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Modeling the Mechanisms of Linear and Nonlinear ENSO Responses to the Pacific Meridional Mode

Journal Article · · Journal of Climate
 [1];  [2]
  1. Univ. of Wisconsin, Madison, WI (United States); DOE/OSTI
  2. Univ. of Wisconsin, Madison, WI (United States)
+ Show Author Affiliations
Interactions between the Pacific meridional mode (PMM) and El Niño–Southern Oscillation (ENSO) are investigated using the National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM) and an intermediate coupled model (ICM). The two models are configured so that the CESM simulates the PMM but not ENSO, and the ICM simulates ENSO but not the PMM, allowing for a clean separation between the PMM evolution and the subsequent ENSO response. An ensemble of CESM simulations is run with an imposed surface heat flux associated with the North Pacific Oscillation (NPO) generating a sea surface temperature (SST) and wind response representative of the PMM. The PMM wind is then applied as a forcing to the ICM to simulate the ENSO response. The positive (negative) ensemble-mean PMM wind forcing results in a warm (cold) ENSO event although the responses are not symmetric (warm ENSO events are larger in amplitude than cold ENSO events), and large variability between ensemble members suggests that any individual ENSO event is strongly influenced by natural variability contained within the CESM simulations. Sensitivity experiments show that 1) direct forcing of Kelvin waves by PMM winds dominates the ENSO response, 2) seasonality of PMM forcing and ENSO growth rates influences the resulting ENSO amplitude, 3) ocean dynamics within the ICM dominate the ENSO asymmetry, and 4) the nonlinear relationship between PMM wind anomalies and surface wind stress may enhance the La Niña response to negative PMM variations. Implications for ENSO variability are discussed.
Research Organization:
Univ. of Wisconsin, Madison, WI (United States)
Sponsoring Organization:
USDOE Office of Science (SC)
Grant/Contract Number:
SC0005301
OSTI ID:
1537006
Journal Information:
Journal of Climate, Journal Name: Journal of Climate Journal Issue: 24 Vol. 29; ISSN 0894-8755
Publisher:
American Meteorological SocietyCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (5)

Revisiting the Pacific Meridional Mode journal February 2018
The Pacific Meridional Mode and ENSO: a Review journal September 2019
Separating the North and South Pacific Meridional Modes Contributions to ENSO and Tropical Decadal Variability journal January 2019
Linking the North American Dipole to the Pacific Meridional Mode journal March 2019
The Relationship Between South Pacific Atmospheric Internal Variability and ENSO in the North American Multimodel Ensemble Phase‐II Models journal November 2019

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