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Factors Affecting ENSO’s Period

MacMynowski, Douglas G. and Tziperman, Eli (2008) Factors Affecting ENSO’s Period. Journal of the Atmospheric Sciences, 65 (5). pp. 1570-1586. ISSN 0022-4928. doi:10.1175/2007JAS2520.1.

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Accurately capturing the observed mean period of ENSO in general circulation models (GCMs) is often challenging, and it is therefore useful to understand which parameters and processes affect this period. A computationally efficient simulation-based approach is used to extract both the dominant eigenvalues and corresponding eigenvectors of the linearized model from the Zebiak–Cane intermediate-complexity model of ENSO without having to directly construct the linearization. The sensitivity of the period to a variety of parameters is examined, including atmosphere–ocean coupling, atmospheric heating parameterization, thermocline depth zonal profile, western boundary reflection coefficient, atmospheric and ocean wave speeds or Rossby radii of deformation, ocean decay time, and the strength of the annual cycle. In addition to the sensitivity information, the spatial structures of the main fields (SST, thermocline thickness, and more) that are involved in period changes are obtained to aid in the physical interpretation of the sensitivities. There are three main time lags that together compose one-half of a model ENSO period: the Rossby-plus-Kelvin wave propagation time for a wind-caused central Pacific disturbance to propagate to the western ocean and back, SST dynamics that determine the lag between eastern ocean thermocline anomalies and eastern ocean SST anomalies, and the “accumulation” lag of integrating a sufficient delayed wave signal arriving from the western ocean to cancel the eastern ocean anomalies. For any of the parameter changes considered, the eigenvector changes show that the largest contributor to the period change is from changes to the last of these three mechanisms. Physical mechanisms that affect this accumulation delay are discussed, and the case is made that any significant change to ENSO’s period is in turn likely to involve changes to this delay.

Item Type:Article
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URLURL TypeDescription
MacMynowski, Douglas G.0000-0003-1987-9417
Tziperman, Eli0000-0002-7998-5775
Additional Information:© 2008 American Meteorological Society. (Manuscript received 21 May 2007, in final form 4 September 2007) We thank Ben Kirtman and an anonymous reviewer for their helpful comments. This work was supported by the James McDonnell Foundation. ET is also supported by NSF Climate Dynamics program, Grant ATM-0351123.
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James McDonnell FoundationUNSPECIFIED
Issue or Number:5
Record Number:CaltechAUTHORS:MACjas08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10663
Deposited By: Archive Administrator
Deposited On:30 May 2008
Last Modified:08 Nov 2021 21:09

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