Evolution mechanism of synoptic-scale EAP teleconnection pattern and its relationship to summer precipitation in China

Abstract

Using ERA-Interim reanalysis daily data and gridded precipitation dataset, the evolution mechanism of East Asia-Pacific (EAP) teleconnection pattern and its relationship to summer precipitation in China were investigated on synoptic timescales based on EOF analysis, composite analysis, and significance test. The results demonstrate that the evolution of synoptic-scale EAP pattern is identified as having a significant relationship with the energy propagation represented by the wave-activity flux (WAF). Such EAP-related WAFs show various features in different levels of the troposphere. In the lower troposphere, the WAF primarily points poleward from the Philippines, playing a vital role in triggering and maintaining the synoptic-scale EAP pattern. A middle tropospheric zonally distributed ridge/trough/ridge wave train provides a favorable westerly waveguide for the southeastward (eastward) energy propagation, converging with a relatively weak poleward WAF over mid-latitude (high-latitude) East Asia. Moreover, the upper-level EAP-related anomalies are partly influenced by two conspicuous eastward WAFs. One may favor the development of Okhotsk anticyclonic (positive) anomaly, and the other one related to the Silk-Road (SR) wave train along the Asian jet converges into the cyclonic (negative) anomaly to greatly strengthen it. Particularly, the highly efficient baroclinic energy conversion responsible for the self-maintenance of SR pattern is also crucial for reinforcing and maintaining this cyclonic anomaly for a prolonged period by extraction of available potential energy from basic flow. In addition, during EAP pattern lifetime, due to the strong moisture flux convergence and upper-level divergence, the long-lasting strong ascents of moist/warm air along a moist and thick layer, therefore induce the summer consecutive extreme precipitation in the middle and lower reaches of Yangtze River.