Planetary Wave Modulations Associated With The Eurasian Teleconnection Pattern

This study analyzes the modulation of planetary waves associated with the Eurasian (EU) pattern-one of the dominant teleconnection patterns seen over northern Eurasia in the boreal winter-through composite analyses using the Japanese 55-year reanalysis dataset to reveal its dynamic mechanism, including wave-mean flow interaction.From the viewpoint of deviation from climatological flow, the EU pattern is known as a stationary Rossby wave teleconnection type with an equivalent barotropic structure and action centers over northern Europe, mid-western Siberia, and Japan. However, from the viewpoint of deviation from the zonal average, the EU pattern modulates planetary wave activities, which include the East Asian winter monsoon as one component.In the positive phase of the EU pattern, corresponding to the enhanced Asian monsoon, the upward and eastward propagation of the planetary wave from Central Eurasia to the North Pacific in the troposphere is enhanced, compared with that of the climatology. The baroclinic energy conversion from the zonal mean to the deviation from that over East Asia contributes to the amplified planetary wave. The enhanced upward and eastward propagating planetary wave converges in the upper troposphere, thereby causing anomalous extratropical direct circulation and cold outflow toward the lower mid-latitude troposphere. These results indicate that the EU pattern is one of the global dynamic modes related primarily to planetary wave activities.