Changes in Wintertime North Pacific Meridional Teleconnection Patterns due to Global Warming: An Energetics Perspective

The western Pacific (WP) pattern, North Pacific Oscillation (NPO), and the Pacific-North American (PNA) pattern are dominant teleconnection patterns over the wintertime North Pacific, which are characterized by a meridional dipole of height anomalies. To comprehensively understand why these patterns are dominant, our previous study systematically extracted 286 meridional teleconnection patterns anchored at various locations spanning the basin from monthly mean fields and investigated the energetics for each of the patterns. The study quantitatively revealed that patterns that efficiently gain kinetic energy (KE) and available potential energy (APE) through the energy conversion from the climatological mean state and high-frequency eddies tend to have larger total energy (KE+APE), which explains the dominance of the specific teleconnection patterns. In addition, we found baroclinic energy conversion from the climatological mean field is the most efficient process for the maintenance of almost all the patterns, arising from the vertically phase-tilted height anomalies embedded in the baroclinic climatological mean state.

This result implies that the dominance of a pattern could change under different background states. The present study further investigated changes in energetics of the systematically extracted 286 teleconnection patterns under global warming through a comparison between d4PDF historical and +4K experiments. We found an increase in the total energy associated with patterns whose node lines are located at 35°N, including the PNA pattern, in the warmer climate, while an energy decrease is found for the patterns with node lines at 45°N, including the WP pattern and NPO. These energy changes are highly correlated with the changes in the net energy conversion efficiency. Changes in barotropic and baroclinic energy conversion efficiencies from the climatological mean state are the primary cause of the net efficiency changes, and those can be explained partly by structural changes in the background Pacific jet and decreased horizontal temperature gradients associated with Arctic amplification and more enhanced warming over land than over the ocean. Moreover, baroclinic conversion efficiency decreases for almost all the patterns due to the changes in the vertical structure of circulation anomalies and the background temperature field. These results provide clues for the mechanisms of the magnitude changes in the meridional teleconnection patterns and implications for the potential predictability in the warmer climate.