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This study investigates the multi-scale processes associated with one type of typical heavy rainfall event in North China, focusing on the interplay among synoptic circulation, mesoscale dynamics, and topographic influences. The synoptic setting, characterized by the East Asian Great Trough, the South Asian High, and a northward-extended Western Pacific Subtropical High, created favorable conditions for moisture transport and convective activity. The event unfolded in two distinct phases: nocturnal and afternoon phases. During the nocturnal phase, an intensified 850 hPa low-level jet transported substantial meridional moisture into North China. Terrain-induced convergence along the Taihang Mountains enhanced lifting, resulting in concentrated precipitation at the foothills. In contrast, during the afternoon phase, the eastward movement of a Mongolian low trough and its associated cyclonic circulation shifted rainfall toward the plains east of the Taihang Mountains. Convective clusters developed locally due to surface heating and were organized along the low-level jet on the eastern flank of the cyclone, further intensifying precipitation. These results underscore three key mechanisms: nocturnal low-level jet-driven moisture convergence, synoptic-scale trough propagation, and terrain-modulated mesoscale convection. Understanding their diurnal variability offers valuable insights for operational forecasting, monitoring, and early warning systems for high-impact rainfall events in North China.

Warm-sector heavy rainfall (WSHR) events in China have been investigated for many years. Studies have investigated the synoptic weather conditions during WSHR formation, the categories and general features, the triggering mechanism, and structural features of mesoscale convective systems during these rainfall events. The main results of WSHR studies in recent years are summarized in this paper. However, WSHR caused by micro- to mesoscale systems often occurs abruptly and locally, making both numerical model predictions and objective forecasts difficult. Further research is needed in three areas: (1) The mechanisms controlling WSHR events need to be understood to clarify the specific effects of various factors and indicate the influences of these factors under different synoptic background circulations. This would enable an understanding of the mechanisms of formation, maintenance, and organization of the convections in WSHR events. (2) In addition to South China, WSHR events also occur during the concentrated summer precipitation in the Yangtze River-Huaihe River Valley and North China. A high spatial and temporal resolution dataset should be used to analyze the distribution and environmental conditions, and to further compare the differences and similarities of the triggering and maintenance mechanisms of WSHR events in different regions. (3) More studies of the mechanisms are required, as well as improvements to the model initial conditions and physical processes based on multi-source observations, especially the description of the triggering process and the microphysical parameterization. This will improve the numerical prediction of WSHR events.

The structure and diurnal evolution of long-lived, eastward-propagating mesoscale convective vortices (MCVs) along typical summertime mei-yu fronts over the east China plains are investigated through composite analysis of a 30-day semi-idealized simulation. The simulation uses lateral boundary conditions that vary only diurnally in time using analyses of recurring MCV events during 1–10 July 2007. Hence, the behavior of convection and vorticity follows a closely repeating diurnal cycle for each day during the simulation. Assisted by the eastward extension of enhanced vorticity anomalies from the Sichuan basin, the incipient MCV forms in the morning hours over the immediate lee (east) of the central China mountain ranges (stage 1). From local afternoon to early evening, as the MCV moves over the plains, convection weakens in the daytime downward branch of the mountain–plains solenoid. This allows the upper-level and lower-level portions of the vortex to partially decouple, and for convection to shift to the east-southeast side of the surface vortex (stage 2). Immediately after sunset, convection reinvigorates above the low-level MCV center as a result of moistening and destabilization from a combination of radiative forcing and an intensified low-level jet. This intensifies the MCV to maturity (stage 3). The mature MCV eventually evolves into an occluding subsynoptic cyclone with strong convection across all sectors of the low-level vorticity center during the subsequent day’s morning hours along the east China coastal plains before it moves offshore (stage 4).

Using a clustering algorithm based on cloud‐to‐ground (CG) lighting data, 72,974 thunderstorms were identified and tracked in the middle reaches of the Yangtze River Basin from May to September of 2016–2020. Thunderstorms predominantly occur in the southeast region and move to the northeast at a speed of 16–64 km/hr. Most thunderstorms have short durations (98.3%, ≤3 hr) and low CG flash frequencies (90.0%, ≤64). Thunderstorms with longer durations are mainly triggered near the mountains and tend to occur (end) earlier (later) in the afternoon (evening). The peak composite reflectivity (CR) corresponding to CG flashes from all thunderstorms is 50 dBZ. Approximately 70% (20%) of CG flashes occur in convective (stratiform) areas. The first CG flash of a thunderstorm tends to occur in convective areas with a higher CR than that of the last CG flash. The average and maximum CRs of CG flashes increase significantly with thunderstorm duration. Plain Language Summary Thunderstorms are known as a type of weather system that is typically accompanied by the presence of lighting and other hazardous weather (high winds, heavy rain, hail and tornadoes). Cloud‐to‐ground (CG) lighting produced by thunderstorms is a highly dangerous weather phenomenon that occurs between a thundercloud and the ground and often causes wildfires, explosions and severe damage to buildings. The middle reaches of the Yangtze River Basin in China are a transition zone between plateaus and plains, with dense urban agglomerations, rivers and lakes. However, thunderstorm activity in such complex underlying surfaces is poorly understood. Based on ground‐based radar and lightning observations, the statistical characteristics of thunderstorm activity in this region during the warm seasons (May to September) of 2016–2020 are analyzed using a lightning clustering method. The CG lighting number, area and displacement of thunderstorms increase with thunderstorm duration. Thunderstorms that last longer are mostly triggered near the mountains and often start earlier in the afternoon and end later in the evening. In addition, CG lighting produced by thunderstorms is associated with high radar echo intensity. These findings are useful for improving the nowcasting of lightning and other hazardous weather caused by thunderstorms. Key Points The cloud‐to‐ground (CG) flash number, area, displacement, etc., of thunderstorms based on lightning data change with increasing thunderstorm duration Thunderstorms with longer durations, mostly triggered near the mountains, occur earlier in the afternoon and end later in the evening Radar echo characteristics of CG flashes from thunderstorms with different durations show certain regularities

