Optimal Perturbations Triggering Weather Regime Transitions: Onset of Blocking and Strong Zonal Flow |
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| Authors: | JIANG Zhin MU Mu and WANG Donghai |
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| Institution: | State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 100081,Key Laboratory of Ocean Circulation and Wave, Institute of Oceanology,Chinese Academy of Sciences, Qingdao 266071, State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029,State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 100081 |
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| Abstract: | In this paper, the approach proposed by Mu and Jiang (2008) to obtain the
optimal perturbations for triggering blocking (BL) onset is generalized to
seek the optimal perturbations triggering onset of the strong zonal flow
(SZF) regime. The BL and SZF regimes are characterized by the same
dipole-like anomaly pattern superposed on the climatological flow, but with
opposite sign. The results show that this method is also superior at finding
the initial optimal perturbations triggering onset of the SZF regime,
especially in the medium range.
Furthermore, by comparing the two kinds of conditional nonlinear optimal
perturbations (CNOPs) triggering onset of BL and SZF regimes, we find that
in the linear approximation, there is symmetry in the sensitivities for BL
and SZF onset, and the perturbations that optimally trigger onset of BL and
SZF regimes at times when linear approximation is valid are also
characterized by the same spatial pattern but with opposite sign. Whereas
when the optimization time is extended to 6 days, the two kinds of CNOPs
lose their out-of-phase behavior. The nonlinearity results in an asymmetry
between the sensitivity for BL and SZF onset. Additionally, we find that the
optimal perturbations have one common property, which is that the second
baroclinic mode contributes more to the initial perturbations while the
barotropic mode dominates the final structures. |
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| Keywords: | linear approximation symmetry nonlinearity asymmetry |
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