[A-CG36] Extratropical oceans and atmosphere

[ACG36-P18] The energetics of meridional teleconnection patterns over the North Pacific in winter: The internally-driven atmospheric variability and their modulations by ENSO

*Ryo Satoh¹, Yu Kosaka¹ (1.Research Center for Advanced Science and Technology, the University of Tokyo)

Keywords:Teleconnection, Energetics, ENSO

The western Pacific (WP) pattern 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 over the basin. 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 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. This result implies that dominance of a pattern could change under different background states. The present study examines changes in meridional teleconnection patterns under different SST conditions. To focus on internally generated atmospheric teleconnections, we utilized d4PDF large ensemble AGCM simulations, where 100 ensemble members are driven by the same historical sea surface temperature, sea ice, and radiative forcing. Atmospheric internal variability was then obtained as deviations from the ensemble mean. Our singular value decomposition analysis revealed that the leading co-varying mode between the magnitude of internal variability (i.e., inter-member variance) of the geopotential height and SST over the North Pacific is associated with ENSO. We then systematically extracted various meridional teleconnection patterns from internal variability for El Niño and La Niña winters separately. We found that most of the patterns over the central and western North Pacific, including the PNA and WP patterns, have lower energy during El Niño than La Niña. Further examination of the energetics revealed that the El Niño-La Niña differences in net energy conversion efficiency and eddy total energy are moderately correlated among the patterns, due primarily to the efficiency change in barotropic KE conversion. This suggests that the more zonally extended Pacific jet during El Niño, which is unfavorable for the KE conversion at the central North Pacific, contributes to the weakening of the PNA and WP patterns.