Abstract
This study examines the Pacific meridional mode (PMM) simulated in the pre-industrial simulations of the Coupled Model Intercomparison Project Phase 5 (CMIP5). The spatial pattern and intensity of the PMM were found to be reasonably simulated by CMIP5 models, as was the subtropical atmosphere–ocean coupling associated with the PMM. However, the persistence of the coupling, which sustains the PMM's duration and extends its pattern equatorward, was found to be underestimated in most of the CMIP5 models. Many of the simulated PMMs do not have a pattern that extends far enough into the tropical Pacific to influence El Niño-Southern Oscillation (ENSO). The CMIP5 models that do produce longer persistence for the PMM coupling show a higher correlation of the PMM with the Central-Pacific (CP) type of ENSO than with the Eastern-Pacific (EP) type of the ENSO. This study concludes that (1) the PMM and its associated subtropical Pacific ocean–atmosphere coupling are important to the generation of the CP type of ENSO; (2) the so-called seasonal footprinting mechanism that sustains an equatorward extension of the PMM is not well simulated in a majority of the CMIP5 models; and (3) the persistence of the subtropical Pacific coupling is more important than the other properties in gauging a model's skill in the PMM simulation.
Highlights
The Pacific meridional mode (PMM; Chiang and Vimont, 2004) is a leading mode of variability in the northeastern subtropical Pacific that is characterized by covariability in sea surface temperature (SST) and surface wind
The PMM is a leading mode of coupled atmosphere–ocean variability in the subtropical Pacific and may play a crucial role in transmitting extratropical forcing into the tropics to impact El Niño-Southern Oscillation (ENSO) activity
We examine the simulation of the PMM in 23 Coupled Model Intercomparison Project Phase 5 (CMIP5) models, with a particular focus on the properties of its associated ocean–atmosphere coupling and its connection to the two types of ENSO
Summary
The Pacific meridional mode (PMM; Chiang and Vimont, 2004) is a leading mode of variability in the northeastern subtropical Pacific that is characterized by covariability in sea surface temperature (SST) and surface wind. The atmosphere continues to respond to the new SST anomalies by producing wind anomalies further southwestward Through this wind-evaporation-SST (WES) feedback (Xie and Philander, 1994), the SST anomalies initially induced by the extratropcial atmosphere can extend southwestward from near Baja California towards the tropical central Pacific to form the spatial pattern of the PMM. The atmosphere–ocean coupling sustains the PMM from boreal winter, when the extratropical atmospheric variability is the most active, to the following spring or. These earlier studies on the relationship between the PMM and El Niño-Southern Oscillation (ENSO) did not consider the existence of different types of ENSO. The possible influence of the skill in reproducing the PMM on the simulations of the two types of ENSO, the CP type, is examined
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