Revealing the Circulation Pattern Most Conducive to Precipitation Extremes in Henan Province of North China

Two catastrophic extreme precipitation events in July 2021 and August 1975 caused tremendous
damages and deaths in Henan, one of the most populated provinces in China. Revealing the relationship
between large-scale circulation patterns and precipitation extremes is vital for understanding the physical mechanisms and providing potential value for improving prediction and hence reducing impacts. Here, nine large-scale circulation patterns are identified for July–August using the self-organizing map. We find daily precipitation extremes under the fifth pattern (P5), characterized with the strongest easterly wind anomalies in Henan, feature the highest frequency and the largest intensity. Seven out of total 11 days in the two catastrophic extreme precipitation events belong to P5, and the top two maximum hourly precipitation extremes over continental China occurred under P5. The larger intensity of precipitation extremes is attributed to the dynamical contribution, suggesting more-intense precipitation extremes under P5 are largely dominated by stronger ascending motions.

Zhang, S., Y. Chen, Y. Luo, B. Liu, G. Ren, T. Zhou, C. Martinez-Villalobos, and M. Chang, (2022): Revealing the circulation pattern most conducive to precipitation extremes in Henan Province of North China. Geophysical Research Letters, 49, e2022GL098034.

Figure 2. The composite daily anomalies of geopotential height (colored shading, unit: gpm) at 500 hPa and column-integrated moisture flux (arrows; units: kg·m−1·s−1) in the 3 × 3 self-organizing map (SOM) nodes. Green lines denote 5,860 and 5,880 gpm contours. The number and occurrence frequency for each pattern are indicated in the upper-right corner. In the lower-left corner, ρ1 represents the mean pattern correlations for 500 hPa geopotential height between the composite pattern and each pattern in the corresponding SOM node, while ρ2 is calculated as the average of the two mean pattern correlations for zonal and meridional column integrated moisture fluxes, respectively

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