A Study of the North Atlantic Oscillation Using Conditional Nonlinear Optimal Perturbation

• Published in: Journal of the Atmospheric Sciences
• Main Authors: Jiang, Zhina, Mu, Mu, Luo, Dehai, Jiang, ZN
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2013
• Subjects: Meteorology & Atmospheric Sciences; Science & Technology; Physical Sciences; FREQUENCY DIPOLE MODES; TELECONNECTION PATTERNS; ANNULAR MODES; PART I; DYNAMICS; BLOCKING; NAO; VARIABILITY; WAVE; ANOMALIES; North Atlantic; North Atlantic oscillation
• Online Access: http://ir.qdio.ac.cn/handle/337002/16390; https://doi.org/10.1175/JAS-D-12-0148.1

The conditional nonlinear optimal perturbation (CNOP) method is used to explore the optimal precursors that trigger the North Atlantic Oscillation (NAO) anomaly pattern with a triangular T21, three-level, quasi-geostrophic global spectral model based on a viewpoint that the NAO is a nonlinear initial-value problem. With a three-dimensional winter climatological flow as the basic state, initially baroclinic localized optimal precursors on the northward flanks of the climatological Atlantic jet undergo wave breaking during their evolution into the NAO-like anomalies. Accompanied with the formation of the NAO, the north-south variability of the zonal mean westerly anomaly has arisen. The conditional nonlinear optimal perturbation (CNOP) method is used to explore the optimal precursors that trigger the North Atlantic Oscillation (NAO) anomaly pattern with a triangular T21, three-level, quasi-geostrophic global spectral model based on a viewpoint that the NAO is a nonlinear initial-value problem. With a three-dimensional winter climatological flow as the basic state, initially baroclinic localized optimal precursors on the northward flanks of the climatological Atlantic jet undergo wave breaking during their evolution into the NAO-like anomalies. Accompanied with the formation of the NAO, the north-south variability of the zonal mean westerly anomaly has arisen. Analysis reveals that in the evolution of optimal precursors, the role played by the self-interaction of perturbations (viz., the nonlinear process) in the onset of the negative-phase NAO (NAO 2) event is stronger than that in the onset of the positive-phase NAO (NAO 1) event. Both the perturbation/ basic-state interaction and self-interaction of perturbations determine whether the NAO 2 event occurs, whereas the nonlinearity process in the NAO 1 onset only appears to modulate the structure of the perturbation to have a dipole mode over the North Atlantic at the optimization time, and meanwhile cause this dipole mode to become zonally extended. That is to ...