Planetary Wave Modulations Associated with the Eurasian Teleconnection Pattern

Abstract

 This study analyzes the modulation of planetary waves associated with the Eurasian pattern–one of the dominant teleconnection patterns seen over northern Eurasia in the boreal winter–through composite analyses using JRA-55 to reveal its dynamic mechanism, including wave-mean flow interaction.

 From the viewpoint of deviation from climatological flow, the Eurasian 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 zonal average, the Eurasian pattern modulates the planetary wave activities which include the East Asian winter monsoon as one component.

 In the positive phase of the Eurasian pattern, corresponding to the enhanced Asian monsoon, the upward and eastward propagation of the planetary wave from the Central Eurasia to the North Pacific in the troposphere is enhanced, compared to 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 Eurasian pattern is one of the global dynamic modes related primarily to the planetary wave activities.