Quasi-linear convective systems (QLCSs) frequently produce severe weather in North China, with multiple QLCSs often forming successively within a short period. However, their formation mechanisms under such conditions remain unclear. This study investigated the formation mechanisms of three successive QLCSs that affected Beijing and its vicinity from the afternoon to evening on 12 June 2022, using in-situ and remote sensing observations as well as high-resolution Weather Research and Forecasting model simulations with a 9-, 3-, 1-km nested grid. The event occurred within the trough of a mature cold vortex, which induced dry westerlies over the western mountainous areas and moist southerlies over the eastern plains of North China. Diurnal solar heating further intensified the zonal thermal and moisture contrasts between the eastern and western domains. Therefore, a southwest–northeast-oriented dryline with a dynamical confluence persisted along the eastern Taihang Mountains. To the west of the dryline, sustained boundary layer turbulent activities eliminated convective inhibition. Meanwhile, episodic weak cold advections induced by the cold vortex modestly increased the convective available potential energy over the northern mountains, providing energy for the generation of convective cell clusters (CCs). These sequentially initiated CCs propagated southeastward under the steering airflow, with distinct outflow boundaries forming at their leading edges. Crucially, the continuous merging between the southeastward-moving CC outflow boundaries and the quasi-stationary dryline strengthened the low-level convergence both in depth and intensity along segments of the dryline zone. The intensified dynamical lifting ultimately triggered convection along these segments, corresponding to the successive formation of three QLCSs. This paper highlights the synergistic effects of cold-vortex forcing, complex-terrain modulation, and dryline–outflow boundary interactions on the formation of organized convection over mountainous areas. The findings benefit the forecasting and early warning of similar severe convective events in North China.

ABSTRACT This study investigates the spatiotemporal characteristics, structural features and environmental conditions of mesoscale convective systems (MCSs) over the coastal region of South China from April to June during 2013–2017, using satellite–gauge merged precipitation, cloud‐to‐ground (CG) lightning data, radar observations and reanalysis data. All analysed MCSs generate rainfall and are classified into two categories based on lightning activity: rainfall‐only MCSs (without observed CG lightning) and lightning‐producing MCSs (rainfall with CG lightning). Their spatial structures, rainfall and lightning behaviours and associated circulation patterns are compared, with emphasis on variations before and after monsoon onset. Results show that lightning‐producing MCSs are generally larger in both horizontal and vertical extent than rainfall‐only MCSs, especially after monsoon onset, when both types become more vertically developed. Before monsoon onset, lightning‐producing MCSs are less frequent but produce stronger rainfall. After monsoon onset, their frequency increases while rainfall intensity weakens. In contrast, rainfall‐only MCSs show increases in both frequency and rainfall intensity after monsoon onset. The formation of lightning hotspots is influenced by both the frequency of lightning‐producing MCS occurrences and their internal lightning intensity, with the latter playing a more dominant role. Circulation types favourable for MCS development differ significantly. Lightning‐producing MCSs tend to occur along the western flank of the subtropical high under southwesterly low‐level winds, with convective instability peaking in the afternoon. Rainfall‐only MCSs are more common within the subtropical high under southeasterly flows, where nocturnal convergence and orographic lifting promote their development. These circulation differences are shaped by seasonal variations in moisture, thermodynamics and topography. This study provides a comprehensive understanding of MCS‐related rainfall and lightning, offering insights for forecasting and model evaluation.

Double rain belts are a unique yet poorly understood weather phenomenon over North China. This study investigates a double-rain-belt event over North China (23–28 July 2025) to elucidate the controlling role of the western North Pacific subtropical high (WNPSH) on compound precipitation events in regions influenced by subtropical highs. The three-stage evolution of the heavy rainfall event—shifting from convective-dominated to warm-frontal-dominated and back to convective rainfall—was dictated by the WNPSH’s abrupt movement. The movement of the WNPSH (westward extension versus retreat) dynamically modulated a transition zone between the WNPSH and the cold air over the mountainous areas of North China, leading to double rain belts with contrasting convective and stratiform properties. When there was a certain distance of the transition zone, deep convective heavy rainfall formed. In contrast, when the WNPSH extended northwestward, the dry and warm lid of the WNPSH suppressed convection, forcing southwesterly warm and moist air to ascend gradually along the cold air mass and produce warm-frontal precipitation with some embedded convective cells. These two distinct types of precipitation, which occurred in alternating periods, formed the observed double rain belts in North China. A key finding is that the rapid retreat of the WNPSH accompanied by its spatial contraction, triggered stronger convection and more intense precipitation than its northwestward extension phase. The authors conclude that the WPSH acted as a critical synoptic-scale forcing of the double rain belts over North China.摘要华北双雨带特征独特, 但其形成机制尚未被充分认知. 本文基于2025年7月23–28日华北典型双雨带强降水过程, 探究西北太平洋副热带高压 (WNPSH) 对该降水过程的控制机制. 此次降水依次经历对流主导-暖锋主导-对流主导三个演变阶段, 阶段转换由WNPSH突发进退调控. WNPSH东西向摆动调控冷暖空气过渡带特征, 促成对流与暖锋降水交替发生, 形成双雨带结构. WNPSH快速东退收缩阶段的对流活动与降水强度, 显著强于其西北伸展阶段. WNPSH是华北双雨带演变的核心天气尺度强迫因子.

