EMS Annual Meeting Abstracts
Vol. 18, EMS2021-265, 2021
EMS Annual Meeting 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Multi-model assessment of the late-winter tropospheric response to El Niño and La Niña

Bianca Mezzina1, Javier García-Serrano1,2, Ileana Bladé2, Froila M. Palmeiro2, Lauriane Batté3, Constantin Ardilouze3, Marianna Benassi4, and Silvio Gualdi4,5
Bianca Mezzina et al.
  • 1Barcelona Supercomputing Center (BSC), Barcelona, Spain (bianca.mezzina@bsc.es)
  • 2Group of Meteorology, Universitat de Barcelona (UB), Barcelona, Spain
  • 3CNRM, Université de Toulouse, Météo-France, CNRS, Toulouse, France
  • 4Fondazione Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC), Bologna, Italy
  • 5Istituto Nazionale di Geofisica e Vulcanologia, Bologna, Italy

El Niño-Southern Oscillation (ENSO) is known to affect the Northern Hemisphere tropospheric circulation in late-winter (January–March), but whether El Niño and La Niña lead to symmetric impacts and with the same underlying dynamics remains unclear, particularly in the North Atlantic. Three state-of-the-art atmospheric models forced by symmetric anomalous sea surface temperature (SST) patterns, mimicking strong ENSO events, are used to robustly diagnose symmetries and asymmetries in the extra-tropical ENSO response. Asymmetries arise in the sea-level pressure (SLP) response over the North Pacific and North Atlantic, as the response to La Niña tends to be weaker and shifted westward with respect to that of El Niño. The difference in amplitude can be traced back to the distinct energy available for the two ENSO phases associated with the non-linear diabatic heating response to the total SST field. The longitudinal shift is embedded into the large-scale Rossby wave train triggered from the tropical Pacific, as its anomalies in the upper troposphere show a similar westward displacement in La Niña compared to El Niño. To fully explain this shift, the response in tropical convection and the related anomalous upper-level divergence have to be considered together with the climatological vorticity gradient of the subtropical jet, i.e. diagnosing the tropical Rossby wave source. In the North Atlantic, the ENSO-forced SLP signal is a well-known dipole between middle and high latitudes, different from the North Atlantic Oscillation, whose asymmetry is not indicative of distinct mechanisms driving the teleconnection for El Niño and La Niña.

The multi-model assessment, with 50 members for each experiment, contributes to the ERA4CS-funded MEDSCOPE project and includes: EC-EARTH/IFS (L91, 0.01hPa), CNRM/ARPEGE (L91, 0.01hPa), CMCC/CAM (L46, 0.3hPa).

How to cite: Mezzina, B., García-Serrano, J., Bladé, I., Palmeiro, F. M., Batté, L., Ardilouze, C., Benassi, M., and Gualdi, S.: Multi-model assessment of the late-winter tropospheric response to El Niño and La Niña, EMS Annual Meeting 2021, online, 6–10 Sep 2021, EMS2021-265, https://doi.org/10.5194/ems2021-265, 2021.

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