EGU2020-10766
https://doi.org/10.5194/egusphere-egu2020-10766
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

How turbulent mountain stress influences sudden stratospheric warming ocurrence in WACCM

Froila M. Palmeiro1, Rolando R. Garcia2, Natalia Calvo3, David Barriopedro4, and Bernat Jiménez-Esteve5
Froila M. Palmeiro et al.
  • 1Universitat de Barcelona (UB), Group of Meteorology, Barcelona, Spain (fm.palmeiro@meteo.ub.edu)
  • 2Atmospheric Chemistry Observations and Modeling Lab, NCAR, Boulder, CO, USA
  • 3Departamento Física de la Tierra y Astrofísica, Universidad Complutense de Madrid, Madrid, Spain
  • 4Instituto de Geociencias (IGEO), Consejo Superior de Investigaciones Científicas – Universidad Complutense de Madrid, Madrid, Spain
  • 5Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland

The implementation of the Turbulent Mountain Stress (TMS) parametrization in the Whole Atmospheric Community Climate Model (WACCM) is found to be critical to obtain a realistic Sudden Stratospheric Warming (SSW) frequency in the Northern Hemisphere. Comparing two 50-year simluations, one with TMS (TMS-on) and one without (TMS-off) reveals lower than observed SSW frequency in TMS-off from December to February, while in March both simulations show SSW frequencies comparable to reanalysis. Meridional eddy heat fluxes in the lower stratosphere are stronger in TMS-on than in TMS-off, except in March. These differences are accompanied by increased orographic gravity wave drag (OGWD) in TMS-off that comes mainly from the Himalayas and the Rocky Mountains in response to stronger surface winds. Two different mechanisms of how planetary and GWs interact are identified in the simulations. In the lower stratosphere, enhanced dissipation of GWs in TMS-off modifies the subtropical jet and thus the conditions for refraction of planetary waves. In early winter, wave geometry diagnostics shows waveguides formation from 55N to 75N in TMS-on, enhancing wave propagation to the polar vortex. On the contrary, vertical propagation in TMS-off is in inhibited above the lower stratosphere and confined to latitudes south of 50N. Compensation between resolved and parametrized GWs is also observed, leading to weaker Eliassen-Palm flux divergence in response to stronger OGWD in TMS-off. In late winter, conditions for propagation are similar in both simulations by late winter, which explains the reduced TMS-off bias in the frequency of March SSWs.

How to cite: Palmeiro, F. M., Garcia, R. R., Calvo, N., Barriopedro, D., and Jiménez-Esteve, B.: How turbulent mountain stress influences sudden stratospheric warming ocurrence in WACCM, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10766, https://doi.org/10.5194/egusphere-egu2020-10766, 2020

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