This study investigates extreme rainfall episodes along the eastern foothills of the Taihang Mountains in North China from 30 July to 1 August 2023. It focuses on two types of extreme hourly rainfall rates (HRRs), i.e., the maximum regional-average HRR and site-observed HRR, which exhibited sequential development over southern, middle, and northern key regions. These rainfall extremes occurred in an environment where a high-pressure barrier over North China prevented the intrusion of cold air masses from the north while a northward-moving typhoon remnant vortex and its associated low-level jet (LLJ) transported warm and moist airflow from the south. Two distinct echo evolution modes and convection initiation mechanisms are identified for the two types of extreme HRRs. The maximum regional-average HRR occurred when the LLJ arrived to the east of the key regions, while the maximum site-observed HRR occurred when the warmer vortex center influenced the regions. Taking the northern key region as a representation, at the time of the maximum regional-average HRR, slantwise ascent of the airflow along a warm-frontal-like boundary released energy related to symmetrical instability, resulting in stratiform rainfall with weak convective cores. The transport of locally initiated convection over the eastern plain region, where the atmospheric stratification was more potentially unstable, also significantly contributed. When the maximum site-observed HRR occurred, the terrain lifting of warm and moist southeast airflow led to intense convection over the mountain foothills. Overall, the passage of the warm-core typhoon remnant vortex and interaction with Taihang Mountains determined the timing and location of extreme HRRs across the key regions.

Synoptic forcings have traditionally played a pivotal role in extreme rainfall over North China. However, there are still large unexplained gaps in our understanding of the formation of extreme rainfall events over this region. This heavy rainfall event, lasting from 29 July to 2 August 2023 (referred to as the “23⋅7” event), is characterized by a long duration, widespread coverage, and high accumulation of rainfall over North China. Overall, the persistent extreme rainfall is closely associated with the remnant vortex originating from Typhoon Doksuri (2305), Tropical Storm Khanun (2306), and the unusual westward extension of the western North Pacific subtropical high (WNPSH), as well as quasi-stationary cold, dry air masses surrounding North China on the west and north sides. Based on wind profiles and rainfall characteristics, the life cycle of the 23⋅7 event is divided into two stages. In the first stage, the western part of the WNPSH was weakened by Tropical Storm Doksuri, where it appeared that the WNPSH retreated eastward with decreasing height. The marginal zone of this subtropical high then became inclined below 500 hPa. Therefore, convection was limited by the tilted WNPSH, with a warm, dry cover embedded in the low-to-middle troposphere. Meanwhile, mountain areas in the western part of North China were occupied by cold air masses above approximately 3.0 km. Combining the orographic and cold-air blocking, only a thin layer of southeasterly wind (between 1.3 and 3.0 km) was able to pass over the mountains. Although the warm and moist southeasterly flows were lifted by orography, no convection was triggered because of the local capped cold and dry air masses overhead. Under this regime, equivalent potential temperature (θe) gradients were established between warm, humid and dry, cold air masses, similar to a warm front, causing warm air to lift and generating widespread but low-intensity rainfall. However, the lifting was too weak to allow convection to be highly organized. In the second stage, the WNPSH was further weakened by the enhancement of Khanun, and thus the embedded warm, dry cover associated with the tilted WNPSH was significantly thinned. Consequently, convection triggered by orographic blocking was able to extend upward and develop further, forming deep convection. Generally speaking, the convection in the second stage is much deeper than that in the first stage. The results may shed new light on a better understanding and forecasting of long-lasting extreme rainfall.

