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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 19
Atmos. Chem. Phys., 12, 9187–9199, 2012
https://doi.org/10.5194/acp-12-9187-2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 12, 9187–9199, 2012
https://doi.org/10.5194/acp-12-9187-2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.

Peer-reviewed comment 11 Oct 2012

Peer-reviewed comment | 11 Oct 2012

Commentary on using equivalent latitude in the upper troposphere and lower stratosphere

L. L. Pan1, A. Kunz*,1, C. R. Homeyer2, L. A. Munchak1,**, D. E. Kinnison1, and S. Tilmes1 L. L. Pan et al.
  • 1National Center for Atmospheric Research, Boulder, Colorado, USA
  • 2Texas A&M University, College Station, Texas, USA
  • *now at: Forschungszentrum Jülich, Jülich, Germany
  • **now at: Science System Applications, Greenbelt, Maryland, USA

Abstract. We discuss the use of potential vorticity (PV) based equivalent latitude (EqLat) and potential temperature (θ) coordinates in the upper troposphere and lower stratosphere (UTLS) for chemical transport studies. The main objective is to provide a cautionary note on using EqLat-θ coordinates for aggregating chemical tracers in the UTLS. Several examples are used to show 3-D distributions of EqLat together with chemical constituents for a range of θ. We show that the use of PV-θ coordinates may not be suitable for several reasons when tropospheric processes are an important part of a study. Due to the different static stability structures between the stratosphere and troposphere, the use of θ as a vertical coordinate does not provide equal representations of the UT and LS. Since the θ surfaces in the troposphere often intersect the surface of the Earth, the θ variable does not work well distinguishing the UT from the boundary layer when used globally as a vertical coordinate. We further discuss the duality of PV/EqLat as a tracer versus as a coordinate variable. Using an example, we show that while PV/EqLat serves well as a transport tracer in the UTLS region, it may conceal the chemical structure associated with wave breaking when used as a coordinate to average chemical tracers. Overall, when choosing these coordinates, considerations need to be made not only based on the time scale of PV being a conservative tracer, but also the specific research questions to be addressed.

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