Association of extreme precipitation over the Yangtze River Basin with global air-sea heat fluxes and moisture transport

摘要

Although the effect of sea surface temperature anomalies in the Pacific and Indian Oceans on precipitation over the Yangtze River Basin (YRB) is well known, the impact of air-sea sensible and latent heat fluxes (SHF and LHF) has not been well studied. Based on the statistical and diagnostic analyses of historical precipitation data over the YRB, SHF and LHF over the global ocean, as well as global atmospheric reanalysis data, the impacts of SHF and LHF in the selected ocean regions on YRB extreme precipitation were investigated. The spatial distributions of the correlation coefficients between the YRB extreme precipitation indices (YRB-EPI) and SHF and LHF over the global ocean were analysed to identify critical air-sea interaction regions affecting YRB extreme precipitation. Results show that a significant positive correlation exists between YRB-EPI and air-sea heat fluxes over the Northwest Indian Ocean, Southeast Indian Ocean, Southwest Indian Ocean and South China Sea regions. Negative correlations were found over Central Equatorial Pacific, while positive lagged correlations exist over East Pacific. Composite analyses of global wind, geo-potential height and water vapour transport were also conducted for ten heaviest and ten lightest YRB precipitation years, respectively. In heavy YRB precipitation years, the atmospheric circulation pattern is generally characterized by a strengthened Western Pacific Subtropical High (WPSH) extending northwestward, a strengthened lower tropospheric convergence zone over the YRB, three distinct moisture transport paths from adjacent oceans to the YRB and low-level mid-latitude northerly wind anomalies. Whereas, in light YRB precipitation years, it is dominated by the southwesterly summer monsoon over the YRB, with a convergence zone displaced to the north of the YRB, a weak WPSH, and only two main paths of moisture transport. These distinctions between the heavy and light YRB precipitation years provide a physical basis for establishing a statistical prediction model for YRB extreme precipitation.