A Review of Research on the Record-Breaking Precipitation Event in Henan Province,China,July 2021

A record-breaking precipitation event,with a maximum 24-h(1-h)precipitation of 624 mm(201.9 mm)observed at Zhengzhou Weather Station,occurred in Henan Province,China,in July 2021.However,all global operational forecast models failed to predict the intensity and location of maximum precipitation for this event.The unexpected heavy rainfall caused 398 deaths and 120.06 billion RMB of economic losses.The high-societal-impact of this event has drawn much attention from the research community.This article provides a research review of the event from the perspectives of observations,analysis,dynamics,predictability,and the connection with climate warming and urbanization.Global reanalysis data show that there was an anomalous large-scale circulation pattern that resulted in abundant moisture supply to the region of interest.Three mesoscale systems(a mesoscale low pressure system,a barrier jet,and downslope gravity current)were found by recent high-resolution model simulation and data assimilation studies to have contributed to the local intensification of the rainstorm.Furthermore,observational analysis has suggested that an abrupt increase in graupel through microphysical processes after the sequential merging of three convective cells contributed to the record-breaking precipitation.Although these findings have aided in our understanding of the extreme rainfall event,preliminary analysis indicated that the practical predictability of the extreme rainfall for this event was rather low.The contrary influences of climate warming and urbanization on precipitation extremes as revealed by two studies could add further challenges to the predictability.We conclude that data sharing and collaboration between meteorological and hydrological researchers will be crucial in future research on high-impact weather events.

The Spatial and Electronic Effects of Substituent Groups on the Thermal Curing of Bio-Based Benzoxazines

To explore the influence of substituent groups on thermally induced curing,eight new bio-based benzoxazines containing different substituent groups with different electron negativity and volumes were synthesized.The thermal curing of these bio-based benzoxazines was studied in detail.Combined with the curing reaction kinetics,simulation and calculation of Highest Occupied Molecular and Lowest Unoccupied Molecular values,the spatial and electronic effects of different substituent groups on the curing of benzoxazine was explored.It was found that when the substituent was located at the position directly connected to the N atom,the steric hindrance effect of the group was dominant.When the substituent group was located on the benzene ring connected to the O atom,both the electronic effect and the spatial effect influenced the curing of benzoxazine.When an electron-withdrawing group was connected ortho position to the O atom,the curing reaction was promoted due to the decreased electron cloud density of O-on the oxazine ring,making the C-O bond easier to break.When an electron-donating group was connected to the meta position of the O atom it also promoted the curing reaction,possibly because it increased the electron cloud density of the+CH2 reaction site and thereby facilitated electrophilic substitution via attack of+CH2 on the cross linking reaction centre.This work provides a deeper understanding of how spatial and electronic effects of substituents affect the curing of benzoxazine.

Extreme large-scale atmospheric circulation associated with the“21·7”Henan flood

From July 19 to 21,2021,Henan,a province in northern China(NC),was affected by severe flooding(referred to hereafter as“21·7”)caused by a prolonged record-breaking extreme precipitation(EP)event.Understanding the extremes of the large-scale circulation pattern during“21·7”is essential for predicting EP events and preventing future disasters.In this study,daily atmospheric large-scale circulations over NC in the summers from 1979 to 2021 were investigated using the circulation classification method of an obliquely rotated principal component analysis in T-mode(PCT).The geopotential heights at 500 hPa and 925 hPa were applied successively in classification.Among the nine summer circulation patterns found at 500 hPa,the three days of“21·7”belonged to the Type 8 pattern,which had the second highest probability of EP days among all patterns.It was characterized by a southeasterly wind toward North China Plain driven by a dipole geopotential height field,with the West Pacific subtropical high(WPSH)extending far north to 30°N and low pressure to the south near NC.Tropical cyclones(TCs)occurred on 72.5%of EP days,in which larger amounts of precipitation and a longer duration of EP days were found along the mountains in NC,as compared with other patterns.The distribution of EP events under this pattern was mainly influenced by the location of the low pressure at 925 hPa in the dipole.The subtype 8-3 circulation,with low pressure in the east of Taiwan Island,included“21·7”and accounted for 1.6%of all summer days.Typhoon In-fa,together with the WPSH,gave rise to intense column integrated moisture flux convergence(IMFC)via the southeasterly wind to Henan,which occurred continuously during the 3 days of“21·7”,resulting in the largest(second largest)mean IMFC among 3 consecutive EP days under type 8(all types)during the past 43 summers in NC.Further analysis revealed that the large-scale dynamic process could not completely explain the record-breaking EP during“21·7”,indicating possible contributions of other dynamic processes related to meso-scale convective storms.