Within a meso‐ γ ‐scale convective storm, dynamic processes play a pivotal role in extreme rainfall production. However, there are still large unexplained gaps in understanding the effects of dynamic processes on the generation of extreme short‐term rainfalls. In this study, a nocturnal rainfall event with an extreme hourly rainfall (EHR) of 184 mm on 7 May 2017 over the coastal city of Guangzhou is examined based on cloud‐permitting simulations, focusing on the generation of the EHR. Results reveal that the EHR is featured by obvious horizontally delivered rainwater ( q r ) from the front to the rear within a meso‐ γ ‐scale convective storm. The horizontally delivered q r from the front of the storm overlayed on the q r produced by cloud microphysical processes locally overhead in the rear of the storm, leading to a deep q r layer with values over 4 g·kg −1 at the lowest 0–4 km levels above the ground. Thus, huge q r poured down in a short time, resulting in the EHR. According to statistical results, at least 80 mm q r was provided by horizontal delivery for the majority of grid points with hourly rainfall over 120 mm. This dynamic delivery mechanism is further confirmed by a trajectory analysis of raindrops. We argue that this mechanism may play a decisive role in EHR formation in particular scenarios while admitting that EHR can also be produced sometimes mainly via cloud microphysical processes. The formation mechanism of EHR proposed herein may help further understand and forecast localized extreme short‐term rainfall.

A climatological study of 206 severe convective wind (SCW) events from April to September during 2016-2023 in Beijing was conducted. Results show events primarily occur in summer, with a peak in the afternoon and a much weaker secondary peak in the early morning. They are relatively more frequent in mountainous areas than in plains,with the southern foothills of Yanshan Mountain being the most affected area. Circulation patterns associated with SCW events, ranked by frequency, include the low-pressure vortex-subtropical high, deep trough, low-level jet, subtropical high periphery, transverse trough, dual low-pressure vortex, and easterly flow patterns. Convective organization modes, also ranked by frequency, consist of cluster cells, broken line, nonlinear-shaped systems, hybrid systems, squall line, individual cell, and bow echo. SCW events are mainly triggered by convective systems coming from the northwest and west. In environments with high precipitable water, such as the low-level jet and subtropical high periphery patterns, nonlinear-shaped and hybrid systems are more prevalent. In contrast, in very dry environments, such as the deep trough pattern, broken lines and cluster cells occur more frequently. Strongly organized convective systems, such as squall lines and bow echoes, often exist in circulations with a westerly low-pressure vortex. Generally, a drier atmospheric environment tends to produce stronger winds, while moist conditions increase the frequency of SCW events. These findings highlight the influence of circulation patterns and environmental conditions in SCW events.

This study examines the multiscale processes leading to three heavy rainfall (HR) episodes over Beijing and its periphery during 19‒21 July 2016. The orographic lifting of lower-tropospheric southeasterly flows of warm-moist air triggered convective lines along the foothills of Mt. Taihang, resulting in HR over the mountainous region during the first HR episode. The southeasterly flows were then enhanced by the formation of a cold vortex and latent heat release associated with HR during the second HR episode. It was the warm-frontal forcing that released conditional symmetric instability and the movement of convective rainbands across similar areas that accounted for high hourly rainfall rates over most of Beijing during the second HR episode. As the cold vortex and the associated warm front advanced northward, the southeasterly moisture flux into Beijing decreased, except in southern Beijing, where intense convection still continued. An analysis of the radar-observed polarimetric variables reveals that cold-rain microphysical processes dominated the first HR episode, with a larger proportion of ice crystals above the melting level in conjunction with greater height of the maximum upward motion, as compared to those during later episodes. In contrast, the second and third episodes were influenced by the stronger advection of warm-moist air with the lower altitude of the maximum upward motion, which favored warm-rain microphysical processes with increasing raindrop sizes toward the ground. Therefore, there was an increased concentration of larger raindrops in the lower troposphere. However, the raindrops during the third episode were relatively smaller than those in the second episode, primarily due to weaker upward motion, while the presence of a dry layer in the midtroposphere played a minor role.

