The effect of orbital forcing on the mean climate and variability of the tropical Pacific

Axel Timmermann, S. J. Lorenz, S. I. An, Amy C Clement, S. P. Xie

Research output: Contribution to journalArticle

80 Citations (Scopus)

Abstract

Using a coupled general circulation model, the responses of the climate mean state, the annual cycle, and the El Niño-Southern Oscillation (ENSO) phenomenon to orbital changes are studied. The authors analyze a 1650-yr-long simulation with accelerated orbital forcing, representing the period from 142 000 yr B.P. (before present) to 22 900 yr A.P. (after present). The model simulation does not include the time-varying boundary conditions due to ice sheet and greenhouse gas forcing. Owing to the mean seasonal cycle of cloudiness in the off-equatorial regions, an annual mean precessional signal of temperatures is generated outside the equator. The resulting meridional SST gradient in the eastern equatorial Pacific modulates the annual mean meridional asymmetry and hence the strength of the equatorial annual cycle. In turn, changes of the equatorial annual cycle trigger abrupt changes of ENSO variability via frequency entrainment, resulting in an anticorrelation between annual cycle strength and ENSO amplitude on precessional time scales.

Original languageEnglish (US)
Pages (from-to)4147-4159
Number of pages13
JournalJournal of Climate
Volume20
Issue number16
DOIs
StatePublished - Aug 15 2007

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orbital forcing
annual cycle
Southern Oscillation
climate
cloud cover
entrainment
simulation
ice sheet
general circulation model
asymmetry
greenhouse gas
boundary condition
sea surface temperature
timescale
effect
temperature

ASJC Scopus subject areas

  • Atmospheric Science

Cite this

The effect of orbital forcing on the mean climate and variability of the tropical Pacific. / Timmermann, Axel; Lorenz, S. J.; An, S. I.; Clement, Amy C; Xie, S. P.

In: Journal of Climate, Vol. 20, No. 16, 15.08.2007, p. 4147-4159.

Research output: Contribution to journalArticle

Timmermann, Axel ; Lorenz, S. J. ; An, S. I. ; Clement, Amy C ; Xie, S. P. / The effect of orbital forcing on the mean climate and variability of the tropical Pacific. In: Journal of Climate. 2007 ; Vol. 20, No. 16. pp. 4147-4159.
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