Characteristic Analysis of the 10-30-Day Intraseasonal Oscillation over Mid-High-Latitude Eurasia in Boreal Summer

The aim of this study is to investigate the characteristics of the intraseasonal oscillation (ISO) with a 10-30-day cycle over mid-high-latitude Eurasia during boreal summer. The leading mode of this ISO is determined using an extended empirical orthogonal function analysis. Through a phase composite analysis, it is observed that a southeastward-propagating wave train with a quasi-barotropic structure is present in Eurasia. The dynamical mechanism and energy conversion affecting its propagation are also analyzed. The negative (positive) temperature tendency appears in the southeastern part of the temperature anomaly in the lower troposphere (upper troposphere), resulting in further southeastward displacement of the temperature perturbation. A diagnosis of temperature tendency shows that the main cause of the southeastward movement is the advection of anomalous temperature by the mean zonal wind. The energy conversion analysis reveals that by converting kinetic energy and potential energy, the ISO perturbation acquires energy from the summertime mean flow during its southeastward movement.