Analysis of the Main Modal Atmospheric Circulation Characteristics of Autumn Flood Precipitation in the Yellow River Basin and its Relationship with SST Anomalies

In this study, the leading modal characteristics of precipitation during the autumn flood season and their relationship with sea surface temperature (SST) anomalies in the Yellow River Basin are analyzed using statistical methods. Precipitation data from 319 meteorological stations in the Yellow River Basin for the autumn flood season (September-October) from 1961 to 2022, NCEP/NCAR reanalysis circulation data, and NOAA linearly optimum Interpolation (OIV) global SST data are employed.The results show that precipitation during the autumn flood season in the basin exhibits prominent interdecadal variability and is currently embedded in an above-average interdecadal background. The leading mode of autumn flood precipitation features a spatially consistent pattern of above- or below-average precipitation, with a variance contribution rate of 45.81%. This leading mode displays alternating interannual and interdecadal variations: from the 1960s to the mid-1980s and after 2000, it is dominated by quasi-2-3-year cycles with notable interannual variability; from the mid-1980s to the 1990s, it is mainly characterized by interdecadal changes. Circulation analyses indicate that the leading mode of basin precipitation is mainly modulated by the intensity and meridional displacement of the western Pacific subtropical high at 500 hPa, as well as the corresponding anomalous cyclonic/anticyclonic circulation near the Japanese Islands at 850 hPa. Such anomalous circulation patterns are likely induced by anomalous vertical motion and meridional circulation over the tropical western Pacific, which are triggered by anomalous SST patterns over the tropical Pacific.It is further revealed that the leading mode of autumn flood precipitation in the basin is closely linked to the evolution and persistence of SST anomalies over the equatorial central-eastern Pacific from the preceding summer to the following autumn. When the equatorial central-eastern Pacific is uniformly warm (cold), precipitation during the autumn flood season in the basin tends to be below average (above average).