09:15 〜 09:30
[ACG32-02] Atmospheric meridional teleconnection patterns over the North Pacific in winter: Energetics and changes under global warming
キーワード：テレコネクション、エネルギー変換
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. Despite many studies, comprehensive understanding of why those patterns are dominant and which processes are important for their maintenance is still insufficient. By using JRA-55 reanalysis and d4PDF large ensemble AGCM simulations, our study systematically extracted 286 meridional teleconnection patterns anchored to various locations over the wintertime North Pacific from monthly mean fields and investigated the energetics for each of the patterns. Specifically, we evaluated energy conversion efficiency, whose reciprocal indicates the time scale for a particular energy conversion process to replenish the total energy associated with a teleconnection pattern. We found that total energy associated with individual patterns is highly correlated with the net energy conversion efficiency from the climatological mean field and modulated transient eddy activity. This result suggests that net conversion efficiency is the key factor for the dominance of a pattern. 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.
We further investigated changes in energetics of those 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. In particular, 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.
We further investigated changes in energetics of those 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. In particular, 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.