EGU2020-6240
https://doi.org/10.5194/egusphere-egu2020-6240
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Influence of Pacific meridional mode on ENSO evolution and predictability: asymmetric modulation and ocean preconditioning

Hanjie Fan1, Bohua Huang2, and Song Yang1
Hanjie Fan et al.
  • 1School of Atmospheric Sciences, Sun Yat-sen University, Guangzhou, China
  • 2Department of Atmospheric, Oceanic, and Earth Sciences & Center for Ocean-Land-Atmosphere Studies, George Mason University, Fairfax, America

This study investigates the mechanisms for the Pacific meridional mode (PMM) to influence the development of an ENSO event and its seasonal predictability. To examine the relative importance of several factors that might modulate the efficiency of the PMM influence, we conduct a series of prediction experiments to selected ENSO events with different intensity from a long simulation of the Community Earth System Model (CESM). Using the same coupled model, each of the ensemble prediction is conducted from slightly different ocean initial states but under a common prescribed PMM surface heat flux forcing. In general, the matched PMM forcing to ENSO, i.e., a positive (negative) PMM prior to an El Niño (a La Niña), plays an enhancing role while a mismatched PMM forcing plays a damping role. For the matched PMM-ENSO events, the positive PMM exerts greater influence than its negative counterpart does, with stronger enhancement of positive PMM events on an El Niño than that of negative PMM events on a La Niña. This asymmetry in ENSO influence largely originates from the intensity asymmetry between the positive and negative PMM events in the tropics, which can be explained by the nonlinearity in the growth and equatorward propagation of the PMM-related SST and surface zonal wind anomalies through both wind-evaporation-SST (WES) feedback and summer deep convection (SDC) response. Furthermore, the response of ENSO to an imposed PMM forcing is modulated by the preconditioning of the upper ocean heat content, which provides the memory for the coupled low-frequency evolution in the tropical Pacific.

How to cite: Fan, H., Huang, B., and Yang, S.: Influence of Pacific meridional mode on ENSO evolution and predictability: asymmetric modulation and ocean preconditioning , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6240, https://doi.org/10.5194/egusphere-egu2020-6240, 2020