A record-breaking heavy rainfall event struck North China from 29 July to 1 August 2023, during which the southwest mountain region of Beijing city recorded a rainfall amount over 2 times that of its eastern plain region. Based on multisource observations and convection-permitting numerical simulations, this study analyzes the thermal structure in these regions and its impact on precipitation. The rainfall was caused by a deep extratropical cyclone, which produced strong low-level southeast winds that transported abundant warm moist air toward North China. The light rainfall on 29 July caused extensive evaporation and cooling, and the increase in low-level easterly wind led to uneven heating in the planetary boundary layer (PBL) during the following two days. The PBL over mountains was significantly colder than over plains. The WRF model reasonably reproduces the evolution of rainfall, but with a dry bias. The simulated differences in rainfall amount and temperature between two regions are similar to the observations. The diagnosis of the vertical momentum budget attributes the enhancement of updrafts to horizontal convergence within the PBL, which mainly resulted from the deceleration of easterly wind over the windward slope. The simulated maximum temperature gradient occurred in the strongest convergence zone. Furthermore, the force analysis indicates the important role played by the thermal contrast in the deceleration of PBL easterly wind. The thermal contrast forced a mountain breeze effect, which together with the topographic blocking significantly decelerated the easterly wind and further enhanced updrafts and rainfall over mountainous regions.

North China experienced devastating rainfall from 29 July to 1 August 2023, which caused substantial flooding and damage. This study analyzed observations from surface rain gauges and S-band dual-polarization radars to reveal the following unique features of the precipitation evolution from the plain to the mountains during this event. (1) The total rainfall was found concentrated along the Taihang Mountains at elevations generally > 200 m, and its spatiotemporal evolution was closely associated with northward-moving low-level jets. (2) Storms propagated northwestward with southeasterly steering winds, producing continuous rainfall along the eastern slopes of the Taihang Mountains owing to mountain blocking, which resulted in the formation of local centers of precipitation maxima. However, most rainfall episodes with an extreme hourly rainfall rate (HRR), corresponding to large horizontal wind shear at low levels, actively occurred in the plain area to the east of the Taihang Mountains. (3) The western portion of the extreme heavy rain belt in the north was mainly caused by long-lasting cumulus–stratus mixed precipitation with HRR < 20 mm h−1; the eastern portion was dominated by short-duration convective precipitation with HRR > 20 mm h−1. The contributions of convective precipitation and cumulus–stratus mixed precipitation to the total rainfall of the southern and middle rain belts were broadly equivalent. (4) The local HRR maxima located at the transition zone from the plain to the mountains were induced by moderate storm-scale convective cells with active warm-rain processes and large number of small-sized rain droplets. (5) During the devastating rainfall event, it was observed that the rainfall peaked at around 1800 local time (LT) every day over the upstream plain area (no diurnal cycle of rainfall was observed in relation to the accumulated rainfall centers over mountain areas). This was attributable to convective activities along the storm propagation path, which was a result of the more unstable stratification with a suitable steering mechanism that was related to afternoon solar heating and enhanced water vapor. The findings of this study improve our understanding and knowledge of the extreme precipitation that can develop from the plain to the mountains in North China.

Abstract. Synoptic forcings have traditionally played a pivotal role in extreme rainfall over North China. However, there are still large unexplained gaps in understanding the formation of extreme rainfalls over this region. The heavy rainfall event, lasting from 29 July to 2 August 2023 (referred to as “23·7” event), is characterized by long duration, widespread coverage, and high accumulated rainfall over North China. Overall, the persistent extreme rainfall is closely associated with the remnant vortex originating from typhoon Doksuri(2305), tropical storm Khanun(2306), and the unusual westward extended western Pacific subtropical high (WPSH), as well as quasi-stationary cold dry air masses surrounding North China on the west and north sides. Based on wind profiles and rainfall characteristics, the life history of the “23·7” event is divided into two stages. In the first stage, the western boundary of the western Pacific subtropical high (WPSH) was destroyed by the tropical storm Doksuri, appearing that the WPSH retreated eastward with decreasing height. As a result, an inclined vertical distribution on the western boundary was established below 500 hPa. Therefore, convections were limited by the tilted WPSH with warm-dry cover embedded in the low-to-middle troposphere. Meanwhile, the orography in the west of North China was controlled by cold air masses above nearly 3.0 km. Combining the orographic and cold air blockings, only a shallow southeasterly layer (between 1.3 and 3.0 km) can overpass mountains. Although the warm and moist southeasterly flows were lifted by orography, no convections were triggered because of the local capped cold and dry air masses overhead. Under this framework, equivalent potential temperature (θe) gradients were established between warm humid and dry cold air masses, similar to a warm front, causing warm air to lift and generate widespread rainfall but low intensity. However, the lifting was too weak to allow convection to be highly organized. In the second stage, the WPSH was further destroyed by enhanced Khanun, and thus the embedded warm-dry cover associated with the tilted WPSH was significantly thinned. Consequently, convections triggered by orographic blocking can move upward and consequently further develop, forming deep convections. Comparatively speaking, the convections in the second stage are much deeper than those in the first stage. The results gained herein may shed new light on better understanding and forecasting of long-lasting extreme rainfall.