Based on the extent and eccentricity characteristics, mesoscale convective systems (MCSs) formed in the middle reaches of the Yangtze River Basin were classified into six subtypes: large circular (LC), large elongated (LE), medium circular (MC), medium elongated (ME), small circular (SC), and small elongated (SE). The lifespans of all L‐scale and most M‐scale MCSs exceed 6 h, whereas the majority of S‐scale MCSs last less than 6 h. The cold cloud coverage frequency for E‐type MCSs exhibits relative uniformity, with high‐frequency regions located south of the Yangtze River. In contrast, C‐type MCSs display a more scattered high‐frequency distribution with higher maxima. E‐type MCSs predominantly retain an elongated shape throughout their life cycles. Additionally, as the area of LE and ME MCSs expands, their eccentricity progressively decreases, leading to a greater inclination towards the east–west direction. For C‐type MCSs, they maintain a circular shape for less than half of their duration but tend to adopt an elongated shape during the development or dissipation stages. These findings provide a foundation for further investigation into the formation mechanisms and associated mesoscale systems of MCSs, which could enhance the prediction accuracy of the location and intensity of severe weather events linked to different types of MCSs. Multivariate distribution of MCS extents, eccentricities, and orientations across various morphological types. Each scatter represents a time step of MCSs. The scatter locations indicate extents (horizontal axis) and eccentricities (vertical axis), while orientations are shown by the color scale, as indicated in the color bar. Blue lines represent the kernel densities of scatters.

South China experienced substantial rainfall from April 19 to April 22, 2024, with accumulated precipitation ranging from 200 mm to 350 mm. This significant precipitation was primarily driven by the combined synoptic influences of the southern branch trough, low‐level jet stream, and the Jiang–Huai cyclone, affecting northern and central‐eastern Guangxi as well as most parts of Guangdong. These synoptic conditions facilitated the initiation, development, and propagation of mesoscale convective systems (MCSs). Specifically, an MCS initiated in the evening over the eastern edge of the Yunnan–Guizhou Plateau (YGP), leading to the formation of a mesoscale vortex with closed cyclonic circulation at 850 hPa, which further promoted the merging of convection cells into an organized MCS. The intensified southerly winds appeared over the eastern parts of the mesoscale vortex, preceding the peak meridional component of moisture convergence by approximately 4–5 h. Moisture budget analysis revealed that the meridional component of horizontal moisture convergence was the primary contributor to the moisture increase over Guangxi and Guangdong provinces. Consequently, the enhanced mesoscale systems (vortices and MCSs) significantly increased horizontal convergence at lower levels, contributing substantially to the moisture accumulation over South China. The intensified low‐level southerly wind associated with mesoscale vortices can be considered a potential forewarning parameter for short‐range precipitation forecasting in such heavy rainfall events. Column‐integrated moisture budget analysis revealed that the meridional component of horizontal moisture convergence was the primary contributor to the moisture increase over South China during substantial rainfall event from April 19 to 22, 2024. The enhanced mesoscale systems (vortices and MCSs) significantly increased meridional horizontal convergence at lower levels, contributing substantially to the moisture accumulation. The low‐level intensified southerly wind associated with mesoscale vortices can be considered a potential forewarning parameter for short‐range precipitation forecasting in such heavy rainfall events.

Electromagnetic interference, which necessitates the rapid advancement of substances with exceptional capabilities for absorbing electromagnetic waves, is of urgent concern in contemporary society. In this work, CoFe 2 O 4 /residual carbon from coal gasification fine slag (CFO/RC) composites were created using a novel hydrothermal method. Various mechanisms for microwave absorption, including conductive loss, natural resonance, interfacial dipole polarization, and magnetic flux loss, are involved in these composites. Consequently, compared with pure residual carbon materials, this composite offers superior capabilities in microwave absorption. At 7.76 GHz, the CFO/RC-2 composite achieves an impressive minimum reflection loss (RL min ) of −43.99 dB with a thickness of 2.44 mm. Moreover, CFO/RC-3 demonstrates an effective absorption bandwidth (EAB) of up to 4.16 GHz, accompanied by a thickness of 1.18 mm. This study revealed the remarkable capability of the composite to diminish electromagnetic waves, providing a new generation method for microwave absorbing materials of superior quality.

