Influences of planetary- and synoptic-scale Rossby waves on the intraseasonal variability of Yangtze River Basin precipitation in summer

The Yangtze River Basin (YRB) is a critical economic and agricultural center in China, and the large summer precipitation variability here causes severe effects on social and economic. It is well known that the YRB precipitation (YRBP) is affected by multi factors, including anomalous anticyclone over the western North Pacific and local cyclone in the lower troposphere, the meridional displacement of the East Asian jet in the upper troposphere, et al. However, from the perspective of wave dynamics, influences of multi-scale Rossby waves on the intraseasonal variability of Yangtze River Basin precipitation are poorly understood. In this study, the authors used the three-dimensional multivariate circulation decomposition to quantify the multi-scale Rossby wave variability associated with the YRBP. Rossby waves with zonal wavenumber (k) being 1-20 are analyzed and categorized into planetary (k=1-3) and synoptic (k=4-20) scales, with waves of larger wavenumbers excluded due to their negligible amplitudes. Results indicate that the planetary- and synoptic- scale Rossby waves associated with the YRBP are favorable to the precipitation by different physical processes. On the one hand, planetary-scale Rossby waves contribute to the large-scale circulation anomalies, including the anticyclone over the western North Pacific, and the zonal cyclone over East Asia in the upper troposphere, which suggests a southward displacement of the East Asian jet. On the other hand, synoptic-scale Rosby waves are featured by a zonal wave train and contribute to local cyclonic anomalies in the lower troposphere to enhance the YRBP. Further lead-lag regression analysis is on-going.