A comparative analysis of the spatiotemporal distribution characteristics of rainfall and lightning in coastal and inland areas of Guangdong Province of China during the pre-summer rainy season (PSRS) from 2008 to 2017 reveals distinct patterns. In the inland target region (ITR), rainfall is concentrated in the central and eastern mountainous areas. It exhibits a bimodal diurnal variation, with peaks in the afternoon and morning. The afternoon peak becomes more pronounced during the post-monsoon-onset period because of the increased rainfall frequency. Similarly, in the coastal target region (CTR), rainfall concentrates around mountainous peripheries. However, CTR’s rainfall is weaker than ITR’s during the pre-monsoon-onset period, primarily associated with the lower-level moisture outflow in CTR, but it strengthens significantly during the post-monsoon-onset period owing to enhanced moisture inflow. CTR’s diurnal rainfall variation transitions from bimodal to a single broad peak during the post-monsoon-onset period, influenced by changes in both rainfall frequency and intensity. In contrast to rainfall, the spatiotemporal distribution of lightning centers remains relatively stable during the PSRS. The strongest center is located over ITR’s plains west of the rainfall center, with a secondary center in the western plains of CTR. Lightning activity significantly increases during the post-monsoon-onset period, particularly in ITR, primarily because of the increased lightning hours. The diurnal lightning flash density and lightning hours show a single afternoon peak in the two target regions, and the timing of the peak in ITR is approximately two hours later than in CTR. Composite circulation analysis indicates that during early morning, the lower atmosphere is nearly neutral in stratification. The advected warm, moist, unstable airflow, combined with topography, favors convection initiation. In the afternoon, solar radiation increases thermal instability, further enhancing the convection frequency and intensity. Improved moisture and thermal conditions contribute to an increase in rainfall and lightning during the post-monsoon-onset period. Moreover, the occurrence of lightning is found to be closely linked to the most unstable convective available potential energy, low-level vertical wind shear, and updraft intensity.

This study examined the rainfall characteristics and related synoptic processes of two extreme rainfall events that affected North China during 29 July–1 August 2023 (“23·7” rainstorm) and 3–5 August 1996 (“96·8” rainstorm), respectively. A stable dual-typhoon circulation pattern was observed in both rainstorm events. The surviving vortex of a landed typhoon, slowly approaching the rainstorm region, was blocked by a high-pressure system as it moved northwestward. Meanwhile, the second typhoon over the western Pacific Ocean facilitated remote northward transport of moisture. The low-level jet between the surviving vortex and the western Pacific subtropical high relayed moist warm air from the area of the South China Sea and western Pacific into the rainstorm region. Although the circulation patterns are similar, the stratification conditions, driving factors, and moisture budget of the two rainstorms differed during the main period of rainfall. The “23·7” rainstorm was categorized as warm-sector rainfall, as a result of the lifting of warm moist air over the eastern foothills of Taihang Mountains. In comparison with the situation of the “96·8” rainstorm, the surviving vortex of the “23·7” rainstorm traveled further northeastward and directly impacted the occurrence and progression of the rainfall, leading to relative northward displacement of the rainfall center, while the stronger net inward moisture flux caused greater regional average rainfall. The “96·8” rainstorm was broadly analogous to precipitation of a cold front, and the rainfall center was observed in the convergence area of warm and cold air masses before the mountains; the surviving vortex did not exert direct impact on the rainfall; and the more unstable stratification led to stronger hourly rainfall. The results derived through comparison of the two rainstorms could serve as valuable scientific reference for operational forecasting of heavy rainfall under similar environmental conditions over North China.

