The Inverse Effect of Annual-Mean State and Annual-Cycle Changes on ENSO

Soon-Il An; Yoo-Geun Ham; Jong-Seong Kug; Axel Timmermann; Jung Choi; In-Sik Kang

doi:10.1175/2009jcli2895.1

journal article Mar 01, 2010

The Inverse Effect of Annual-Mean State and Annual-Cycle Changes on ENSO

Soon-Il An

Yoo-Geun Ham

Jong-Seong Kug

Axel Timmermann

Jung Choi In-Sik Kang

Journal of Climate Vol. 23 No. 5 pp. 1095-1110 · American Meteorological Society

View at Publisher Save 10.1175/2009jcli2895.1

Abstract

Abstract
The influence of the tropical Pacific annual-mean state on the annual-cycle amplitude and El Niño–Southern Oscillation (ENSO) variability is studied using the Max Planck Institute for Meteorology coupled general circulation model (CGCM) ECHAM5/Max Planck Institute Ocean Model (MPI-OM1). In a greenhouse warming experiment, an intensified annual cycle of sea surface temperature (SST) in the eastern tropical Pacific is associated with reduced ENSO variability, and vice versa.
Analysis showed that the annual-mean states, especially the surface warming in the western Pacific and the thermocline deepening in the central Pacific, which is concurrent with the strong annual cycle, act to suppress ENSO amplitude and to intensify the annual-cycle amplitude, and vice versa. The western Pacific warming acts to reduce air–sea coupling strength and to shorten the ocean adjustment time scale, and the deepening of central Pacific thermocline acts to diminish vertical advection of the anomalous ocean temperature by the annual-mean upwelling. Consequently, ENSO activity is suppressed by the annual-mean states during the strong annual-cycle decades, and the opposite case associated with the weak annual-cycle decades is also true. Furthermore, the time integration of an intermediate ENSO model forced with different background state configurations, and a stability analysis of its linearized version, show that annual-mean background states during the weak (strong) annual-cycle decades are characterized by an enhanced (reduced) linear growth rate of ENSO or similarly large (small) variability of ENSO. However, the annual-cycle component of the background state changes cannot significantly modify ENSO variability.
Using a hybrid coupled model, it is demonstrated that diagnosed annual-mean background states corresponding to a reduced (enhanced) annual cycle suppress (enhance) the development of the annual cycle of SST in the eastern equatorial Pacific, mainly through the weakening (intensifying) of zonal temperature advection of annual-mean SST by the annual-cycle zonal current. The above results support the idea that climate background state changes control both ENSO and the annual-cycle amplitude in opposing ways.

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Details

Published: Mar 01, 2010
Vol/Issue: 23(5)
Pages: 1095-1110

Authors

S

Soon-Il An

Department of Atmospheric Sciences/Global Environmental Lab, Yonsei University, Seoul, South Korea

Y

Yoo-Geun Ham

School of Earth and Environmental Sciences, Seoul National University, Seoul, South Korea

J

Jong-Seong Kug

Korea Ocean Research and Development Institute, Ansan, South Korea

A

Axel Timmermann

International Pacific Research Center, University of Hawaii at Manoa, Honolulu, Hawaii

J

Jung Choi

Department of Atmospheric Sciences/Global Environmental Lab, Yonsei University, Seoul, South Korea

I

In-Sik Kang

School of Earth and Environmental Sciences, Seoul National University, Seoul, South Korea

Cite This Article

Soon-Il An, Yoo-Geun Ham, Jong-Seong Kug, et al. (2010). The Inverse Effect of Annual-Mean State and Annual-Cycle Changes on ENSO. Journal of Climate, 23(5), 1095-1110. https://doi.org/10.1175/2009jcli2895.1

The Inverse Effect of Annual-Mean State and Annual-Cycle Changes on ENSO

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