Impacts of Multi-Scale Solar Activity on Climate. Part II: Dominant
Timescales in Decadal-Centennial Climate Variability |
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Authors: | Hengyi WENG |
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Institution: | State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics,
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029 |
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Abstract: | Part II of this study detects the dominant decadal-centennial timescales in
four SST indices up to the 2010/2011 winter and tries to relate them to the
observed 11-yr and 88-yr solar activity with the sunspot number up to Solar
Cycle 24. To explore plausible solar origins of the observed
decadal-centennial timescales in the SSTs and climate variability in
general, we design a simple one-dimensional dynamical system forced by an
annual cycle modulated by a small-amplitude single- or multi-scale ``solar
activity.' Results suggest that nonlinear harmonic and subharmonic
resonance of the system to the forcing and period-doubling bifurcations are
responsible for the dominant timescales in the system, including the 60-yr
timescale that dominates the Atlantic Multidecadal Oscillation. The dominant
timescales in the forced system depend on the system's parameter setting.
Scale enhancement among the dominant response timescales may result in
dramatic amplifications over a few decades and extreme values of the time
series on various timescales. Three possible energy sources for such
amplifications and extremes are proposed. Dynamical model results suggest
that solar activity may play an important yet not well recognized role in the
observed decadal-centennial climate variability. The atmospheric dynamical
amplifying mechanism shown in Part I and the nonlinear resonant and
bifurcation mechanisms shown in Part II help us to understand the solar
source of the multi-scale climate change in the 20th century and the fact
that different solar influenced dominant timescales for recurrent climate
extremes for a given region or a parameter setting. Part II also indicates
that solar influences on climate cannot be linearly compared with non-cyclic
or sporadic thermal forcings because they cannot exert their influences on
climate in the same way as the sun does. |
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Keywords: | sun-climate relationship decadal-centennial climate
timescales nonlinear forcing-response resonant mechanism bifurcation
mechanism scale enhancement for extremes |
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