
  • 1Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA
  • 2National Oceanic and Atmospheric Administration, Boulder, CO 80305, USA
  • 3Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
  • 4National Centerfor Atmospheric Research, Boulder, CO 80301, USA

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 HIPPO and 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 cycles are more constant as a function of pressure using Mθe as the horizontal coordinate compared to latitude. Furthermore, short-term variability of 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 at 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.

Yuming Jin et al.

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Latest update: 29 Sep 2020
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Short summary
We propose a new atmospheric coordinate (Mθe) based on equivalent potential temperature (θe) but has mass as unit. This coordinate is useful in studying the spatial and temporal distribution of long-lived chemical tracer (CO2, CH4, O2 / N2 and etc.) from sparse data, like airborne observation. Using this coordinate and sparse airborne observation (HIPPO and ATom), we resolve the Northern Hemisphere mass-weighted average CO2 seasonal cycle with high accuracy.
We propose a new atmospheric coordinate (Mθe) based on equivalent potential temperature (θe)...
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