Warm-sector heavy rainfall events over southern China are difficult to accurately forecast, due in part to inaccurate initial fields in numerical weather prediction models. In order to determine an efficient way of reducing the critical initial field errors, this study conducts and compares two sets of 60-member ensemble forecast experiments of a warm-sector heavy rainfall event over coastal southern China without data assimilation (NODA) and with radar radial velocity data assimilation (RadarDA). Yangjiang radar data, which can provide offshore high-resolution wind field information, were assimilated by using a Weather Research and Forecasting (WRF)-based ensemble Kalman filter (EnKF) system. The results show that the speed and direction errors of the southeasterly airflow in the marine boundary layer over the northern South China Sea may primarily be responsible for the forecast errors in rainfall and convection evolution. Targeted assimilation of radial velocity data from the Yangjiang radar can reduce the critical initial field errors of most members, resulting in improvements to the ensemble forecast. Specifically, RadarDA simulations indicate that radial-velocity data assimilation (VrDA) can directly reduce the initial field errors in wind speed and direction, and indirectly and slightly adjust the initial moisture fields in most members, thereby improving the evolution features of moisture transport during the subsequent forecast period. Therefore, these RadarDA members can better capture the initiation and development of convection and have higher forecast skill for the convection evolution and rainfall. The improvement in the deterministic forecasts of most members results in an improved overall ensemble forecast performance. However, VrDA sometimes results in inappropriate adjustment of the initial wind field, so the forecast skill of a few members decreases rather than increases after VrDA. This suggests that a degree of uncertainty remains about the effect of the WRF-based EnKF system. Moreover, the results further indicate that accurate forecasts of the convection evolution and rainfall of warm-sector heavy rainfall events over southern China are challenging.

This study investigates the influences of urban land cover on the extreme rainfall event over the Zhengzhou city in central China on 20 July 2021 using the Weather Research and Forecasting model at a convection-permitting scale [1-km resolution in the innermost domain (d3)]. Two ensembles of simulation (CTRL, NURB), each consisting of 11 members with a multi-layer urban canopy model and various combinations of physics schemes, were conducted using different land cover scenarios: (i) the real urban land cover, (ii) all cities in d3 being replaced with natural land cover. The results suggest that CTRL reasonably reproduces the spatiotemporal evolution of rainstorms and the 24-h rainfall accumulation over the key region, although the maximum hourly rainfall is underestimated and displaced to the west or southwest by most members. The ensemble mean 24-h rainfall accumulation over the key region of heavy rainfall is reduced by 13%, and the maximum hourly rainfall simulated by each member is reduced by 15–70 mm in CTRL relative to NURB. The reduction in the simulated rainfall by urbanization is closely associated with numerous cities/towns to the south, southeast, and east of Zhengzhou. Their heating effects jointly lead to formation of anomalous upward motions in and above the planetary boundary layer (PBL), which exaggerates the PBL drying effect due to reduced evapotranspiration and also enhances the wind stilling effect due to increased surface friction in urban areas. As a result, the lateral inflows of moisture and high- θ e (equivalent potential temperature) air from south and east to Zhengzhou are reduced.

针对职业本科工业机器人教学中存在的位姿变换计算、模型建立困难以及学生难以理解等问题,文章以IRB1410型机器人为研究对象,从理论上建立了机器人的D-H坐标系并列出参数表,作为建模的关键数据,推导出机器人的运动学模型,并通过Matlab软件仿真检验所建模型的准确性.文章提出的模型对于职业本科的教学理论和实践操作提供了一定的方法思路.

