Mechanisms for a PNA-like teleconnection pattern in response to the MJO

Abstract

inematic mechanisms of the Pacific/North American (PNA)-like teleconnection pattern induced by the Madden?Julian oscillation (MJO) is examined using an atmospheric general circulation model (GCM) and a barotropic Rossby wave theory. Observation shows that a negative PNA-like teleconnection pattern emerges in response to MJO phase 2 forcing with enhanced (suppressed) convection located over the Indian (western Pacific) Ocean. The GCM simulations show that both forcing anomalies contribute to creating the PNA-like pattern. Indian Ocean forcing induces two major Rossby wave source (RWS) regions: a negative region around southern Asia and a positive region over the western North Pacific (WNP). The negative RWS to the north of the enhanced convection in the Indian Ocean arises from southerly MJO-induced divergent wind crossing the Asian jet. Unexpectedly, another significant RWS region develops over the WNP due to refracted northerly divergent wind. A ray tracing method demonstrates three different ways of wave propagation emanating from the RWS to the PNA region: 1) direct arc-like propagation from the negative RWS to the PNA region occurs in the longest waves; 2) shorter waves are displaced first downstream by the jet waveguide effect and then emanate at the jet exit to the PNA region; and 3) waves with zonal wavenumbers 1 and 2 exhibit canonical wave propagation from the positive RWS at the jet exit to the PNA region.