EGU21-3113
https://doi.org/10.5194/egusphere-egu21-3113
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Thermodynamic cycles in the stratosphere

Jonas Nycander1, Paolo Ruggieri2, and Maarten Ambaum3
Jonas Nycander et al.
  • 1Dept of Meteorology, Stockholm University, Stockholm, Sweden (jonas@misu.su.se)
  • 2Fondazione Centro Euro-Mediterraneo sui Cambiamenti Climatici, Bologna, Italy (paolo.ruggieri@cmcc.it)
  • 3Dept of Meteorology, University of Reading, Reading, United Kingdom (m.h.p.ambaum@reading.ac.uk)

Large-scale overturning mass transport in the stratosphere is commonly explained through the action of potential vorticity (PV) rearrangement in the flank of the stratospheric jet. Large-scale Rossby waves, with their wave activity source primarily in the troposphere, stir and mix PV and an overturning circulation arises to compensate for the zonal torque imposed by the breaking waves. In this view, any radiative heating is relaxational and the circulation is mechanically driven. Here we present a fully thermodynamic analysis of these phenomena, based on ERA-Interim data. Streamfunctions in a thermodynamic, log(pressure) – temperature space are computed. The sign of a circulation cell in these coordinates directly shows whether it is mechanically driven, converting kinetic energy to potential and thermal energy, or thermally driven, with the opposite conversion. The circulation in the lower stratosphere is found to be thermodynamically indirect (i.e., mechanically driven). In the middle and upper stratosphere thermodynamically indirect and direct circulations coexist, with a prominent semiannual cycle. A part of the overturning in this region is thermally driven, while a more variable indirect circulation is mechanically driven by waves. The wave driving does not modulate the strength of the thermally direct part of the circulation. This suggests that the basic overturning circulation in the stratosphere is largely thermally driven, while tropospheric waves add a distinct indirect component to the overturning. This indirect overturning is associated with poleward transport of anomalously warm air parcels.

How to cite: Nycander, J., Ruggieri, P., and Ambaum, M.: Thermodynamic cycles in the stratosphere, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3113, https://doi.org/10.5194/egusphere-egu21-3113, 2021.

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