A Mechanism for PNA-like teleconnection pattern in response to the Madden-Julian oscillation

Abstract:

The relationship between the MJO and PNA-like pattern is examined by reconstructing each term in streamfunction equation using the output of the atmospheric general circulation model (GCM) simulation. In the result of simulations performed with a single diabatic forcing along the equator, it is found that the negative PNA-like pattern is clearly evident when either diabatic heating near 50°E-100°E or diabatic cooling near 130°E-160°W is forced. This indicates that both tropical forcing which corresponds to the MJO have its significant role on the PNA-like pattern formation. The required time to form this pattern is different depending on the location of tropical forcing and this difference is the key of the pattern maintenance. The tropical forcing-induced divergent wind anomalies mainly contribute to the generation of the Rossby Wave Source (RWS)and the barotropic Rossby wave emitted from the RWS anomalies propagates into the extratropics based on the vorticity perturbation advection by the climatological rotational wind.

Furthermore, the relationship between the MJO and PNA-like pattern depends on the condition of basic state modified by ENSO. In La Niña years with a northward-heading exit of jet, the Rossby wave induces strong and clear propagation pattern, while in El Niñoyears when the exit of jet is biased to the south the generated pattern is vague. These results help better understanding of the MJO-PNA teleconnection and contribute to the improvement of the weather forecast on the intraseasonal time scale.