EGU21-5311, updated on 12 Jun 2023
https://doi.org/10.5194/egusphere-egu21-5311
EGU General Assembly 2021
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

The Combined Influence of the Stratospheric Polar Vortex and ENSO on Zonal Asymmetries in the Southern Hemisphere Upper Tropospheric Circulation during Austral Spring and Summer

Marisol Osman1,2,3, Theodore Shepherd4, and Carolina Vera1,2,3
Marisol Osman et al.
  • 1Centro de Investigaciones del Mar y la Atmósfera, Buenos Aires, Argentina (CIMA/CONICET-UBA)(osman@cima.fcen.uba.ar)
  • 2Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Ciencias de la Atmósfera y los Océanos.
  • 3Instituto Franco-Argentino sobre Estudios del Clima y sus Impactos (UMI-IFAECI/CONICET-CNRS)
  • 4University of Reading, Reading, UK.

The influence of El Niño Southern Oscillation (ENSO) and the Stratospheric Polar Vortex (SPV) on the zonal asymmetries in the Southern Hemisphere atmospheric circulation during spring and summer is examined. The main objective is to explore if the SPV can modulate the ENSO teleconnections in the extratropics. We use a large ensemble of seasonal hindcasts from the European Centre for Medium-Range Weather Forecasts Integrated Forecast System to provide a much larger sample size than is possible from the observations alone.

We find a small but statistically significant relationship between ENSO and the SPV, with El Niño events occurring with weak SPV and La Niña events occurring with strong SPV more often than expected by chance, in agreement with previous works. We show that the zonally asymmetric response to ENSO and SPV can be mainly explained by a linear combination of the response to both forcings, and that they can combine constructively or destructively. From this perspective, we find that the tropospheric asymmetries in response to ENSO are more intense when El Niño events occur with weak SPV and La Niña events occur with strong SPV, at least from September through December. In the stratosphere, the ENSO teleconnections are mostly confounded by the SPV signal. The analysis of Rossby Wave Source and of wave activity shows that both are stronger when El Niño events occur together with weak SPV, and when La Niña events occur together with strong SPV.

How to cite: Osman, M., Shepherd, T., and Vera, C.: The Combined Influence of the Stratospheric Polar Vortex and ENSO on Zonal Asymmetries in the Southern Hemisphere Upper Tropospheric Circulation during Austral Spring and Summer, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5311, https://doi.org/10.5194/egusphere-egu21-5311, 2021.

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