During July 17-22.2021. a disastrous extreme rainfall event occurred in Henan Province, China, with the maximum 6-day accumulated rainfall obtained from meteorological observations being 1122.6 mm (Hebi City). The maximum hourly rainfall reached 201.9 mm (Zhengzhou city), which broke the record in the inland of China. The daily rainfall of 1/6 of the national rain gauge stations in Henan Province exceeded their respective records. In this study, a comprehensive review and a preliminary investigation on the multi-scale atmospheric processes are conducted by using rain gauge observations, sounding data, Doppler weather radar observations and the ERAS reanalysis data. Results show that this extreme rainfall event was caused by the joint effect of multi-scale atmospheric systems in the middle and low latitudes, and the effect of local topography: (1) The western Pacific subtropical high is abnormally northerly and strong, as compared with the mean circulation in July during the 30-year period of 1991-2020. It prevented the tropical cyclone "In-fa" from moving northward, and was conducive to the westward movement of "In-fa" along its southern periphery. An easterly low-level jet formed between the subtropical high and "In-fa". which strengthened the water vapor transport to East China. (2) The water vapor was transported from the South China Sea to the Northwest Pacific by the southwest monsoon, and then was carried northwards by the tropical cyclone "In-fa". The water vapor over the Northwest Pacific was transported to Henan Province by the easterly jet on the north of "In-fa" and the southeast flow around the southwestern periphery of the western Pacific subtropical high. This abnormal remote water vapor transport associated with the tropical cyclone caused a positive anomaly in precipitable water in Henan. (3) In the upper troposphere, the location of Henan Province was in front of an upper-troposphere trough. In the lower troposphere, there was a low-level vortex or an inverted trough over Henan and its periphery. The synoptic conditions over Henan were conducive to the convergence and upward motion of lower-tropospheric atmosphere. In addition, the Funiu and Taihang mountain ranges favored the convergence of water vapor and the uplift of the approaching easterly or southeasterly airflow. (4) The subtropical high and the abnormally strong continental high connected and formed a "high-pressure dam", which prevented mid-latitude cold air from moving southward. The extreme rainfall in Zhengzhou occurred in a warm-humid environment which resulted in a low-centroid precipitation resembling tropical precipitation. During the two days with the heaviest rainfall in Zhengzhou, convection was initiated continuously and merged into the main convective cluster from the southeast, south and southwest respectively, which helped maintain the mesoscale convective system in Henan for a long time.

The extreme heavy rainfall event in Henan Province during 17-23 July 2021 with 1-hour rainfall intensity breaking historical record in the inland of China, ranks second among the top 10 weather and climate events in China in 2021. Previous studies have investigated the rain gauge observations collected by the meteorological ground stations to analyze the rainfall situation and count the extreme value of the "21·7" process. Considering the rainfall is uneven in space and time, the observations from a single source has great uncertainty which may miss the actual rainfall extreme value. By comparing the rainfall observations between meteorological and hydrological rain gauge stations, the objectivity and accuracy of the rainfall records from two business systems are analyzed for the "21·7" extreme heavy rainfall event. It is found that the observations exhibit good agreement in the accumulated rainfall distributions of various levels, and the temporal evolution of daily and hourly rainfall. However, the positions and values of accumulated rainfall and hourly rainfall intensity extremum are different in detail according to these two systems. The systematic deviation between the meteorological and hydrological observations is less than 1% in the heavy rainfall area (6-day accumulated rainfall more than 600 mm). These differences are related to the distinctness in the number, location, density of stations, and the accuracy of observation instruments. In addition, the inhomogeneous features of the rainfall in time and space also lead to the deviation of rainfall records between meteorological and hydrological observations.On the other hand, the meteorological and hydrological rainfall data in top 3 accumulated rainfall cities (Zhengzhou, Hebi and Xinxiang) are merged. The results show that merged rainfall data can present more detailed rainfall distributions and more objective rainfall evolution characteristics compared to single source data. Based on the merged rainfall data, the rainfall features in these three cities are summarized. The strongest rainfall period in Hebi and Xinxiang are about 26 hours and 28 hours later than that at Zhengzhou, respectively, while the rainfall events happened in these three cities are characterized by large accumulated amount, extremely strong hourly intensity, concentrated location and sudden increase of rainfall intensity.

This study examines the development of a series of heavy rainfall events over four different geographical regions from central to north China on 19-21 July 2016, with the maximum 48-hr-accumulated and hourly rainfall amounts of 875 and 139 mm, respectively. Results show that the heavy rainfall events occurred in an environment with an anomalous deep trough associated with unusual extratropical cyclogenesis during this warm month and a pronounced moisture anomaly compared to a 30-year climatology. The cyclogenesis coincided with dry-air intrusion from the lower stratosphere, and its merging with a northwest and a southwest vortex in the lower troposphere, After its formation, the cyclone moved northward on the east side of Mt. Taihang and then northeastward across Mt. Yanshan. The presence of the southwest vortex and an abnormally strong western Pacific subtropical high contributed to the maintenance and intensification of a southwesterly low-level jet (LLJ) carrying ample moisture, leading to the heavy rainfall in central China. The further enhanced southwesterly LLJ through the cyclogenesis and its accompanying southeasterly LLJ provided much needed precipitable water for the heavy rainfall events over north China. It was the quasi-geostrophic forcing of the extratropical cyclone, together with its cold/warm frontal systems, and especially its northward movement with the approaching airflows near-perpendicular to the general mountain orientations that provided optimized settings for the generation of a series of heavy rainfall events along the windward foothills of the major mountains in north China.