145 Understanding Anomalous Eddy Vorticity Forcing in Pacific-North American Teleconnection Pattern Events

Thursday, 29 June 2017
Salon A-E (Marriott Portland Downtown Waterfront)
Jie Song, IAP, Beijing, China

An alternative eddy-eddy interactions mechanism is proposed in this study to understand anomalous synoptic eddies vorticity forcing (SEVF) associated with the Pacific-North American teleconnection pattern (PNA) events. Using a modified Geophysical Fluid Dynamics Laboratory (GFDL) dynamical core atmospheric model which can realistically reproduces the general dynamical properties the PNA, a series short-term control experiments (CEs) is conducted. In each case of CEs, there are no obvious PNA-like circulation anomalies. Subsequently, a corresponding series PNA+_Exp (PNA-_Exp) is also performed by introducing some appropriate small perturbations into the initial-value fields of CEs. In PNA+_Exp (PNA-_Exp), there are noticeable positive (negative) PNA-like circulation anomalies. Utilizing the results of CEs and PNA+_Exp/PNA-_Exp and the anomalous EVF decomposing procedure proposed by Song (2016), the anomalous nonlinear SEVF associated with the positive/negative PNA in the model can be decomposed into two linear eddy-eddy interaction terms and an unimportant nonlinear eddy-eddy interaction term.

The analysis results show that, the deformed part of synoptic eddies (denoted as Ψ'd ) for PNA+_Exp (PNA-_Exp) locates to the downstream (upstream) of the original synoptic eddies of CEs (denoted as Ψ'c) slightly, forming a sandwich-like structure. Therefore, Ψ'c and Ψ'd interactions are inevitable. The behaviors of decomposing terms of the anomalous SEVF associated with the PNA events in the model can be properly explained by Ψ'c and Ψ'd interactions and the Ψ'd self-interaction, indicating that the anomalous SEVF associated with the PNA events is resulted from eddy-eddy interactions.

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