During mid‐July 2021, an extreme heavy rainfall event (HRE) occurred in Henan Province (hereafter “21.7” HRE), with extreme hourly precipitation of 201.9 mm appearing at Zhengzhou station. Our preliminary analyses of the “21.7” HRE using the observations and ECMWF (European Centre for Medium‐Range Weather Forecasts) ERA5 reanalysis data, reached the following conclusions. Favorable configurations of various synoptic weather systems (e.g., strong upper‐level high‐pressure ridge, intense middle‐level low‐pressure trough) acted as crucial background conditions for the occurrence of the “21.7” HRE. A 21‐h long‐lived mesoscale convective vortex (MCV), mainly located in the middle and lower troposphere west of Zhengzhou city, was a key system that produced the extreme hourly rainfall of 201.9 mm·h−1. The MCV's development/sustainment was dominated by the vertical transport of cyclonic vorticity and tilting, as well as the horizontal import of cyclonic vorticity to the vortex's key region. In contrast, the divergence‐related vertical shrinking was the most detrimental factor. Lagrangian moisture transport analysis showed that moisture for the extreme heavy rainfall in Zhengzhou on July 20 mainly came from levels below 2200 m, driven by airflows on the peripheries of tropical cyclones IN‐FA and CEMPAKA. To enhance the understanding of “21.7” HRE, we suggest more in‐depth investigations in the future. China is located in the East Asian monsoon region, which experiences relatively frequent heavy rainfall events in summer. Generally, the heavy rainfall frequency and accumulated amount in South China are higher than those of North China, whereas, the intensity of heavy rainfall in North China is similar to or even higher than that of South China. In July 2021, a record‐breaking heavy rainfall event occurred in Henan Province. The maximum observed precipitation in the whole event exceeded 1000 m, and an extreme hourly rainfall of 201.9 mm occurred in Zhengzhou. The major favorable large‐scale circulation conducive to heavy rainfall in North China during this event includes an extratropical‐cyclone/low‐pressure area between the continental high pressure and intensive subtropical high. The moisture related to two tropical cyclones IN‐FA and CEMPAKA was transported from the Western Pacific and the South China Sea to Henan Province. A mesoscale convective vortex was a key system to produce the extreme hourly rainfall of 201.9 mm in Zhengzhou city on 20 July, 2022.

A wave-number-frequency spectral decomposition technique is used to analyze the high-resolution NOAA/Climate Prediction Center morphing technique (CMORPH) precipitation data set and to explore the differences and similarities of the diurnal variation of warm-season precipitation in the East Asia and North America downstream of big topography. The predominant phase speed of precipitation at different time scales for North America, averaged over all warm-season months (May–August) for 2003–2010, is ~20 ms−1, which is faster than the speed of ~14 ms−1 calculated for East Asia. Consistent with the recent studies of the precipitation diurnal cycles for these two regions, the difference in the diurnal phase propagation is likely due to the difference in the mean steering level wind speed for these two regions. The wave-number-frequency spectral analysis further reveals the complex, multi-scale, multi-modal nature of the warm-season precipitation variation embedded within the diurnal cycle over both continents, with phase speeds varying from 10 to 30 ms−1 and wave periods varying from diurnal to a few hours. At the diurnal frequency regulated by the thermodynamically driven mountains–plains solenoids (MPSs), increased precipitation for both continents first originates in the afternoon from the eastern edge of big topography and subsequently moves downslope in the evening and reaches the broad plains area at night. More complex diurnal evolutions are observed in East Asia due to the more complex, multistep terrains east of the Tibetan Plateau and the associated localized MPS circulations. Nevertheless, increased variation of precipitation at smaller spatial and temporal scales is evident in the active phase of the dominant diurnal cycle for both continents.

Based on hourly rain gauge data during May–September of 2016–20, we analyze the spatiotemporal distributions of total rainfall (TR) and short-duration heavy rainfall (SDHR; hourly rainfall ⩾ 20 mm) and their diurnal variations over the middle reaches of the Yangtze River basin. For all three types of terrain (i.e., mountain, foothill, and plain), the amount of TR and SDHR both maximize in June/July, and the contribution of SDHR to TR (CST) peaks in August (amount: 23%; frequency: 1.74%). Foothill rainfall is characterized by a high TR amount and a high CST (in amount); mountain rainfall is characterized by a high TR frequency but a small CST (in amount); and plain rainfall shows a low TR amount and frequency, but a high CST (in amount). Overall, stations with high TR (amount and frequency) are mainly located over the mountains and in the foothills, while those with high SDHR (amount and frequency) are mainly concentrated in the foothills and plains close to mountainous areas. For all three types of terrain, the diurnal variations of both TR and SDHR exhibit a double peak (weak early morning and strong late afternoon) and a phase shift from the early-morning peak to the late-afternoon peak from May to August. Around the late-afternoon peak, the amount of TR and SDHR in the foothills is larger than over the mountains and plains. The TR intensity in the foothills increases significantly from midnight to afternoon, suggesting that thermal instability may play an important role in this process.