The Dynamics of the Pacific-North American Teleconnection Pattern

This study uses NCEP-NCAR Reanalysis data (primarily 2-PVU potential temperature) and NOAA OLR data to examine the dynamical evolution of the Pacific/North American (PNA) teleconnection pattern. For the NCEP-NCAR data, the data covers the period from 1948 through 2008.

Both phases of the PNA are found to be excited by anomalous tropical convection. The triggering of the positive PNA is associated with enhanced (weakened) convection over the western Pacific (Indian) Ocean, whereas the beginning of the negative PNA coincides with enhanced (weakened) convection over the Indian (western Pacific) Ocean. Over the Pacific Ocean, for the positive (negative) PNA, the primary impact of this convection is to zonally extend and strengthen (contract and weaken) the subtropical jet. For both PNA phases, the anomalous tropical convection is followed by cyclonic wave breaking of synoptic-scale waves on the poleward side of the subtropical jet. The breaking waves propagate eastward until they encounter the jet-exit region, which is displaced eastward (westward) relative to that of the climatological subtropical jet for the positive (negative) PNA. The resulting anomalies take on the form of the optimal structure for nonmodal growth. An analysis with the streamfunction tendency equation shows that subsequent PNA growth develops from both stationary eddy advection and linear dispersion. For both phases, the PNA pattern is maintained by breaking, synoptic-scale waves which are initially located upstream of the PNA region. Once these upstream disturbances are no longer present, the PNA anomalies decay via linear dispersion and mixing.