Rectification of ENSO variability by interdecadal changes in the equatorial background mean state in a CGCM simulation SCIE SCOPUS

Cited 27 time in WEB OF SCIENCE Cited 26 time in Scopus
Title
Rectification of ENSO variability by interdecadal changes in the equatorial background mean state in a CGCM simulation
Author(s)
Dewitte, Boris; Yeh, Sang-Wook; Cibot, Carole; Terray, Laurent
Publication Year
2007-05
Abstract
The link between the changes in equatorial background stratification and El Nino-Southern Oscillation ( ENSO) modulation is investigated using a simulation from a 260- yr- long coupled general circulation model (CGCM). The work focuses on the role of nonlinearities associated with equatorial wave dynamics. As a first step, the low-frequency change in mean stratification is diagnosed and documented from the shallow-water parameters derived from a vertical mode decomposition of the CGCM. The parameters vary differently according to the baroclinic mode order, which may explain why a flattening thermocline does not necessarily lead to reduced ENSO activity. Estimations of baroclinic mode contributions to zonal current anomalies indicate that the decadal variability projects differently for the baroclinic modes as compared to the interannual variability. In particular, the high-order modes associated with decadal variability have a more pronounced signature in the western Pacific, whereas that associated with interannual variability (i.e., ENSO) shows more energy in the eastern Pacific. In the light of the results of the CGCM vertical mode decomposition, an intermediate coupled model (ICM) is used to test whether the nonlinearities associated with the changes in the baroclinic mode energy distribution can lead to coherent ENSO modulation. The results indicate that rectification of the interannual variability ( ENSO time scales) by the interdecadal variability associated with changes in the oceanic mean states takes place in the ICM. The rectified effect results mostly in an increased variability and skewness of the zonal advection, which tends to produce a zonal seesaw of the sea surface temperature anomaly. A tropical mechanism for producing ENSO modulation is then proposed that reconciles both the rectified effect resulting from nonlinearities associated with equatorial wave dynamics and the tropical decadal mode of thermocline depth arising from Ekman-pumping anomalies located in the central South Pacific.
ISSN
0894-8755
URI
https://sciwatch.kiost.ac.kr/handle/2020.kiost/4703
DOI
10.1175/JCLI4110.1
Bibliographic Citation
JOURNAL OF CLIMATE, v.20, no.10, pp.2002 - 2021, 2007
Publisher
AMER METEOROLOGICAL SOC
Subject
PACIFIC DECADAL VARIABILITY; NINO-SOUTHERN OSCILLATION; EL-NINO; CLIMATE VARIABILITY; AMPLITUDE-MODULATION; ATMOSPHERE MODEL; NORTH-AMERICA; COUPLED MODEL; OCEAN; ASYMMETRY
Type
Article
Language
English
Document Type
Article
Publisher
AMER METEOROLOGICAL SOC
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