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El Niño: A coupled response to radiative heating?
Author(s) -
Sun DeZheng
Publication year - 1997
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/97gl01960
Subject(s) - radiative transfer , radiative forcing , atmospheric sciences , sea surface temperature , climatology , environmental science , atmosphere (unit) , forcing (mathematics) , oscillation (cell signaling) , latitude , tropical climate , climate change , physics , geology , meteorology , oceanography , geography , chemistry , biochemistry , archaeology , quantum mechanics , astronomy
The very existence of El Niño— the oscillatory behavior of the tropical Pacific climate—may be due to the warmth of the tropics (relative to the coldness of the high latitudes). This is elucidated by subjecting a mathematical model for the coupled tropical ocean‐atmosphere system to a varying radiative heating. The temperature of the deep ocean is kept fixed. In response to an increasing radiative heating, the coupled system first experiences a pitch‐fork bifurcation that breaks the zonal symmetry imposed by the solar radiation. The resulting zonal sea surface temperature (SST) gradients increase with increases in the radiative heating. When the zonal SST gradients exceed a critical value, a Hopf bifurcation takes place which brings this system to an oscillatory state, a state that closely resembles the observed tropical Pacific climate. Further increases in the radiative heating result in increases in the magnitude of the oscillation. The results shed new light on the physics of El Niño and suggest that climate change due to anthropogenic forcing may occur through the same dynamic modes that sustain natural variability.